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I live on a boat with a 24V LiFePO4 battery system that has a large capacity and discharge capability, but I don't have a large inverter for using AC gear.

I have a MIG welder, that takes AC and transforms it to direct current electrode positive or DCEP for welding aluminum.

I would like to cut out the mechanism that does the transformation (transformer???) and power it directly from my batteries.

  1. Is that possible?

  2. How do I do it? My gut tells me to look for the biggest wire after the big heavy looking thing "transformer" and connect the positive terminal of the battery to it, and the ground clamp to the negative of the battery and it should just work, but the unit has a display, and wire feed motor and a whole bunch of circuit boards sooooo maybe I'm crazy to just try that.

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    \$\begingroup\$ It’s for sure possible but easiest and safest solution would be to get an inverter large enough to drive the welder as-is. \$\endgroup\$
    – winny
    Sep 25 '20 at 10:21
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    \$\begingroup\$ @SVSavannah: It will almost certainly not be as simple as you hope. It's an almost certain bet that your welder doesn't operate on 24VDC internally. Even if it does, you wouldn't find the correct place to connect it as you think you can. Finally, even if you could just hook it right up to some 24VDC internal bus, you'd have to disconnect the existing 24VDC power supply. \$\endgroup\$
    – JRE
    Sep 25 '20 at 11:09
  • \$\begingroup\$ What they both say BUT it may be possible. You want somebody with some experience with electronics. THere is both the main welder voltage and the electronics. You MAY be able to isolate the DC welder feed and MAY be able to power the electronics via the normal mains supply with a small inverter. Looking and seeing is really the only way, alas. \$\endgroup\$
    – Russell McMahon
    Sep 25 '20 at 11:20
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    \$\begingroup\$ The type of welder is important also; TIG for instance has a "spark starter" (4kV or more) to begin the arc from a distance. At least someone has tried this, and seems to have it working... although it is YouTube, so is automatically incredulous. \$\endgroup\$
    – rdtsc
    Sep 25 '20 at 12:00
  • \$\begingroup\$ @SV Savannah This is another one of those questions (there have been many of this kind here in EE.SE) about things that may be possible, BUT, would require direct examination of a person with more knowledge and experience. Did you consider acquiring one generator? \$\endgroup\$
    – mguima
    Sep 25 '20 at 12:21
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If you can, just stringing batteries together and using a spool gun such as a Ready Welder (TM) directly is a LOT more efficient and so allows you much more power for less money. However, depending on what you're welding, 24v may be the "wrong" voltage and you may need lower or higher - we found 36v (3x 12v batteries) was good for reasonably robust field-repairs on vehicles.

I don't recommend butchering your welder to achieve this unless it's a cheap one you don't care about.

You need to check how the internal parts (wire feed motor & gas solenoid) are powered - if they accept 24vDC you may be able to do this if 24v will work for what you want to weld... but many components are AC, and powered from a separate stable supply (secondary winding on the transformer) as obviously when you're welding the "main" output / battery voltage will vary as the arc forms and put a lot of spikes etc. up the wire.

Also, do not wire DC to the wire coming out of the transformer - you'll toast the winding - you need to find the rectified side (after the diodes), which would be pretty close to the final output connected to the torch & ground connections on the welder. Unfortunately these are most probably after the contactor so you have no on/off control over them.

Products like the Ready Welder are fairly popular among off-roaders, it's a long time since I looked at them, and spool guns are a common thing in industry. There are (or were) a lot of cheap copies around from China so one of those could be worth a shot if only to prove the concept.

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