Author Topic: Dumb battery charger  (Read 298 times)

Dumb battery charger
« on: June 25, 2020, 08:21:02 am »
I just ordered a BL700N which seems to be the recommended battery charger but its flaw seems to be that it doesn't see totally flat batteries. These need a quick kick with a dumb battery charger to get some life into them before being charged properly in the BL700N.
So the question is does anyone have a recommendation for a cheap dumb Nimh battery charger to use for this purpose (that does AA and AAA preferably) ?
Its difficult to tell from the product details on Amazon juts how dumb a charger is ....
I think you'll find it's a bit more complicated than that.

Re: Dumb battery charger
« Reply #1 on: June 25, 2020, 03:52:09 pm »
I think Kim had a trick to getting them to start, you use some wires to connect a known good battery in parallel with the empty battery for long enough that the charger starts to do its thing. Once there's a little juice in it then it'll recognise it for a full set of charge/discharge cycles.

(I don't have this problem as I have an old dumb charger lying around for this very reason.)
"Yes please" said Squirrel "biscuits are our favourite things."

Kim

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Re: Dumb battery charger
« Reply #2 on: June 25, 2020, 04:23:28 pm »
My usual approach is to connect them to a bench power supply, set to constant-current mode at some suitably low value (like 0.1C or something).  Obviously that's easy if you've got a bench power supply to hand, but if you did you probably wouldn't be asking this question.

Wiring in parallel with a good cell isn't a terrible idea.  Maybe stick a resistor in there to limit the current so it doesn't hurt the good one.

Price used to be a good indicator of dumbness, though less so as charge control chips get cheaper.

You really want something that can charge cells individually.  Unfortunately, many of the dumb chargers tend to do them in pairs.
Careful, Kim. Your sarcasm's showing...

Re: Dumb battery charger
« Reply #3 on: June 25, 2020, 05:26:36 pm »
I stand the 'flat' battery +ve (pimple) side down on a knife alongside a slightly less flat one and using a special tool that looks remarkably similar to my kitchen scissors I connect the two negative terminals together for a second or two.  This makes my BL700 less grumpy and it will then charge the battery.

Re: Dumb battery charger
« Reply #4 on: June 25, 2020, 06:02:03 pm »
I stand the 'flat' battery +ve (pimple) side down on a knife alongside a slightly less flat one and using a special tool that looks remarkably similar to my kitchen scissors I connect the two negative terminals together for a second or two.  This makes my BL700 less grumpy and it will then charge the battery.

I use metal kitchen tongs, always works well.

Re: Dumb battery charger
« Reply #5 on: June 26, 2020, 09:47:12 am »
Thanks JB and BSB, works very well!