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Old May 24th, 2004, 12:43 PM   #1
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firebrd10 is offline
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VFD Question (Home Project)

OK Guys!

A friend of mine just bought a piece of equipment that requires 3 phase power to run.
He wants to run it in his garage were there is only single phase.
He heard you could hook up a VFD and make it work.
I have never heard or do I believe that this is possible but I am willing for someone to prove me wrong.

208 3PH
Trying to make run with 110/220 1PH.

Any Ideas are appreciated.

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Old May 24th, 2004, 01:01 PM   #2
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I've done projects where there was only 230 single phase available but needed 230 3-phase to operate pumps. It can be done but with a few caveats. The VFD must be sized (approx. do your own current calculations) 4 times higher than necessary to handle the power requirements of changing single phase to 3 phase (SCR size). The drive must also be disabled for phase imbalance. If your motor is 15HP 230 3-phase then you will need approximately a 75 HP VFD to give you the output power necessary to run at full load. It can be done but do the calculations to determine your input and output loads. For that size of VFD you'll probably be better off getting a transformer.
Matt Stefanski

Go Dayton Flyers!
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Old May 24th, 2004, 01:06 PM   #3
Jiri Toman
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yes you can

There are all kinds of Drive makers out there that produce
a single phase in, 3 phase out AC drive. Check out Reliance, part of
Rockwell now. I have used their single phase in, three phase out drives on few projects and they work great.
You should also make sure that you have enough power in your garage
to run 15 HP motor.
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Old May 24th, 2004, 04:04 PM   #4
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It can be done, but you had best expect to pay several thousand dollars for the drive. Perhaps you might fine a used one, but it will still be some fairly large bucks.

LJBMatt is right, depending on the manufacturer of the drive it will need to be oversized from 2x to 4x to get it to work properly. Plus your garage and wiring will need to be able to carry the loading. If you were running three phase the motor would be carrying 42 amps. On single phase it will be much more than that, so wiring to the VFD will have to be capable of carrying the excess current.


Last edited by icky812; May 24th, 2004 at 04:06 PM.
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Old May 24th, 2004, 04:49 PM   #5
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If you take a good look at the spec sheets from ANY brand you will find that if they can be connected to a single phase (and most of them can) you need to versize the drive by xxx. Usually only one size up.

So for a 2HP motor, if the size would be a 3 HP drive, hen you select a 5 HP drive and it works pretty good.

The problem is never the output of the inverter but the input size. To charge them capacitor you need to pass as much current into one phase as you would in three, so the need for a bigger inverter, for the INPUT side of things.
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Old May 24th, 2004, 06:42 PM   #6
Thomas Sullens
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Hi firebrd10

Why don`t you build him a phase converter they are simple and work good. Go to google and type in phase converter and you`ll get more info than you can say grace over.

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Old May 24th, 2004, 11:06 PM   #7
Shawn Cassidy

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I've worked on something called a Rotophase before. They're common in lathe and milling machine applications where 3 phase power is not available. This converter connects to 240 volt single phase (house voltage) and outputs 600 volt 3 phase. It consists of a step-up transformer (240v to 600v single phase) a bank of capacitors and a motor used as a generator... I believe. You can select different models to suite your specific application. You select according to the HP of your motor. I don't know if this product is still on the market? I think the company was based in Toronto, Canada. The model I worked on was a 10HP, 600 volt. / is a site that offers something similiar to a Rotophase.

Last edited by Shawn Cassidy; May 24th, 2004 at 11:16 PM.
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Old May 25th, 2004, 07:59 AM   #8
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A couple of things on this subject need to be clarified. First, the normal derate for VFD output current when single-phasing the input is 50%, not 4/1 or 6/1. Second, a VFD is a poor choice for a phase converter if the motor or motors are to be start/stopped independently of the inverter. Throwing a stationary motor across the output of an inverter that is "up to speed" will almost surely result in an inverter fault. Acceptable operation is only possible by starting and stopping the motor and inverter as an operationally- matched pair.

In my view, the old rotary converters, while inefficient, are still the best choice when you are dealing with multiple motors and random start/stops.

And, yes, the size of the single phase service gets pretty hefty at 15hp. Let's see here, 15hp is 11.2kw so the single-phase service will have to supply that plus a little for inefficiencies. At 220VAC single-phase, that would work out to 51amps plus whatever the losses and inrushes are. A 100amp service wouldn't be too large, would it?
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Old May 25th, 2004, 09:01 AM   #9
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You may want to check out these rotary converters.
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Old May 25th, 2004, 05:40 PM   #10
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Another option are Static Converters, which are basic cap banks that fake out the phases, not as efficent as rotarys.

Here's a site for them -

Quote from site -

"The static phase converter does not actually generate 3-phase power continuously as a rotary phase converter does, but only long enough for it to start up. Once the motor has started the static phase converter circuitry disconnects itself and the motor continues to run on single-phase power; because only two of three windings receive power during running, power output is reduced to 1/2 to 2/3. A 15 HP motor will start with the power of a 15 but run as a 7.5 for example."
Inside every complex and unworkable program is a useful routine struggling to be free.

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Old May 25th, 2004, 07:18 PM   #11

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What about a 3 phase diesel (or petrol/gasoline) electric generator?
This will give heaps of power, and I think they are not too expensive.
Just have to be run outside, and watch for fumes.

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Old May 25th, 2004, 11:05 PM   #12
Eric Nelson
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While searching for something completely different, I stumbled across THIS old thread which may be helpful to Tim.

Maybe Pierre can give us an update on what he wound up doing?...


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Old May 25th, 2004, 11:59 PM   #13
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I recommend rotoary phase converters over static converters. Static converters sometimes (not always) generate emf / rf interference.

I belive that rotary units are less expensive.

Trying to figure out a rotary unit one time, my best guess is as follows:

A motor, possibly with a permanent magnet armature, is configured for 3 phase open delta (two windings). Single phase input hooked up to motor windings A and B, 3 phase output to A and B and C. Armature turning induces current (magically?) from first winding to second winding. Due to design, it automatically phase shifted. It all makes perfect sense when seeing how electric utilities get by with suplying open delta 240 to older factories and the majority of farms around the country. Normal winding is center tapped for 120/240 normal house wiring and the wild leg on the open winding floats voltage wise with load. Wild leg is typically 208 volts to ground and should only be used for third phase. They are typically 1.5-2 times the size of the motor that you want to use.

Hopefully, this makes sense, it is perfectly clear in my mind.

Anyway, I figured it out from literature for this link....

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Old May 26th, 2004, 01:29 AM   #14
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15 hp is kinda large, and the price of a converter will be also. A new 25hp 240 listed on eBay was $1295, and 15hp ranged from $875-$1995.

As an electrical contractor, I've received a lot of calls from people who bought 3-phase equipment because it was a bargain. New electric service is 2-3 times more expensive, and locally, all utilities charge extra for 3-phase service, whether you are using it or single phase loads. Usually the calls are from restaurants or smalll tavers that found a great deal on a cooler. Generally, the wing up with a new single phase motor by the time they are done comparing all the costs.

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Old May 26th, 2004, 09:25 PM   #15
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VFD Question

I saw this done once in NC. This fellow had a milling machine in his garage. It had a 5 hp 3 phase motor on it. To generate the 3 phase for it, he had another 3 phase motor acting as a generator in this manner. The single phase 240 was wired to 2 of the 3 phase motor leads. The 3 leads from the milling machine were wired to the 3 leads on the other 3 phase motor. He had another motor yet (single phase) turning the 3 phase motor with a belt and pulleys. By having the motors spinning. the 3 phase was induced in the generator motor and sent to the milling machine. If I had not seen it, I would not believe it. Hope this helps.
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