Re:Servo braking resistor in series with motor armature

I think you have the right idea, except for the resistance you calculated. In your example you came up with a total resistance of 1.5 Ohm needed, and your motor plus wiring totaled 0.5 Ohm. It seems to me you then need a 1.0 Ohm added resistor instead of the 10 Ohm you stated. Perhaps you meant 1.0 Ohm but made a typo? The continuous power rating would indeed be fairly high. At 19 Amps the power in the resistor would be I^2*R or 19^2*1.0=361 Watts. The resistor would reduce the voltage on the motor by 19 Volts at full current, and would indeed have an effect on acceleration.

The reason something is needed is that a motor acts like a generator when decelerating, and can pump quite a lot of current back into the power supply during this time. If you have a lot of mass (weight) in addition to the motor armature that must decelerate, the time the current flows will be longer, in effect acting like a flywheel. This current will charge the power supply filter capacitor to a higher voltage than normal, and may damage something in the power supply or motor controller if this voltage exceeds the rated voltage of a transistor for example. Sometimes the power supply will have over-voltage protection to protect it but it depends on the design and rating of the protection circuit.

Bob

---------------------------------
Looking for last minute shopping deals? Find them fast with Yahoo! Search.

[Non-text portions of this message have been removed]