Welcome to the bikecurrent FAQ

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This FAQ (Frequently Asked Questions) document is now maturing somewhat.  The maintainer is currently William Burrow (aa126@fan.nb.ca).  Please include the word "FAQ" in your message subject line.  The purpose of the document is to gather the collective wisdom of the bikecurrent bicycle mailing list in one place.  Bikecurrent is a mailing list all about electricity for bicycles, especially bicycle lighting.

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Table of Contents

  1. About this FAQ
  2. About Electrical Units
  3. About Batteries
  4. About Chargers for Batteries
  5. About generators or dynamos
  6. About Lights
  7. About cyclocomputers


1. About this FAQ

So far, this FAQ is a collection of knowledge from the bikecurrent bicycle mailing list.  Most of the information here concerns the use of electricity on bicycles.  The primary use is usually for lighting purposes, and can involve batteries or generators or dynamos as a source of power.  A small section on cyclometers has been added, though there is not as much discussion of them on bikecurrent as there is on batteries, chargers and lights.

1.1 Other bicycle lighting related FAQs

There are several other FAQs available about lighting systems, some which go into considerable more detail than this FAQ.  Please visit them for more information:

NEW! Now there is also a collection of Reviews available excerpted from the bikecurrent list.

1.2 Bikecurrent list archives

Also find the actual archives of bikecurrent list members at:

1.3 Other resources

Here are some miscellaneous other resources of use to the bicycle electrician (NOTE: the FAQ holder does not endorse any of these companies):

Also, check your local Radio Shack (Tandy in the UK) and electronics and hobby stores.  Usually found listed in the Yellow Pages of your telephone directory.

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1.3.1 Personal Bike Light Pages

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2. About Electrical Units

There are some basic electrical units that are often encountered in this FAQ.  Most refer to DC current, and so can be manipulated easily.  AC current has a few tricks up its sleeve, but most of what applies to DC circuits might seem to work for AC current.

2.1 Basic DC circuit units

The common units encountered in DC circuits are voltage (unit is volts, expressed as V), current (unit is amps, expressed as A) and resistance (unit is ohms, expressed as the Greek symbol omega). 

The voltage from a battery or power source is the potential difference available and is measured across the power source terminals.  The actual voltage may differ under a load, depending on what the source is. 

The current is the amount of flow in the circuit.  It is measured in line with the circuit, never across any component in the circuit. 

The resistance is the amount resistance to current flow in the circuit.  The relationship between voltage, current and resistance is called Ohm's Law, and often expressed as:

	Volts = Amps x Resistance 


	V = I x R        where V is volts
			       I is current
			       R is resistance

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2.2 DC unit of power

Another unit often mentioned is the Watt.  This is a compound unit indicating the power used in the circuit.  It is often expressed as:

	Power (Watts) = Amps x Voltage 


	P = I x V        where P is power
	                       I is current
	                       V is volts

Note that power can also be expressed as volt-amps, or VA, which is more correct for AC circuits.  Both Watts and VA are identical for DC circuits. Also note that one can rearrange units from Ohms Law algebraically and substitute them into the equation for power.  This is generally not needed for bicycle lighting systems, as we often know the power consumed and voltage of the system.

2.3 DC unit of battery energy

Most batteries have a usable energy rating that is given in Amp-hours (symbol is Ah).  This is the amount of energy the battery could give over a given period of time at a certain current draw.  Algebraically, this can be expressed as:
        Amp-hours = Amps x time (hours)

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2.4 DC circuit examples

Some simple calculations involving Ohm's Law:

Q. How much current is my 10 watt light drawing on my 12V sealed lead acid battery lighting system?

A. Knowing from the battery section that a 12V sealed lead acid battery supplies about 13.6V fully charged and the equation for DC power, then we have:

	V = 13.6V
	W = 10W

	Power = Amps x Volts  ==>  Amps = Power / Volts 

	Amps = 10VA / 13.6V   (note the V's cancel)
	Amps = ~0.74A  About 3/4 of an amp current draw.

Q. I installed a new 10W halogen bulb in place of the 2.4W bulb in my headlight, but it does not look all that much brighter after a short while of use, what could be wrong?

A. It might be possible there is a voltage drop between the battery and the bulb.  Check the connections to be sure they are clean and mate firmly.  Note that the section on lights and bulbs specifically mentions that halogen lamps operate most efficiently in a narrow voltage band.  By checking the voltage at the light bulb while it is on, you find 12.0V.  Knowing your battery is fully charged, you check it and find it is 13.0V while the light is running. What resistance is your wiring offering to the current?

	delta V = 13.0V - 12.0V = 1.0V
	V = 13.0V
	W = 10W

	delta V = I x R		   ; Ohm's Law

	P = I x V  ==>  I = P / V  ; Figure out current drawn by the system
				     from the power and voltage given

      Substitute current drawn into Ohm's Law and rearrange for resistance:

	delta V = ( P / V ) x R  ==>  ( delta V ) / ( P / V ) = R

	==> R = ( delta V ) / ( P / V )

	R = 1.0 V / ( 10 VA / 13.0V )

	R = 1.0 V / ( 0.77 A )

	R = 1.3 ohms
This is a rather inadequate section of wire for the purpose because of the voltage drop between one end of the wire and the other, and should be replaced with a heavier gauge of wire. 

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2.5 Wire gauge conversions

Wire comes in various sizes, which are commonly rated by the AWG system in North America, and sometimes cross-sectional area of the wire by other places.  The AWG system uses a set of numbers to indicate size, with larger numbers usually indicating smaller wire (there are exceptions for particularly large wire).  Each successive AWG number indicates a multiple of the cubed root of two in cross-sectional area.  The following table illustrates some common sizes encountered:

Table 2.1 Table of Wire Gauges

Wire Gauge% power lostDiameter (mm)Area (mm^2)
18.5%1.0 0.79

For good performance, 18 AWG wire at 0.5% loss would be recommended.  Stranded zip cord for lamps has been recommended on the list, so long as one can tell one wire from the other (usually just a ridge down one side is sufficient).

Also note that smaller wire (higher AWG numbers) may suffer from heating due to current passing through them, thus raising the resistance of the wire.

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2.6 Light Output

Steve Kurt pointed out that one factor of importance to those designing bicycle lights is the light output of the lamp and how it is measured. He sends this link to a site on light output definitions and measurements:


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2.7 Listing of DC electrical units

Thang Vu contributes the following listing of DC electrical units (edited with suggestions and corrections from Jonathan Edelson and John Retchford):
Charge capacity is measured in coulombs:
    -  1 ampere [A] = 1 coulomb of electrical charge
                      passing a given point in a
                      wire or circuit per 1 second.
		    = 1 coulomb / 1 second
    -  1 ampere = 1,000,000 microamperes [uA]
                = 1,000 milliamperes     [mA]
                = 0.001 kiloampere       [kA]
                = 0.000 001 megaampere   [MA]
    -  1 ampere-hour [AH] = 3,600        coulombs
                          = 1,000,000    uAH
                          = 1,000        mAH
                          = 0.001        kAH
                          = 0.000 001    MAH

Work is measured in joules, it is a unit rarely used in electronics.

Power (or the rate of work) is measured in watts:
    -  1 watt [W] = 1 joule of energy transferred
                    (or work done) per 1 second
                  = 1 joule / 1 second
    -  1 watt = 1 ampere * 1 volt
    -  1 watt = 1,000,000 microwatts    [uW]
              = 1,000 milliwatts        [mW]
              = 0.001 kilowatt          [kW]
              = 0.000 001 megawatt      [MW]

Energy (or capacity for work) is measured in joules:
    -  1 joule = 1 volt * 1 coloumb
    -  1 joule = 1 watt * 1 second = ( 1 joule / 1 second ) * 1 second
    -  1 watt-hour [WH] = 3,600         joules
                        = 1,000,000     uWH
                        = 1,000         mWH
                        = 0.001         kWH
                        = 0.000 001     MWH

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3. About Batteries

Batteries are one common form of electrical power on a bicycle.  Batteries are generally not well understood by the general population (of which I was one until I read the bikecurrent list :).  For most people, it is a matter of buying the brand of battery they like that fits the flashlight or whatever, and that is that.  When it comes to bicycle lighting, the situation is a bit more complicated, and a bit of knowledge can go a long ways to helping understand your lighting system and getting the best performance from it. 

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3.1 What types of batteries are there?

There are many types of batteries.  Commonly available ones today are:

There are other types, but this section is not complete yet. 

See Yahoo! for more links related to batteries.

For information about NiMH batteries as applied to digital cameras (including many tips and links to other resources), check out the Batteries for AA-compatible digital cameras document.

3.1.1 What are primary and secondary batteries?

Primary cells are typically those that are good for one use only.  They are discharged to obtain their full capacity then disposed of.  Alkalines are an example of primary cells.

Secondary cells are typically rechargeable cells, good for many use many times.   They are not fully discharged typically, in order to preserve their life time.   Sealed Lead Acid, and NiCad batteries are examples of secondary cells.

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3.2 How much capacity does my battery have?

The capacity of a battery depends on many factors, including the type of battery, the load on the battery and often its physical size.  The rating on most NiCad and SLA (Sealed Lead Acid) batteries is given on the battery as amp-hours.  The symbol for amp-hours is Ah.  Examine the battery or cell for a number, such as 1.25Ah or 2.8Ah or some such.  This is the rating over a 20 hour period, often cited as amp-hours over 20 hours (typical for SLA batteries; NiCad batteries may be rated over shorter periods). 

An amp-hour is a compound unit obtained by multiplying the current in amps drawn from the battery by the period of time (for rating purposes, usually 20 hours) until the battery must be recharged (in the case of rechargeable batteries). 

Nomenclature:  Note that the amp-hour rating from a battery is often referred to by the single letter:  C. 

Example:  A 4.0 Ah SLA battery has C=4.0.  Fractional quantities are often referred to when speaking of current drain on a battery, so that for a battery with C=4.0 Ah, a C/10 current drain would refer to a current drain of 0.4 A (amps). 

See also section 3.26 for the capacity of a battery pack made of multiple cells.

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3.3 Why do I not get the capacity from my battery I expect?

From: Marty Goodman MD KC6YKC <MARTYGOODMAN@delphi.com>:

Folks on this mailing list from time to time post questions of the form:

I have a 20 watt lamp, and I'm powering it from a 12 volt 4 amp hour sealed lead acid battery.  I calculate that it should run for 4Ah/1.7A = 2.3 hours.  But when I find I only get 1.5 hours of run time.  What's wrong with my battery?

The answer to questions like this is that the actual capacity of a lead acid battery DRASTICALLY decreases as you start putting high loads on it.  The rated capacity is measured at a load of C/20.  That is, measured by drawing a current in amps equal to one twentieth of the amp hour number of the battery.  When you start drawing high loads, the total capacity you can get out of the battery drops.

One fellow in Grizzly Peak Cyclists used a 6.5 amp hour sealed lead acid battery to power a 50 watt lamp.  His bulb drew 50VA/12V = 4.2 amps, meaning he was putting a load on the battery of about .6C (where C = 6.5 amp-hours).  At this load, the ACTUAL expected amp hour capacity of a "6.5 amp-hour" capacity battery is more like 4 amp-hours.  Thus, he could expect his battery to power that lamp for just UNDER one hour (4Ah/4.2A = ~0.95 hr or so).

3.4 What capacity do sealed lead acid batteries have at various loads?

Table of Battery Capacity vs. Current Draw For a 1.0 Amp-hour Battery

      Current	Capacity  Amps	Usable
      (Amps) 	(Hours)		Amp-hrs
      -------	-------   ----  -------
      C/20	20 hr	  0.05	 1.0
      C/10	 9 hr	  0.10	 0.90
      C/5	 4 hr	  0.20	 0.80
      C/2	 1.3 hr	  0.50	 0.65
      1C	33 min	  1.0	 0.56
      2C	12 min	  2.0	 0.40

The discharge rate is given as a fraction of C, and the time to full discharge is given in hours next to this.  Below the dashed line, the current drain in amps is shown, and next to that is the total amp hours that one actually can get out of the battery.

Multiply values in the last two columns by however many amp hours your battery actually is to get the numbers for your lead acid battery. 

By examining this table, you can see that if you drain a sealed lead acid battery at a rate of C/2, you will get out of it only 65% of the rated amp hours.  If you drain the battery at a rate of 2C, you'll only get 40% of the official rated amp hours out of it. 

This is excerpted from a table in a brochure put out by Power Sonic, a maker of sealed lead acid batteries, and of sealed lead acid battery chargers. 

Note that Power Sonic has a nice graph depicting how load affects a battery (in straight lines on log graph "paper"!)

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3.5 What capacity do Hawker Energy (Gates) Cyclon cells have at various loads?

Glenn Wegener sent me some interesting information on a special kind of sealed lead acid battery:

Hawker Energy (Gates) Cyclon cells

These cells have significantly better performance than ordinary sealed lead acid batteries (SLA's).  They come in single 2 volt cells, in D size rated at 2.5 amp hours, and X size (somewhat larger than D size, but shaped like a D size cell) rated at 5.0 amp hours.  The 5.0 amp hour cells can be had, Glenn tells me, for $8.00 each.  Meaning a 6 volt 5 AH Cyclon battery pack will cost you $24.00 in batteries to make up (the batteries have tabs you can solder to make the three cell pack).

The following table shows the degree of "degradation" of available amp hour capacity as Hawker Cyclon cells (a 5.0 amp hour one in this case) is drained at higher and higher current levels. 

At the extreme right in this table I show for comparison (for some of the table entries) the % degradation of amp hour capacity at that fraction of C current drain for an ordinary technology SLA battery.

Table of Battery Capacity vs. Current Draw for Cyclon batteries

       fract  disch    AH          % of   Comparision to ordinary   Relative
        C      rate   Capacity    rated   (PowerSonic) SLA battery  performance
       ----   -----   ------     -------  ------------------------  -----------
       .1      0.5     5.0        100     (90% for ordinary SLA)     110%
       .2      1.0     4.8         96     (80% for ordinary SLA)     120%
       .42     2.1     4.3         86
       .78     3.9     3.9         78
      1.00     5.0     3.75        75     (56% for ordinary SLA)     134%
      1.40     7.0     3.5         70 
      2.00    10.0     3.3         66     (40% for ordinary SLA)     165%

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3.6 What capacity do NiMH cells have at various loads?

Suzanne Jackson <suzyj@bigpond.com> writes:

According to Varta's NiMH data, one gets the following discharge capacity vs current:

Table of Battery Capacity vs. Current Draw for NiMH batteries

     Current         %Capacity
     -------         ---------
      0.2C            100%
      0.5C            95%
      1C              93%
      2C              88%

Also, see Duracell's performance data sheets at:

NiMH data sheets

(Disclaimer: neither Duracell nor Varta batteries are endorsed by the FAQ holder)

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3.7 What Amp-hour ratings do alkaline batteries have?

Bruce Ingle writes the following piece on alkaline batteries based on Duracell's data sheets:

I finally figured out how to get an Ah rating out of the Duracell graphs for 5 alkaline D-cells driving different wattage 6V bulbs.  The charts show service hours vs discharge resistance and service hours vs discharge current, so if we do R=V^2/P to get an equivalent resistance for the bulb (using a nominal 6V) and divide it across 5 cells, we get the equivalent resistance/cell.  We can then find the expected service life to 4V (.8V/cell) and correspond that to an equivalent constant discharge current using the second chart.  By multiplying the service life and equivalent constant discharge amperage, we get the Ah life for the battery at different wattages.  Here is what it yields (I apologize for the abbreviated column headings, but I don't want the chart to scroll):

Table of Battery Capacity vs. Current Draw for D-cell Alkaline batteries

			Ohms/   Service
	Watts	Ohm/6V	cell	(hours)	mA	mAh
	-----   ------  ------  ------  --      ---
	.5	72	14.4	220	75	16500
	.7	51	10.3	160	100	16000
	1	36	7.2	100	160	16000
	1.5	24	4.8	70	200	14000
	2	18	3.6	45	280	12600
	3	12	2.4	30	380	11400
	5	7.2	1.4	12	800	9600
	7	5.1	1.0	8.5	950	8075
(Sorry, the discharge resistance graph doesn't go below 1 Ohm/cell.)

Of course, trying to see with a 6 Volt bulb at 4 Volts is another problem entirely.  :) So is trying to figure out battery capacity using these graphs with constant-power (PWM input) usage instead of constant-resistance (a close approximation of driving the bulb directly) or constant-amperage usage.

Bruce N. Ingle <ingle_bruce@micro-e.com>
Mechanical Engineer, MicroE, Inc.

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3.8 How much capacity does my battery have in the cold?

Vincent Taegar <VTaeger@mdsroc.com> writes:

There's a chart at http://www.homepower.com/hp/sitesfrm.htm that gives these figures:

                               Temperature (F)
                               104   32   -20
			       ---  ---   ---
Capacity Lead Acid Gel Cell    108%  87%   40%
         Sintered NiCad         98%  90%   78%

This agrees with other information I've seen.

One fact to note is that during discharge the NiCad reaction is exothermic (generates heat) while the lead-acid reaction is endothermic.  This will help keep NiCads warmer at any ambient temperature.  Also, while no figures are available, it should be noted that alkaline primary cells do very poorly in the cold.  Lithium primaries are better than alkalines in the cold.

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3.9 Which type of battery should be used for bicycle lighting?

Marty Goodman <MARTYGOODMAN@delphi.com> writes:

Lead Acid vs NiCd batteries Copyright 1997 Marty Goodman

Folks often ask me about which battery to get with their bicycle lighting systems:  Lead Acid or NiCd batteries.  This is intended as a "canned" first response to such questions. 

The two most common technologies of rechargeable battery used in bicycle headlight systems are Sealed Lead Acid ("SLA") and Nickel-Cadmium ("NiCd").  Low to medium price ($70 to $150) systems will feature SLA batteries, and medium to high priced systems ($140 to $400) will feature the NiCd batteries. 

The short version of my advice:

If you do a great deal of night riding, such as many nightly commutes per week, you should get a NiCd battery-based system.  If you do only occasional night rides, you'll likely do fine with a SLA-based system. But in either case, you will probably be VERY wise to invest in a third-party battery charger, and NOT use the battery charger supplied with the system you buy. 

Long version of my advice:

(a) battery characteristics

Lead Acid batteries are about 2 to 4 times less expensive at time of purchase than are NiCd batteries. 

However, NiCds, IF PROPERLY CARED FOR (this is a key operative qualification!) can be recharged 3 to 5 times as many times before they wear out as can be SLA batteries. 

Cost of a high quality third party charger for either system is roughly the same ($45 to $90).  Note that SLA batteries require a DIFFERENT charger from that required by NiCd batteries. 

Overall, NiCd batteries are at least as inexpensive, and probably actually somewhat LESS expensive a source of power than SLA batteries IF you are using them frequently, over the course of their total life. However, if you are using the battery infrequently, for, say, 20 rides per year, then the more expensive NiCd will probably die due to its shelf life expiring before you use all its available charges. 

NiCd batteries are, overall, about 30% lighter for a given amount of power capacity than SLA batteries.  A significant, but not utterly overwhelming difference. 

SLA batteries retain nearly their full charge for two months or more just sitting on the shelf, unattached to a charger.  NiCd batteries lose about 1% of their charge per day when sitting on the shelf, due to internal "self-discharge". 

NiCd batteries have a flatter voltage vs time curve during discharge than do SLA batteries.  This means your lights will remain relatively more constantly bright during the entire useful discharge life of the battery with a given lighting system than would be the case for a SLA battery of comparable amp hour capacity and voltage. 

BOTH NiCd AND SLA batteries can be severely damaged by being deeply discharged to down below 75% of their rated voltage.  With either system one must never run the battery "into the ground", letting ones lights go from yellow to orange to dim orange.  TURN YOUR LIGHTS OFF when they get noticeably yellow, else you risk permanently damaging your battery.

Many ignorant folks claim NiCd batteries are subject to "charge memory".  This is false.  As used by cyclists for night lighting applications, there is NO "charge memory" problem with NiCd batteries.  PERIOD.  I can give you a detailed explanation of the myth of "charge memory", and why so many folks make such utterly ignorant and false statements about it, if you wish to get in touch with me about this. 

Some manufacturers who supply SLA batteries with their lighting systems (such as VistaLite with its VL4xx systems) choose the Hawker Industries (formerly called "Gates") Cyclon type SLA batteries.  This particular make and model of SLA battery is significantly superior to ALL other SLA batteries.  If you are replacing a SLA battery in your existing lighting system, get a Hawker Industries Cyclon battery pack (available in 2.5 amp hour and 5.0 amp hour six volt modules).  These offer greater usable battery capacity for a given amp hour rating, are able to withstand deep discharge somewhat better than ordinary SLA batteries, and they last thru more recharge cycles than ordinary SLA batteries. Interestingly, the retail price for a Hawker Cyclon SLA battery is not all that different from the price of a similar ordinary SLA battery.  Power Sonic (headquarters in Redwood City, CA) sells Hawker Cyclon batteries.  Locally in Berkeley, Al Lashers can order and sell these batteries. 

Permission is explicitly given to Sheldon Brown to post this essay on his web site.  Permission is given to reproduce this in printed and electronic publications that are NOT FOR PROFIT. Reproduction in any FOR PROFIT publication is explicitly PROHIBITED without consent of the author. 

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3.10 How many Amp-hours does a battery pack built of single cells have compared to a single cell?

Don Perley <dperley@netheaven.com> writes:

When hooked in series (head to tail) the volts do add up.  Amp-hours do not add up.  In the example where you have 10, 1.2V, C-cells connected to yield 12V, you *do* however get 10 times as many watt-hours as you would with one cell.  A 12 volt bulb with the same power rating would take 1/10 as many amps as a 1.2 volt bulb.

How long a 10 cell pack lasts depends on the power of your lamp, naturally.

Steve J Kurt <kurtsj@mtco.com> adds:

Just as an added note:  the amp-hour rating indicates how many hours the cell can supply a given current into some particular load.  The voltage times the Ah gives the watt-hours (a measure of energy) that the cell can provide.  When you hook a number of cells in series, make sure they all have the same Ah rating.  Since they are hooked together in series, they will all be delivering/carrying the same current.  The goal is to get them to run out of energy at the same time.  If one runs out of energy before the others, the remaining cells will still force current through the discharged cell.  Not such an awful thing if you are using primary (non-rechargeable) cells like alkalines.  It is a bad thing when using secondary (rechargeable) cells like NiCad or NiMH's, since this can damage the cell severely.

You can add Ah only when you hook batteries or cells in parallel.  In this case the voltages must be matched.  If they are even slightly different, then there will be large currents flowing between the batteries, which may cause them to overheat and/or catch fire.  Isolation diodes (a.k.a. "or'ing" diodes) are often used when batteries are used in parallel.  In other cases, if paralleled NiCad are charged in parallel, they can be used in parallel if you don't change the configuration.

Going back to the issue of figuring out run times by looking at the amp-hour rating.  You need to know how many amps your load is drawing.  For instance, I use 6 D NiCad cells rated at 4.4 amp-hours.  My light draws 2 amps, therefore I should get about 2.2 hours of use.  In practice, I get closer to 2 hours, but it's close enough.  How do you figure out how much current your load uses??  Well, I can hook up my meter and find out.  Otherwise, you need to look at the voltage and wattage of the load.  My light is rated at 6v and 15W.  Since power (watts) = voltage x current, the light should use (15/6)A, or 2.5 amps.  I've measured the voltage and current of the light, and it doesn't use 15W.  However, it is close enough to give you a close idea of what sort of run time to expect.

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3.11 What is a good holder for individual NiCad or Alkaline cells?

Steve J Kurt <kurtsj@mtco.com> writes that he has successfully used Keystone battery holders for many years.  The version that he has is completely aluminum in construction.  Newer designs have a phenolic backbone with insulated steel plates at the end.  The Keystone holder is advertised as "corrosion-resistant holders with fully-insulated, stainless steel contacts recommended for shock or severe vibration environment."  The holder is available from popular electronics suppliers such as Newark, DigiKey or Mouser (see Section 1.3 for links).

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3.12 Where can I find batteries suitable for a bicycle light?

For a large lead acid battery, check your local hobby shop.  They stock 12V 7Ah SLA batteries.  They may also have a suitable charger, though beware of anything that is cheap and seems to be nothing more than a regular wall wart (though there is no easy way to tell without a voltmeter).

For NiCad batteries, try Radio Shack, one of the electronics houses listed in this FAQ or elsewhere, or the NiCad Lady.

Also, try these two hobby sources (NOTE: the FAQ holder does not endorse these or other suppliers):

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3.13 What is a chopper or PWM or what is pulse width modulation?

A PWM or chopper is a device that uses a specific technique called pulse width modulation to efficiently lower the voltage from a DC source.  The result is a pulsatile waveform that has an effective (RMS) voltage that is lower than the input.  The circuit can be made very efficient especially when used with lights, which require no special filtering of the output voltage. 

Note that a simple PWM or chopper does not regulate the voltage in any way, it merely makes the apparent voltage to the bulb lower to act as a dimmer.  Also note that this is not an efficient way to dim a light bulb, as you can see from the efficiency curve in the graph in Section 6.2.

A very highly efficient method of voltage regulation is possible using the PWM technique, however.  By using analog or microprocessor circuits, it is possible to achieve a high degree of regulation.  NiteRider's digital lights use such a circuit.   Willie Hunt has also designed such a device and made it available for sale.  For more information and ordering information see his LVR information page.  Similar devices are also available from electronics supply houses, though they typically have lower rated efficiencies than Willie Hunt's device, around 85% or less, compared to 99% or better for the LVR.

Also see Steve Kurt's note in section 3.21 on why the PWMs available from electronics supply houses have typically lower rated efficiencies and why. 

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3.14 How can I efficiently regulate the output from my battery?

The most efficient method for regulating the output from a battery for bicycle lighting purposes, is to use a PWM-based voltage regulator.  Willie Hunt has developed such a device and sells it for a modest sum.  See his LVR information page for more information.

The advantages of using a regulator can be summed up as:

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3.15 Where can I find tech notes on battery performance?

There are numerous sources for information about batteries.  Search on battery maker's web pages for such information.  Here are some web pages:

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3.16 Can I charge my battery after coming in from the cold?


Below about 5 deg C (40 deg F), batteries are not able to accept a full charge.  Especially not NiCads, which can be a serious fire or explosion hazard when charged cold.  Move your battery inside your house or apartment for one to three hours (depending on the size of your battery) to warm up before charging.  Avoid charging your batteries in a cold, unheated garage in the winter, as they will not warm up sufficiently.  If you can find or make a temperature compensating charger, by all means use that.

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3.17 Do I need a fuse for my battery?


Batteries, especially NiCad batteries, are capable of putting out incredible amounts of current.  When a short circuit develops for whatever reason in the circuit between the battery and the lamp(s), the battery will deliver a considerable amount of current.  Not only that it will get hot.  Hot enough to start a fire (in the wires, the bag the battery is in, etc.).

To be effective, the fuse should be placed as close as possible to the battery.  It does not really matter which side of the battery you put the fuse on, though some people have a preference.  Simple blade fuse holders can be had from Radio Shack and a spare blade fuse taped to the holder for easy replacement on the road.

The issue really is, what size fuse do you need, found in the next section.

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3.18 What size fuse do I need for my light set?

You should use the smallest effective fuse that will not blow with regular use.  You can calculate the fuse you need by using the rule of thumb to double the expected current used by the lights and pick the nearest next largest size available fuse.

For example, a single 20W bulb in a 12V system draws about 1.5A (see the DC circuit section).  Double that is about 3A.  If the only fuses available are 2A, 3A, 5A and higher, then a 3A fuse would be appropriate.

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3.19 Should I connect two or more battery packs together in parallel to get more capacity?

The conclusion on the list seems to be that it is not advantageous to connect two batteries of the same capacity and voltage in parallel for greater capacity.  It is possible to see when you are at half the capacity of your batteries when they are separate, when the lamp first starts to turn yellowish.

It is recommended that battery packs (not necessarily cells) be charged separately to extend the life of the packs.

Packs that are not the same capacity and voltage should never be placed in parallel.  There is a risk that one of the packs will run out before the other and be destroyed in the process.

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3.20 Where do I get 3V Lithium D batteries?

Wookey <wookey@aleph1.co.uk> writes:

As ever the answer to this question (put it in the FAQ somebody :-) is CPC:  http://www.cpc.co.uk/

(all plus VAT and small order charge of up to a fiver if you spend less than 30 quid (it's not hard to spend more than this usually :-)) [Prices in UK Pounds Stirling - wab]

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3.21 Why are some PWMs less efficient?

Steve Kurt <kurtsj@mtco.com> comments:

[Section 3.13] glosses over the distinction between a PWM chopper and a PWM switching power supply (this is what is being referred to as having efficiencies of 85% or less).  A PWM chopper simply turns power on for a while, then turns it off.  This is repeated over and over, and at a rather high frequency (at least above the flicker frequency of 30Hz).  The output is useful only for light bulbs, or perhaps heating elements.

By contrast, a switching power supply uses inductors and capacitors to store energy, and provide a rather smooth DC output voltage.  Great for computers, radios, and all manner of electronics.  The act of storing energy tends to involve a number of sources of losses, which is why they are less efficient.

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3.22 How do I clean off battery contacts after a battery leaks?

Pawel Danielewicz <duncan@silver.nscl.msu.edu> advises:

...use the spray for cleaning car battery terminals.  This then needs to be cleaned using distilled water or first tap and next distilled. Finally, the device needs to dry.

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3.23 How do NiCad batteries fail?

Marty Goodman writes:

In answer to your question about how NiCd batteries fail:

My understanding is that principly they fail in one of two ways: The first is gradual.  Their capacity gradually decreases bit by bit with each recharge over time, until it drops below a level that's acceptable for the application in question.  Arbitrarily that level is often listed as 85% of original capacity, but of course if you are in an application where the batteries when charged have two or three times the capacity you need the definition of "dead" may be more generous.  This is seldom the case for night bicycle lighting, however, where we usually want nearly full capacity for issues of run time and weight.  There the 85% rule probably is more or less correct.

However, NiCd batteries also fail in a second way: They grow "dentrites" internally, which internally short out the battery. Dendrites gradually grow, but it's only when they actually complete the internal short circuit that you notice them.  Thus, they can produce what appears to be a sudden failure of the battery.  This will be experienced typically with a battery that has sat on the shelf too long.  It's not usually something you encounter DURING the operation of an already working battery.  It's typically seen when you try to charge up a pack that has been sitting on the shelf, and discover it won't take ANY charge at all.  At that point, you'll find that one or more cells in the battery pack will have a ZERO pole to pole resistance... behaving as if it's totally shorted out (which, of course, it IS... internally).

There is a debate about whether and how to try to rejuvinate internally shorted NiCd batteries.  Some argue for zapping the batteries with a fat capacitor or blast from some high current source, to vaporize the dentrites.  Others take a more pessimistic attitude, arguing that even when you vaporize the dentrite's connection, most of the dentrite remains, and it will soon again grow and short out the cell.  I've experienced both in a few isolated experients with zapping shorted NiCd's: On occasion I've gotten reasonable extra use out of cells I've zapped, and on other occasions I've found that the repaired, zapped cell very quickly fails again. To what extent, if any, this is related to exactly how one zaps the battery in the first place I have no idea.


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3.24 What is NiCad memory?

Dan from Oz has a straightforward say about memory effect on his web page, titled: Dan's Quick Guide to Memory Effect, You Idiots (offsite).

In message: <0.700001764.1200242557-1463792126-1013062744@topica.com> Thang Vu <tv_4@yahoo.com> writes about what is NiCad memory (edited with suggestions from Jonathan Edelson):

**** "MEMORY EFFECT" ****

"Memory effect" is an incorrectly used term.  Originally it referred to spacecraft in orbit, using NiCds. Where I am in BC, Canada, many bike light companies and bike shops still advocate memory effect in their everyday business dealings.

**** VOLTAGE DEPRESSION (in general) ****

Voltage depression just means that the usable voltage of the battery is DEPRESSED or LOWER than normal.  The charge capacity of the battery REMAINS THE SAME, whether voltage depression or no voltage depression. Some energy capacity is lost due to the drop in voltage, because energy delivered = charge delivered * voltage Even though the charge delivered remains the same, the lowered voltage results in lower energy capacity. Charge capacity is measured in coulombs.  There are 3600 coloumbs per ampere-hour.  Energy capacity is measured in joules.  There 3600 joules per watt-hour.  See the section on electrical units for more details. In industry and commerce, though, people prefer to say mAH, AH or WH. Maybe they like the idea of knowing, for a given AH, say, how many amperes you get for 1 H or how many hours for 1 A -- who knows? Ditto for the other proper units of measurement. In the battery industry (including bike batteries), there is the popular "C/n" saying, where they mean that "C" represents the charge capacity of the battery.  The result of C/n has units of A or mA. Therefore, C and n must have units of AH (or mAH) and H, respectively. Back to NiCds: there are two (2) types of voltage depression -- anode voltage depression and cathode voltage depression.

**** Anode Voltage Depression ****

Anode voltage depression occurs when part or all of the NiCd battery is not used for a "long time." This can mean leaving it on a bookshelf, in a box, on a bike, on the floor, etc, etc, for a "long time." This can also mean partially discharging it repeatedly (by the same amount of discharge, roughly speaking): the unused part is, IN EFFECT, equivalent to being left alone for a "long time." Why does anode voltage depression occur? Because (and without getting overly-technical), the cadmium metal inside the battery anodely tends to form into larger and larger crystals, if you leave it alone for a "long time." These crystals do not break down easily into smaller and smaller crystals, which is needed to ensure normal usable voltage and low internal battery resistance.  The result: a DEPRESSED usable voltage. Voila. Solution to anode voltage depression? "Once in awhile," drain the battery completely and charge it completely.

**** Cathode Voltage Depression ****

Cathode voltage depression occurs when the NiCd battery is overcharged AT A LOW RATE.  (Note: Overcharging at a high rate is unrelated to cathode voltage depression; this will permanently partially or wholly damage the battery, depending on the overcharging current and how long you allowed this current to exist.) Why does cathode voltage depression occur? Because after a full charge, the overcharge current cannot create any more chemical energy; instead, it is forced to dump its electrical energy into heating the cell or battery.  This heat causes beta-Ni(OH)2 to turn into gamma-Ni(OH)2.  The voltage of the latter is 40-50 mV/cell less than former.  The result: a DEPRESSED usable voltage.  Voila. Solution to cathode voltage depression?  Do not overcharge at a low rate.  Do not excessively overcharge.  If you do, just use the battery as normal, and charge again without overcharging. Note that it is required to slightly overcharge a grouping of cells (called a battery) to ensure that all the cells are fully charged.  This is because one or more of the cells may become fully charged before the rest are charged.

**** DENDRITES ****

All right, so you've babied your NiCd from cradle to grave.  Why does it still eventually fail? Nothing lasts forever (except taxes and death).  When the cell or battery is charged up, ideally the stuff that moved from one place to another during usage is now forced back to the original place.  However, this stuff does not distribute evenly in the original place.  Some parts of the original place will receive more than others, causing "dendrite" (needles or crystals) to form.  The current density will be higher here, which yet causes the needles to grow even more.  Eventually the needles will short circuit the destination place and original place.  Now, the cell or cells is/are useless.  Voila.  (Note: the needles penetrate the insulating material in the battery. -wb-) Another cause of eventual failure: degradation of material.  The more the battery is used, regardless of whether that be partially or wholly, the more material is eventually degraded more and more.  Plainly said, it wears the battery out more and more.  This is normal and expected; largely speaking, it is BEYOND your control, so don't lose sleep over it.

**** COMPROMISE between anode voltage depression & degradation of material ****

Many sincere but ignorant bike light manufacturers and bike shops will advise their clients/customers to "completely drain their NiCd EVERY TIME." Others advise "draining every 3 or 4 times." While there is some truth to their advice, there is also misrepresentation and/or a lack of understanding of NiCd chemistry in their advice. There is a **** COMPROMISE **** between avoiding anode voltage depression and degradation of material.  You must realize this! Avoiding one thing necessitates approaching the other.  That is a consequence of NiCd batteries.  On one hand, avoiding anode voltage depression means draining the battery completely.  On the other hand, avoiding degradation of material means not draining the battery.  Some cyclists completely drain their NiCd after arriving home every time, which means the accumulated runtime in all of those draining periods can add up to an appreciable amount unnecessarily thrown down the toliet when you consider the battery lifetime.  IMO, this equates to an appreciable portion of the purchase price of the battery also being thrown down the toliet. You need to balance between anode voltage depression and degradation of material, in the exact same way that you need to balance between overvolting a halogen bulb (which increases luminous efficacy) and avoiding exponentially-reduced bulb lifetime.

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3.25 How do I care for NiCad batteries?

Read the sections on how NiCads fail and what is NiCad memory (particularly near the end, under "Compromise").  Select a good charging system, see what is a good charger for NiCads.  Use your batteries regularly and avoid overcharging them.  Avoid draining the battery completely.  If you must use all the capacity of the battery every time you use it, consider a larger capacity battery in future.

Some on the list have recommended storing unused batteries in the freezer.  If you do this, be sure that they warm up before you use them. Never charge a cold battery, doing this is a fire hazard and may damage the battery.  See section 3.16.

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3.26 How do I calculate the capacity of a battery pack wired in series? in parallel?

To calculate the capacity of a battery pack made up of matched batteries, first check if they are wired in series or parallel.  When in series, battery voltage multiplies by the number of batteries, but the total Ah capacity of the pack is the same as any of the cells.

e.g. Four AA NiCad batteries of 2000mAh each in series make a 4.8V nominal pack with 2000mAh charge capacity for a total of 9600mWh energy capacity.

On the other hand, the same batteries in parallel make a battery pack of 1.2V nominal at 8000mAh charge capacity for a total of 9600mWh. Note that the energy (Wh) in the two packs is the same.  This makes it easy to double check, just measure the voltage and work your way back to Ah or the number of cells.

If the pack has some batteries in parallel, then those parallel packs in series, first work out the capacity for each parallel pack.  Similarly, work out the capacity of series packs (which is trivial) then the capacity for the series packs in parallel for the converse.

Note: The list recommends against wiring batteries in parallel.  Many do make packs of parallel cells, though, carefully matching cells to avoid potential damage.

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3.27 What is the best way to charge Lithium Ion batteries?

The Battery University (Cadex) states that Li-Ion batteries have very strict charging regimens as specified by the manufacturor.  The battery must be charged using the technique and equipment indicated - there is no magic charger.  Like alkalines and lead-acid batteries, the charge state of Li-Ion batteries can be determined by measuring the voltage of the battery.  Typically, cells are at full charge at 4.20V and near half charge around 3.80V.

Li-Ion batteries usually will not discharge below 2.50V, since that is when safety circuitry will open making the battery appear dead.  Allowing a Lithium Ion battery to discharge to 1.50V or lower will cause damage to the battery that will prevent safe recharging.  Do not attempt to recharge such batteries. 

Note that lithium Ion and Lithium Ion Polymer batteries are similar, but the latter use a gel based electrolyte. 

Based on an article from the Battery University on Charging Li-Ion batteries.

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3.28 How do I get the most useful life from Lithium Ion batteries?

The Battery University (Cadex) notes that Lithium Ion batteries are constantly being improved over time and that new chemistries are being introduced frequently.  However, there are some basic rules that work well for now.

Typically, Li-Ion batteries only last 2-3 years and for about 300-500 cycles. Charging a partially discharged pack is better than fully discharging the battery completely.  However, some packs with fuel gauge circuitry will require a full discharge about every 30 charges to recalibrate the circuitry. 

Heat and high charge levels (storing the battery unused at full charge) will shorten the life of the battery.  Store Li-Ion batteries at 40% charge or so in a cool place (do not freeze).  Avoid storing in a hot car or in your laptop while running off mains power.  Some laptop manufacturors recommend leaving the battery in the laptop to prevent damage to the battery pack.

Avoid buying Li-Ion batteries in advance or as old stock, even at clearance prices - they won't be a bargain.  Be sure to check the manufacturing date, Lithium batteries start to age as soon as they are made.

Based on an article from the Battery University on prolonging the life of Li-Ion batteries.

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4. About Chargers for Batteries

4.1 What is a good charger for sealed lead acid battery?

From: JerryK <JerryKofSJ@aol.com>

Charging 12V SLA batteries is a known technology nowadays.  Simply go to the Mouser Electronics web site and order yourself a Power-Sonic model PSC-12500A [PSC-6250A for 6V -wb] "wall wart", Mouser Electronics Stock number 547-12500A ($40).  Plug it into your battery every night and forget it.  My batteries last about 2 years this way, with 5-day/week usage.

From: Marty Goodman MD KC6YKC <MARTYGOODMAN@delphi.com>

To summarize what both I and Glenn noted in this thread on the VistaLite VL4xx charger matter:

Most makers of lead acid batteries note (often on the battery) that their batteries can be happily INDEFINITELY be connected to a regulated source of about 6.9 volts.  (Glenn quotes one maker who expresses this as 6.81 - 7.05 volts).  [13.5 - 13.8V for 12V batteries -wb]

They also note that for faster charging the battery can be connected to a regulated voltage source of about 7.2 volts (Glenn's example was a recommendation in the range of 7.35 to 7.65) [14.4V for 12V batteries -wb] for some limited period of time (typically 24 to 48 hours).  If LEFT connected to such a higher voltage source, tho, beyond this time, the battery will be injured.

Thus, the kind of VistaLite charger that puts out about 7.5 or more volts is a BATTERY COOKER if left attached to the battery for more than a day or so. 

Thus, also, comes my recommendation for a simple, tinkerers' battery charger consisting of nothing more than an unregulated DC supply that puts out about 10 or so volts (and that can supply no more than about a half amp or so, to intrinsically limit initial current to the battery) hooked to a simple linear voltage regulator (such as an LM317) to yield a source of regulated 6.9 volts.  This can be hooked to the battery and left connected to it indefinitely. 

It is a decent charger.

More fancy, sophisticated chargers are available thru third party outlets (PowerSonic, A&A engineering, etc.).  These are smart enough to charge the battery at a lower voltage if it's really low, then go to a higher voltage to complete charging quickly and fully, then drop back to a lower voltage when the battery is full, going into a trickle charge state where only low current is applied.  OR (in some cases) shutting down entirely, but monitoring the battery voltage and giving it a bit of a goose when needed to keep it fully charged.

Smart SLA chargers can be purchased from Power Sonic, at a cost of about $50 to $80 for chargers appropriate to existing bicycle lighting systems. You have to add your own cable, of course, to attach the charger to your particular system.  Tinkerers should note that a proper trickle charger for SLA batteries is a regulated power supply set to 6.90 to 6.95 volts for a "6 volt" SLA battery, and to 13.8 to 13.9 volts for a "12 volt" SLA battery. 

All of the above applies ONLY to lead acid battery technology, NOT to NiCds, where other considerations apply.

Also note, that one can build a smart SLA charger using various ICs from companies such as Unitrode.  A datasheet for Unitrode's U3906 chip can be found here.

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4.2 Why are some Vistalite chargers not good for your battery?

Certain Vistalite (VL4xx series) light sets are provided with sealed lead acid batteries and an unregulated, dumb charger that is destined to damage the battery if left connected as recommended incorrectly by the manual. 

This is not a problem with Vistalite light sets equipped with NiCad battery packs.

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4.3 What is a good charger for NiCad batteries?

Marty Goodman <MARTYGOODMAN@delphi.com> writes:

With the exception of the Nite Rider Digital Pro 6 and Xcell Pro (formerly called NiteHawk) lighting systems, virtually [all] bicycle lighting systems on the market supply inexcusably cheap, often quite destructive to the battery type of chargers.  The problem is that with most supplied chargers, they charge the battery rather slowly (require 10 or more hours to provide a full charge) THEN then keep JAMMING current into the battery after it's full, heating it up and ultimately destroying it. MANY cyclists have destroyed their $140 replacement cost NiCd water bottle battery by leaving it hooked up to the charger for some days or weeks. 

While NOT a "smart" charging system, the NiteRider Xcell Pro and Digital Pro 6 systems do have a reasonably safe "set it and forget" charging system, tho only when used with their supplied battery.  Their system charges the battery at a modest rate for 10 hours, then a timer switches over to a 3 times slower charging rate for maintenance of the battery. Their system is not a "smart charger" in that it DOES NOT in ANY WAY sense actual battery condition. 

To more quickly charge SLA or NiCd batteries (full charge in 2 to 4 hours), one needs a "smart charger".  Such a charger senses battery condition during charging, pours current into the battery as long as the battery needs it, senses when the battery is full, and then cuts back to a much reduced current flow (or pulses of current at intervals) to keep the battery filled without harming it. 

NiCd batteries really benefit from a proper smart charger. Unfortunately, one has to press into service chargers made for other purposes if one wants a smart charger for one's bicycle lighting system.  Or make one oneself from scratch.  I've done both, successfully.  Certain DeWalt and Black and Decker power tool chargers can be converted into very effective smart chargers for bicycle lighting system batteries.  The DW9106 and DW9104 in particular are good choices.  (NOTE:  ALL the DeWalt chargers have 110 volts AC at BOTH battery terminals.   Touching the exposed terminals while charging may result in a LETHAL shock.)  Some cam-corder and cell phone 6 volt NiCd battery chargers may be suitable as smart chargers for 6 volt NiCd bicycling batteries.  I've built from scratch two smart chargers for my battery systems using a Maxim MAX 713 smart charger controller chip.  Both work very well.  Some have used the more modern 2002 NiCd smart charger controller chip made by Maxim, Benchmarq, and Unitrode.  Contact Marty for details if interested. 

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4.4 Why are most power tool battery chargers not suitable chargers?

Marty Goodman writes:

The reason I and others have been recommending DeWalt (and Black and Decker) brand power tool chargers for use with bicycle NiCd battery packs is that we KNOW they are negative delta V - sensing smart chargers.  They connect to the battery with ONLY TWO WIRES... the plus and minus of the battery.

MANY ... most, I believe... other power tool battery charger systems on the market (I don't know about Bosch specifically) use a TEMPERATURE SENSOR inside the battery, and can only properly charge batteries with the exact right kind and wiring of temperature sensor (thermistor) inside the battery pack.  Such chargers, which are UNACCEPTABLE for charging anything other than the specific make and model of battery pack they were designed to be used with, are often identified by the fact that they connect to their battery pack with THREE or more contacts, NOT the two used by the Black and Decker / DeWalt chargers.

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4.5 What lighting systems come with acceptable chargers?

The NiteRider Digital Pro-12, Digital Pro-6 and Trail Rat lighting systems come with a charger that is described as plug and forget.  While these chargers are said NOT to be intelligent, in that they do not sense the battery condition whatsoever, these chargers will not overcharge the batteries.  After a specific period of time charging, they will reduce their charge rate to a safe trickle rate that will not damage the battery.

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The rest of this section is not done yet.

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5. About bicycle generators or dynamos

5.1 What is a generator or dynamo?

First off, the terms generator and dynamo refer to the same thing, but common usage tends to favour one term over the other depending where you live.  The rest of this document will refer to this type of device as a generator.

A bicycle generator is a mechanical device that generates electricity from the rotational energy acting upon it, typically from a bicycle wheel.  One part of the generator rotates (the rotor) and the other part stays still (the stator).  The rotor is made up of permanent magnets of some type and the stator is made up of coils of wire.  The magnetic field of the turning rotor passes through the coils of the stator, inducing electricity which is then drawn off and used to power the light.

There are several other FAQs that cover generators as well.

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5.2 What are some types of generator?

There are several types of generators, classified primarily by where they get their power from the bicycle wheel:

Bottle generators
Shaped like a bottle with the turning end at the top, the bottle generator gets its power usually from the side of the tire.
Bottom Bracket generators
This type of generator is located just below the bottom bracket, and is in contact with the tread of the rear tire.
Spoke generators
The FER generator is probably the only of its type, which takes power from a wheel turned by the spokes.  This type of generator has a belt in it that does wear out over time.
Hub generators
The most efficient and lowest drag generators are found in specially designed hubs for the wheel.

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5.3 What are some reputable brands of generator?

Steve Bush <Steve.Bush@rbi.co.uk> writes:

Axa, Union and Nordlicht are all 3W and well regarded.  Union also make a roller dynamo which has low drag.  FER make a 3W spoke dynamo.  Early ones (I am told, I have no direct experience) wear out there pulley-belt drive train and cannot be repaired.  Later ones are supposed to be better.  There is a 6W (12V) FER expected soon.  There are simple units available that switch over automatically to dry cells when you stop.  I have tried the Pifco unit and it works well.

The rest of this section is not done yet.

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6. About Lights

6.1 Another Bicycle Light FAQ

Bicycle Lights FAQ

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6.2 What effect does voltage have on a light bulb?

The performance of a light bulb is affected by a change from its rated voltage as depicted by the graph:

Awful ASCII rendering of a graph.
A nice, alternative, graphical rendering by the FAQ author provided courtesy of Myra Van Inwegen on her website.  Note: this graph depicts curves derived from the equations below, but may not show all curves from the following formulae.

The curves depicted follow the following relationships (so you can plug them into a graphing calculator or draw them yourself):

         Life          = v ^ -12      where v is variation in voltage
         Luminous flux = v ^ 3.5        and ^ is the symbol for raise to
         Efficiency    = v ^ 2                   power of

As can be seen by the graph, a slight undervoltage to the bulb dramatically increases its expected lifespan, while an overvoltage to the bulb similarly shortens the life of the bulb.  Conversely, undervoltage decreases the light output and efficiency of the bulb, while overvoltage to the bulb increases the efficiency and light output of the bulb. 

From this, it can be seen that for a sacrifice in lifespan, greater light output and efficiency can be achieved.  Also, it can be seen that the bulb puts out significantly less light and is less efficient at lower than rated voltages. 

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6.3 What alternatives to bulb headlights exist?

Vincent Taeger <vtaeger@mdsroc.com> writes:

It's not that there's no interest in non-bulb light sources.  The trouble is that none of the current alternatives are suitable for a headlamp. Keep looking because someday you'll find something, but be aware of the problems and what your looking for.

All the alternatives I've seen have one or more of the following problems:

  1. Price [Metal Halide]
  2. High minimum wattage [Metal Halide]
  3. Poor white light output [LEDs, electro-luminesence]
  4. Cannot run at low voltages, requires expensive or inefficient voltage converters [Metal Halide, fluorescence]
  5. Wide angle and poor Lumens/m^2 require large optics. [fluorescence, electro-luminesence]
  6. Size.
  7. Low lumens/Watt (for electric lamps).
  8. Low lumen hours/kg (for all lamps).
  9. Poor resistance to vibration, wind or rain.  General PITA. [carbide, propane and other 'flame' lamps].

Most of us use red LED tail lights.  I also have a flashing green electro-luminescent belt.  These are both used as "be seen" lights rather than headlamps.  High lumen/watt, non-white colors and wide viewing angles are a plus for marker lights.

Headlamps have a different set of requirements.  They should be white (or at least close) with a tight beam.  A beam requires a compact light source (or large optics).  So far the alternatives are, at best, competitive with the average bulb and worse than the best bulb systems (e.g. with a PWM regulator).  The alternatives are slowly gaining, I suspect a 2W LED headlamp will be better than a 2W bulb in a year or two, but for higher power it will be a while.

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6.4 What suppliers are there for 6V MES screw-base and other bulbs?

Wookey <wookey@aleph1.co.uk> writes on finding screw-base 6V bulbs:

OK. people I _know_ can supply these bulbs, have a good range and are happy to ship to the US for GBP 1.50 (~$2) are:

US. suppliers who can probably help are:

P.S. Caving supplies isn't the only specialist supplier in the UK by any means (as another poster suggested!).  Ones who definitely stock these bulbs (and probably have 10W in stock are:)

Others in the US who may be able to help:

When asking caving suppliers for these bulbs you want to talk about 6V MES fitting or 'oldham headset screw-fit' or 'FX5 bulbs'.

Mark Siminoff suggests:

Peter White Cycles carries some types of 2.4W generator bulbs, including the HS3 bulb with notched flange:

Marty Goodman suggests that higher quality HOT (overvolted) MR-11 bulbs can be had from original equipment manufacturors such as: NiteRider, NightSun, or VistaLite.

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6.5 Can I hook my Cateye HL500 Micro II lamp to an external 6V battery?

Note that the bulb in the Micro II lamp is rated at 4.8V, such that connecting it to a 6V source will cause the lamp to prematurely fail, possibly within a few hours or minutes.  See Section 6.2 for more info.

The astute reader will notice that the four 1.5V alkaline AA batteries that are typically used in the Micro II add up to 6V.  However, due to the internal resistance of alkaline batteries under load, in fact only about 4.8V to 5.2V are supplied to the bulb.  This can be verified with a simple voltmeter.

Using alternative batteries, such as NiCads, does not damage the bulb either, because NiCads are actually rated at 1.25V, and so supply only about 5V under load.  Users have also reported successfully using Lithium batteries, though the FAQ holder has no actual data concerning these.

Though in the past Cateye advertised the availability of an external battery pack for the Micro II lamp, to date none is available. However, Cateye has announced the release of a new Micro halogen lamp with a 6W bulb and a rechargeable pack.

In conclusion, if the user fabricates and uses an external pack, either a PWM regulator should be used to regulate the voltage to 5V, or the pack should be created only to supply up to 5V.

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6.6 What are MR-11 and MR-16 bulbs?

Myra Van Inwegen <Myra.VanInwegen@cl.cam.ac.uk> writes:

MR11 are the little (they look like they would almost fit into a 35mm film can) bulb + reflector combination in use in lots of systems, like VistaLite 500, NiteRider, Specialized Proview, etc.  They come in 6 and 12V versions.  MR16 are bigger version of the same - maybe 2" lens diameter [they are 50mm - ed].  I think they also come in 6V and 12V versions.  I think they are mainly used in NightSun products.

You can also get 6V 5W or 6W MR11 bulbs from VistaLite and NiteRider, but again you'd need a lamp housing to put them it, and anyway they use different connectors from the NightSun ones.

The FAQ holder notes:

The MR-16 bulb is commonly available in stores in the lighting section in 20W and 50W versions both with spot beam and flood beam.  The spot beam is the most useful for homebrew bicycle lights.  It is also possible to find a 10W version if you know of a good source for these bulbs.

The MR-11 bulb is not commonly available, and must be ordered through a bike shop.  The selection of wattages is much better.  Some bulbs are custom made for specific bicycle lighting companies and are available only from that company.  Note that some custom bulbs have different connectors and may not be interchangable with your lamp assembly.  See the next question for two interchangeable brands of lamps.

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6.7 Are NiteRider's 6V bulbs interchangeable with VistaLite's VL5xx series bulbs?

Marty Goodman MD KC6YKC <MARTYGOODMAN@delphi.com> writes:

NiteRider's 6 volt bulbs ARE interchangeable with the 6 volt bulbs used in the VistaLite VL5xx series.  BUT, you must first remove the metal heat reflector that's added to the bulb and glued to it on NiteRider MR11 bulbs.  Similarly, to use a VistaLite VL5xx bulb in a 6 volt NiteRider system, you need to get such a heat reflector (from a dead NiteRider bulb) and glue that to the bulb with silicone sealant.   Be sure NOT to use a 6 volt VistaLite bulb in a 12 volt (13.2 volt) NiteRider system!

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6.8 What is the difference between standard bulbs, vacuum bulbs, krypton bulbs and halogen bulbs?

Small bulbs for flashlights and bicycle lights are typically vacuum filled (that is, they are not filled).  Krypton bulbs are an inert gas fill with krypton, argon or xenon as a component, which allows a higher light output.  Halogen bulbs use a fill with a halogen compound that, in combination with high operating temperature and a quartz bulb envelope, gives even higher output.

In halogen bulbs, the halogen cycle causes tungsten that boils off the surface of the bulb element to be redeposited onto the element.  This prolongs the operating life of the element and keeps the bulb from blackening (at normal operating temperatures).

Frank Krygowski <frkrygow@cc.ysu.edu> writes in rec.bicycles.tech <3CCDD7F4.9DE32EF3@cc.ysu.edu>:

But the general idea is, as you move from Standard (or Vacuum) to Krypton to Halogen, you're generally getting more light from the same amount of electricity.  And not only are Standard bulbs dimmer to begin with, they gradually darken the inside of their glass as the bulb ages, so the light drops off with time.  Halogen bulbs are worth the money. Assuming your light can stand the higher temperatures at which they run.

Some links to other pages on light bulbs:

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7. About cyclocomputers

7.1 What cyclocomputers are waterproof?

Apparently, not too many cyclocomputers are designed to be used in the rain.  There is speculation that most riders do not ride in pouring rain, nor do they leave their cyclocomputers in the rain for long periods of time.

The following brands claim to make cyclocomputers that can be used in pouring rain or used even fully submerged:

The Vetta can also be worn on the wrist, then snapped off and used on the bike.

While it is recommended not to use cyclocomputers in the rain that are not rated for wet use, the following units gave their owners little complaint or only required drying out with a hair dryer to get working again:

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7.2 What can be done to waterproof a cyclocomputer?

One reader suggested the surefire method of placing a plastic bag over the cyclocomputer and mount.  This waterproofs both the unit and the mount.

It was also suggested that for otherwise waterproof units, that the contact points be sealed with silicone compound.  This is available in small tubes from auto parts counters.  Vaseline was suggested as an alternative, since the silicone compound resembled vaseline in texture.  In addition, vaseline was noted to reduce corrosion on the contacts significantly.

Finally, it was suggested that wireless computers might be more immune to water penetration overall.

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7.3 How to splice cyclocomputer wires together

Marty Goodman replies to a question about splicing cyclocomputer wires:

>>> Marty:

When I get my Screamer next month, I'm going to install two Cateye Astrale computers on it.  I'd like to run both computers off the same pick-ups, which will mean splicing the wires.  I recall that you did this for Zach's Screamer.  Do you have any tips as to how best to go about splicing the co-ax wires on the Astrale harness?

FWIW, when I've spliced Avocet wires in the past, I've simply twisted the strands of wires together, smeared non-corrosive RTV on 'em to keep things waterproof, and covered the splice with heat-shrink stuff.  I've never tried to solder anything, as I'm [not confident of my soldering skills].  <<<

Marty's reply:


CatEye sensor wires on the Astrale and most other of their modern cycling computers are by far THE most difficult sensor wires to splice that I've dealt with (and I've spliced a half dozen or more different brand and model type cycling computer sensor wires in my day).

It's actually CatEye's very very high quality of construction that causes this:  They are made of VERY finely stranded copper, with EACH STRAND shellacked with insulating coats.  These strands are intermingled with fine nylon thread strands.  The result is a very strong, thin, flexible wire that can handle high frequency pulses cleanly.

While the wire may LOOK like its bare when you strip it, IT'S NOT! You will NOT make contact by twisting the strands together.

My technique involves at least modest soldering skill.  I first cut the nylon strands off and out of the way.  Then I put a glob of solder on the tip of my (high quality Weller WCTPN temperature-controlled soldering station) soldering iron.  I then bathe the strands of the CatEye wire in that solder glob until the varnish boils off and I see the strands get tinned.  Only THEN can I work with the strands in terms of twisting them, soldering them, etc.

The more I learn about splicing cycling computer sensor wires, the better and more knowledgeable I get about doing it, but the more reluctant I am to actually DO a splice if there's an alternative.

I've learned that with reed switch pickups (all cycling computers except higher end Avocets, and even those on their cadence sensor) open circuit is truly INFINITE resistance, and a "closed" circuit (closed switch) is seen by the cycling computer for anything less than about 600,000 ohms.  What this perhaps obscure techno babble means is that even a VERY VERY high resistance short between the two sensor wires... of the kind that can occur is a poorly weather protected splice gets just a little wet... will cause the cycling computer to see a permanent short on the sensor line, and "lock up".

I learned this the hard way, after an extensive splicing job on Zach's Rans SCREAMER went bad after he rode it in the rain.  Eventually (with excellent help from more knowledgeable folks on BikeCurrent list, as well as some effective testing and deduction of my own) I understood just what was the problem, and painstakingly re-did most of the many splices (we had three computers, in two locations, sharing two different pickups for cadence and speed) in a fashion designed to thwart that problem.

My technique for splicing now involves a number of tricks aimed at preventing such nasty high resistance shorts:  I cut the wires to quite differing lengths (by a distance of 2 or more inches) so that the two splices for the two sensor wires wind up distant from each other. This greatly increase the path needed for a short to form between the two wires.  I use heat shrink tubing after soldering the joint. I use either plasti-dip or silicone sealant (or both) to seal the ends of the heat shrink tubing.  I use heat shrink tubing again over both wires, to make the joint look a little more pleasing, and to add strength to that joint, and I AGAIN use plasti-dip and/or silicone sealant on that second sheath of heat shrink, globbing the wires with this weather sealant then putting the heat shrink over that and shrinking it down, then making sure the ends of the heat shrink are solidly plugged with the weather sealant goop.

As you can see from reading the above, my technique is painstaking and time-consuming.  SO much so that I tend to recommend to folks, whether they're considering attempting to do a splice themselves or paying me to do the splice for them, to consider (if it's possible with available wire run lengths) just running two separate cables and sensors.  For making a really RELIABLE splice, that won't fail when used in the pouring rain repeatedly, is not a trivial matter.

For those technically interested, the sensors on the CatEye (and all other cycling computers that use a reed switch and single rotating magnet) MUST be designed to be sensitive to a very high resistance short... to have what we'd call in electronics a "very high impedance input"...  because sensors electronics that would register only a real dead short draws more power from the cycling computer, too much so to be consistent with running a cycling computer off a tiny coin sized battery for years at a time.  We've had discussions on BikeCurrent about possible tricks to get around this, but the bottom line is that these high impedance sensors for the reed switch are the simplest and least expensive by far solutions to the problem of a reliable sensor that doesn't draw too much power.

Anyway, the summary of the above is: you CAN splice computer sensor wires, but to do a good, weather-proof job is tricky, and requires at least moderate skill.  And patience.  And time.  And you need to know what you're up against, and deal with it accordingly.

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7.4 What cyclocomputers have interval distances?

Interval distances are a feature useful for centuries, brevets and other guided bicycle events with cue sheets with distances to landmarks. By resetting the distance interval at each major landmark, cumulative discrepencies between the cue sheet and the cyclocomputer can be kept minimized.  The following cyclocomputers have this feature:

The Echowell J-12 has a countdown type distance display that may be just as useful, though Marty Goodman <MARTYGOODMAN@delphi.com> writes that this computer only displays speed with whole numbers rather than tenths.

Judy Colwell <Judy.Colwell@stanford.edu> writes that the Trek Radar is difficult to setup and use.  It also has a reliability problem with respect to the placement of the magnet and pickup.

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7.5 How to secure cyclocomputer wires

Sheldon Brown recommends using clear packing tape to secure wires to the frame so that they do not snag or get caught in something. Another reader suggests black electrician's tape, as it is more durable.

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7.6 What cyclocomputers can display cadence and speed at the same time?

The Echowell J-12, CatEye Solar CC-2000, Cateye Astrale and Polar Xtrainer+.

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Last updated and verified: $Date: 2011/03/28 00:36:30 $
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