High Current Short Circuit control, 24v welder

[Sandman614]

I hope this is the right crowd for this level of techincal question.  The welding forums that I've asked this on just blather like a neanderthal "Learn how to burn some 7018 rod, and take batteries out of multiple peoples trucks".

I have built a portable battery powered Mig welder, but it lacks control over voltage and current.  The build uses a 4p8s LifeP04 battery pack with 200a JKBMS, the wire feeder from a cheap inverter mig welder(24v feed motor) with a 5a pwm controller, a 24v high current solenoid, and 0.035 welding wire.  My end goal is a portable battery welder that will mimic/enhance the practice of stick welding using 2 car batteries and a set of jumper cables, for offroad trail repairs.  Generally these repairs are larger chunks of metal like tie rods, axles, and various brackets.

So to the point, what I am looking for is a means to vary the amperage on a 24v DC system from 30-200amps.  What I am finding are similar to the PWM motor controller I have already used but they only seem to go up to the 60a range and I don't think that a PWM controller is the correct device for the intended use. I have already tried setting the "Continuous discharge current" in the BMS but that does not seem to be limiting the current like I believe it should.  My amp clamp has gone MIA so I have not had a chance to verify this yet.

[Kryptychon]

Hi,

what you basically need to implement/get your hands on is a controllable current chopper.

I guess you can re-purpose a mains powered welding inverter to work with DC. Basically, inside a welding inverter, mains is rectified, fed into a high voltage DC bus from which in turn the actual inverter circuit is fed.
Of course there is a transformer involved to achieve galvanic isolation, but that's not a concern if you're using batteries.

My approach would be to get my hands to an actual mains MIG/MAG inverter and have a look into the electronics and if the DC bus can be fed externally somehow.
I can imagine the DC bus voltage in an actual inverter will be much higher that your approximately 30V (8s LiFePO4), so this needs some thinking.
As you have 4p8s, you could reconfigure your pack to get around 120V of DC...maybe that's a starting point. Of course, your battery pack must be fused(!) and you will need a different BMS.

Be warned, if you're going down that road, the energy stored in the DC link caps of a mains powered welding inverter is substantial. It's high voltage, high amp DC - very dangerous to fiddle around with that.
The same applies for a 120V battery pack.

Good luck!

Regards
Kryp