Electronics 2000 Forum

[BurningSmell]

The NiCd batteries in my old drill finally gave up the ghost. They were tagged 4/5 C cell size, 1.2V 1700mAh. Since you can't get NiCds any more, I replaced them with tagged 1.2V 3300mAh NiMH.

Now when I did some drilling I got a distinct hot smell and when I took the drill apart again I found that one of the tags had got so hot that the solder had melted.

Any suggestion why such a thing should happen given it was a straight battery swap out?

[Biffo]

I was lucky, I managed to get some new (last of)Nicads for my trusty old drill a couple of years ago.Because of the increased capacity of the newer type its only the charger I have to keep an eye on as its gets a bit warm now but once they are charged these new batteries seem to go on forever.
My capacity was orginally 1700 MAH and the new ones are something like 2500 MAH

Have a look in the tool catalogues and I dont think NIMhs were a bit hig with cordless drills (the Lithium ones you would need a different charger for)

You could probably get some spec and advice from whoever sold you the tag bats, and see what the current drain is between a Nicad and Nimh as drill motors may put demands on Nimhs that they find
hard to cope with? maybe the inclusion of a suitable resistor could help?

but on the other hand If the heating is confined to one tag then maybe either you have a faulty cell or its in round the wrong way ?

[ccayser]

If you have two cell's one is one way and second one is opposite to the first one(+battery- -battery+) then according to krichoff voltage law, the voltage measured from one cell to other is zero. to determine if one of the cells is wrong way in, then measure the output voltage, and if it is not what it suppose to be, then something is wrong( I dont mean, that there is 11.7V instead of 12V but when you have 10,8 instead of 12V, then something is wrong). Also there might be a physical error...e.g + and - were connected

And the main precaution, you may not charge NiMH cells with NiCD charger, it may end with fire or explosion.