servo motor voltage 5

[sparky27770]

hi all
this is my 1st posting so i thought id try a question thats been bugging me for a while .and one which im in no doubt will be quite simple for the more imformed than myself (most of u i imagine).
i work in car manufacturing and the press shop within which im active (some of the time)uses various types of AC DC indution and servo motors and drives ....however could anybody explain why all of our DC motor are rated at 200V when surely (to me anyway) it would be more efficient to design motors to use rectified line voltage .....anyone who can throw any light my way i thank you in advance

 

[rmw]

What are the HP or torque requirements of the DC servo motors you are referring to??

While there certainly are 90 VDC motors that I am familiar with for smaller servo units, which are supplied DC from rectified line voltage, the HP or torque requirements often drive the same types of devices to 180 VDC motors, rectified, of course, from higher voltage AC voltage.

Maybe this is what is driving your situation.

I can't give you the HP threshold where the shift has to be made, but I am sure there are guru on this forum who can.

rmw

 

[sreid]

The voltage rating for DC motors is often the voltage that will spin the motor at maximum rated RPM.

 

[Barry1961]

I think the motor is designed to run at rated speed at 200V. The speed of the motor increases with the voltage in normal operation. Unless you are running at full speed the motor will not see the 200VDC.
The voltage produced by the servo drive may be more than the "standard" voltage you would expect from just a full wave bridge.
There have been several really great past threads on PWM (pulse width modulation)control which you could probably search here or do a search on the web.

Barry1961

 

[sparky27770]

thanks for the replies i ...i cant provide the motor hp spec at mo as im off until monday lucky me
i think i have worded my question somewhat babdly tho so here goes hope this gives clearer indication of what im trying to ask
line voltage is around 415 vac so 3 phase ac motors r designed to run at 415 ....so why are dc motors rated at 200 and 90vdc .i imagine it has somethimg to do with the way in they are designed but cant understand why its mainly those two voltages...hope thats a bit clearer....sorry

 

[aolalde]

For small DC motors (less than 1 HP) NEMA standards recommend; 75, 90, 150 and 180 Volts for Single-phase primary power source. 240 Volts for Three-phase primary power source.

Industrial size DC motors recommended voltages are 240, 500 and 550. It is assumed that the primary power source is Three-phase.

My opinion is that you allow some margins for variable speed control.

 

[sreid]

I'll bet that some of the voltage standards go all the way back to the begining of electrical power. 150 and 180 volts make some sense today, 120 V rms full wave rectified and capacitor filtered is 170 VDC. The lower voltages may be due to early rectification limitations, full wave rectified-no filtering, half wave rectified or the use of inductor/capacitor filters. There also could have been "standard" battery voltages.

 

[jbartos]

Suggestion: NEMA standard ratings of industrial dc motors for 240V and 500/550VDC supply voltages are given in Tables 10-4 and 10-5 in NEMA Std MG-1