Ansmann ACS 410 safe for use with AA's?

[Resqueline]

I have an Ansmann ACS 410 universal NiMH/NiCd microcontroller charger that I was hoping to use with my slightly modified Sigma Sport Halogen FL100 bike light.
The problem is that the charger is happily cooking away at the batteries as they are passing 40-45C. I don't like this and I don't intend to test at which point it might shut off.. It does this with both battery brands I have tried and I fear it damages them.
The charger puts out 600mA and the present batteries are Varta Photo Accu 1900mAh. The charger seems to work in all other aspects.
Does anyone have any experience with these chargers, or any ideas as to what the reason behind the overzealous charging behaviour might be?
I modified an identical charger for a friend of mine to put out twice the current for use with a 7000mAh NiMH pack and it seemed to work great, peaking the pack with little or no heating.

 

[SilverFox]

Hello Resqueline,

It sounds like your charger missed the end of charge termination signal and was in the process of overcharging your battery pack.

If your charger uses -dV as its charge termination method, the battery manufacturers recommend charging at a rate that completes the charge of a discharged cell in 1 - 2 hours. With your 1900 mAh cells, this would be charging at 950 - 1900 mA.

Another reason for missed charge terminations with battery packs is that over time the cells within the pack can get out of balance. The way to correct cell imbalance in a battery pack is to give the pack a 16 hour charge at 0.1C. With your 1900 mAh cells, this would be charging at 190 mA.

Tom

 

[Resqueline]

Yes, it doesn't seem to interpret the NiMH's 0dV charge termination requirement correctly. The box states it uses a voltage gradient shutoff, but not its magnitude. Maybe it's a compromise that undercharges NiCd's & overcharges NiMH's, or maybe it's just plain broken in some way.
Maybe the cells weren't balanced to begin with, I can't recall giving them a trickle charge, they were new and are hardly used. I know an imbalance or a low charge rate would give the packs a less pronounced 0dV timing, but I think a good charger should be able to deal with this fairly common occurrence.
After all the manual says it charges anything from 4 to 10 cells with 500 to 3000 mAh in 50 minutes to 6 hours, using 700mA. It detects faulty packs and is independent of their initial state of charge.
So if it uses -dV it seems I'll have to either get a NiMH specific one, up the charge rate, or decrease the battery capacity...:thumbsdow
Or maybe I'll just go back a couple of decades and use the good ol' C/10 charging method..