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#206042 05/14/12 08:54 PM
Joined: Jul 2007
Posts: 1,335
I have some trying to tell me that it is much easier to control a 480 motor on a VFD verses a 208V motor?

The problem is the motors will require a step up transformer that will be running 24/7 just to run a few motors when needed.


"Live Awesome!" - Kevin Carosa
Joined: Apr 2002
Posts: 7,333
Likes: 7
From experiences over the years, 208 and 480 volt motors running air handling equipment (5 to 25 HP) both were no issues with VFDs.

You may have different results depending on the use/duty of the motors.

Transformer losses may be an issue IF you are a high KWHr $$$.

Joined: Mar 2004
Posts: 947
twh Offline
Smaller wires on 480 volt?

Joined: Jun 2004
Posts: 1,273
The VFD can be of a smaller frame size in the higher voltages.

Other than that the actual control of a VFD is the same at either voltage.

( VFD's generate their waveforms by tapping a 'tank' of electropotential -- held up by a DC / rectifying circuit. This means that a VFD -- correctly sized -- can generate 3 phase power from a single phase source. This truth is ruining the market for rotary phase converters -- since the Chinese are now exporting VFDs at astonishingly low prices. Check out eBay. )

( When tapping a single phase power source, the VFD will be oversized -- quite a bit -- since it will have only the one wave to rectify. This is often still very much cheaper than a rotary phase machine -- which has to run, and run, and run... if you expect to have 3-phase power on tap. So, as a general rule, purchase a 15hp VFD to run a 5hp machine if you are limited to single phase power. )

The cost of adding a transformer in front of a VFD so that it can be downsized one frame size is uneconomic.



I rather suspect that the nostrum got started when a new generation 480V VFD was compared to an older generation 208V VFD.

ALL of the new stuff is now electrician friendly. That is: expect it to be able to link into multiple control schemes -- including building automation.

( HVAC is a HUGE user of VFDs these days. Blowers and compressors running at reduced speed mean astounding energy savings. So much so that when explained the normal civilian response is incredulity -- to the point of tuning you out. So don't ever get technical with the average Joe on this matter. )

( Fluid friction scales to the CUBE of the fluid speed: twice as fast requires eight times as much energy; four times as fast requires sixty-four times as much energy. The inverse, that cutting the speed by 75% reduces energy by 63/64ths is too much to comprehend. )

( It gets worse if you ever mention PWM or any other technical details. So don't. ) ( Pulse Width Modulation )

Joined: Jul 2007
Posts: 1,335
That's good info actually. I'm a bit of an electro nerd. The info is rather useful. Thanx!

"Live Awesome!" - Kevin Carosa
Joined: Jul 2007
Posts: 1,335
Smaller wires but requires a sizable transfromer $$$

"Live Awesome!" - Kevin Carosa

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