The Artful Bodger

12-19-2010, 12:46 AM

I have a small electric motor which I believe is two phase.. it came from an old radar installation and I believe drove the 'nodding dipoles' on a GCA system.

The motor is about 3" diameter and maybe 4" long, it has three connections one of which has two of the internal wires going to it, the other two connections have one wire each. According to my meter there is 150 Ohms betweens each of the single connections and the double connection and 300 Ohms between the two single connections. This makes me think it is just two windings in serial.

The only markings are the markers name Evershed & Vignoles, London, and a hand written date of 1942.

There are no brushes etc.

100V AC across one of the windings and an unknown capacitor across the other gets the motor to run nicely, I increased the volts to 200V AC with no sign of heating though it was a lot noisier.

Peeping through the ventilation holes shows very fine windings, maybe 28 gauge or so.

Now the question is, knowing the resistance of one coil and the frequency of the mains, how to calculate an appropriate capacitor?

Thanks.

The motor is about 3" diameter and maybe 4" long, it has three connections one of which has two of the internal wires going to it, the other two connections have one wire each. According to my meter there is 150 Ohms betweens each of the single connections and the double connection and 300 Ohms between the two single connections. This makes me think it is just two windings in serial.

The only markings are the markers name Evershed & Vignoles, London, and a hand written date of 1942.

There are no brushes etc.

100V AC across one of the windings and an unknown capacitor across the other gets the motor to run nicely, I increased the volts to 200V AC with no sign of heating though it was a lot noisier.

Peeping through the ventilation holes shows very fine windings, maybe 28 gauge or so.

Now the question is, knowing the resistance of one coil and the frequency of the mains, how to calculate an appropriate capacitor?

Thanks.