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Old 04-26-2012, 11:38 AM   #1 (permalink)
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3 phase to 1 phase motors

I tried to search but got some conflicting info.

I have a chance to get a 5hp air compressor for a really cheap price.

Only down fall is that it is 3 phase.

I was told that I could just get a 5hp single phase motor and install it on there and I would be good to go.

Another place told me that a 3 phase 5 hp motor is much more powerful then a single. That if I put a single on there it wouldnt run it very well.

Seems that I could get a single phase air compressor motor for around 3-400.

I would think that this compressor would be well worth that by looking at it and seeing it pump. Its a older DeVelbliss (spelling).

Anyone have any thoughts on that?

Thanks
Adam
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Old 04-26-2012, 11:39 AM   #2 (permalink)
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HP is HP but from what I understand a 3 phase motor is more efficient.
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Old 04-26-2012, 11:52 AM   #3 (permalink)
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Well that is what I was thinking but the couple places I called acted like it wouldnt work at all.

I would think that the single might be a little slower starting and draw more current on startup?
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Old 04-26-2012, 12:35 PM   #4 (permalink)
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The problem is in the physical size of the motor your 5 hp 3 phase is much smaller then a 5 hp single phase.

You will get into fabricating a new motor mount and most likely new belts as well.

Depending on this compressor it could be as simple as drilling new holes in the base to making a whole new base.

There are different options and it can be done.

Is this compressor unit in good shape other then being 3 phase??

That is what some places might mean saying it will not work.

It is not going to be a direct bolt on swap.
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Old 04-26-2012, 12:56 PM   #5 (permalink)
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yea the compressor is still running and pumping great. just the 3 phase is what hurts it for me.
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Old 04-26-2012, 01:00 PM   #6 (permalink)
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yea the compressor is still running and pumping great. just the 3 phase is what hurts it for me.
Build a phase conveter
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Old 04-26-2012, 01:11 PM   #7 (permalink)
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Old 04-26-2012, 01:46 PM   #8 (permalink)
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Most often by the time you replace the 3ph with 1ph motor the deal is really no longer a deal at all, this is why you often see 3ph equipment selling for good "deals" in the first place.

Sure you can slap on a cheap 1ph motor but now your not comparing apples to apples with what you originally were thinking you were going to get.
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Old 04-26-2012, 02:05 PM   #9 (permalink)
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Another thing is a 3 phase motor will have a lower running amps then a single phase. So changing out a motor to make it work could over load what you got for a service. There is 3 legs that feed a 3 phase motor. 120 / 208 is the most common and 277 / 480. So looking at going to single phase that has two legs making up your 240 your amps are going to be more to run it then a 3 phase system.
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Old 04-26-2012, 04:11 PM   #10 (permalink)
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Another thing is a 3 phase motor will have a lower running amps then a single phase. So changing out a motor to make it work could over load what you got for a service. There is 3 legs that feed a 3 phase motor. 120 / 208 is the most common and 277 / 480. So looking at going to single phase that has two legs making up your 240 your amps are going to be more to run it then a 3 phase system.
But power is sold in WATTS which are equal, so less amps is no savings on the monthly bill, it just means he has to have a bigger circuit ( breakers, wire and plug).
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Old 04-26-2012, 04:20 PM   #11 (permalink)
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But power is sold in WATTS which are equal, so less amps is no savings on the monthly bill, it just means he has to have a bigger circuit ( breakers, wire and plug).
Well at least you look at your bill. Now if you read what I posted I never stated anything about his bill and how it was charged. I was letting him know about the possibility he could need to change more then a motor. I know how a electric bill is charged seeing I been a LINEMEN for 15 years for the local power company...
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Old 04-26-2012, 04:29 PM   #12 (permalink)
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Well at least you look at your bill. Now if you read what I posted I never stated anything about his bill and how it was charged. I was letting him know about the possibility he could need to change more then a motor. I know how a electric bill is charged seeing I been a LINEMEN for 15 years for the local power company...
I don't doubt it, but I have seen far to many people try to equate a cut in amperage with a cut in the bottom line. While it saves you on your initial cost (smaller wire, etc.) the month to month difference is infinitesimal.

I was not nocking your insight, just adding to it.
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Old 04-26-2012, 04:37 PM   #13 (permalink)
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I don't doubt it, but I have seen far to many people try to equate a cut in amperage with a cut in the bottom line. While it saves you on your initial cost (smaller wire, etc.) the month to month difference is infinitesimal.

I was not nocking your insight, just adding to it.
I agree, usually making anything that was 3 phase to single is not a cost savings.
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Old 04-26-2012, 04:52 PM   #14 (permalink)
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I don't doubt it, but I have seen far to many people try to equate a cut in amperage with a cut in the bottom line. While it saves you on your initial cost (smaller wire, etc.) the month to month difference is infinitesimal.

I was not nocking your insight, just adding to it.
ok take me to school here

i have always been told if you have a motor at a given size and can chose how you many volts you put to it (which increases or decreases the amps) determines how much it consumes= cheaper to run

the electrician that wired my shop said if you can get 3 phase stuff to do so because of the smaller wire size ( higher volts) and lower amps that they run. the meters read the leg with the highest amp load.

if your shop is 200 amps and you have three legs going in and your pulling 100 from one and 20 from the other that your only paying for the 100 amps. so he said once im all hooked up he would come in with an amp clamp and balance the panel to have 60 amps on each leg.

can you guys shed light on this
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Old 04-26-2012, 05:22 PM   #15 (permalink)
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ok take me to school here

i have always been told if you have a motor at a given size and can chose how you many volts you put to it (which increases or decreases the amps) determines how much it consumes= cheaper to run

the electrician that wired my shop said if you can get 3 phase stuff to do so because of the smaller wire size ( higher volts) and lower amps that they run. the meters read the leg with the highest amp load.

if your shop is 200 amps and you have three legs going in and your pulling 100 from one and 20 from the other that your only paying for the 100 amps. so he said once im all hooked up he would come in with an amp clamp and balance the panel to have 60 amps on each leg.

can you guys shed light on this
The reason most shops run 3 phase is to carrier more load. 3 phase can come in many voltages. 120/208 277/480 240 power banks and so on. The rule is higher the voltage = lower the amperage or lower the voltage higher the amperage. Meaning you can run more on the higher voltage with lower amperage. So more motors, lights, welders can be running at onetime. Having your electrician coming back to balance off the load is helping you. This way your not overloading a leg coming in from the street which can lead to trouble inside.

I hope this helps. I am not great at teaching part. lol
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Old 04-26-2012, 06:53 PM   #16 (permalink)
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i understand the volts to amps and the need balance the load but really what sparked my interest was the discussion on how you are charged. does balancing the panel help with the monthly bill as well as running things at a higher voltage, so you do not consume as many amps.
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Old 04-26-2012, 07:19 PM   #17 (permalink)
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i understand the volts to amps and the need balance the load but really what sparked my interest was the discussion on how you are charged. does balancing the panel help with the monthly bill as well as running things at a higher voltage, so you do not consume as many amps.
If you have a unbalanced service can make your bill go up. Lets just say your shop is pulling 100 / 106 / 178 amps on your 3 phase. The one leg that is pulling 178 amps will cause anything on that leg to work harder then the other two and cause a voltage drop. A 3 phase motor needs all 3 phases to start up. With one leg low on voltage makes it struggle to get up to running speed. You can never balance off a service 100% but running it way off can lead to equipment to fail in time.
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Old 04-26-2012, 07:27 PM   #18 (permalink)
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i understand the volts to amps and the need balance the load but really what sparked my interest was the discussion on how you are charged. does balancing the panel help with the monthly bill as well as running things at a higher voltage, so you do not consume as many amps.
WATTS = Volts X Amps

The reason is you buy electricity by the KW (kilowatt) no matter how you play with the volts and amps, you don't change the WATTS.

You do save money by using smaller wire and a smaller service as well as the equipment seems to be more efficient.
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Old 04-26-2012, 10:01 PM   #19 (permalink)
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Well here is what u want to know. I bought a 5 horse 3 phase compressor and changed it out to a single phase motor. When u buy your motor make sure u match the frame and shaft size. I checked NFPA 70 for the amperage on a 5 horse motor and at start up its only 27amps. 10 guage wire is good for 30 amps. That's how mine is set up and it works grate. It's an ingersol rand t30 35 cfm single phase and I got 700 in it. A new t30 cost over 2000.00
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Old 04-27-2012, 05:25 AM   #20 (permalink)
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Thanks for the replys guys. They only want 150 bucks for the compressor. I can get a single phase motor for 3-600 depending on if I want to go up to 7.5HP. I think if i cant make it work for for 600 total, ill call it a wash and buy a new one. Just a thought worth looking into.
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Old 04-27-2012, 08:52 AM   #21 (permalink)
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Thanks for the replys guys. They only want 150 bucks for the compressor. I can get a single phase motor for 3-600 depending on if I want to go up to 7.5HP. I think if i cant make it work for for 600 total, ill call it a wash and buy a new one. Just a thought worth looking into.
Exactly, there is the issue
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Old 04-27-2012, 08:23 PM   #22 (permalink)
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Thanks for the replys guys. They only want 150 bucks for the compressor. I can get a single phase motor for 3-600 depending on if I want to go up to 7.5HP. I think if i cant make it work for for 600 total, ill call it a wash and buy a new one. Just a thought worth looking into.
look into used equipment suppliers for the woodworking and machinery industries, you will find the motor you need for about 1/4 of the price.
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Old 04-28-2012, 12:44 AM   #23 (permalink)
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Yes when buying a new motor it is possible to get the same frame and shaft size.

But sometimes buying a new motor kills the deal from the start.

I made my first statement based on scrounging a suitable motor or having one laying around.
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