# Dc Motor Voltage Rating

Discussion in 'Electronic Basics' started by Peter Walinsky, Aug 18, 2005.

1. ### Peter WalinskyGuest

What would happen if I had a motor that has markings saying it is a 2.25 hp
motor, 130 volt, 18 amp and I pulsed it with a 50% duty cycle of 170 volts.
Could it fry my motor, if yes, why? Or would the capacitance and inductance
smooth the voltage and amperage it is getting.

My other question was, if I rectify 120 VAC and smooth it with a capacitor,
what will the resultand DC voltage be, assuming there is only a little
ripple. From what I understand it would be about 120 * 1.414 = 170

Thank you
Pete

2. ### Guest

Rectified 120VAC:
120*sqrt(2)=170VDC

3. ### kellGuest

If it's a DC motor you can use pulse width modulation. I tried that on
a cordless drill and it worked. I think I used about 20 kHz.
On an AC motor I think you would use the technique lamp dimmers use.
It truncates part of each cycle. For a small motor, an actual lamp
dimmer might work. Not for the motor you decribed though. Lotta
power. Besides the high power level, the motor "dimmer" also has to
withstand inductive spikes that you don't get with lighting. I
remember reading a post somewhere by a guy that did use a lamp dimmer
to control a power tool, but it was a small handheld one like a detail
sander.

4. ### Jasen BettsGuest

my dad's cheap corless drill uses PWM at a lower frequency (sounds like about
5Khz)
yeah for universal motors thjey do that, there are also special electronic
controllers available controlling induction motors (like are typically used
to power fans) the ones I saw were in australia and for 230V so chances are
they're not what the original poster wanted... try a wholesaler.
I've seen it done on a ceoilng fan - it was an induction moto and with the
dimmer on 1/4 to 1/2 way it tended to get very hot...
these ones I saw were rated at 500 watts IRC. but larger versions of the
same concept ar available - they use them in electric trains.

Bye.
Jasen