Do battery chargers only charge up to the rated capacity?

[knightmb]

A thought hit me today while working on one of my battery packs. The wires going in that connect the charger, the positive lead had come lose. So I had to repair it inside the pack. Figured since I had the top off, I would check all the voltage on the cells to gauge how healthy things were inside. Usually the chargers just sit out in the garage and do their job, have been for years. I had to bring one in to charge the pack on the table to make sure the connections were good. While carrying the charger inside, I noticed on the bottom that it said it was rated for 24 volt NiMH packs (7-10AH). I started to think that all of my testing with these packs (doing a slow discharge test using the CA to measure AH and power) that they always did about 10AH during the test.

Whenever the packs are fresh off the charger, they have a perfect 28 volts right on both the CA and my digital multimeter, so I figured that's charged and ready to go.

Is it possible for a charger with this rating to only charge to a 10AH capacity for a 12AH capacity battery pack?

Figured since I had the pack apart, might as well take a picture. This is what the old batteryspace.com 12AH NiMH packs looked like on the inside :wink:

 

[Ypedal]

as far as i know, all chargers stop by

- peak voltage
- Voltage dip at end of charge
- Temp cutoff
- Max time

I do not know of any chargers that calculate AH delivery..

 

[knightmb]

That's what I thought, just wanted to make sure I wasn't missing something. While charging the pack, I have a meter on the pack to watch the voltage. I've noticed that once the voltage hit 28.0 volts, the charging is still charging. Like right now the battery voltage is at 28.44 volts. But I know it takes about 6 hours to charge these batteries from the discharge state. They are still cool to the touch. Usually when I run them through the smart charger, I come back and they are usually very warm. I know that NiMH heat when they get past that 80% charge state, it's just kind of weird to watch it from start to finish and doesn't exactly fit what I've read about how NiMH should behave during recharge.

I kind of wonder if my smart chargers aren't so smart, maybe pushing these NiMH a little harder than the should during the recharge phase.

 

[Ypedal]

I found my nimh packs to remain cool during most of the charge, 80 % + as you found, depending on the cells, some can be charged faster than others, if the bulk charge keeps them cool it`s likely ok.

The cells can go 1.44v or so before charging ends, so 28.8v on your our 20 cell packs is about right ..