buzzing welder transformer?

You won't get a voltage on a wire thru the hole.

If the hole is not in the field of the core then that core material is wasted. Not bloody likely!

That's true. It shouldn't be a problem.

Actually you will. The wire throught the hole get some of the flux change. To get an idea of the magnitude I ran a wire through a hole in a microwave oven transformer that I just happened to have on the bench. Without power applied to the transformer, I had a 22 mv reading. With power to the transformer the reading was 169 mv. And to check that it was not stray magnetic fields coupling to the wires going to the meter, I pulled the wire out of the hole and connected the meter. Now 22 mv without power applied and 21 mv with power applied to the transformer.

Dan

OK, so there's a little potential one end of the wire to the other. As long as the wire is insulated from everything else, I don't see that much current can flow. With little current flow, little energy is dissipated in resistance.

If I scuff my tennis shoes on my carpet, I can measure quite a bit of voltage too, but what's relevant here isn't a bit of charge piling up somewhere, it's does this materially affect the welder.

Just another point of view. Lotta respect for Dan Caster and Don Foreman both.

Grant Erwin

One thought - Might not be the core itself - might be how it is mounted ? - rattle in the box ? Might be just a wedge on the mounting point or some dope there as well.

Martin Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

Grant Erw>

Even if the bolt isn't insulated, you won't get much current. It will not materially affect the welder.

Dan

Grant Erw>

It depends on how you route your meter leads, Dan. Voltage is induced in proportion to the area enclosed by a conductive path normal to a varying B field -- and that circuit includes the meter leads. That's somebody's law, don't recall whose at the moment. Line integrals of a vector field and all that crap. Whatever. Matter of fact, the path need not be conductive -- but a voltage induced in a non-conductive path isn't usually of any interest or consequence unless it's one hell of a high-frequency B-field far beyond saturation flux density in transformer steel.

If you run the meter leads from the ends of the wire parallel to the direction of flux (not easy to do), you'll not see a potential. A wire perpendicular to a varying magnetic field does not produce an EMF. The voltage you saw was induced in your meter leads that formed a loop that was closed by the piece of wire thru the hole. Honest! If you move the meter leads around enough, you will find a null position.

All of which is sawing sawdust, of course. Bottom line: sticking a bolt thru a corner of a transformer core is not usually a problem but it never hurts to insulate it. A coat of varnish and insulating (or varnished) washers won't hurt and might help. A few scratches in the varnish wouldn't matter at all.

Right! It's not a worry, go for it.