Date: Sun, 06 Jun 1999 23:07:16 -0400 (EDT) From: Marty Goodman MD KC6YKC Subject: Comments from Willie re: battery capacity with LVR Message-id: <01JC3IDCG2XE8XETH9@delphi.com> Here's a copy of a note I got from Willie Hunt in reply to some implied questions I'd asked him about battery capacity in the face of different current or watt hour drains: > If you put a filter capacitor across your battery pack then the pulses > will mostly come out of the capacitor and the batteries will see more > of a constant (reduced) current as they charge the capacitor back up. If you put a sufficiently large cap across the battery pack (NOT on the LVR output), the peak current will be reduced to the average current and the battery will show even more capacity. Measurements, and calculations I have made show that this can add up to 5% for some alkalines setups. However, this is a small gain considering the large (like 0.1 F) capacitor needed to accomplish this. The 2 important factors with alkaline batteries and a LVR are the discharge rate (watts per cell; power draw), and the final discharge voltage. Ultimately, this determined the total power (watt hours) you get out of the cell. Watt Hours is what is important since that translates directly into Lumen Hours. Here's a few data points for Energizers based on a 0.833 volt cutoff: AA cells (advanced formula) watts/cell Runtime watt hours/cell ----------------------------------- 0.396 3.40 1.35 0.302 5.30 1.60 0.262 6.82 1.78 0.225 9.30 2.09 0.197 11.18 2.21 C cells (advanced formula) ---------------------------------- 0.836 3.25 2.72 0.597 6.00 3.58 0.418 10.95 4.58 D cells (advanced formula) ---------------------------------- 1.042 5.14 5.45 0.694 10.66 7.41 0.416 26.82 11.17 nominal 1.5 V Lithium AA cells (new formula) ---------------------------------- 0.521 5.45 2.84 0.321 9.22 2.95 0.208 14.78 3.08 The cutoff voltage is very important for C and D cells. An increase to a 1.0 cutoff could decrease runtime by approx 20%, or a decrease in cutoff to 0.6 could increase runtime by approx 20%. With the AA alkaline a 0.6 cutoff translate into a very small, like 1 or 2%, increase in runtime, however a 1.0 volt cutoff may decrease runtime by 10%. Some other noteworthy facts is that 4 AA alkalines always out perform 1 D cell alkaline, and weigh less. This is because the AA is a much better designed cell. On that subject the 1.5V Lithium AA cells totally blow away the alkalines in load handling and weight. Heres a quick comparison of Energy Densities: Battery test run hours Watt Hours / kg ----------------------------------------------------------- 3V D Lithium Saft ~10 ~230 1.5V AA Lithium Eveready 15 212 1.5V AA Lithium Eveready 5.5 196 1.5V AA Alkaline Eveready 11 96 1.5V C Alkaline Eveready 15 77 4.5V Flatpack Duracell 12 74 1.5V D Alkaline Eveready 11 52 1.5V D Alkaline Eveready 27 79 Notice that D cells SUCK!, unless you use them over a VERY long discharge. On the other hand, the Lithiums RULE! AA alkalines aren't bad. Some fuel for thought Willie