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Tips/Techniques Power requirements for a Plasma cutter

Tips/Techniques

historicalarms

Ultra Member
Well we got Jim's compressor issues pretty much hashed out so on with another one.
I said in one of my post's that the topcic has renewed my interest in acquiring a small machine capable of "severing" 1/2" mild steel. Most of my cutting these days is 1/4-3/8" but if the need arises "better to have wat you need than need what you don't have".
When I first looked at Plasma, to cut 1/2" was in the $1100 to $1500 range minimum, now Amazon .ca must have seven pages of them from $250-$400 for the same size Cut50 machine.
Most of these machines are 110-220 dual power requirements, I understand how that works, its the amps requirements that confuse me. The charts show that when cutting in 110 that these machines cut up to 1/4 easily at a 30 amp setting, My shop 110 system has 20 amp breaker (keep that in mind). My welding 220 system has 40 amp breaker....here is my question, my welder runs on that 40 amps quite well, I can burn 5/32 rod at the max amp setting of 225 ( it is hard starting but will burn if I do everything right). At a lower setting of 150 or so that welder will burn 3/32 rod all day
The quandry Im in is how does that welder produce 225 amps with a 40 amp breaker feeding it and will those small multi power plasma cutters build the 50 amps required to cut 1/2 like my buzz box welder will to weld with.
 
....you're burning 5/32 at 225a??? That's gotta be a typo...that's pretty much incinerate amps for a 5/32

A 50a plasma will cut 1/2 ok, and a 40a breaker will feed it no problem

The welders are able to make the high amperage because the welding arc is a relatively low voltage, 18-30v for MIG and 10-50v for stick, you are essentially trading voltage for amperage
 
My limited understanding is that the transformer steps the voltage down but increases the amperage.
So 240v/40A in get reduced down to maybe 40v/200A (just guessing at the numbers here)
 
My limited understanding is that the transformer steps the voltage down but increases the amperage.
So 240v/40A in get reduced down to maybe 40v/200A (just guessing at the numbers here)

Right on. For any given power rating P = VI

So 40 Amps at 240Volts is the same power as 240amps (not 200) at 40Volts.

That's also why a smaller cable works fine at higher voltages. For a given cable, the resistance doesn't change. So if you run higher voltage you need less current for the same power.
 
Good ol' grade 10 electronics, the power wheel has all the relevant formulas

summary-basic-formulas.gif
 
Jeeez we had nothing like that when i was in grade 10, the stone wheel that such things were chiseled in kept breaking.

Most of you guys are a few years older than me ;) plus I went to a technical highschool, you could major in just about any trade (electrical, HVAC, plumbing, autobody, carpentry...etc, etc)
 
Right on. For any given power rating P = VI

So 40 Amps at 240Volts is the same power as 240amps (not 200) at 40Volts.

That's also why a smaller cable works fine at higher voltages. For a given cable, the resistance doesn't change. So if you run higher voltage you need less current for the same power.
I'll restate this with units
P = V*I or
Watts = Voltage * Amps

So 10 Volts * 40 Amps = 400 Watts also
40 Volts * 10 Amps = 400 Watts

So for welding

Input: 240 Volts * 40 Amps = 9600 Watts

Transform this to welding voltages and you get!

9600 Watts / 12 Volts = 800 Amps.
 
Can I go back to technical high school? sounds like fun.

Ha it was...so many blown up capacitors, and robots for the robotics games....yea that's a thing or was, no it's not battle bots

We also had a lathe, in the electrical/electronics department, figure that out, I did get to make a few little things on it though, bonus !

I did figure out pretty quickly there was not much of a career fixing VCR's, so didn't pursue it beyond highschool, but it has definitely come in handy !
 
Good ol' grade 10 electronics, the power wheel has all the relevant formulas

There was no electronics in grade 10 when I went to highschool.

I have a horrible memory. I'd forget where I put a wheel like that unless it was stone. But even I can remember V=RI & P=VI. Not hard to rearrange those as needed.

Also seems really odd to see E instead of V.
 
I knew when I posted this tread that it had the chance to get far deeper than I would ever have an understanding of....but I did get the answer I wanted before got too deep LOL

I had to chuckle when a member posted a wheel of information and then a couple posts later says "I think this stands for this on that wheel".
 
To clarify I always knew I was amperage/amps, I just never remember what the I actually stands for, probably because it doesn't sound as cool as electro motive force
 
General rule of thumb when it comes to nomenclature that doesn't seem obvious, its usually always the French LOL.
OTOH, when you are one of the founding discoverers, you earn the right to choose the name & the Greek symbol.
Yes looks like E is for Electromotive force. Apparently Volta, of Italian decent, was either bilingual or published in English

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