I need to know how to properly select the right value filter capacitor and how many to put in parallel for a PWM motor controller I am building. I know how to select capacitor values for 120 hertz full wave rectification of AC ripple voltage and 60 hertz half wave rectification ripple voltage, but this design has DC going in and it will only have dips when the MOSFET switches ON as well as how much load is placed upon the motor's shaft when the MOSFET is ON thereby causing more current draw. So how would I properly select the capacitor value to account for these transient voltage dips? I do have some Panasonic FM series FM1V152 1500uF low ESR capacitors, but I think these may be overkill...

Here is a picture of the power side of my motor controller:

http://img157.imageshack.us/img157/3...torhelpfd7.gif

 

It depends upon the ripple current you can tolerate. The formula is C = (IxT)/Vripple where I is the motor current and T is the maximum time the switch is on.

 

SuperTech just view the PWM circuit/Mosfet as a simple SPST switch-you noted above you know how to calculate the filter cap for a rectification circuit. Just use the analysis you described above; half or full wave will use the same procedure to calculate the filter cap.
C=I(dt/dv)
where:
dt=time between 60 Hz or 120 Hz peaks-dependant here on the power source frequency only.
dv=voltage rise of the 60 Hz or 120 Hz voltage peaks
I=motor current (Amps) = [(0.25 Hp)*746 W/Hp]/(12 volts)