# What's the relationship between DC braking torque and AC turning torque for a given current on a BLDC motor

Given a 3-phase AC motor, it will have a torque vs AC current curve

The same motor will also start braking with a constant DC current through any two of the wires, again with the amount of braking torque proportional to the current

My question is for a given current, what is the relationship between the spinning torque caused by the AC current vs the braking torque caused by the DC current? is it a factor of 3 because only one of the three "phases" is being energized? does it involve a RMS-offset because of a constantly changing AC current? will it vary from motor to motor, or will it remain proportional across different motor configurations (# poles, magnet strength, etc.?)

• I have never heard of braking a BLDC motor with 'constant DC current'. Can you provide an example? Nov 12 '16 at 2:29
• @BruceAbbott I was counting poles of a BLDC motor from this guide - method #2, and this question occurred to me as I was testing it with different current values - not sure how it would be used in a practical application, but I was curious as to what the relationship would be Nov 12 '16 at 3:38