Replacing NiCd camcorder battery with NiMH

I belive it boils down to the chargers capabilities. If it is not compatable with NiMH then do not do it. Perhaps you can find a third party charger that can. If Sony says there carger cannot do NiMH then I would belive them.

Thanks for the reply. Sony did not actually say the charger would not do it they were more interested in selling me one of thier batteries. If I do decide to buy a new NiCd then it will not be a sony but a compatible one. My camcorder is 13 years old and does not see much use but is usefull at times. So what is the difference between charging NiCD and NiMH.

The charge profiles are somewhat different.

NiCd charge profile: Constant current, usually time limited. Trickle charge ok. Advanced chargers measure temperature and cell voltage and cut the charge to trickle during the -dv/dt part of the profile. Peak voltage is not usually an issue (because the peak voltage can vary so widely for NiCd)

NiMH Profile: Constant current or current limited (fast charge mode). Peak voltage detection required. Trickle charge ok. Charge controllers should measure -dv/dt and temperature.

In general, most available charge controllers for these types of battery handle both (NiCd / NiMH). (See, for example,

You may find it difficult to get new NiCd (or you'll pay a premium) because of their chemical content (heavy pollution issues). I would try and find out if your charger is NiMH compatible.

Cheers

Petes

In article , Happy Friar wrote: :Thanks for the reply. Sony did not actually say the charger would not :do it they were more interested in selling me one of thier batteries. :If I do decide to buy a new NiCd then it will not be a sony but a :compatible one. My camcorder is 13 years old and does not see much use :but is usefull at times. So what is the difference between charging :NiCD and NiMH.

I understand that NiMH batts lose their charge, when stored, much more quickly than NiCds - I would find it annoying to discover my batts are flat when I want to video something, so would choose to continue with NiCds - but that's me.

David

Happy Friar wrote:

| The charge profiles are somewhat different.

Really, they're pretty much the same.

If you're fast charging (faster than C/10 or so) then the peak that you're looking for is smaller on NiMH cells than NiCd cells. If your charger cannot detect the smaller peak, it may just miss the peak and keep charging. This is the real danger. Also, most NiMH cells don't like charging at over C or so, where SubC NiCd cells can tolerate even

Both will tolerate slower charging OK, but NiCd can suffer from voltage depression if you continue slow charging after it's full too much. (I think NiMH will too, but to a smaller degree.)

Another danger with switching to NiMH from NiCd is that since the self-discharge rate is so much faster (about 3x as fast), and the cells themselves have so much more capacity (2-4x as much) that the self discharge rate may be as large as the charge rate of your original slow charger, so the batteries may not get fully charged even if you give it days to complete. | NiCd charge profile: | Constant current, usually time limited. Trickle charge ok. Advanced | chargers measure temperature and cell voltage and cut the charge to | trickle during the -dv/dt part of the profile. Peak voltage is not | usually an issue (because the peak voltage can vary so widely for NiCd) | | NiMH Profile: | Constant current or current limited (fast charge mode). Peak voltage | detection required. Trickle charge ok. Charge controllers should | measure -dv/dt and temperature.

Peak voltage varies on both considerably. Your charger needs to look at dv/dt and look for the drop. Stopping charging based on peak voltage just doesn't work for NiCd or NiMH.

Checking the temperature works too, but at high charge rates you'll already be damaging the battery by the time the temperature starts really rising.

| You may find it difficult to get new NiCd (or you'll pay a premium) | because of their chemical content (heavy pollution issues). I would try | and find out if your charger is NiMH compatible.

NiCd cells are pretty easy to find, and they seem to be a little _cheaper_ than NiMH cells for the same physical size. Though I'm talking about individual cells and not assembled battery packs, and I'm thinking of what we buy for R/C use rather than what a camcorder would use.

Apparantly only a few factories make NiCd cells anymore, for the reasons given, and lots of places make NiMH. NiCd are generally better for high drain applications (power tools, R/C motors) but NiMH cells have mostly caught up. I'm guessing that most of the low end power tools use NiCd rather than NiMH cells now because 1) they're cheaper, and 2) they handle abuse a little better. The lower internal resistance is good, but NiMH cells have just about caught up.