# Can I substitue NiMh for NiCd?



## DoctaDink (May 6, 2007)

A little off flashlight topic here. But I thought you battery gurus might answer this for me. I have a Wahl beard trimmer that uses a 1.2v Sub C NiCd (part #00745-200) that needs replacement. Can I substitute with a NiMh battery?
Wahl wants $8.00 for the NiCd, plus $9.00 for shipping. I would like to get a longer lasting, and cheaper battery. Any suggestions. 
Thanks in advance, and sorry about the non-flashlight post.

Dean


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## EngrPaul (May 6, 2007)

I did it to a cordless phone with success (been working for years). I tried it on a shaver and it wouldn't work.


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## rdh226 (May 6, 2007)

Iffy.

The primary problem is that NiMH batteries do not like to be force-fed/overcharged, and
that is exactly what NiCd "low-end" chargers do: they are basically constant-current
"trickle" chargers (low current, takes many hours to charge, then keep feeding this
same charging current even after the NiCd is fully charged). NiCd batteries just shrug
off this excess charging current, but it will eventually "cook" your NiMHs.

That said, NiMH will pack much more punch into given size...so if you don't leave it on
constant charge (drain it, charge it overnight, then unplug it once "properly" charged)
it should work quite well.

Of course if you ditch the crappy little wallwart "charger" and hook it up to a proper
NiMH charger, it'll work Great!

Good Luck!

-RDH


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## DoctaDink (May 6, 2007)

Thanks guys. I appreciate the reply....now off to buy a battery.


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## DoctaDink (May 7, 2007)

RDH,
One more question...What sort of charger would you recommend? Any source for the two pronged connector?

Thanks.


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## rdh226 (May 7, 2007)

DoctaDink said:


> RDH,
> One more question...What sort of charger would you recommend? Any source for the two pronged connector?
> 
> Thanks.



Ya know, I have no idea what charger to use as an inexpensive single-cell NiMH charger.

Other than the expensive zillion-purpose hobby chargers which can do "as little as" a single cell, I
think the closest I can come is one of the AA/AAA chargers that do two to four independently. Kinda
krocky solution, but doable (just tap into one of the bays), although might lack that spousal approval
factor.

Try google?

Good luck.

-RDH


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## DoctaDink (May 8, 2007)

Thanks again for the help.
Maybe I can Kludge together an adapter for my MaMH-C801 charger. Think that would work?


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## bullpup (May 8, 2007)

I have a Siemens wireless phone system. It takes two AA 1.2volts Nicd. I have always had four of these phones in the sytem. Everytime I needed baterries I would swap out the batteries from the phone. Since up until recently they were never discharged so when I used them they died very quickly (besides being 800ma). THe owners manual says it can use both NIMH and NIcd.





I replaced them with energizer 2500 Ma NIMH. They worked fine on three of the phones. THe fourth phone when I picjed it up was burning hot. I am wondering if the voltage capicity size is too high on the forever trickle charge is too much. Be careful when swapping.


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## MrAl (May 8, 2007)

Hi there,

The NiCd charger doesnt do a very good job of charging NiMH, but if you use
a higher rated NiMH in an application that had a smaller NiCd cell it tends to work
to some degree.
For example, in my shaver they had some tiny NiCd cells, i think were rated for
250mAh or some low value like that (maybe 500mAh). I didnt feel like buying
those tiny cells so i substituted two 2000mAh rated NiMH cells.
The thing is, the NiCd charger only puts out about 90ma, so it's not too bad on the
much higher rated 2000mAh cells, so it works out pretty well leaving it on charge
for long hours. If the replacement cells were much lower rated i wouldnt think of
doing this, but because they are much higher rated they can put up with the
constant charge of 90ma or so.
The rule seems to be if you must replace NiCd with NiMH then you need to use
a much higher rated cell and the charge current shouldnt be higher than about
100ma.
I have been running my shaver for about 6 months or more this way and so
far so good. The NiMH cells are doing well.
If it turns out in the future if they go bad, i'll still replace them with two more
higher rated NiMH cells, not those tiny little good for nothing NiCd ones ha ha.
Try it, you'll like it.
Of course this assumes that the charger uses a low constant rate
of 100ma or so. If it's a smart charger (checks for minus delta V)
it may or may not work.

BTW, the cells i used were those four for six dollars brand type cells.
I have two more waiting to be used for something.


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