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Tool Talk Discussion Forum

welder from AC to DC

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old art

04-03-2007 15:48:02




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i have an sears 295 amp stick welder can it be changed to DC from AC by adding a high current diode or is there a kit of some sort todo this.
to change the heat range the knob moves part of the transformer armeture thanks for and help you can give old art




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Stan in Oly, WA

04-03-2007 20:27:15




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 Re: welder from AC to DC in reply to old art, 04-03-2007 15:48:02  
A few years ago a guy I worked with loaned me a pretty decent Monkey Wards Power-Kraft 295 amp AC welder which his grandfather had given him. The grandfather had built a rectifier for it to put out DC current. It worked fine but it was inconvenient to use because I had to take it out of my basement whenever I wanted to use it. The rectifier was about the size of a liquor box that holds 12 fifths (750ml nowadays.) It's good for teaching you to weld according to the weld characteristics w/o reference to the amperage setting because there's really have no (uncomplicated) way to know what's coming out as DC---only that it's less than the amount of AC current going into the rectifier. What I mainly learned from it was how to do a lot of welding with AC and like it.

All the best, Stan

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souNdguy

04-04-2007 07:49:21




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 Re: welder from AC to DC in reply to Stan in Oly, WA, 04-03-2007 20:27:15  
Remember.. you can do an RMS calculation to figure some of that 'unknown' stuff out.. DC V is .707 of peak of the ac waveform..

Soundguy



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Stan in Oly, WA

04-04-2007 09:43:34




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 Re: welder from AC to DC in reply to souNdguy, 04-04-2007 07:49:21  
Hi souNdguy,

You're right about the calculation, and a person who went to grade school before 1970 would be able to do that elementary arithmetic in their head. Also, if you use one welder all the time all you really have to know about it is what to set it at for the circumstances of the job in front of you. The dial could have letters on it instead of numbers and soon enough you'd learn that you have to set it somewhere between k and n to run vertical up with 1/8" 6011 on 1/4" plate, for instance.

I use lots of different welders, and have had a fair number pass through my hands for one reason or another. Even the good quality DC welders in the Community College welding shop where I work seldom agree with each other exactly about output, and cheap AC welders are all over the map. Add the unknown efficiency of someone else's homemade rectifier to the uncertainty of the actual output of a Power Kraft AC welder and I think it would be fair to say you have little idea of how much current is flowing through your leads. That's all I meant.

All the best, Stan

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souNdguy

04-04-2007 10:15:32




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 Re: welder from AC to DC in reply to Stan in Oly, WA, 04-04-2007 09:43:34  
Dials and numbers or letters and effeciency aside.. I'd say that a welder should have a good idea o fthe current flowing through his leads based on how his bead is coming out...

Soundguy



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135 Fan

04-03-2007 16:59:19




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 Re: welder from AC to DC in reply to old art, 04-03-2007 15:48:02  
You need to have a rectifier to get DC current. Dave



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old art

04-04-2007 19:04:09




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 Re: welder from AC to DC in reply to 135 Fan, 04-03-2007 16:59:19  
thanks for your replys you convinced me to not try to do it my self but keep my eye opened for a AC DC unit on a sale new or used.



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