RE. dc motor problem ??

Use a amp-meter to measure the current that every DC motor is using. So you only power one motor at a time and measure the current of each motor. You than add the two currents, this will give you a good idea of the total current of the two motors. This total current must be a bit lower than 40amp, if higher the trip breaker will  trip. Now that you know the total current, you can buy a trip breaker that is adapted to the total current. 

The bigger the mechanic load for the motor the higher the current gets !

Regards,
Johan

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hi i have i problem, how does not :))

well i have to DC motor they run on 36v and they have a 40amp trip
breaker , ho yes i forgot its a big scrubber.   well the problem is
this if a let run but motor for i while the breaker will trip and if a
disconect one motor the breaker will not trip. i check both motor i
think i swap back and forth and both motor works as long one only run.
is any way to see if the breaker is bad or one of the 2 motor.