Need help modifying a 55mA charger to slow charge 350mAh nimhs

[ScienceGuy]

We are building several 8 cell packs of 350 mAh nimhs from maxwatts.com. We would like to properly format the cells by slow charging at C/10 but my Triton has a minimum charge setting of 100 mA. We do howver have several Hitec transmitter chargers rated at either 55 or 65mA at 10.8 volts.

Would it be possible to add a resistor inline with one of these chargers to decrease their output to 35mA and use them for a C/10 charge. If so, what would the correct resistance be. I understand the basis of Ohm's law but don't have faith in using it in this case.

Thanks so much for you time and wisdom.

Hugh & the Newark Electric Flyers

[Andy W]

"constant current" slow chargers are nothing but "constant".. :) I'd plug one in to your battery and see what it actually puts in.
..a

[ScienceGuy]

How does this sound? Since we're making up several packs we could make a harness and parallel charge two packs at once with the 65mAh charger. I know that it isn't appropriate to fast charge nimhs this way but at C/10 it would seem to be safe and effective. Two 350 mAh pack sharing 65 mAh yeilds a bit less than C/10 rate.

Does this seem safe and effective to you?

Thanks for informed feedback.

Hugh

[slipstick]

That would work. So long as both packs start at approximately the same charge level they will share the current reasonably equally. Just don't try parallel charging two packs when one is empty and one full ;).

Steve

[ScienceGuy]

Andy,

Great idea...... we have an Astro Micro Wattmeter so we can monitor the charge and see what really happens.

Hugh

[ScienceGuy]

Steve,

I can just imagine how hot things would get in a very short time. The initial charge will be with factory direct cells. We will check them but I bet they will be at a pretty similar state of discharge. We will certainly need to be careful on future slow charges of already used packs.

Hugh

[adamdb]

Or put each pack on the Triton and discharge it to a known point first. Then charge in parallel. I don't recall hearing of any issues with discharging a NimH pack before charging it.

Adam

[feihu]

Hugh:

From my xmtr output, I use a 47 ohm resistor which brings down the charge current to 25 ma for charging my 8cell 230mah battery.

Why not try a 33 ohm resistor on your xmtr output and measure the current with an ammeter? Better yet, get a variable resistor and vary it until you get your 35 ma out. then substitute the nearest fixed resistor.

feihu