Newbie Ni-Cd to Ni-Mh Battery Question

I've just changed the NiCd batteries in my "Bostik" soldering iron with NiMH. Runs and charges like a beauty, and I can get even more heat out of it now.

It had two 1200mAh C cells and they were changed to 2700mAh. The original plug-pack charger works happily without getting too hot.

Hope this helps, Peter

Don't use NiMh. NiCd have much lower internal resistance than NiMh so are more suited to high current devices like drills.

Also, NiCd are much more robust and tolerant when it comes to charging. NiMh cells are exothermic during charging so they can get hot real quick and hence get damaged more easily.

Stick with NiCd. Dave :)

My 14.4V cordless drill recently lost performance due to a couple of shorted cells, this in turn popped the thermal fuse in the wall wart charger. There was no safe way to bodge the charger transformer other than find another wall wart transformer with the same ratings, the shorted cells were cleared by using a 12V lead battery with both filaments of a H4 bulb in parallel to limit the current and immediately giving the pack a full charge on the repaired charger - its worked good as new since.

no. most NiCd chargers can't correctly charce NiMh cells.

Bye. Jasen

Thanks for the replies, much appreciated.

I looked for NiCd's without success, seems NiMh are now the only readily available rechargeables available from the department stores / Jaycar / DSE / etc..

With concerns about the charger too, in the end I decided against refreshing them ;) Thanks again for the advice.

Cheers

Jaycar have plenty of NiCD cells! Solder tab versions are available in AA,Sub C, 1/2 Sub C, 4/5 Sub C, and 2/3A Page 196 in the catalog.

Dave :)

go to a battery place. not a toy shop.

Bye. Jasen

My local store didn't have any stock of the ones I thought I needed. The

1.8AH SUB C were what I thought would be ok and better, the other 1.3AH would be much the same as the original batteries I thought and very little point in replacing given the cost.

I was even going to try higher rated AA (as they would physically fit) but the highest in stock were 1000mAh.

I guess it's probably safer anyway that someone like me didn't do it ;)

Thanks all again.

Ta for that, probably a good thing I did go the NiMh route then.

Cheers

Actually, model toy shops would most likely have the high-performance NiMH batteries that he wants.

I'm curious though, do these drill packs still use temperature sensing for charge cutoff? Or do they use delta V with temperature as a safety backup? If they still use temperature, would the temperature change of a NiMH pack be close enough to that of NiCads?

No, NiMH have an exothermic charging process and generate a lot more heat (and internal pressure) during and at the end of charging, totally different to NiCd.

Only the expensive drills have any sort of proper charging design. The cheap $15-$50 Bunnings drills have no cutout at all.

Dave :)

Have a look at the next (December) issue of Silicon Chip - this exact topic is covered in a feature and also a charger controller to stop you coooking the batteries in the future.

Ross Tester

Han wrote:

NiCd charging is endothermic, so the increase when they fill up and go endothermic is more pronounced.

it could work.

Bye. Jasen

On 2006-11-08, I

~~~~~~~~~~ eXothermic

Bye. Jasen