ReplyHmmmmn.......directly rectifying 220 without an isolation transformer is living on the edge. I don't know the specs on a plasma cutter to compare this to.
WeldingWeb Journeyman
A gentleman on the yahoo welding group has produced a DIY plasma cutter and has posted the schematic for others to use. Could someone please look over the schematic and let me know how practical this is. His cost was about $277.00 or so. Thanks
WeldingWeb Tradesman
Hmmmmn.......directly rectifying 220 without an isolation transformer is living on the edge. I don't know the specs on a plasma cutter to compare this to.
Needs a little further design work. No fuse or circuit breaker!!!
No ground.
Kind of "Rube Goldberg"
WeldingWeb Journeyman
here is a regular one
Master Welder
I think even without looking at it carefully he has dam near 300$ in it and for twice that or 1000 you are going to get something that works well. With the labor its not a bargain to build. Tuning a plasma to work well is going to be complex and engineers with all the resources are going to way better job on something so sophisticated. If he could build it an afternoon for 75$ it might be worth a shot,,, or if one like that cost 2000$ it would be a different matter. That cant be any better than a Chicago Electric junker at 600$.
Master Welder
We have seen some DIY stuff here and the home made tig might have been passable. The one that did actually impress me was the engine drive, which would have been ok for occasional use like a lot of guys might need. The reason I thought that one was good was that a couple of the major parts could have been salvage items such as engine and alt and it would have been quite cheap. Also with a slightly better alternator and couple hp larger motor it was upgradeable.
WeldingWeb Tradesman
Wait until you see my 28 volt 100 amp alternator on a 10 hp engine for a mig welder.
Solderer
Actually, this is very possible. My whole electronics career has been spent designing AC phase control circuitry. I've found some plasma cutter power supply designs that were much more simple than most can imagine. Typically those $2500.00 machines that cut 1 inch steel use less than $600.00 in parts, and some use less than $400.00. If the system uses a transformer, that's when it gets expensive and heavy. Typical mains isolation transformer will run $321.00 for a 12KW toroidal, and weighs 130 pounds.
I do have a power supply design which is not isolated from the mains, but is completely amperage limited and adjustable. No high frequency start but should give at least 40 ampere @ 300VDC cutting current and cost less than $200.00 to build. Uses capacitive reactance to limit current, so no dangerous water resistor with chemicals etc. Total package should weigh less than 40 pounds. You should just buy the torch off ebay etc for $100.00 and then build the power supply.
I do have an itch to try it just to see it work. So if I do I will tell you how it goes and any pitfalls that I find.
Tad
Solderer
How did the the DIY Plasma Cutter Turn out?? Can I have the design?
Flashoser
Solderer
hey dudes... I have successfully built a plasma torch plus the power supply. The torch parts are constructed from PVC pipe, ball valve, and copper. Too much details to list, but sure will give detail information if anyone of you would reply... The power supply is portable, similar to a on-board welder (engine driven alternator)... .. if interested, give me a shout, happy to help anyone who are interested in designing power supply for welding, cutting ...etc.
BeePig
WeldingWeb Foreman
Feel free to post what you know, it sounds interesting to meOriginally Posted by BeePig
Solderer
I should start with the power supply...the power supply is engine driven alternator. The engine must at least 5 hp, it doesn't't matter whether is horizontal or vertical shaft.
The alternator must have an output of at least 50 to 60, the higher the better and must be modify.( I will explain why).
The modification is very simply, you have to remove the voltage regulator and the ****ty rectifier (diodes) inside the alternator, sometimes you may find the voltage regulator located on the outside of the alternator on some older model.
As soon as you have finished the above process, the alternator must have three poles on the stationary coil. The power are come from the stationary coil not the rotor coil.
Don't be surprise, an alternator is very different then a generator, but serves the same function, except different design.
I will give more detail information once you have fully understand the above ...
Beepig
WeldingWeb Tradesman
I understand the above, so lets hear more! I am very "thrifty" and always looking for more info.
Solderer
Ok, A plasma cutting machine is use DC not AC, because the plasma arc has to be in transferred mode.. the ions tend to move from the Neg to the positive elctrode.
An Alternator has three pole, and is three phase, if rectified it will give almost clean DC .. however, if a not clean DC is use in a plasma cutter, the electrodo and/ or the nozzel will erode very quickly, so after the rectifier, you will need to filter out the ripples ^^^^^^^^ to -----------..... so the arc will transfer smooter and the cut will preform better.
I used two types of filter, one is Capacitor rated at 1500v @ 400uf. and an inductor. an inductor is almost like an transformer, but not quite.. it coils around an iron ring or rod. (notes. too much of a loop will decrease the voltage)
My torch head is made out of solid copper rod....... machined to the desire size, the starting process is 1) start engine (warm up), 2) supply field current to the alternator rotor 3) increse engine's rpm 4) torch is already hooked up to compressor 5) created a shot circut to the torch (electrode and nozzle is touch at this point) 6) turn on air valve, then the pressurized air will escape through the nozzle by pushing the nozzle away from the electrode, then a spark will created.... 7) Boom, there you go, the pressurize clean dry air will then swire around the electrode and mix with the arc and shoot out to the work picece in which you already have ground.
WeldingWeb Tradesman
When do I get to see pics of [(mainly) the torch] and the rest of the setup. I have a good picture in my mind of the rest, but the torch I'm havin trouble with. I have lots of guys tellin me I'm going to blow something up.
Solderer
I cannot send you any pics because my computer is currently under virus attack, I am using the Library's CPU to send you this message.
I would like to send you some pics of the plasma torch, but i really want to know what are you trying to do. What are you going to blow up?
Tell me your progress
WeldingWeb Tradesman
I don't intend on blowing anything up. I am a do it yourselfer and while some projects have failed, they've never blown up. Alot of the guys I hang with are not inclined to do anything so they keep saying "your going to blow yourself up one of these days". I have too much money invested into my tool collection to be able to afford a store bought plasma cutter (getting divorced doesn't help either) so I would like to build my own. My math isn't strong enough to finish electronic engineering and build one by myself, so I am following along your path. I have no need to make one other than to help myself finish other projects and to prove the naysayers are lost.
Solderer
hey hobweld, could you let me know how to get your shcematic in a better resolution?
thanks, please keep on posting DIY PLASMA information!!!!!!!
Solderer
Hobweld --if your looking for a big charge out of your life then go ahead an try this cocomame thing so called plasme cutter . i have a real one that is a esap 1250 plasma cutter and the amount of power it takes on start up is large , it says that you need a 100 amp designated circuit for start up an runs on 80 amp when cutting and that it also needs 280 cfh of air supply while cutting . it is a sweet unit never let me down an haven't found a thing you can't cut with it . doug
KEEP STICKING
Solderer
I would like to have the details if possible.Will pay any costs incurred.
beemerb
WeldingWeb Craftsman
I would also love to make a plasma torch as the one you did Beepig!
Mind to show what you did when you can?
Solderer
Would like to see picture as well
WeldingWeb Tradesman
same here
WeldingWeb Foreman
As MikeW said, the original circuit sketched at the beginning of this thread would be a potential killer due to lack of isolation from the power line.
You know how careful product designers are to be sure that the user or a passer-by cannot make contact with electrically energised parts of their product? And yet, we read about workmen being electrocuted by touching the body of a defective tool.
Well, the circuit as sketched would connect your entire welding table and work piece to the line, creating a situation in which it would only be a matter of time before someone would be injured or killed. The diode bridge does nothing to eliminate this lethal problem.
awright
WeldingWeb Tradesman
wow,,,,i'd buy new unit
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