Have a Vex 393 2-wire motor and I'm using a 6-40V PWM driver @ 5A max.

My question is this...

The Vex was spec'd at 4.8A stall current and 0.37A no-load current at 7.2V.

From what I've read here and elsewhere it would appear that it would be okay if I run this motor using PWM sourced with a 12V battery as the PWM will limit the current flow and not burn out the motor. I'd need to start worrying if I was to use a 100V source but at 12V the risk is minimal or non-existent.

However the conflicting info I have seen seems to say that it should only be run with 7.2V but this is coming from websites that are talking about specs for some robot competition and of course the Vex site which has its own controllers that only run on 7.2V. I'm thinking that the 7.2V might be a max allowed to keep the playing field even and the Vex controller is using a driver chip spec'd for something like 4-8V Vcc?

I just need confirmation my initial thinking is correct and that I CAN use the 12V PWM to run the Vex motor even though it has been spec'd at 7.2V.


1 Answer 1


I'm inclined to agree with you. A suggestion: Find out which the nominal current (or the maximum for the load you want to move) when operating at 7.2 V DC. Let's call it "Im". Then apply a 12 V PWM signal varying its duty cycle from 0 up to reach the "Im" current. Done. Now just make sure that the applied duty cycle is not more than that.


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