Message-ID: <01603F7CF8C7D111B9B80000F80463F7437C39@wcgmrke101.wilcom.com> From: "Leonardelli, John" Subject: RE: Sealed Gel Lead acid chargers Date: Thu, 8 Oct 1998 10:07:28 -0500 Smart Chargers John Leonardelli (leonard@astral.magic.ca) Mon, 11 Nov 1996 14:51:11 -0500 (EST) After frying a few 6V Gel-Cells (SLA) I sought a better solution to charging my batteries. I wanted a " set and forget " way of charging batteries and felt a Smart Charger of sorts was needed. I think I found the ideal charger that met my needs. The Smart Battery Charger from A&A Engineering offers kit, or built versions using the Unitrode UC3906 chip. The UC3906 offers 3 distinct operating states. Initially it controls the charging current to a pre-set bulk value and when this bulk current tapers down to a specific level it then tops off the battery with an elevated full charge voltage (7.2V). After top off, it enters the maintenance mode where it dutifully maintains the battery at a precision float value level (6.9V). This charger can be connected to the battery indefinitely, it will not overcharge your battery. It will charge batteries from 3 to 120 ampere-hours based on a change in components.It has a power on LED as well as an Overcharge LED indicator. The chip has a sense function that monitors the battery voltage before and during charge in order to choose which charge mode to be in. Their standard kit is 12V 0.5 or 1A. The kit is $60 US or assembled for $80 US. They also offer schematics and a bare board for $7.50 US. Key components are a UC3906 chip, a TIP42 transistor, a diode bridge and a 16 to 25V transformer. Precision resistors are used to set the voltage and cell count. I built a 6V .5A 3 cell version. Optional volt or ampere meter connections are available on the PCB. The kit building went really quickly and was done in an evening. Of course like many things I build I still have to find a suitable cabinet for it. I have used this charger for a few months now and it works extremely well. I have found the batteries are charged properly and a well maintained and seem to have given me more "light time". I was never able to charge my batteries properly before using a wall adapter or LM317 based power supply without having to monitor the battery voltage and adjust voltages on the charger accordingly. Now it is all simpler. A&A modified the original design that appeared in QST magazine in April 1987 (I think the date is right). Note that this device will not charge Nicad batteries. For a more full proof charging method use a Maxim chip (see marty's excellent article in a past thread). I believe Ramsey also offers a similar type of charger for Gel-cells but I do not have any experience with that unit or all the technical details. Since A&A has a $20 minimum on credit card orders it would be best to buy two boards and two chips (or even two kits) and use 1 for 6V batteries and the other for 12V batteries. A&A Engineering 2521 W. La Palma Unit K Anaheim, California 92801 USA (714) 952-2114 ALL DISCLAIMERS AS SUCH ARE INCLUDED P.S. For those that are into Photography there are many battery supplies available for Vivitar 283 type flashes that are nothing other than a 6v gel cell. One could easily cobble up a pack for this flash and use the same charger decribed above for this purpose as I have done. Just buy the appropriate battery connecting cord for your flash but please ensure that this is for 4 AA type units. John Leonardelli