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Old 02-05-2015, 11:50 PM   #21
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VFDs are much better at running A motor, not A shop, for the reasons' micromind already said.

But here's the rub on something like your 15HP compressor as well. Yes, a VFD can accept single phase input and run a 3 phase motor, but above 3HP at 230V, you must at least double the size of the VFD with respect to the motor. So your 15HP compressor will require you to buy at least a 30HP VFD. Then the NEC now requires that the conductors feeding a VFD are to be sized based upon the VFD maximum amps, not the motor. A 30HP 230V VFD is going to be rated for 85A, which would mean conductors rated for 106A minimum, so 1ga. building wire, even though the load is actually only going to be around 45A. Then even though you could use a 60A breaker because it really only has to cover the 15HP motor, that size cable is unlikely to fit in the lugs of a 60A breaker, etc. etc. etc.

Bottom line it's rarely practical to power large 3 phase motors from a single phase service through a VFD. Were it me, I would maybe build my own RPC, but for that much power, you might want to inquire about getting a 3 phase service.
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Old 02-05-2015, 11:51 PM   #22
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Originally Posted by mr.photon View Post
What do you guys think of this one? is it a good price?

http://www.ebay.com/itm/75HP-3-PHASE...-/261752941603
Seems they went out of their way to not mention any brand name or part numbers, that would be a HUGE red flag for me...
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Old 02-05-2015, 11:57 PM   #23
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Quote:
Originally Posted by JRaef View Post
VFDs are much better at running A motor, not A shop, for the reasons' micromind already said.

But here's the rub on something like your 15HP compressor as well. Yes, a VFD can accept single phase input and run a 3 phase motor, but above 3HP at 230V, you must at least double the size of the VFD with respect to the motor. So your 15HP compressor will require you to buy at least a 30HP VFD. Then the NEC now requires that the conductors feeding a VFD are to be sized based upon the VFD maximum amps, not the motor. A 30HP 230V VFD is going to be rated for 85A, which would mean conductors rated for 106A minimum, so 1ga. building wire, even though the load is actually only going to be around 45A. Then even though you could use a 60A breaker because it really only has to cover the 15HP motor, that size cable is unlikely to fit in the lugs of a 60A breaker, etc. etc. etc.

Bottom line it's rarely practical to power large 3 phase motors from a single phase service through a VFD. Were it me, I would maybe build my own RPC, but for that much power, you might want to inquire about getting a 3 phase service.
That makes sense. I think its coming down to either a huge rotary on its own service line or running 3 phase straigh from the pole.
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Old 02-06-2015, 12:45 AM   #24
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This is the start of the thread.

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Originally Posted by mr.photon View Post
So i am kind of torn between getting a vfd or rotary converter for 3 phase in my home shop. I need something in the 20-30 hp range. All Advice welcome.
This is the end. After telling us there are multiple motors, drill presses, two compressors, and that you have a 200 amp single phase service in your shop.

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Originally Posted by mr.photon View Post
That makes sense. I think its coming down to either a huge rotary on its own service line or running 3 phase straigh from the pole.
Now your telling us three phase is available at the pole!

Did you buy all the three phase equipment before or after you built or moved into the shop?

Not to mention you think you're an Electrical Engineer!

Borgi
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Old 02-06-2015, 01:08 AM   #25
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Originally Posted by Borgi View Post
This is the start of the thread.



This is the end. After telling us there are multiple motors, drill presses, two compressors, and that you have a 200 amp single phase service in your shop.



Now your telling us three phase is available at the pole!

Did you buy all the three phase equipment before or after you built or moved into the shop?

Not to mention you think you're an Electrical Engineer!

Borgi
Im going to clear all this up. I have plans to build a shop on my property in the spring. I already have the ability to have 200 amp service when i build the shop. I am planning on having 3 phase equipment instead of single phase. I I already know what equipment i need.

When I said its available at the pole, i meant have them run 3 phase service from the local mains, not from my property, or any kind of converter.

I am sorry for any problems i have caused.
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Old 02-06-2015, 12:36 PM   #26
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Originally Posted by mr.photon View Post
Im going to clear all this up. I have plans to build a shop on my property in the spring. I already have the ability to have 200 amp service when i build the shop. I am planning on having 3 phase equipment instead of single phase. I I already know what equipment i need.

When I said its available at the pole, i meant have them run 3 phase service from the local mains, not from my property, or any kind of converter.

I am sorry for any problems i have caused.
You haven't caused any problems at all. Your question is completely valid and was answered by several people who know what they are doing.

With the new info, I'd look hard at the cost of a 3 service.

When I built my house in 1996, a single phase service cost $1700, 3 was $3600. I already had a bunch of 3 equipment, so having 3 power was well worth the extra expense. Plus, my well pump and both my A/Cs are 3 which offset the expense to some degree.

3 power from the POCO is always better than making your own from a single phase source.

For your shop, a 120/240 3 4 wire open ∆ system would work just fine and would likely be less $$$ than a 4 wire Y or a closed ∆.

If you need more info, just ask. If you can ignore the jerks, there are at least a few people who will give helpful answers.

Rob
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Old 02-06-2015, 12:43 PM   #27
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Originally Posted by micromind View Post
You haven't caused any problems at all. Your question is completely valid and was answered by several people who know what they are doing.

With the new info, I'd look hard at the cost of a 3 service.

When I built my house in 1996, a single phase service cost $1700, 3 was $3600. I already had a bunch of 3 equipment, so having 3 power was well worth the extra expense. Plus, my well pump and both my A/Cs are 3 which offset the expense to some degree.

3 power from the POCO is always better than making your own from a single phase source.

For your shop, a 120/240 3 4 wire open ∆ system would work just fine and would likely be less $$$ than a 4 wire Y or a closed ∆.

If you need more info, just ask. If you can ignore the jerks, there are at least a few people who will give helpful answers.

Rob
I have no problem helping, if the original poster gives valid information at the beginning of the thread.

Several members gave valid advice, only to have the original poster change the parameters.

I agree, three phase from the utility is ideal! But, that wasn't an option at the beginning.

Nobody was being a jerk. I was being quite understanding, all things considered!

Borgi

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Old 02-06-2015, 06:50 PM   #28
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Thank you all for your advice.
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Old 02-06-2015, 07:13 PM   #29
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Now that all the hugging and back patting is done, here's another little dose of reality for you.

The cost of getting 3 phase service will depend GREATLY on whether or not there really are all 3 phases on your pole or not. In far flung rural areas, it's not unusual for there to be only 2 wires, maybe even one (SWER), which means single phase service only. So if the nearest 3 phase tie in point is 5 or 15 miles away from you, they will make you pay for running the extra cables the entire distance, and it gets REALLY expensive. A quick way to tell is if any of your neighbors have 3 phase services. If so, you are OK.

Then assuming this is OK, the next issue is that with 3 phase service, you also often get another nasty little surprise you may not be used to now, a Demand Meter. Public utilities can't charge residential users for Peak Demand, but they can for commercial and industrial users, and depending on the utility, that definition is often tied to 3 phase service drops. So just be very thorough in your investigation, don't assume anything and you shouldn't have any surprises.
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Old 02-06-2015, 07:16 PM   #30
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Thanks. I know that 3 phase is available within half a mile from my property, so thats not a problem. I will have to look into all the costs though.
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Old 02-07-2015, 03:06 PM   #31
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Seems they went out of their way to not mention any brand name or part numbers, that would be a HUGE red flag for me...
My bet says "Marathon"
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Old 02-07-2015, 04:07 PM   #32
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My bet says "Marathon"
Why, because of the Marathon "Blue Max" color?

I've always thought that was an interesting choice of marketing names. People from the WWI era would not have liked it, it would be kind of like calling your product the "Jihad Series" now. But by the time Marathon started using it most of the WWI era people were either dead or at least out of the workforce, so almost no backlash I guess.

For those who don't know, the Blue Max was a German medal of honor given to WWI pilots for getting 20 confirmed kills in air to air combat. There was a movie about that in the 60s, my grandfather about blew his stack when it was released. He was a cook in the rear lines in WWI, but had been strafed many times by German planes, which he though was cowardly because they were unarmed. Plus his childhood friend was a pilot who was killed in the air by the German pilots. He hated them to his dying days.
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