Re: On Board Plasma Cutter Problems
For anyone trying to build a plasma cutter! Read this first!
Build in a low air pressure disconnect into your primary circuit!
The air/CO2/Nitrogen/Argon or whatever you are using, if the pressure drops the heat in the torch chamber will do MAJOR BURN DAMAGE, and possibly electrocute you in a matter of a second or two!
(if you have to ask how I know this you are NOT ready to try and build one of these things)
I used a 35 PSI 'Hobbs' normally open switch wired to the rotor feed on the alternator/generator, and moved up to a 50 PSI switch after the first near catastrophe...
Plasma cutters are volume hungry, so have plenty of reserve tank for your air compressor.
A moisture filter is pretty much a requirement if you are using an on board air compressor.
Moisture does weird sh--- Uh... Stuff to the primary arc. Unpredictable stuff...
Actually, I remember you TiminMb from 3 years ago, and I appreciate the ideas/help!
You seemed to have a pretty good head on your shoulders, so please speak right up!
I started out with microwave oven parts... BUT...
As for forced step up, I am using a circuit very similar to a 'Hot Shot' or 'Stun Gun' for the pilot, and it's working well.
(I actually used a cheap stun gun in testing, but 9 volt batteries were getting expensive, and when I tried 12 volts, it let out the magic smoke...)
Easy to delay for air flow (555 or 556 timer), cheap to build, and easy to install.
555 or 556 works good for purge/cool down after the burn also! You can build the entire circuit for about $6. and you can't beat that with a stick!
As for over current...
I think you and LEVE may have hit it right on the head...
I was staring at my set up sheet, and I didn't figure my pulley speeds correctly.
I'm looking at 60 to 80 amps as near as I can tell, and this thing will wack off 3/8" plate nearly as fast as you can pull the torch. 1/2" plate takes only slightly longer, but comes out very clean... As clean as 3/16" does on my shop cutter.
I REALLY need to get an amp gauge that will work with this thing!
I just can't figure out why it's not melting plastic parts or burning the swirl ring to ashes...?
I've cooked those parts on my shop cutter, and I just can't figure out why I'm not doing it on this one.
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There was a guy on the diy welder list (list since MIA) that built a homemade plasma cutter by simply using a diode bridge and a water resistor to limit current through the 220 mains.
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Two questions & a comment...
1. What's "list since MIA"? Don't know the shorthand...
2. Where is the DIY Welder list you are talking about?
I use water resistors when I do carbon arc smelting when I cast metal parts (iron, aluminum), and they can be VERY dangerous!
I've had several near misses... Now I do it out in the yard with long cables!
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Get that working and you should make a fortune!
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This is the alternator that I tried to recommend here for an on board welder and everybody gave me crap...
The self anointed 'Electrical Engineer' (you know, 'trail ride' or whatever, the guy that didn't know how an alternator worked, and didn't know how a diode worked...) declared my ideas 'CRAP'...
... AND YOU CAN'T TEACH A PIG TO SING...
Trying only wastes your time, and annoys the pig...
So far, with the same unit I can do,
MIG (with a CO2 bottle) straight or reverse,
TIG (with a CO2 bottle) straight & reverse or AC,
Stick, both 3 phase AC and DC straight & reverse polarity,
Plasma cutter, (not quite got that perfected yet...) You will need CO2 or air compressor...
115, 220, 220 3 phase AC & DC power,
And a 160 amp continuous load, adjustable regulator alternator.
Several of the farmers around here are using ones I made for them, and lots of the guys at the race tracks use ones I've made...
The OBW's I made in high school are still working in the fields of our family farms.
But the guys here all said my idea wouldn't work, and if they are sure it won't work, there is no point in beating my head [img]/ubbthreads/images/graemlins/wall.gif[/img] against a wall trying to educate them...[img]/ubbthreads/images/graemlins/wall.gif[/img]
I suggested two alternators, neither of which was the GM SI series they were used to seeing.
You know how those self appointed 'On Board Welding Gods' are...
Just like the self appointed 'On Board Air Compressor Gods' were when I suggested an electric compressor, or smaller compressor switches...
Or the "GM HEI in I-6 Gods" were when I suggested using the larger cap and rotor instead of scrapping the entire ignition system...
If anyone has any CONSTRUCTIVE ideas, comments, links or rants...
I'd SURE like to hear them!