dave-in-nj:
question about alternate ways to control the pump.will this work ?
12v to the pump.
pump lead to a mosfet
pwm out to the mosfet at 30% duty cycle.
No, it will likely burn out the motor. You'll have to experiment with the
duty cycle.
PWM with a single MOSFET is not linear in the PWM value, not even
slightly, and its load-dependent. You have to use an active rectifier or
fast decay mode in an H-bridge for the PWM duty cycle to accurately control
average voltage, otherwise the inductance just prevents the current dropping
during the off part of the cycle.
And you need a freewheel diode anyway, or you may burn out the MOSFET.