1 hp motor
2 hp better

AC variac and make switch for varying direction of motor.
130 v out 16 amp continuous variac\
for dc
20 amp rectifier


You can run a permanent magnetic DC motor from any source that has an average DC voltage. This can be with or without filtering, half or full wave rectified AC, or some pulsed source. Obviously there are some assumptions to this statement.

A typical motor has a moderately long mechanical time constant due to its inertia. If the electrical input pulse rate to the motor is fast relative to the mechanical time constant, then you will get moderately smooth mechanical output speed. 60 Hz and most motors meet this criteria.

The advantage of full wave rectification and filtering is that you reduce heating within the motor.

If you use sufficient capacitance in a capacitor input filter to make the ripple small, then for a sine wave input your average output DC voltage is approximately sq-root of 2 (1.414) times the input Vrms.

Whether the ripple is high or low, and half wave or full wave rectification your capacitor voltage rating needs to be substantially above the AC peak voltage given by the above 1.414 calculation.



Notes:
  1. F1 fuse, 10 Amp slow-blow or time delay type
  2. S1 switch 15A AC rating
  3. T1 isolation transformer, at least 1200VA rating
  4. T2 Variac, 10 Amp rating, however, 8 Amp continuious, 10 Amp short time only
  5. All parts above must be approved by your local electrical authority. IE: CSA, UL, ETA, etc.
  6. The bridge rectifier diodes, 400V, 15 Amp, (higher rating is better) heatsink may be required for heavy loads.
  7. R1 is the ballast resister that R!@ff suggested. It will limit the inrush current to the 7000uF if the unit should be powered up with the variac set to maximum... try to avoid that. I'm not sure if this is required since there may be enough resistance in the circuit to do the job. What is the surge rating for the diodes and the caps?
  8. Suggestion: Make F2 a cartridge fuse that can be easily changed from the front panel. F2 can be any value that approximately 50% more than the worst case expected DC load, upto 10 Amp maximum. IE if you are powering a circuit that is not going to need more than 0.8 Amp, then use a 1 Amp fuse for F2. That way if there is a problem (short) then the minimum amount of damage will be done
Anything else?
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