# Power factor correction for a SCR power supply/welder?

• posted

It is causing blown breakers and wires that get too warm. If I could get same power out of this welder, but at 75% of amps, that would be fantastic. (that way O could also get a little higher welding amperage out of it)

i
• posted

If the welder is tripping breakers, the branch circuit might be undersized for that welder. Or the phase converter.

You might want to consider examining the PF at the input of the phase converter. If its low there, its possible that the correction scheme might be simpler to implement at this point.

• posted

That's true, I think, but I have to live with this circuit now.

Yes, indeed, that is my plan.

i
• posted

problem but I'm trying to

single phase will now be 6

Nope, it is 4 "blips" per cycle, per phase in the input current. Should look something similar to the "Line current" diagram at

With the conditions he specifies however, his scrs are probably phased full on any way.

jk

• posted

For TRANSFORMER welders, using inductance to limit the current, yes, they can. FOr this case, however, capacitors can only do so much. They can not eliminate the harmonic content with capacitors. Once you get to the phase converter, things get a little hairy. I am not sure where the harmonic currents are going to flow, I think they will still end up in the line connection to the phase converter.

WIth capacitors you can only reduce the displacement power factor, and not the harmonic power factor. jk

• posted

No, The scr start conducting when you trigger it (assuming it is forward biased) and contin8ues to do so, until you try to reverse the current flow through it, usually by reversing the voltage. Essentially You start conducting at some point, and stop when the voltage goes through a zero crossing.

I don't think he did. All other things being equal (and they won't be) your maximum current occurs when you short your leads. Maximum KW will occur at some point, that depends on how you are limiting current, how much resistance and inductance the circuit sees, and how you control your scrs.

There are other ways to do this, the same way they are done for PF corrected com;uter supplies and lighting ballasts.

jk

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