Re: Protecting a DC motor


The OP should get some data from the motor manufacturer about damage due
to overloads over time.

Any scheme is going to have to allow for the motor's starting
characteristics. The protection must allow the 80A, 100 ms starting
current, but operate at 80A for durations beyond that.

No, not necesssarily. The 80A is full torque. If you don't need full torque
at startup then you don't need the full current. In fact chances are he only
needs the amount of current that will overcome friction. (even if it rotates
at 1rph...) This should be quite low. Of course you don't want to wait for
ever for the motor to get up to full speed so it really depends on what the
motor is driving.

It's easy to implement anyways. A simple resistor-cap delay that prevents
the current limiting device from triggering.

Circuit breakers or thermal devices with the proper I-T curves can be
matched to the motor's characteristics. It would also be possible to
design a foldback circuit that would allow the starting surge but then
step up its sensitivity to just above the normal full load operating
current.


It's all going to depend on the specific problem that is causing it to jam
and the type of solution that they want.


.

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