Transformer Turns Question

I think you'll have so much leakage inductance that the number you get will be very rough.

Other methods:

• estimate the volume of wire, measure it's diameter, get the length, then estimate the turns from the area.

• Weigh the thing, estimate the weight due to copper, measure the diameter, get the length, ditto.

D'oh. Measure the DC resistance, measure the wire diameter, use the conductivity of copper or a copper wire table to estimate the length ...

Whoa! "leakage inductance"?? Where's that coming from already? Concentrically-wound transformers are a perfectly valid topology AFAIAA.

Not so simple. The windings aren't single layer; they're stacked about

That can work. It might be better to drive the relay coil from a signal generator and measure the added winding voltage as the secondary.

For more accuracy, measure the DC resistance and the inductance of the relay coil, pick a good frequency, and do the math to account for the copper loss. Or Spice it.

Don't expect an exact turns count, but you should be able to get into the ballpark. If you "close" the relay (push the armature down) there will be less flux leakage error and you might get within 1%.

Certainly *safer* I guess!

Not sure what you mean by "a good frequency" - how do I determine that? I also thought maybe pulling the iron core out (if possible) and replacing it with a ferrite rod in case saturation might be an issue?

I would add more than ten turns. Why? I don't know, I just feel you would have more accuracy with 100 or 200 turns.

Mikek

Well, you need to do a little math and maybe some measurement. The frequency should be high enough that the voltage drop in the inductance is above the voltage drop in the copper resistance. And stay below the self-resonant frequency.

A nonlaminated iron core in a DC relay will have a lot of loss at high frequencies, too.

If you are willing to disassemble the relay, you could use a better, closed core. Or unwind and count!

Just curious, why do you want to know the number of turns?

If you drive it from both sides, and compare the ratios, maybe you could compensate for that?

snip

Good advice. And place the turns right on top of the existing coil, and use a much lower frequency and watch the excitation voltage because what you will have is a high turns count step up ratio and you could easily short turns in the coil, especially if it was 'scatter wound'.

Assuming a ten volt 60Hz excite on a 100 turn primary, the secondary would be at 500 volts. It is a 50 to 1 ratio.

So, one could easily determine what the actual turns count is by simply reading the 'secondary' voltage and the ten volts into 100 turns makes all the math easier too. Keeping the freq low is better as well, especially if it is as was said a non-laminated steel core.

Don't answer that, Chris. It's a trap. ;-)