DC Power Source for PWM Motor Controller

[TimeBandit]

I'm new to PWM Motor Controllers. I see many reference using a battery(s) for the DC source. Any reason an SMPS can't be used, assuming the output voltage is in the range spec'd by the controller, and the amps are sufficient for the motor in question?

[jwet]

A DC power supply Linear or Switcher would work.  There are a few things to watch out for though.

Batteries are a pretty nice source and are unconditionally stable with any load, you may wear them out a bit quicker with big pulsed loads but they won't misbehave.  Regulated power supplies aren't like this- they can overshoot and in extreme case oscillate with squirelly loads.  I'm not trying to scare you but weird things can happen.

A run of the mill SMPS(Chinese/Ebay) might not like having its output hammered on by a rapidly pulsing inductive load that a PWM would give it.  This is actually a common torture test for power supplies.  I would add a large capacitance to the output of the switcher with a PTC device in series to limit the inrush current to the caps to something like the max rating of the supply.  If the supply makes noise when you turn it on, there is likely too much inrush.  Once these caps are charged, they will handle the fast edges and the supply will only have to refresh their charge and won't have too much trouble.  Be a bit careful with layout too- don't have a lot of excess wire wiring around with high frequency PWM signal on it.  The wires have inductance and will try to store the current spikes and generate voltage spikes, etc.  It would be good to look at the supply output with a O'scope if you have one.  Measuring inrush current with a low value shunt would be good too.

Another option which is probably cheaper is a unregulated linear power supply.  This is just a transformer, bridge rectifier and bulk caps like above.  Get a transformer with an AC output of about 80% of your required voltage, add a bridge and a cap and then use this to run your PWM.  This kind of supply is common for pwm stepper drivers and audio amps- you don't need precision regulation, the pwm speed control does this basically and the voltage regulation stuff actually gets in the way.  There are online calculators for designing these circuits- google around a bit.  The better ones will even show you what the ripple etc will look like on a scope trace. 

Good luck,