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
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