 KenPremium,MVM
join:2003-06-16
Markle, IN | reply to 49528867
Re: How To Install A 3 Phase A/C Unit On A Camper. Three phase A/C for a camper, that would have to be a pretty big compressor. |
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 cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | said by Ken:Three phase A/C for a camper, that would have to be a pretty big compressor. Does three phase necessarily indicate size? I know that three phase is typically for larger applications, but can you have a small 3-phase motor, such as were you'd typically find a small 120v motor like a box fan? |
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TheMGPremium
join:2007-09-04
Canada
kudos:1 | said by cdru:Does three phase necessarily indicate size? I know that three phase is typically for larger applications, but can you have a small 3-phase motor, such as were you'd typically find a small 120v motor like a box fan? The main reason large motors are 3-phase is that such motors are more efficient, more reliable and more practical than a large sized singe-phase motor. It's also much easier to accurately control the speed of a 3-phase motor than single-phase.
The main reason smaller motors are single-phase is because they are typically used in places that do not have access to a 3-phase power supply. Yes, a 3-phase box fan motor would be perfectly doable. It would not be anymore expensive either. But who has access to 3-phase to plug in a box fan? |
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Reviews:
 ·Choice Cable TV
| reply to cdru
said by cdru:said by Ken:Three phase A/C for a camper, that would have to be a pretty big compressor. Does three phase necessarily indicate size? I know that three phase is typically for larger applications, but can you have a small 3-phase motor, such as were you'd typically find a small 120v motor like a box fan? Certainly you can have small 3-phase motors. I work at a large manufacturing facility were there are plenty of conveyor belts and similar equipment. I once noticed in one of the lines that a small gearmotor in one of the conveyors was labeled "480 VAC" which in that facility is used only for 3-phase equipment. I asked the engineer in charge if this motor was really 3-phase and he said it was and the main reason was simply reliability and durability. A similar one-phase motor is not as reliable for some reason. |
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 shdesignsPowered By Infinite Improbabilty DrivePremium
join:2000-12-01
Stone Mountain, GA | said by printscreen: I asked the engineer in charge if this motor was really 3-phase and he said it was and the main reason was simply reliability and durability. A similar one-phase motor is not as reliable for some reason. Single phase will likely have a run capacitor, a lower start torque and be less efficient. The capacitors often fail and leak oil.
3-phase motors are much simpler.
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Scott Henion
Embedded Systems Consultant,
SHDesigns home - DIY Welder |
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public
join:2002-01-19
Santa Clara, CA | reply to Ken
said by Ken:Three phase A/C for a camper, that would have to be a pretty big compressor. Better units have a bldc motor with a controller, making the supply irrelevant |
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 Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to TheMG
said by TheMG:said by cdru:Does three phase necessarily indicate size? I know that three phase is typically for larger applications, but can you have a small 3-phase motor, such as were you'd typically find a small 120v motor like a box fan? The main reason large motors are 3-phase is that such motors are more efficient, more reliable and more practical than a large sized singe-phase motor. It's also much easier to accurately control the speed of a 3-phase motor than single-phase. The main reason smaller motors are single-phase is because they are typically used in places that do not have access to a 3-phase power supply. Yes, a 3-phase box fan motor would be perfectly doable. It would not be anymore expensive either. But who has access to 3-phase to plug in a box fan? According to the article he referenced a black, white and green wire. That folks is single phase wiring.
I've been in industrial electrical/Instrument/HVAC maintenance for 35 years and this thread is a joke. God I hope no one uses information from these threads as a guide to do electrical work.
The speed of a 3 phase motor is no more or no less easier to control than a single phase motor. Number of poles in the stator determines the base speed of the motor i.e. 2 poles = 3600, 4 poles = 1800 and so on. To have variable speed you need to change the frequency and voltage. 120 volts @ 60 hz = 1800 rpm with a 4 pole motor. 60 volts @ 30 hz = 900 rpm with the same 4 pole motor.
As far as the RV roof ac being 3-phase not likely at all. |
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 Lurch77Premium
join:2001-11-22
Oconto, WI
kudos:4 | reply to Jack_in_VA
said by Jack_in_VA: I've been in industrial electrical/Instrument/HVAC maintenance for 35 years and this thread is a joke. It became a joke once people started taking anything here seriously.
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Only a biker knows why a dog sticks his head out the window. |
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TheMGPremium
join:2007-09-04
Canada
kudos:1 | reply to Jack_in_VA
said by Jack_in_VA:The speed of a 3 phase motor is no more or no less easier to control than a single phase motor. Number of poles in the stator determines the base speed of the motor i.e. 2 poles = 3600, 4 poles = 1800 and so on. To have variable speed you need to change the frequency and voltage. 120 volts @ 60 hz = 1800 rpm with a 4 pole motor. 60 volts @ 30 hz = 900 rpm with the same 4 pole motor. You can't easily use frequency to change speed of a single-phase AC motor. That's why I said it's easier with a 3-phase motor.
If you've got a single-phase motor with a centrifugal switch for the start winding, you can only slow the motor down so much before the switch clicks back in and you fry the start winding.
PSC single phase motors, you need different values of capacitor for the motor to operate efficiently at different frequencies.
Shaded pole motors, forget about it.
3-phase motors are ideal for usage with variable frequency drives.
said by Jack_in_VA:As far as the RV roof ac being 3-phase not likely at all. You're taking this thread way too seriously. The very first post was basically laughing at the misinformation found on "eHow". We all know it's a load of crock. |
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Reviews:
·Choice Cable TV
| reply to Jack_in_VA
said by Jack_in_VA:As far as the RV roof ac being 3-phase not likely at all. That was the whole point of the thread. The article in the link referred to 3-phase but when you read the description of the wiring it was plain jane single phase 120 VAC. It is clear that the author has no idea what is 3-phase. |
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 n1zukmaking really tiny tech thingsPremium
join:2001-10-24
Malta
kudos:2 | That air condition must be three phase. it has a Low, Med, and High setting.  |
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 macsierraBaby NewfoundlandPremium
join:2003-11-30
Minden, NV
·Charter
| reply to printscreen
said by printscreen:said by Jack_in_VA:As far as the RV roof ac being 3-phase not likely at all. That was the whole point of the thread. The article in the link referred to 3-phase but when you read the description of the wiring it was plain jane single phase 120 VAC. It is clear that the author has no idea what is 3-phase. Even if he thought he knew something, then we throw the "stinger leg" delta at him he would be totally dumbfounded.
This teacher must be the prince of the DIY's.. 
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Early 2009 Mac Pro 10.6.4 Charter 10 meg Windows 7 & Mac OSX working simultaneously with VMware Fusion 3.0.1
Elect anyone BUTT Harry Reid! |
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 CKizerAd eundum quo nemo ante iitPremium
join:2003-01-29
Tijeras, NM
kudos:2 | reply to n1zuk
said by n1zuk:That air condition must be three phase: liquid, gas, and solid. |
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