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NiMH in series: can it be charged by an 'intelligent' Lead Acid charger???


I have tons of NiCd battery packs and tons of (sometimes) corresponding cordless drills. Only with a complicated discipline, involving several chargers, I can count on enough performance for a hard day's work. I did rejuvenate the individual cells by zapping; some packs improved, some packs died. The 'electric hubcap' site : http://members.shaw.ca/Craig-C/, states that a home made NiMH battery battery pack (several chains of 10 cells in parallel) can be charged and re-charged hundreds or thousands of times, and have a better performance than Lead-Acid...  Is it worth the investment???

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verence6 years ago
For your title question: "NiMH in series: can it be charged by an 'intelligent' Lead Acid charger???"
Answer: No. No. Just: No.
Totally different chemistry, totally different loading strategy.

Good investment if you need tools for heavy duty work? Buy the heavy duty stuff, not the DIY line of tools. Yes, the professional tools are more expensive, but it usually pays in the long run. (If you're going to use them a lot, that is)

Buy a cordless drill and one ore more extra power packs and the charger of course. Charge one pack while working with the other. Less tools, less chargers, less hassle. (And no danger of exploding cells while charging ;-)

BobS (author)  verence6 years ago
I had my suspicions about the 'solutions' from the hubcap web site. I use tools as an enthousiast hobbyist, right now frequently, building another greenhouse. I don't buy cordless tools but FIND tons of them, often including chargers, in our city recycling center. I managed to assemble a few half decent battery packs from zapped cells. It would have been really convenient though, to have a few NiMH packs, to be charged by a car battery charger...

Would a slow NiCd charger (12 , 14.4 or 18V) work for a NiMH pack? (I would assemble the pack myself)
verence BobS6 years ago
> I had my suspicions about the 'solutions' from the hubcap web site.
Me too ... ;-)

> I don't buy cordless tools but FIND tons of them, often including chargers, in our city recycling center.
Okay, I see. I would be hard to find decent professional tools there.

> Would a slow NiCd charger (12 , 14.4 or 18V) work for a NiMH pack? (I would assemble the pack myself)
'Slow' in the realm of charging is determined not by the voltage of the charger (that has to match that of the akku pack) but by the current it drives into the akku.

Charging a NiMH from a NiCd charger should work, _BUT_ stopping the charging process most probably won't work. As steveastrouk wrote: The trick is in stopping the charging. NiCd and NiMH behave differently when being fully charged, so one charger can't detect that the other kind of chemistry is now full.

You might go with a very slow charger with I << 0.1Z so even a full akku doesn't get destroyed by the extra charge, but that would take more than 10 hours for each charge cycle (Just like the very early NiCd chargers did.)
+1. Basically NiMh is charged with a constant current, Lead acid, with a constant voltage (and current limiting). There are tricks to STOPPING charging too.
lemonie6 years ago

Is there any cash (metals) value in old NiCds?

L
They can certainly be recycled, and should be to keep the metals (especially the cadmium, which is significantly toxic) out of the waste stream. Whether that produces more value than it consumes, I couldn't tell you ... but a websearch probably could, eventually.