How to run 3-phase motor on 1-phase AC

Thread Starter

Babu Mistry

Joined May 25, 2019
8
Hi, Need to know how to run a 3 phase motor on single Phace 240v need a complete drawing with and how to change the motor rotation.
Is it advice able to run an Air compressor for long hours.
Thanks.
Lofty.
 

cmartinez

Joined Jan 17, 2007
6,898
Hi, Need to know how to run a 3 phase motor on single Phace 240v need a complete drawing with and how to change the motor rotation.
Is it advice able to run an Air compressor for long hours.
Thanks.
Lofty.
The only way to do that, is to install a variable frequency drive with single phase input to three phase output capability. What's the motor rated power?
 

MaxHeadRoom

Joined Jul 18, 2013
20,441
I suspect that with the possible high initial load/current, you will have to start the compressor motor using an unloader until up to speed.
Max.
 

Thread Starter

Babu Mistry

Joined May 25, 2019
8
The only way to do that, is to install a variable frequency drive with single phase input to three phase output capability. What's the motor rated power?
Hi Sir Thanks for your response to my question, the motor is 10 HP 7.5 KVA, can you tell me how much is Variable frequency drive coast.
 

cmartinez

Joined Jan 17, 2007
6,898
Here's a 7.5KW VFD for your consideration. I suggest you read the specs, and make sure it's exactly what you need.

EDIT: The drive I've suggested is for motors working at 380VAC
 

Toughtool

Joined Aug 11, 2008
63
Here is my schematic. It is for a 2 HP 3 phase motor. The motor needs to be about the same size as the motor you have on the compressor. It gets more difficult when starting larger motors as the starting current on the rotary converter can be really high if you are starting a large motor, particularly on an air compressor. I think the Variable frequency drive is your best bet for a 10 HP motor. I have posted the Fitch version (PDF) of a 10 HP that may help. I think I got it from the Practical Machinist forum.

Rotation doesn't matter on the idler motor. Changing the rotation on a 3 phase motor (your compressor) is as simple as swamping any two phase connections. i.e. A and B, or B and C, or C and A. Then re-label the outputs A, B, and C, if you wish.

Error report: I just noticed an error in the schematic. The two motor windings at "C" should have a dot, meaning they are connected. Also the two (Oil filled). capacitors Ci and C2 crossing at "B" are also connected to "B"
 
Last edited:

MisterBill2

Joined Jan 23, 2018
5,796
The only way to do that, is to install a variable frequency drive with single phase input to three phase output capability. What's the motor rated power?
Certainly the variable speed drive is a very good choice, and it can improve the efficiency of a compressed air system by allowing the compressor to be run at a speed that only supplies the required air flow. I have suggested that to several associates and it has worked quite well for them.
There are devices called "cyclo-converters" that are suitable for some seldom used home shop applications, and I DO NOT recommend them.
 

MaxHeadRoom

Joined Jul 18, 2013
20,441
I have posted the Fitch version (PDF) of a 10 HP that may help.
I also built the Fitch Williams RPC back a couple of decades ago. But personally prefer the VFD route.
I have worked with compressors up to the 100hp range, from piston to high RPM Turbine types.
IMO, the compressor should run at its max RPM in order to maintain tank pressure ASAP.
There is no real advantage to running longer/slower, it usually ends up with the compressor running longer as apart from very small types, they have a reservoir tank.
IOW, the VFD would be set for the motor rated frequency.
Max.
 

GetDeviceInfo

Joined Jun 7, 2009
1,702
I also built the Fitch Williams RPC back a couple of decades ago. But personally prefer the VFD route.
I have worked with compressors up to the 100hp range, from piston to high RPM Turbine types.
IMO, the compressor should run at its max RPM in order to maintain tank pressure ASAP.
There is no real advantage to running longer/slower, it usually ends up with the compressor running longer as apart from very small types, they have a reservoir tank.
IOW, the VFD would be set for the motor rated frequency.
Max.
Curious, what derating would you apply to the motor for such a supply?
 

MaxHeadRoom

Joined Jul 18, 2013
20,441
Curious, what derating would you apply to the motor for such a supply?
I only used them as a RPC, Rotary Phase Convertor, using a 5HP motor to produce 3phase to drive a 2Hp 3phase on a Mill.
The VFD manuf. should have a recommendation, some do not suggest de-rating as the internal VFD power supply is made to suit.the limit, whether 5HP or 10HP.
Max.
 
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