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3-phase conversion

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Rob (On)

01-18-2002 19:13:54




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Working on installing an air compressor that had a 3-phase motor on it. Problem is we have single phase power. A phase converter is an option but not practical for intermitent use with a compressor. We were told that the 3-phase can be converted to single? my understanding of electric motors is that this is not easily done and that the most effective thing to do is to replace the motor? Any comments?

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tools

01-24-2002 10:52:29




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
One more option is a static phase converter. This essentially adds a start circuit to a 3 phase motor. There will be some imbalance, so the motor must be derated by about 30%. In other words, make sure it doesn't draw more than 70% of it's full load amperage. You can do this on your air compressor by using a smaller pulley (you guessed it, about 30% smaller) on the motor and just living with about 30% less capacity that the thing had originally.

Static phase converters are completely automatic and work great for air compressors. They cost about as much as a single phase motor though, so no real advantage comes until you need the phase convertor for yet another application.

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Chris mf-35

01-19-2002 14:58:16




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
try this link for a rotory phase conv.



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chris mf35

01-20-2002 14:25:52




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 Re: Re: 3-phase conversion in reply to Chris mf-35, 01-19-2002 14:58:16  
this is the link: metalwebnews.com/howto/ph-conv/ph-conv.html
why can't i get links to work?



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kendall

01-22-2002 10:02:49




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 Re: Re: Re: 3-phase conversion in reply to chris mf35, 01-20-2002 14:25:52  
chris
make sure you have the entire link, including Link in the "Optional link URL:" box and something in the "Link Title" box as well.



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MarkB

01-19-2002 07:05:06




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
The short answer is that you can't convert a three-phase motor to run single phase. One reason is that three phase motors don't have starter circuits, because they don't need them. Single phase motors all have some sort of starter circuit.

Either swap the motor or rig up a phase convertor. Or get three-phase service.



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JK

01-19-2002 05:49:42




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
Rob,
I have run 3 phase motors on single phase by simply connecting two wires of a spare 3 PH motor of the same size or larger than the one you want to run to 220 single phase. Then connect all three wires from the idle moter to the one you wish to run and it will run. I assume less HP is available but haven't had any problems there. One problem I have had with some idle motors is that they don't want to start by themselves and some of them tend to want to overspeed. To solve or prevent these problems, I simply connect a fractional HP single phase motor physically to the shaft of the idle motor with a short length of hose & clamps and turn it on first. It starts the idle motor and prevents it from overspeeding.
Since the current draw would be higher and the motors must be started in sequence, I don't think this setup would be desirable for an air compressor but works fine for a 3PH tablesaw & sausage mixer that are not used very often.
John

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Frank

08-12-2003 01:30:56




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 Re: Re: 3-phase conversion in reply to JK, 01-19-2002 05:49:42  
John,

Your description of the 3-phase conversion is not complete enough for me to implement. Would you be willing to detail the wiring and configuration more accuratly for me? It appears that there are 2 motors required? I have a 230VAC 1 HP 3-phase motor (in a commercial SUN dynamic wheel balancer) that I'd like to run on my 230VAC single(split) phase home wiring. Hopefully I can get it running without purchasing another 3-phase motor?

Thanks,

Frank

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Rod (NH)

01-18-2002 22:16:20




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
I doubt very much that there is any quick fix for converting a 3-phase motor to single phase use without seriously reducing the motor capacity. I have looked into the phase converter route in the past...that is to be able to fully utilize 3ph equipment with a 1ph source. The only ways that I was able to find were 1) Motor-gen (MG) set or 2) electronic (I think). Neither was cost effective for me. I suggest the best solution is to replace the motor, especially if the HP is low enough to work off one of your existing 1 ph circuits.

Rod

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Ray,IN

01-18-2002 20:19:07




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 Re: 3-phase conversion in reply to Rob (On), 01-18-2002 19:13:54  
I can't find the printout of the diagram, but I ran a search of the net for 3ph convertors and found this site describing how to use a spare 3ph motor to step 1ph to 3ph to run your 3ph compressor. Perhaps you can locate the website. Good Luck!



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G Taylor

01-19-2002 08:10:20




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 Re: Re: 3-phase conversion in reply to Ray,IN, 01-18-2002 20:19:07  
The extra three phase idler motor does work but the phase angles & values of voltage/current are significantly imbalanced. If the compressor for example requires a full shaft 5HP & the compressor motor is 5HP it will over heat two of the phases. An matched set of oversize idler motor & capacitors is required for true conversion. It's simpler & cheaper to just use single phase up to 10 or 15 HP then get a three phase service or generator for larger loads requiring three phase. A variable frequncy drive to develop three pahse will give more satisfaction than the idler motor set-up & allow speed changes.

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