On 9/17/2012 4:07 PM, Konstanty, Walter (GE Energy) wrote:
If you have no field and apply voltage to the armature, the armature windings in series are very low resistance and it will cause high current to flow (like when the meter pegs and the tractor doesn't move if the field relay is open, fields are open or grounded).
This is where I am hanging up here: Technically if you have a compound motor you have two sources of field flux: The first is the normal shunt field, which provides most of the flux strength. The second is the field that is in series with the armature. It provides flux in proportion to the current going through the armature.
If it's a pure shunt motor with the field at zero then the armature will act as a dead short and pull a lot of amps without moving. Because you have nothing but a magnet sitting in a metal tube (the motor housing). That is what the E12 and E15 motor seem to do.
The E20 was different. When I applied 12 volts on the bench to it with no field the motor would turn. Oddly, which made me wonder till I hooked up the field and it spun normally. Since there had to be a source of flux for the field my conclusion was that it's more of a compound motor, and the current through the armature as a short induced a field through the series windings which turned the motor.
I'll fiddle with this more over the weekend. What I do not want to do is run either motor without field for any length of time to avoid blowing something up.
Chris