AA NiMH charging question
 

What is the most common Amperage to charge AA's? I have a bunch of these in various capacity's, some rated for high current charging.. So what's the general idea for charging them? What cutoff are y'all using?

They are getting used in transmitter's.

generally 1 amp max charge rate, however the slower the better. i charge my gp2000 aa cells at .5 amps unless im in a hurry.

what cutoff do you use?

Aren't most NiMH chargers delta-peak chargers? When they sense the peak voltage (the voltage starts to drop) then they stop charging. In the sub-C days, most cells would peak around 1.5v.

Yes, but the delta peak is adjustible. lower it and the charger ends its cycle early. Raise it too much and the charger will overcharge. This is true no matter cell size. We would have to adjust delta peak drop constantly when the sub c NiMH cells were updated. Early cells liked to be a little warm at the end of the cycle. As the formula changed in later cells.. especially ib's...they would not tolerate that. They needed to be about ambiant to preserve their performance.

Nearly all chargers will set a delta based on cell type and count, but it is ballpark figure. Really...for some aa's it is probably close enough. I was just trying to see if somebody had a more precise number.

.5 an amp is pretty safe, i would avoid charging them in the radio. If 1 cell overheats and vents you it can cause damage to your'e radio.

That's a good point hoyt.. I am charging with an Orion Twinspec, and I use a AA 4 count holder for the cells. The delta peak is the biggest issue i'm having right now. Trying to find the proper number so I can get a full charge. I have it set to 13m/v right now and the cells are only taking about 800 ma before cutoff.. They aren't even warm at a 1A charge rate.

I have Orion 2700's and some 2800's that I am charging so they should be taking more than this.

When using the big charger I use 0.5 amp and a 5mv per cell delta, seems to work OK. But whenever possible I charge outside the radio with a charger that does each cell
individually.

Off subject a little. but I really like Low Self Discharge AAs for transmitters. Only charge every few months. Also known as Ready To Use.

Costco carries the Sanyo Eneloop ones. They claim to hold 75% charge after 3 years of non-use.

Unless you run them dead, you're really only re-peaking the cells. I'm not familiar with your'e charger, so i couldn't give precise advice, however you could try to up the Mv and keep a careful eye on the temp.

I've charged my eneloops at about 1c or 2 amps quite a few times without worry. I see the 1 hour quick chargers out there for NIMH and figure that's got to be putting out 1c or so if it takes an hour? Will have to look at one and read the output specs on it. They do get a bit warm but work perfectly fine.

I'm too impatient to wait 2hrs+ for my 2000mah TX batteries to charge using 1 amp or less

What I am seeing is the higher rate I charge them at, the quicker they peak, putting fewer MaH into the cells. Also the voltage drops much quicker in use.

I have 12 cells, charging 4 at a time. I got my best results yesterday charging at 1.3A with a cutoff of 13Mv. They came off slightly warm and I put about 1200 MaH in each group of 4 before they peaked. My next race is Saturday, so I'll see then how well they hold their voltage thru the day.