how do i power an a.c. PWM controller with a d.c. source?

pulled apart a treadmill which of course pluggs in to the wall but i d like to apply its guts toward an electric vehicle project of mine

No can do, at least under most circumstances. I say most since it is remotely possible that the AC is converted to DC then converted to a dimmer with PWM.

I read back that you have an AC "dimmer" circuit, controlled by a TRIAC (or TRIode for Alternating Current). A TRIAC uses the existing sine wave from the AC source and cuts off the "inner" part of the ac source. The sine wave still exists.

What happens is as the AC source crosses 0, the TRIAC waits until the source rises above a certain threshold voltage and only then allows the voltage through. The TRIAC continues to send voltage through until the next zero crossing, then turns off and repeats the cycle

On the other hand, a DC PWM pulses the DC source and creates a duty cycle base on time. There are no zero crossings, and a TRIAC is not involved.

Good luck, and try not to shock yourself!