Plasma Info?

[Chris_]

Hiya guys I weren't really sure where to post so i thought this was the closest.

Can anyone tell me the difference between the power outputted by a traditional AC MMA welder and the Input power for an average Plasma cutter.

I'm having strange and wonderful ideas, that need beating out of me before i go to far

 

[shenion]

Plasma is DC normally 200-300 volts

MMA is AC normally 24-80V.

 

[peterd51]

Hi,

that's the output voltages of both...

I think Chris is asking the input power to the Plasma after the inital power unit, posibly to replace the power unit with something more reliable?

Sorry, I have no idea what the answer is.

Regards
Peter

 

[irondarren]

a 30 amp plasma cutter normally runs on a 13 amp fuse, a good quality 30 amp unit should cut 8mm thick no problem

 

[Chris_]

Yeah, i was basically thinking would it be possible to use my stick welder as the power supply to a plasma torch, hook it up to the compressor and use it to cut up some thin curvy bits. Basically i'm just fed up of buying cutting discs for the grinder

Edit: Crikey, 300volts? is that really low amps? i would have thought those sort of voltages would get a little dangerous?

 

[peterd51]

Hi,

there are tutorials around the net on DIY plasma cutters...

here's a good one:
http://www.jblankenagel.net/plasma cutter construction.pdf

However, even though I'm handy with a soldering iron and generally willing to have a go at most things, I decided that this project is too risky.

Especially as it's possible to buy one off ebay for less than £200 delivered.

Regards
Peter

 

[shenion]

Yeah, i was basically thinking would it be possible to use my stick welder as the power supply to a plasma torch, hook it up to the compressor and use it to cut up some thin curvy bits. Basically i'm just fed up of buying cutting discs for the grinder

Edit: Crikey, 300volts? is that really low amps? i would have thought those sort of voltages would get a little dangerous?

Yes, it is high voltage. My 130A MIG and my 25A plasma both will trip a 15A breaker (120V).

I think my plasma runs at about 100V, but has an open circuit voltage near 200V.

There was a thread about recalled plasma cutters recently that had exposed power connections. 300VDC will definitely hurt especially if it has the HF start running.

 

[mishka]

here's a good one:
http://www.jblankenagel.net/plasma cutter construction.pdf

"good"... in what sense? An interesting way to exit this mortal coil?

 

[peterd51]

Hi,

'good' as in it seems to work and is said by the writer to have been written by someone who understands electronics.

I didn't fancy the water cooled resistors!

Regards
Peter

 

[mishka]

Well, as someone else who understands electronics I can see this as being a veritable death trap. Or as one poster on weldingweb said: "a trial lawyer's dream come true". I remember the first time I saw this and couldn't believe that anyone could be so stupid! Especially as he proclaimed that he was some kind of senior electrician (again, see the page on weldingweb).

Two points that stick out straight away (there are more, but I'll stick to two) are:
1) there is NO mains isolation on the main power circuit, so the "work" is electrically connected to the mains;
2) water and electricity mix rather too well, so the "innovative" water-cooled resistor provides a nice conductive path to the mains.

 

[peterd51]

Hi,

yes, Like I said, I didn't fancy it as it looked too risky!

Hovewer, that (and what you've found) doesn't mean that no-one else should have a go if they consider the risks worthwhile.

Regards
Peter

 

[mishka]

True, but at the same time in order to make that call you have to know all the facts, otherwise you're making an ill-informed decision. With this plasma cutter design I simply cannot see any reason for choosing to build it, unless you're fed up with life and want an interesting way to end it.

 

[shenion]

Having the work ground 160V from earth ground is a recipe for disaster.

As we are split-phase, each input is only 110V from ground, there it would be 240V or 330VDC from the neutral.

No fuses at all. Design is by someone non-technical.

A better design would use microwave power transformers, already isolated and near the right voltage.

 

[peterd51]

Hi,

yes, but can't you see what you're saying?

You don't fancy it, same as me, but you're making the decision for someone else...

it's nothing to do with us whether some one thinks it's OK to build one and use of these.

It's entirely their decision.

Regards
Peter

 

[mishka]

it's nothing to do with us whether some one thinks it's OK to build one and use of these.

Agreed, I was simply expressing my own opinion. This is, after all, a discussion forum