NI-Cad Battery Welding?

"Glenn" wrote: I have a bunch of nicad battery packs I want to mix and match to make a few good packs out of. Problem is welding the tabs back on. (clip) ^^^^^^^^^^^^^ I've always been able to solder tabs on ni-cads with a Weller soldering gun. Rubbing with the tip through a film of hot flux seems to be the secret.

I have done that in the past also but the results are less desireable than spot welding. The heat of soldering has always concerned me. Glenn

As long as you don't melt the vent valve you are OK. Need a HOT iron - hit fast and run!.

What he said.

Freshly sandpaper tabs and terminals, apply acid flux. Tin and solder quick, cool with spit on finger, wash battery and finger well.

Well, ok .. done that many times and it works. But I want to do something with this darn transformer and a mini spot welder just seemed so cool :) You are correct though .. I could solder tabs on a LOT of batteries in the time it would take to turn this into a reasonable tool for spot welding.

Thanks Glenn

Freeze the cell, then do a quick , hot solder joint. Pat

Glenn - check out :

I believe the way this is done in production is with a capacitor or a bank of same. An RC network, in other words. C for the energy control, R for the duration control. You'll want copper for contacts, not tungsten, that'd likely stick.

I've soldered tabs myself, but have vented a few cells that way, too. Really hard getting up to soldering temperatures when the water is boiling on the other side of the case. Hard to avoid some cell damage with soldering.

One other way is to clip the tabs in the center when removing good cells and solder across the remains with a short wire bridge.

Stan

Thanks Rob, I have a bunch of big old caps and SCR's etc so that is a doable solution. The link to the commercial welders with the welding "pen" is more the way I want to go. I have a regular spot welder good for 2 10 guage pieces welded together but it is a bit over kill for the batteries :) The pens give me some ideas I may want to pursue. Glenn

Only problem with the capacitor type is it turns into a rather large box to store :) The transformer and power control would fit in a rather small box .. 5"X5" or so. The transformer has enough power to do the welds. I just need to come up with a nice way to hold the electrodes. Thanks Glenn

The heat may be an issue and it may take some practice, but the results of a good solder job are likely preferable to a spot weld - increased contact are of lower resistance. The R/C airplane/car folks tend to solder theirs, though carefully. My former boss had a plane he referred to as a "flying welder" - in reference to the current draw, not the method of assembly (which was solder).

Google a bit and you can probably find how-to articles on R/C sites. Those goes aren't willing to take any chances on cell damage, either.