I may want to try and rewind my power transformer for my Airline Autotune motor. See my want ad: viewtopic.php?f=15&t=193358

Is there a way to determine how long a given wire size must be to get a specific ohm?

i.e. if I have 28 gauge wire, how long should it be to get 16 ohms?

I have never done this so any guidance is appreciated.

Thanks

This may sound a little vague and wish-washy, but your simplest bet is to determine the approximate gauge of the old wire and use a wire of that size or a little larger. The wire must be big enough to handle the motor current.

Now, just as with rewinding any coil, the most important factor is getting the same number of turns as the original. One simple way to do this, if the old coil is still intact, is just stretch the old coil wire out and determine how long the wire is. Cut off that length of the new wire and start winding. You'll get the same magnetic effect and inductance if you have the original number of turns. Don't be concerned about ohms.

Finally, the precise number of turns is not critical, just like most of the components in a radio. If you duplicate the number of turns within about 10-15 per cent, it should work fine. Just be sure that the new wire is at least as thick as, or thicker than, the original.

Its not the DC resistance (ohms) that is the critical spec here. Its the number of turns. If you use the same gauge wire you can get into the ballpark using resistance as your guide. Counting turns on the old winding would be more accurate if you can do so.

But to find the resistance of a given length of wire you need a wire gauge table.
They're all over the internet, like this one:
http://diyaudioprojects.com/Technical/A ... ire-Gauge/

Here is a simple one with a handy calculator:
http://www.cirris.com/testing/resistance/wire.html

Ok, think I got it, the number of turns on the coil are more important, and I need to stay with the same wire gauge or slightly larger. Since I am rewinding a magnetic coil if I go with slightly larger wire, which will equal less turns, I should not notice any difference, right?

Now to rebuild my crude coil winder and add a counter.

If there is ample space, your best bet is to use a piece of wire that is the same length as the old one. That, essentially, will insure that you get the same number of turns, hence the same performance.

You don't really mean "power transformer" I assume, but the main winding from that motor.

You'll need to drive out the two pins and remove the bobbin from the core. If you can avoid messing with the shading coil (the exposed winding with the large gauge wire) so much the better. I've never seen one like this, but I assume low-voltage AC is applied to that coil, in one polarity or the other, to run the motor forward or in reverse.

If the old bobbin is strong enough, you can re-use it. You'll need a fixture to hold it for unwinding and rewinding, and ideally some way of counting turns. Count them as you remove the old wire, and then put the same number back on. The old winding will probably be layer-wound with paper between layers, but modern wire insulation is good enough that you can simply scramble-wind the replacement. You will absolutely need washers or something supporting the bobbin cheeks, to keep the pressure of the wire from pushing them outward while winding. Also put something inside, the same dimensions as the core (wood is fine) to keep the bobbin from collapsing while you wind. It's really annoying when you can't slide the nicely rewound coil on to the old core. Or when you can't slide the coil off the temporary mandrel, so don't make the winding too tight, and use a couple of shims inside, that you can pull out later to release the coil.

Measure the diameter of the old wire and use the nearest size to replace it. Borrow a micrometer or dial caliper.

Alan, yes I meant the main winding for the motor. I plan to remove the original wire and use the original bobbin, counting the turns as I go. The shaded wire (large gauge wire) is actually a replacement for the wire loop pictured below. The original was open so I removed it and used what I had on hand to make a temporary replacement. I was just testing the motor to see if the shaded loop was the only problem. I believe the gauge on the shaded wire looks to be 30 or 34 and the main motor winding looks to be 28 gauge. The shaded wire is center tapped into the motor winding.

OK, that makes some sense. You'll probably have to rewind the shading coil too. Modern wire enamel is very tolerant of abuse but the old enamel gets brittle and cracks.