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Spot welder power supply how to

JP Machining

Stainless
Joined
Jul 15, 2006
Location
Wisconsin
Still looking at some used spot welders. Alot of them seem to be 440v single phase.

How to get that from 220 volt single phase? Most transformers I see are all 3 phase, of which I have one after one of my phase perfects to get 460 volt for my Alpha Lathe but then thats 3 phase not single.

Maybe its just late at night but my head is spinning and need some help on this. Looking for around 20kva welder so possibly need appropriately sized transformer.
 
Doubtful you’ll find a single phase transformer in the size you’ll need. That said, there’s no reason you HAVE to power something off all three legs.
No matter HOW the power is created, either at the power plant or by VFD or RPC, etc. at some point you’ll need (and be using) less than three hot legs.

It seems you are already generating your third leg?

And already running a three-phase, 480V machine, transformed up from said generated source?

If the existing system is capable of producing the amperage needed for your spot welder then take two of the hot conductors from the stepped up side of the transformer to run the welder and call it a day.

If whatever currently exists was designed for, or is marginal, for the lathe, you can likely get away with nothing more than a bigger transformer.

I would have a circuit for the lathe:
Breaker-RPC-transformer-breaker-lathe

And a second circuit:
Breaker-transformer-breaker-welder

If you’re feeling frisky, you can probably lose the breaker before the transformer, give the transformer full amperage and get by with circuit protection only before the welder.


Be safe and stay healthy



Jeremy


P.S. I am NOT an electrical engineer. And I have had several beers at this point. Theoretically I am comfortable with the advice I’ve given...
 
Just wire the spot welder to the phas that passes through the RPC. This will use the transformer without loading your idler.
 
Thats pretty much What I have figured out, not too sure about pulling high amp single phase load through the phase perfects but could just as easily get another transformer and only use 2 coils.
 
Still looking at some used spot welders. Alot of them seem to be 440v single phase.

How to get that from 220 volt single phase? Most transformers I see are all 3 phase, of which I have one after one of my phase perfects to get 460 volt for my Alpha Lathe but then thats 3 phase not single.

Maybe its just late at night but my head is spinning and need some help on this. Looking for around 20kva welder so possibly need appropriately sized transformer.

I avoid the 460-480 ones. I got one in a lot of welders and ended up stripping the parts to be spares for other welders. Then sold the steel body and transformer to the scrap man.
 
DONT DO WHAT Jermfab or Strotsky said! You dpo not have an RPC, I know what a phase perfect is and you will absolutely smoke it! (Guys it's a digital phase converter, works great but all solid state)

You cant pull a pair of legs off a Phase Perfect and leave the other dangle, the unit will trip. Also I find it hard to believe you are even getting away with doubling your voltage after the PP.. This would require a unit sized for over double the 480V load due to the 66% power factor going into the unit. Not sure how you are getting away with that without causing damage or a trip.

However you can get away with another 3phase Txfmr and simply connect 2 legs on the primary and use the same two on the secondary. Your sine wave will be way out of whack, but a spot welder won't care.

Also i'm pretty sure it's against the NEC (National Electric Code) to use a Txfmr backwards that's not specified that way (i.e. using a std step down to step up voltage) This isn't to say it won't work, but it's just not code if it is ever inspected (or burns your shop down)

I'm not a EE, but I could play one on TV

YMMV
 








 
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