220v vs 440v air compressor

RUn2it

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This message is a reply to an archived post by ws price on October 04, 2011 at 20:27:20.
The original subject was "220v vs 440v air compressor".

I know this is an old thread but sure people still find it in a search, read the whole thing and never saw an accurate description of the difference between 220 1ph and 220 3ph so here goes. Single phase 220 has 2 hot wires, each is 110v to ground (220/240 or 110/120, consider it the same for this explanation)single phase is 60 hz (cycles)that means the voltage goes from 0v to 120v 60 times per second, each hot, they both are 0v at the same time, and both are at 120v at same time only in opposite directions when viewed on a sinewave (refer to the crude sine wave diagrams I made with paint)So from 1 hot to the other is 220v with a volt meter. NOW 220v 3 phase = there are 3 hot leads, each is 220v to ground and all 3 are staggered start from zero times so there is NEVER 0v in operation, as 1 phase starts downward (on the sinewave)the next phase is on the way up (this is why you don't find capacitors on 3 phase as voltage is never zero, 1 phase with compressor starting under load has to have capacitors to start or the motor would just hum and trip the breaker) so a 220 3 phase motor has more torque than a 1 phase of the same HP. If this doesn't click just study the sinewave and think of 1 phase starting under load. If you remember point ignitions on older vehicles the condenser is actually a capacitor, when points open they would arc and burn if there wasn't a cap to give the electricity someplace to go, charging the cap, with compressor the motor uses the discharge of the cap to give it the extra bump in power to start. There's probably a formula to determine how much bigger a single phase HP rating motor needs to be to replace a 3 phase motor. If a 3 phase motor connected to 220 single phase using a rotary converter it will run but now you can see that you have 2 120v to ground feeds and a spinning converter motor to replace 3 220v to ground power wires. Lee

PS can't upload sinewave drawing for some reason, will check back to verify
 
Actually 220 single phase is just two hot wires. A 220 single phase motor will run with only the to hot wires. The ground is just for safety. The motor doesn't need it. Each of the hot wires provides the neutral when they go positive to negative as they are out of phase 180 degrees. 220v three phase is three 110v lines 120 degrees out of phase with each other. It's considered 220V because you can use a meter on any two wires and it reads 220V. 440v would be measured as 440v between any two wires. The type phase the motor has really doesn't have that much to do with HP, the motor is what it is. It's just three phase is more economical for companies to use.
 
(quoted from post at 09:28:15 11/28/16) Actually 220 single phase is just two hot wires. A 220 single phase motor will run with only the to hot wires. The ground is just for safety. The motor doesn't need it. Each of the hot wires provides the neutral when they go positive to negative as they are out of phase 180 degrees. 220v three phase is three 110v lines 120 degrees out of phase with each other. It's considered 220V because you can use a meter on any two wires and it reads 220V. 440v would be measured as 440v between any two wires. The type phase the motor has really doesn't have that much to do with HP, the motor is what it is. It's just three phase is more economical for companies to use.

The live line does not become a neutral.
 
While far from perfect its good enough for a non sparky (and Billy Bob and Bubba) to perhaps begin to understand lol Its like I often say, its IMPOSSIBLE to explain in a paragraph what may take volumes and a lot of study to fully comprehend BUT STILL A DARN GOOD EFFORT FOR WHICH I SAY THANK YOU

John T Too long retired Electrical Engineer
 
Three phase motors have very impressive startup torque and torque under load.
So the HP under load is a great advantage as well as efficiency for 3 phase motors.
The startup cap for single phase motors provides a 90 degree phase shifted second phase for a startup winding.
The startup torque can be very high depending on the design but can not hold a candle to 3 phase motors.
Respectfully,
Greg

BTW, if you need more torque under load for single phase motor and the duty cycle is low, you can manually switch in the startup cap to the startup winding.
I do this on my 37 year old radial arm saw.
Actually I have a manual switch for startup and I will switch it back in before I cut very thick lumber to prevent stalls. I put the switch in when the startup contactor went out.
It was later when I tried cutting heavy stuff that I switched in the startup cap/ winding and was very pleased with power to get through the cuts.
 
I came across an old ski-lift with a Single-phase 60HP motor on it. It had a cabinet of capacitors that was about 5 ft tall and 4 ft wide that was used for starting. The required HP was only 50; so it was derated for the application.

I went to GE to see if they would quote another one for a new project I was working on, and they told me 'no way'. One was enough.
 
Hello John T,

AAAAAANNNNNNDDDD! Its all theory. HA HA.....

That 110 120 always gets me though,

Guido.
 

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