How to make a homemade inductor?

I am testing my IGBT inverter. One of the big issues with it is presence of a large inductor before the inverter.

My previous tests were done with a tiny DC power supply with little inductance.

I would like to test my snubbing circuit with some inductance and higher currents.

I have a 20A variable voltage power supply pictured here

And I want to put some inductance in series.

My thought was to take a 1-2 lbs signal transformer, which I have, and to use its primary winding as the inductor. That is, DC would go in through the white wire and leave through the black wire.

Is that a sensible plan?

I have some 12 gauge solid wire, I'll see if getting "the other end" ie easy enough.

Did not realize that saturation would be an issue.

Thank you.

Thanks John. I will try to see if I have any wire spools with both ends of the wire available. That could be an easier method.

unless you plan on running DC thru your inductor, in which case no - it will saturate. why not just get a reaal of cable, find both ends and use that as an air-cored inductor....

Cheers Terry

Thanks. I used a roll of wire from Home Depot. It was kind of fun to watch, to see the wires flex on the roll under current.

I tried to guesstimate inductance of my inductor made of about 2/3 of

To my surprise, my estimate turned out to me comparable to inductance of my welding machine's inductor, in some millihenrys.

I used this webpage:

That means that what I did yesterday, was a quite sensible test of my bridge wrt inductance of the source.

This is the way microwave oven transformers are typically made, with the E's and I's stacked already.

You can mount long bolts through the laminations, which are welded together, and cut them apart using an angle grinder. Just cut out the weld which is 1-2mm deep. The bolts stop all the lams falling apart.Then reassemble with an air gap if needed.

You can probably use the existing primary as your winding, but please remove the secondary completely.

Clifford Heath.

I wouldn't use a file card - I'd tamp the ends of the lams flat, and use 1 mil mylar tape. :-)

Cheers! Rich

A 1 mil gap won't allow for much of a DC rating with the core size that ig might use (anything bigger than a thimble). I have some laminated inductors the size of two fists that have about 1/8th inch gap spacers. I think you generally want the DC rating based on the wire heating and based on the core saturation to roughly match for good utilization of copper and iron, but I might be wrong about that.

One safe bet is store all the DC energy in the air gap L*Idc^2=mu,air*B^2*Vgap.

I'll have to take your word on this, I have done zero study on it. :-)

I just remember having heard that _any_ air gap drops the inductance dramatically, but never really heard about what it does to the saturation current of the whole unit, umtil just now. :-)

Thanks! Rich

The effect on both inductance and saturation current is approximately proportional to the gap thickness, as long as the gap thickness is small, compared to the length and width of the pole pieces the gap is against. As the gap approaches the smallest dimension of the pole piece, fringing fields lessens the effect of additional gap thickness, as the field spreads out over a larger area than the pole piece ends.

OK, here's one: Is there a discontinuity from 0 to >0? Or is that impossible to determine, because an actually zero gap can't be made with separate Es and Is?

Maybe what would appear as a discontinuity could be accounted for by their interleaving in the other case. Hmmm... :-)

Thanks! Rich

Interleaved E's and I's get pretty close to a zero gap core. Tape wound toroids d a bit better, approaching the effective permeability of the metal. Alternate stacks of two or three E's and I's act like a bit more gap. Stacking all the E's and putting the I's on top act like more gap. Then you add more by putting spacers under the I's. But once the spacer is more than a few mils, it dominates the total gap and the approximate proportionality I mentioned takes over.

Thanks! I guess, since you learn something new every day, I can go back to bed now. ;-P

Cheers! Rich