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Dc motor voltage rating

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

Reply to
Peter Walinsky
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Peter, You can pwm this motor as long as you do not exceed 18 amps. Yes the voltage would be 170 volts but cap will probably not be large enough to give the 170 volts under a load.

Ray King

hp

volts.

inductance

capacitor,

Reply to
rayjking

rayjking> Yes the voltage would be 170 volts but cap will probably rayjking> not be large enough to give the 170 volts under a load.

[OP asked whether rectifying and filtering 120VAC would give ~170VDC (=120*1.414)]

I thought 120VAC was the RMS of the peak-to-peak voltage. So, if you rectify it, you should get a half-wave from 0-85VDC peak, filter it and get ~60VDC. Damn, now I have to poke a 'scope probe into an AC outlet, just to see.

dhm

Reply to
dave madden

dave madden wrote this in :

Uh, this sounds like random ramblings from your side. Yes, 120VAC is RMS, but of the half wave. But when you rectify, effective voltage becomes Top-voltage, which is 170.

--
MVH,
Vidar

www.bitsex.net
Reply to
Vidar Løkken

"rayjking" wrote in news:PfUMe.24537$ snipped-for-privacy@bignews5.bellsouth.net:

So then what is the 130 V rating on the motor mean if I can pwm it with 170 volts? Thanks

Reply to
Peter Walinsky

My guess would be that you'd be fine to at least 500 volts if you keep the motor from getting hot. If you're not sure you could take a look at the insulation on the wires...

Reply to
bhauth

snipped-for-privacy@gmail.com wrote in news:1124420944.997917.286850 @g47g2000cwa.googlegroups.com:

Thank you All

Reply to
Peter Walinsky

I "think" you are answering a question I have after poking around in a power supply.

It has a step down transformer from 120 VAC to 28 VAC and then goes through a bridge rectifier. The resulting DC Voltage measures 42 VDC.

Is this because of the RMS you are referring to?

Lurking, Ace

Reply to
Ace

Ace wrote this in :

No. Multiply with sqrt(2), which is 1.41, so you should have around

39.4V, not 42... So You probably have more than 28VAC. Depends on how the multimeter measures, if it is true RMS, or such. But, yes, mainly you got it right. 
--
MVH,
Vidar

www.bitsex.net
Reply to
Vidar Løkken

Peter, If you start with 120 volts ac and add a fullwave ( 4 diode bridge or a controlled bridge using scr's in a phased controlled circuit ) the out put is the 120 volt rms converted to a dc average voltage which will be near 130 volts. This voltage is higher than the 120 volts because the dc motor generates a counter emf ( voltage ) that is inductive but the dips in the rectified dc voltage is filled in by the motor acting as a generator.

Ray King

170
Reply to
rayjking

Peak to peak of 120 V RMS would be 120 *2.828, or 339.36 volts P-P.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

rayjking wrote this in :

First, top posting is rude. Second, what have you been smoking? If you rectify 120VAC RMS you get

170VDC, albeit a bit less unless you have a huge capacitor for storing between the peaks.

And for the motor acting as generator...? I doubt it. The motor genarating power == power lost on motor shaft.

--
MVH,
Vidar

www.bitsex.net
Reply to
Vidar Løkken

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