dynamic braking resistor
- Thread starter matlark
- Start date
I usually size the DB resistor so the maximum braking current is about 150% of the motor full load current. 150% of 7.5 amps = 11.25 amps. The resistance value is 90v / 11.25A = 8 ohms. The peak wattage rating of the resistor would be 90v x 11.25A = 1012 watts. However, since the brake will not be on continuously, the resistor does not have to be able to carry the 11.25 amps continuously. Depending on how often the motor is stopped, a duty cycle of 5-10% could be used. Most resistor manufacturers have graphs for rating their resistors for intermittent duty. You could probably use a 150 watt resistor for this application.
DickDV
Member
The answers given the OP in this thread are valid for maximum possible braking only. The first key question when dealing with braking is to determine how much braking IS REALLY NEEDED. It could be more than the motor hp or even much less. That's the resistance value you need.
In my experience, I've encountered braking applications where the braking hp is 1/10 of motoring hp and on one occasion where the braking hp was 4 times the motoring hp. In that case, the drive and motor had to be sized to the braking rather than the motoring hp.
In my experience, I've encountered braking applications where the braking hp is 1/10 of motoring hp and on one occasion where the braking hp was 4 times the motoring hp. In that case, the drive and motor had to be sized to the braking rather than the motoring hp.
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