Base single to 3phase system

[John Hasler]

One of the problems with the clutch rewind is that the wire size used is not a readily available size (.017" without insulation) here in the US, and the clutch circuit is tightly controlled for amperage (5-5/8 ampere fuse). There's not a lot of wiggle room. Resistance of a coil is critical. One must either use slightly larger wire and add turns, or smaller wire and lose a few turns to end up with the proper resistance.
H

Or design a power supply to provide the correct ampere-turns (IIRC you already counted the turns). This can be as simple as a standard transformer and a series resistor.

[John Hasler]

No, they mean including insulation. This information is essential for winding coils. They should give the resistance per meter somewhere, though. Perhaps it's in the standards somewhere.

[Harold_V]

No, they mean including insulation.

Thanks for that bit of information. I carefully stripped the varnish so I could measure the wire. Now I'll measure over the varnish (when I next spend time on the project, which is now on hold) and determine if the wire size is one that is available. Knowing to measure over the varnish was something I did not know.

This information is essential for winding coils. They should give the resistance per meter somewhere, though. Perhaps it's in the standards somewhere.

None of that information is made available to the consumer from the company that made the clutches. They are still in business, although they no longer provide the clutch. Knowing the number of turns and having other clutches to measure resistance makes it possible for me to do, however. As you suggested, resistance of available wire in regards to length is information that is readily available.

H

[Bill Shields]

Cross section of wire is wire.. insulation does not factor into electrical calculations.

Generally this type of wire is insulated with what appears to be varnish

The big question is how it is wound. Some coils are wound with layers of paper insulation. You will not know until you cut it apart....assume it is potted?

A resistance measurement will give you an idea of the length of wire so that when you wind a new one you will know if you have done it correctly...too little wire and.. poof...

[John Hasler]

They give the diameter including insulation because it is needed when calculating the dimensions of a coil.

The strength of the magnetic field is proportional to the product of the number of turns in the coil and the current through it. This means that as long as your new coil has the same number of turns as the old one you can get it to perform like the old one by adjusting the current through it to match the measured current through a working coil even though the resistance of the new coil and therefor the voltage across it may be different. It's the current and the number of turns that matter (Within limits. The wire must fit in the available space and can't be much smaller than the original or it may overheat.)

Of course you could also adjust the number of turns and compensate by adjusting the current the other way so that N*I remains the same.

[Harold_V]

Cross section of wire is wire.. insulation does not factor into electrical calculations.

What I didn't know was that the advertised diameter of the wire includes the varnish (insulation). Armed with that knowledge, it may be one of the available sizes.

The big question is how it is wound. Some coils are wound with layers of paper insulation. You will not know until you cut it apart....assume it is potted?

No paper. The failed clutch is still in the machine, but one with the same part number was dismantled some time ago, and the coil removed. As you alluded, the coil is potted, which I removed by machining, then hand picking the potting that couldn't be machined. A slow, but successful process. The coil has 509 turns. They were counted by cutting the coil in half, then bundling wires in groups of ten, with the groups bundled in lots of ten. Simple, and foolproof.

A resistance measurement will give you an idea of the length of wire so that when you wind a new one you will know if you have done it correctly...too little wire and.. poof...

That I fully understand, and is the point I was making when I assumed the wire size available may not be correct. I now suspect that it is. If not, the variation will be slight, and I can adjust by adding or subtracting a few turns. There's ample room to do so if I must add a few.

H

[John Hasler]

That I fully understand, and is the point I was making when I assumed the wire size available may not be correct. I now suspect that it is. If not, the variation will be slight, and I can adjust by adding or subtracting a few turns. There's ample room to do so if I must add a few.

H

You can change the number of turns but you need to keep the NI (turns times current) product within perhaps 5% of the original.