Recently I have had my second 2,500 mah, 14.4 volt, AA NiMH battery pack failure after less than 12 months use. Both customers were operating USA Trains GP38-2 locos. One was on board the loco, the other was in a trail car. Both were trickle charged only using the RCS charger I make. These chargers were designed for NiCd chemistry and not NiMh. Although it is possible that the chargers caused the failures, I doubt it because I have plenty of other customers who have the same packs and have not experienced any failures using the same chargers. The above is of concern to me, so I asked my battery supplier what the maximum current draw from these tabbed 2,500 mah AA Sanyo cells would be. The answer surprised me. Because of the physical construction of the cells, the maximum continuous draw is ½ an amp. They are designed to give a low current draw for a very long time compared to NiCd cells. They can withstand short 1 amp current draws but nothing more without causing irreparable damage to the cells. Sure, the NiMH cells will sustain the high current draw, BUT! this damage will drastically reduce the life of the cells from a claimed 500 recharges to possibly no more than a few dozen. Roughly the same current draw restrictions apply to AA NiCd cells as well. If you don’t believe me, go ask your battery supplier to put into writing that they can handle the draw you require from them. SO. For small locos that do not draw more than ½ amp total continuous, AA NiMh cells will be OK. For larger locos that can haul a lot of cars stick with cells that can handle the current. Here in Australia I cannot economically justify the odd sized cells you can get in the USA. They are hard to obtain and expensive. In Australia I recommend SuB C cells or larger. Either NiMh or NiCd. As an aside, NiCd’s last twice as long. I am currently installing two Sub C 7.2 volt 1700SCR twin stick packs in the USAT GP38-2. Pictures will follow shortly to show you how. The replacement batteries ahve been installed, the loco tested and delivered back to the owner. Firstly I removed two front stanchions from over the fuel tank. The holes in the floor show where they had been. I CA’ed small square plastic tubing to support the battery packs up off the chassis to allow wires to reach underneath. I then drilled four 3/16th’s holes to allow plastic zip ties to thread through the chassis.
The 2 x 7.2 volt 1700 SCR NiCd battery packs were tacked together with silicone roof and gutter sealant and mounted in place. The two plastic zip ties wre cinched up tight and the excess cut off.
I used an RCS Y Cable kit to join the two packs in series to get 14.4 volts and feed the power down into the fuel tank where the ON-OFF switch and sound system are located.
