On 9/18/2012 7:41 AM, Konstanty, Walter (GE Energy) wrote:
Your E20 probably turned due to residual magnetic field plus they usually shifted these brushes off neutral for best commutation which gives the motor a "series" affect and can cause it to turn. Don't expect any torque though. One test for larger DC (400HP +) is to apply 400 amps to the armature and see if the rotor turns without field... little dangerous but checks symmetry and neutral. If it is off much, it will try to take off.
That might be it then. Another thing is that I connected it straight to three Hawker 26ah batteries, which can put out insane amounts of current. That much current could have turned even a light compensating field into enough to make it go. On the E15 with a single string of SAFT BB600's through the normal old and crufty wiring of an elec-trak the current might have been less. Likewise on my E20 I have a very low resistance path to the motor, with clean contactors all the way and everything bolted down properly (including new copper lugs on all of the shunt connections on the E20)
Let us know what you see when driving an E15 and E20 around. I might try bypassing the interlocks on the E15 this weekend to see if it does the same thing as the E20 or if it puts the nose in the air when given full power straight up.
Chris