Battery tab welding?

[BatteryCharger]

As some of you saw in a previous thread I happen to have an enourmous amount of AA batteries. Many of them will be made into 18v battery packs, and I'll probably need to weld tabs on them to do that. I don't want to try to solder them, I'll just end up cooking them...

First of all I understand how "normal" welding works. I have, in the past, used three car batteries hooked in series to arc weld 1/4" steel plate. I have also seen some DIY battery tab welders that seem to all use capacitors charged up to 25v or so discharged through copper electrodes.

I don't have any capacitors and don't want to buy enough to build a welder. Couldn't I acomplish the same thing with 2 or 3 car batteries the same way I can weld steel with it? Basically we're just talking about a quick, high amperage, ~25v or so "jolt" through 2 electrodes, right? Car batteries will easily give a few hundred amps...

 

[uk_caver]

I think the idea with the capacitors is that they give a brief pulse, enough to make the weld but not melt the tab.

Possibly an [adjustable] timer set to give a brief pulse of current might do the same job?

 

[BatteryCharger]

I was thinking maybe two 'pointy' copper electrodes, keep one in contact, and then touch the other really quickly. Kinda like accidently shorting a battery. I wonder if it wouldn't just fuse to the battery and blow up though....

Maybe I could come up with a foot pedal that would only give a brief pulse.

Does anybody know where I can buy cheap battery tabs? I guess I need to experiment a little bit...

 

[hopkins]

This 'how-to page' and videos (lower down page) shows the solution to spot weld battery tabs on AA batteries. The tabs need to be narrow enough so that one of the 2 spot welding electrodes can
push down on the 'to-be-welded-tab' and the 2nd electrode can touch the battery itself. A wide fat tab would not allow this.

The vid also shows how to make this simple spot welder out of a microwave oven transformer.
Seems a brilliant and simple solution.

link
http://hackaday.com/2009/06/23/how-to-build-your-own-spot-welder/

 

[jasonck08]

You can make a battery tab welder for about ~$100 in parts. All designs I've seen use a capacitor or bank of capacitors.

http://www.ledhacks.com/power/battery_tab_welder.htm

And http://www.philpem.me.uk/elec/welder/

The hardest thing is finding decent capacitors for a decent price. The guy in the first link used a car audio capacitor. Most of those caps are WAY WAY over rated. I remember someone doing a test on the capacitance and finding that they were <10% of their rated capacity. Computer grade caps would be better, but more costly unless you can salvage some.

 

[hopkins]

Yes I'd always heard about capacitor banks for spot welds also but the simplicity of this microwave transformer design is hard to beat. No power supply needed.
No worry over overcharging the caps. Plus it'll spot weld other stuff, not only batteries. Looks robust and could be free it you lay hands on the transformer from a junk pile.


Here's the AA battery tab welding youtube
http://www.youtube.com/watch?v=9spgDiU3_nw&playnext=1&list=PL2A8ECA9C8F48D7B4

 

[jasonck08]

Yes I'd always heard about capacitor banks for spot welds also but the simplicity of this microwave transformer design is hard to beat. No power supply needed.
No worry over overcharging the caps. Plus it'll spot weld other stuff, not only batteries. Looks robust and could be free it you lay hands on the transformer from a junk pile.


Here's the AA battery tab welding youtube
http://www.youtube.com/watch?v=9spgDiU3_nw&playnext=1&list=PL2A8ECA9C8F48D7B4

Doesn't look safe. The welds look huge. Battery welds should be small, and be done very quickly so there is no damage done to the battery. I like the CD welders better.

 

[hopkins]

Doesn't look safe. The welds look huge. Battery welds should be small, and be done very quickly so there is no damage done to the battery. I like the CD welders better.

jasonck08 - Agree as shown looks absolutely unsafe: a franenstein hack. Could you suggest some modifications to lessen the chance of accidental burns?
And yes smaller welds would stress the battery less saving its functionality. Can you explain why tiny contact points like on a CD spot welder cannot also work on a transformer spot welder?

Also agree that time taken welding spots on the battery tabs must be very short. Is there a MAX spec for safe welding time of tabs onto AA NimH cells??

I see you meant that the difference in rise times of the current pulses from the CD versus the transformer welder is 20x faster? 50uS for CD and about 1mS for the transformer. Is 1ms just too slow to spot weld tabs on AND will absolutely fry the cell?

 

[jasonck08]

hopkins, don't mistake me for a battery welder expert. I know very little about the subject. I've done a small amount of research and thought about building one, but then decided not to unless I can find good quality cheap high-capacity computer grade caps.

I would just imagine that the pulses from a CD welder would be faster than a transformer based welder, making it easier for smaller faster welds. Because I think you should be able to pulse higher currents for less time, leading to faster welds. The nice thing about a CD welder is you have some control over the welds. You can adjust the voltage from the power supply that charges the capacitor, and this might be needed to get good welds depending on the thickness of the nickle tab.

In the video you can see the nickle tab heat up and glow red for about 2 seconds. This can't be good for the cell.

 

[qwertyydude]

For all that money and the time to set up it's going to be easier to invest in a good soldering iron and solder the batteries. Just sand the ends lightly and dab a bit of paste flux. Then just solder a small blob onto that battery end. Then tin the connector and press onto the tinned battery, heat with the iron and presto it's soldered. I've done literally hundreds like this, never once cooked one because ideally you're not heating the battery for more than a couple seconds.

A good soldering iron should be a temperature regulated minimum 60 watts and for battery soldering it's good to use a high mass tip like a nice fat chisel tip, this maximizes the instant heat transfer that gets the soldering surface hot enough to wet but doesn't raise the temperature of the object being soldered enough to damage it.

 

[LuxLuthor]

In the video you can see the nickle tab heat up and glow red for about 2 seconds. This can't be good for the cell.

It's not. You need the high watt welding power delivered in short 0.5 to 5.0 ms "pulse width" depending on the tab metal and thickness, and application material needing the tabs.