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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
If the transformer has similar ratings as a welder transformer (don't know exactly but I believe it is ca. 24-50V and ca. 150A max. current), then you can just build a variable inductive ballast (reactor) to control welding current.
If it has the needed power rating but different output voltage, the sec. winding needs to be rewound.
If it doesn't have the needed power rating, you must get a bigger transformer
As for controling the power - you can use SCRs. If you are going to rectify it (some wealdin sticks require DC) just change the "upper" two diods with a SCRs and build a zero-crossing circuit (Something similar to S. Conner's OLTC power supply).
P.S. Used this circuit for TIG wealding and worked OK (it needs an inductor though) .
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. H. wrote ...
As for controling the power - you can use SCRs.
Yes, but you actually need to include a ballast which sets the maximum current, along with the SCRs (or TRIACs) for control. If you don't do this, the transformer will get hotter than it was intended to (or the maximum available current will be less).
Registered Member #1751
Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16
Most of the DIY welders needs rewinding of MOTs but i dont want to do tat since i have my own welding unit. I was planning to use a 230v, .5 or 1kva tfmr but then i can go for higher ratings if reqd. As i wont be using them for actual welding i decided to keep the ratings low. Is it really necessary to change my voltage and current ratings, afterall its just the power rating that matters rite? Anyway, i suppose a current limiting inductor is the easiest option. How should i design this inductor?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Nikhil wrote ...
Most of the DIY welders needs rewinding of MOTs but i dont want to do tat since i have my own welding unit. I was planning to use a 230v, .5 or 1kva tfmr but then i can go for higher ratings if reqd. As i wont be using them for actual welding i decided to keep the ratings low. Is it really necessary to change my voltage and current ratings, afterall its just the power rating that matters rite? Anyway, i suppose a current limiting inductor is the easiest option. How should i design this inductor?
So what is your application? Well, 10000Volts at 0.1A is the same power as 10V and 100A, but you can't weld with neither of these.
If you have MOTs, you can cut off the "I" core section and insert a core spacer to set the current through the primary winding. If more power is needed, you can use a few MOTs in parallel, with the same core gap.
Another approach is to get a large "I" laminated iron core, stick it into a spool of some 12Awg wire, and control the current by moving the core in or out of the spool.
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Welding Transformer
