Battery Spot Welder Suggestions?

[metrologist]

I'm looking for an inexpensive spot welder for batteries. Any suggestions? Something analogous to the venerable Hakko soldering iron...

[james_s]

You can get them from Sunstone Engineering, they're expensive though so I built my own. It's just a big capacitor bank, roughly 1F and a variable current limited power supply. Big SCR to trigger.

[metrologist]

Thanks. That sounds easier than the recycled microwave transformer route. Which SCR would you suggest?

[ovnr]

SCRs aren't really ideal for low voltage stuff, but w/e.

One tip: Avoid higher voltages. I've got a 25mF 200V cap bank, and while it does weld beautifully 9 out of 10 times on around 70-100V, the other times it causes very exciting explosions with lots of sparks, which tend to burn holes in the batteries. This is not an optimal outcome.

[james_s]

I used the biggest stud mount SCR I could find, I think it's rated 1200V 150A, the actual pulses are somewhere on the order of 10kA but very short and the SCR has held up fine. Ideal? Probably not, but it was cheap and it works. The power supply in mine is a very simple circuit build on perfboard around a LM317, range is up to 24V which is pushing the 25V rated capacitors a bit hard but they've held up for years of occasional use. Charging current is limited by the built in current limit in the LM317, I was going to design something better but never got around to it. When power is shut off there's a relay that discharges the cap bank through a power resistor and there's also a fault LED connected across the output. If the SCR has shorted that will illuminate to warn not to touch the welding probes to anything.

The whole thing is rather hacked together on the inside, with exception of the capacitors the whole thing is a junkbox special I put together in an afternoon. I initially tried one of those 1F car stereo capacitors and it worked for a few dozen shots and then failed. I replaced that with a bank of 22,000uF capacitors I got from a surplus dealer, they're installed in banks soldered to bare #10 solid copper wire buses which all tie into larger buses I made of flattened copper pipe. The whole unit is mounted in a box that formerly contained some sort of obsolete server room monitoring device. I could do better if I were going to build it again but it works fine so I've left it as is.

[mtdoc]

These cheap Chinese made one on ebay work fine for 18650 battery packs. They are built to a price but are ok for casual use. I bought one and so far it works fine. There are some youtube videos and blog posts about repairing them when they die (usually the triac)  Syonk has a nice review and teardown of one.

[metrologist]

I immediately went looking for my car audio cap, thinking I'd try a few manually, like with a couple probes directly to the cap and set one probe and drop the other in the right spot for a quick spark   

[stj]

http://ultrakeet.com.au/write-ups/cdWelder
 

[metrologist]

Sparkelicious

[Platonas]

Hello,
I made a spot welder for home use, using a transformer.
I use 2 transformers, one is 150VA and the other 250VA.  They had a secondary of 24V which I replaced wit a 10mm (multi core) wire wound to around 10 turns.  That gives me about 2-3v but at high currents.  You can get best results if a food switch is used at the primary site so no spark would result while touching the copper probes. 

[stj]

similar

[jwm_]

I thought this was a cool super hacky build that does it a little differently than the standard invert a microwave oven transformer trick. https://youtu.be/PHCFM5Gu5cU  basically a ZVS oscillator like you might find in an induction heater and a single wrap secondary. But uses a small transformer and high frequency so you can make it compact and battery powered. Plus, gotta respect that guys recycling skills.

[jpanhalt]

Here is a link to a DIY tab welder: http://www.philpem.me.uk/elec/welder/

I followed that design with a few modifications to make my device (attached below).

As for the SCR, any large one should work that has an adequate surge current current rating.  They can be obtained at relatively low prices on ebay or from other industrial used/surplus dealers.  My circuit development was done with a Semikron SKKT 92/16E SCR.  The final design used a Powerex T500108005AQ (http://www.pwrx.com ).  It is rated at 80A/1000V and has a surge current rating of  1800A.  The complete datasheet is available from Galco  (http://www.galco.com/techdoc/prx/t500_dat.pdf ).

John

[all_repair]

These cheap Chinese made one on ebay work fine for 18650 battery packs. They are built to a price but are ok for casual use. I bought one and so far it works fine. There are some youtube videos and blog posts about repairing them when they die (usually the triac)  Syonk has a nice review and teardown of one.

I got  Sunstone welder (earliest model probably) and China battery welder.  I am using the China welder.  They are made for battery makers.  Sunstone is not a good buy for me, and I paid many more time than the China welder.