Continous power dc motor

[Dave]

anonymouse, W = I x E, or Wattage = Current x Voltage...

Dave Purola,
N8NTA

[anonymouse]

anonymouse, W = I x E, or Wattage = Current x Voltage...

Dave Purola,
N8NTA

Thanks for the reply, I was interested to know how continuous power of a motor is derived (formula perhaps).Is the peak power of a motor measured under un/loaded conditions, if their are other parameters in calculating the continuous power of a motor, i.e derating factors for continous use,heat dissipation etc. Similar factors to working out the csa of a conductor, but using the motors rated peak power as that is all I have to work from.
cheers

[mackrackit]

Are you able to run the motor under the given load as a test?
If so then measure the amps.

The load will determine the amps.

[anonymouse]

Are you able to run the motor under the given load as a test?
If so then measure the amps.

The load will determine the amps.

My problem is Dave that by the nature of a dc motor the motor current reduces to zero as the rpm increases due to the back emf, so the current is non linear (motor will be at various pwm from 0 to 100). Thus I am not sure how manufacturers come to derive the continuous power. I understand that peak power can be upto 5x continuous power depending on manufacturer, and I cannot work back to the motor constant (to see if their are equivalents) as I am missing peak torque data.
Thanks for your reply

[aratti]

as I am missing peak torque data.

350 watt seconds (Wsec) is equal to 350 newton meters (N-m)

Al.

[amgen]

Does the load change or is it constant ?? are you going to continually read power or just make some estimations for your project ??
The motor current is related to the loading of the motor (how much effort the shaft is requiring ) , so if the current goes to zero, there is no power being consumed (E X I) by the motor at that time, in fact if the load tries to turn the motor shaft faster then it would normally run at that voltage, the motor then becomes a generator and current tries to flow back to the supply.
Power,
....you have instanteanous power, the E X I at an instant
....average power, a sumation over a period of time say 1 second
....and watt/hours or kw/hours

for PWM and power, I think you can relate the PWM % to the voltage, for example 12 volt DC at 50% PWM would be 6 (for E) X I (current). take 10 or 100 readings per second and do some calculations to obtain power usage.

don
amgen

[anonymouse]

Thanks for the replies, what i have is a dc motor which only lists its peak power of 350 Watts @ 24 Volts on its rating plate. To conform to legal specs the maximum allowable "continuous "power of the motor equals 200 Watts, this is my dilema, to convert the peak to continuous power to see if this motor complies. I am interesting in finding out how the motor manufacturers come to a continuous rating, being that the peak power can be a multiple of e.g 2 to 5 times continuous power. Under a steady load the motor current will ramp up under start, usually clamped via a controller to improve motor efficiency ratings, then ramp down to zero as the rpm rises to maximum (back emf). Whether the manufacturer maps these figures @ set temperature @ set load and finds the mean value or uses an algorithm containing other data is where I am stuck at.
Many thanks