Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Largest Manufacturing Technology Community on the Web
Stay Connected:
Single phase motors, 3-phase power
- Thread starter Airborne
- Start date
- Replies 15
- Views 33,794
Can the motor run on 120v?
Can you re-wire the motor to run on 120v??? If so, just do that, and it would work fine. SOME single phase motors are able to run on 2 legs of a 3 phase system, does it say 208v on it?? If so, it will probably run, try it and see what it does. Worst case scenario is it won't run, so long as you don't leave it stalled for more than a few seconds, it will be fine. Just be ready to pull the plug. If the motor groans, or makes funny noises, you'll also want to pull the plug. It should just draw a little more current. Just make sure it doesn't get super hot.
Can you re-wire the motor to run on 120v??? If so, just do that, and it would work fine. SOME single phase motors are able to run on 2 legs of a 3 phase system, does it say 208v on it?? If so, it will probably run, try it and see what it does. Worst case scenario is it won't run, so long as you don't leave it stalled for more than a few seconds, it will be fine. Just be ready to pull the plug. If the motor groans, or makes funny noises, you'll also want to pull the plug. It should just draw a little more current. Just make sure it doesn't get super hot.
440roadrunner
Hot Rolled
- Joined
- Jun 4, 2006
- Location
- N Idaho
Many modern motors--I used to work in HVAC--are rated for 208-240.
I would simply hook the thing up and monitor it for awhile for heat. If you have a clamp on ammeter, I'd measure the current draw under load, and see how that compares to the namplate rating.
As above, just hook to any two hot legs
I would bet you have a good chance of no problems
I would simply hook the thing up and monitor it for awhile for heat. If you have a clamp on ammeter, I'd measure the current draw under load, and see how that compares to the namplate rating.
As above, just hook to any two hot legs
I would bet you have a good chance of no problems
peterh5322
Diamond
- Joined
- Dec 15, 2002
- Location
- Monterey Bay, California
"How does one run single phase 220v motors on 208/120 3-phase power?"
120/208 is a Y system. 120/240 is a ∆ system.
Actually, the motor cannot tell the difference, so you give it two lines, which would be 208 line-to-line in the first case and 240 line-to-line in the second case, and a "starting means", and it will work.
And, most motors cannot tell the difference between 208 and 240 volts, although such motors are usually marked 208-240 or 208-240/480.
Now, the "starting means" may be a simple static converter such as a Phase-a-Matic, or it could be more complicated.
In the simplest case, the "starting means" is a potential relay which senses the voltage between L3 and L2, and a starting capacitor between L1 and the potential relay.
Once the motor is up to speed, the potential relay drops out, thereby removing the capacitor from the circuit, and the motor continues to run, but at a maximum of 67 percent of nameplate HP.
120/208 is a Y system. 120/240 is a ∆ system.
Actually, the motor cannot tell the difference, so you give it two lines, which would be 208 line-to-line in the first case and 240 line-to-line in the second case, and a "starting means", and it will work.
And, most motors cannot tell the difference between 208 and 240 volts, although such motors are usually marked 208-240 or 208-240/480.
Now, the "starting means" may be a simple static converter such as a Phase-a-Matic, or it could be more complicated.
In the simplest case, the "starting means" is a potential relay which senses the voltage between L3 and L2, and a starting capacitor between L1 and the potential relay.
Once the motor is up to speed, the potential relay drops out, thereby removing the capacitor from the circuit, and the motor continues to run, but at a maximum of 67 percent of nameplate HP.
ToughTool
Hot Rolled
- Joined
- Apr 9, 2007
- Location
- Panama City, Florida 32401
Peter,
Wouldn't a single phase motor on a cheapo bandsaw have it's own starting means? Like an internal centrifugal switch, start winding, and sometimes a capacitor? Joe
Wouldn't a single phase motor on a cheapo bandsaw have it's own starting means? Like an internal centrifugal switch, start winding, and sometimes a capacitor? Joe
Last edited:
frenchelectrican
Plastic
- Joined
- Jul 30, 2007
- Location
- NE Wisconsin
Useally most single phase motor will have sorta a starting aid useally start winding , capacitor and yes most have centrifual switch as well unless you got PSPC motor [ perment split phase capaitor { both run and start winding is used all the time }]
Merci,Marc
I think peter was referring to a static type converter and how they are started with a potential relay and start capacitor. But there are alot of single phase motors that use the same setup, Franklin electric uses that setup for there deep well single phase pumps, as with Gould, Myers, ABS, the list can go on and on.
DaveKamp
Titanium
- Joined
- Oct 3, 2004
- Location
- LeClaire, Ia
Deep science...
Hee hee... Not that complicated- just hook up two legs and flip the switch.
My main utility feeder is 120/240 single phase.
My 'small' backup generator is 15kva 208/125Y three-phase.
When under emergency power, my disconnect/transfer switch hooks two phases of the genset to the single-phase feeder... and the neutral leg to gen neutral (center of the Y).
Yep, everything works... no difference really. Does it seem 'wierd', yes, but in reality, the phase relationship of the two loaded phase make no difference to the motor- it's only seeing the difference between two phases- the neutral is essentially irrelevant.
(My hookup system is actually a bit more sophisticated, as I have all three phases loaded, feeding buildings off of different 'splits' of a/b, b/c, a/c... and when I really need power, I can fire up a 35kva 120/240 single-phase power plant... and the changeover switches will sort it all out, but you get the idea)
Hee hee... Not that complicated- just hook up two legs and flip the switch.
My main utility feeder is 120/240 single phase.
My 'small' backup generator is 15kva 208/125Y three-phase.
When under emergency power, my disconnect/transfer switch hooks two phases of the genset to the single-phase feeder... and the neutral leg to gen neutral (center of the Y).
Yep, everything works... no difference really. Does it seem 'wierd', yes, but in reality, the phase relationship of the two loaded phase make no difference to the motor- it's only seeing the difference between two phases- the neutral is essentially irrelevant.
(My hookup system is actually a bit more sophisticated, as I have all three phases loaded, feeding buildings off of different 'splits' of a/b, b/c, a/c... and when I really need power, I can fire up a 35kva 120/240 single-phase power plant... and the changeover switches will sort it all out, but you get the idea)
ToughTool
Hot Rolled
- Joined
- Apr 9, 2007
- Location
- Panama City, Florida 32401
I was just poking a little fun at Peter because it looked like he had a brainfart
. Anyway good to know some single phase motors need an external starter system too. Just in case I need to use a deep well, single phase pump motor on my old cheapo band saw. Would like to see a photo of that 
. Thanks guys, always learn new stuff from this site. Joe
. Anyway good to know some single phase motors need an external starter system too. Just in case I need to use a deep well, single phase pump motor on my old cheapo band saw. Would like to see a photo of that . Thanks guys, always learn new stuff from this site. Joe
peterh5322
Diamond
- Joined
- Dec 15, 2002
- Location
- Monterey Bay, California
"Anyway good to know some single phase motors need an external starter system too"
All single-phase motors need a starting means.
For easy to start loads, a split phase motor can do the job.
For more difficult to start loads, a capacitor start motor can do the job.
Where capacitors are involved, so also is a secondary winding, usually in quadrature to the run winding. The quadrature winding is 90 degrees displaced in time from the run winding. The capacitor inherently provides a +90 degree phase lead to the start winding. The motor starts as a two-phase motor.
For best starting performance, and highest running power factor, higher even than three-phase, a capacitor start/capacitor run motor is the obvious choice. The motor starts and runs as a two-phase motor. These are obviously the most expensive.
All single-phase motors need a starting means.
For easy to start loads, a split phase motor can do the job.
For more difficult to start loads, a capacitor start motor can do the job.
Where capacitors are involved, so also is a secondary winding, usually in quadrature to the run winding. The quadrature winding is 90 degrees displaced in time from the run winding. The capacitor inherently provides a +90 degree phase lead to the start winding. The motor starts as a two-phase motor.
For best starting performance, and highest running power factor, higher even than three-phase, a capacitor start/capacitor run motor is the obvious choice. The motor starts and runs as a two-phase motor. These are obviously the most expensive.
ToughTool
Hot Rolled
- Joined
- Apr 9, 2007
- Location
- Panama City, Florida 32401
Single phase hermetic motor applications like refrigeration compressors (sealed to keep refrigerant in) and submerged pumps (sealed to keep water out) typically use external starting circuits. It just would not do to have arcing start contacts inside a compressor housing. You would not want internal capacitors either.
BTW, if you find that you *really* need 240V for your motor, such as if it draws too much current at full load at 208V, you can get small buck-boost transformers to adjust the voltage to the load. They have ~12V secondary windings, sometimes multi-tapped, of appropriate current ratings. You connect the primary across the supply and hang the secondary in series so that it is in phase to boost the supply voltage. Buck configuration is used to get 208 from a 240V delta supply. These transformers are small and relatively cheap.
Here is a reference:
http://en.wikipedia.org/wiki/Buck-boost_transformer
ToughTool
Hot Rolled
- Joined
- Apr 9, 2007
- Location
- Panama City, Florida 32401
It is Airborne, who wanted to use a 220 volt, single phase motor on his cheapo band saw, not me, by powering from a three phase 208 volt power source. To answer his question, just connect any two of the three phase lines to the motor and it should work fine. peter5322 said it would work and I for one will not doubt it in the least. I am inclined to believe Peter knows electrical motors and power very well.
As far as using a single phase hermetic motor like a refrigeration compressor to power a band saw, it would create even more problems with coupling to the band saw than a deep well pump motor would. Other than the fact of access, I'm not sure why it would be bad to use "arcing contacts", inside a sealed compressor housing since there is only Freon and compressor oil inside. No oxygen or water present.
The compressor companies would love to sell a whole compressor when the contacts or coil burns up. I'm surprised they haven't thought of that idea already. Anyway, my Ridgid band saw came with a 3/4 HP motor so I don't need one.
JoeA) It is Airborne, who wanted to use ...
B) As far as using a single phase hermetic motor like a refrigeration compressor to power a band saw...
C) Other than the fact of access, I'm not sure why it would be bad to use "arcing contacts", inside a sealed compressor housing since there is only Freon and compressor oil inside. No oxygen or water present.
A) ToughTool, I was not replying directly to you. I quoted you because it was convenient and relevant.
B) Out of scope. Obviously.
C) Arcing will ionize the freon releasing free radicals which will react with the oils and insulation forming corrosive decomposition products which would rapidly destroy the compressor.
