Dear every body, I have a permanent magnet DC motor 12Vdc, the motor has 3 wires!!. I wondered why
there is 3 wires instead of the usual 2 wires. So I opened the motor body and found that:

2 wires are connected to the two brushes.

the third wire is connected to a coil of about 100 turns and has a diameter less than the
motor diameter and placed in the same horizontal plane of the brushes, and the second end
of the coil is connected to one brush..



Now, what is the acyual function of this coil?????

I wait for your help..

Thanx a lot

Shendy

 

Good thought Alberto, but would'nt the extra mechanical hardware be noticed? Maybe current sensing or temperature or ... Guess we wate for more inf.

 

Some Ford starter motors (series wound) had an extra coil as a speed limiter. In other words they had three "field" coils. Two were really for the field and the third was the regulator.

I suspect a limiter coil like that could be added to a PM motor for the same purpose. Don't connect the wire and see how the motor runs.

John