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#170594 - 11/06/07 05:39 PM Using a VFD to drive a single phase 50 Hz load.  
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US

I need to drive a 230 V single phase 50 Hz water bath for a couple of weeks during the design / build phase of a laboratory sampling system. All of the other components use switching power supplies for power, so I can power them off of the wall outlets. This chiller needs 50 Hz for the compressor and the circulating pump.

My thought is to purchase a small VFD that takes 120 60 Hz in and puts out 230 3 phase 50 Hz. Do you think that I would have to equally load each phase?

I'll call some vendors in the morning, but I figured I would tap into the knowledge bank here first.


Larry C

Work Gear for Electricians and the Trades

#170621 - 11/07/07 11:11 AM Re: Using a VFD to drive a single phase 50 Hz load. [Re: LarryC]  
JValdes  Offline
Joined: Jun 2007
Posts: 301
South Carolina
Sorry you cannot use a VFD on single phase motors. Now, you could use single phase input, but it would output 3 phase.
50hz is no issue. VFD's can operate on either 50 or 60 hz.
You just need a three phase motor and single phase supply.

Note: VFD's over 5hp require that you derate the VFD in single phase applications. 5hp and lower it's a non issue. ( most manufacturers)

www.automationdirect (best for small VFD's)
for the VFD.

Check Grainger, Baldor or Weg for the motor. Weg is less money with fantastic quality. Made in Brazil

3 phase motors are less money than single phase.

#170629 - 11/07/07 01:16 PM Re: Using a VFD to drive a single phase 50 Hz load. [Re: JValdes]  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
Actually, there is no reason "in principal" that this would not work. The output phase relation (and phase count) of a variable speed drive is entirely arbitrary; I am sitting next to an 18 phase VSD right now. Solid state frequency converters are available that use essentially the same electronics as a VSD, but with significantly different details and control software.

However there are certain to be significant _practical_ issues. For example, if the VSD measures output current, it probably assumes a balanced three phase load, and might be confused by single phase loading. You might even trip some protection circuitry. The VSD output is switched at extremely high frequency (2KHz and above), and depends upon the inductance of the load to smooth out the current flow; this could cause serious problems if the load is not a simple motor.

If I had the parts on the shelf, are were willing to smoke them, then I would try running the chiller from a VSD via a transformer (the transformer to smooth the current flow and to balance the loading), and give it a good 50% chance of working.

If I had a job to do quickly, I'd just rent a frequency converter. Google for '50Hz' and you will find several.


#170662 - 11/08/07 11:24 AM Re: Using a VFD to drive a single phase 50 Hz load. [Re: winnie]  
JValdes  Offline
Joined: Jun 2007
Posts: 301
South Carolina
Good discription, but a little over kill for this application, would you not agree?

I wish the poster would have told us the HP of the motor. If he had, I could have provided him with a ball park price on the VFD and motor.
I would be willing to bet the VFD and 3 phase motor would be less money than the converter. I used to sell both.
Drives and motors have become so inexpensive today. Today you pay less for a 3 phase motor that you did 10 years ago. Same with the VFD's. You can buy 1/3hp VFD's today.
I have a 1hp "kb" VFD on my book shelf I paid $85.00 for.

#170666 - 11/08/07 01:29 PM Re: Using a VFD to drive a single phase 50 Hz load. [Re: JValdes]  
Alan Belson  Offline
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Am I missing something? Why do you need 50hz for circulating pump and refrigeration pump motors? I can't see why a 50hz machine would not operate satisfactorily on 60hz, given that the voltages approximately agree. The pumps run faster. Where's the criticality?

Wood work but can't!

#170677 - 11/08/07 05:41 PM Re: Using a VFD to drive a single phase 50 Hz load. [Re: JValdes]  
LarryC  Offline
Joined: Jul 2004
Posts: 783
Winchester, NH, US
To All,

The unit is a small circulating chiller that will be used to freeze beer smile samples. We purchased the unit new and according to the manufacturer, the warranty will be voided if ran on 60 Hz. I opened it up and the first motor I saw, was listed for 50 Hz only. I don't know enough about refrigeration systems to be comfortable running the compressor over frequency.

I contacted a local testing lab and their facility has a 50 Hz generator for the building. For a reasonable amount, I am just going over there, plug the system in, and watch the beer freeze.

Thanks for everybody's suggestions. The low cost for doing it right, allows me to sleep alot better than jury rigging something together and hoping the unit doesn't fail.


#170711 - 11/09/07 03:12 PM Re: Using a VFD to drive a single phase 50 Hz load. [Re: LarryC]  
JValdes  Offline
Joined: Jun 2007
Posts: 301
South Carolina
Alan, 50Hz will run on 60Hz, but for how long. The reason being is 50Hz motors are designed to operate at a different voltage. Not our US standard 120,240,460 and 575 VAC

Example: IEC standards on a 3 phase motor at 50Hz would require 380 volts ac, not 460.

I have had customers that received 50Hz motors on equipment and wanted to know if we could rewind for 60Hz, which we could. But, we usually told them to run it until it quits and buy another 60Hz meteric motor to install when needed. This was for smaller motors. Larger motors we told them to pull it and give us the required time to rewind or replace.
If it was on a VFD then we would just program the drive for 50Hz.

#170798 - 11/12/07 05:14 AM Re: Using a VFD to drive a single phase 50 Hz load. [Re: JValdes]  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,405
Vienna, Austria
No longer 380 but 400, but not much of a difference (unlike in the US European motor nameplate voltage rating and nominal line voltage are identical, so a European design motor would have to be rated 480V to run on a 480V feed within its specifications).

Aren't there any simple inverters that give out simple 50Hz instead of a variable frequency?

#170810 - 11/12/07 11:54 AM Re: Using a VFD to drive a single phase 50 Hz load. [Re: Texas_Ranger]  
JValdes  Offline
Joined: Jun 2007
Posts: 301
South Carolina
Yes, You can buy simple inverters. But they are rotary and more expensive that a simple VFD. VFD's are so cheap now, I can't see a better option.
Give me a motor spec and I can tell you what it would cost.

ps....I see 380 and 400 volts all the time (metric). it's a manufacturer thing I think.

Last edited by JValdes; 11/12/07 11:56 AM.

#170926 - 11/15/07 04:48 AM Re: Using a VFD to drive a single phase 50 Hz load [Re: JValdes]  
jraef  Offline
Joined: Jul 2004
Posts: 101
San francisco, CA, USA
Although I don't think LarryC needs any more help with this, I'll post for the sake of future readers.

You can apply VFDs to SOME single phase motors, but not most of them. The reason is, most 1 phase motors are capacitor start and / or cap run designs. The capacitors in the motors look like a short circuit to the VFD transistors and incrementally damage the transistors themselves, leading to rapid failure. The motors also have start switches that switch out the starting caps at +90% speed, but will re-close if the speed is reduced with a VFD (not really applicable to LarryC's situation though). The two kinds of 1 phase motors that can be used on VFDs are Shaded Pole and Permanent Split Capacitor (PSC) type. The shaded pole motors can also be speed controlled with a simple rheostat, so buying a VFD is kind of a waste. PSC motors work OK because the capacitors are in series with the windings, not in parallel, so there is always some extra inductance in the VFD output that prevents the cap charging current from doing damage.

So to that end, IF your little compressor uses a PSC motor, there ARE 1 phase VFDs out there on the market.
Anacon is one,
Bardac is another
(in reality, both are brand-labeled from a UK company called Invertek)
If you tried to hook up a 3 phase output VFD to a single phase PSC motor, every one of them I know of would trip on output phase imbalance.

Last edited by jraef; 11/15/07 04:51 AM.


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