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Are 3 phase motors used for 3 phase converters?

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#41 ·
It depends on how good electric you need. You can do anything you want with rotary converters.

If you need plain cheap 230v 3 phase, then you just need standard rpc.

If you need 230v 3 phase wye, then you need a rpc and a delta to wye transformer.

If you need 460v wye, then you need either 460 single phase input (which is very rare) and a rpc, or you have 230v single phase and you need 230v 1p to 460v 1p transformer then 460v rpc, then delta to wye transformer, or you have 230v 1p input, then you rpc to 230v 3p then 230 to 460 transformer then delta to wye transformer.

If you need perfectly phased electric, then you need to get your 3 phase in a wye (can be delta, but why at this point), then phase correct it so all 3 phases are equal.

But at the end of the day, if you really need good 3p electric, you need to get 3p brought in to your building.

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#42 ·
Country Metals said:
It depends on how good electric you need. You can do anything you want with rotary converters.

If you need plain cheap 230v 3 phase, then you just need standard rpc.

If you need 230v 3 phase wye, then you need a rpc and a delta to wye transformer.

If you need 460v wye, then you need either 460 single phase input (which is very rare) and a rpc, or you have 230v single phase and you need 230v 1p to 460v 1p transformer then 460v rpc, then delta to wye transformer, or you have 230v 1p input, then you rpc to 230v 3p then 230 to 460 transformer then delta to wye transformer.

If you need perfectly phased electric, then you need to get your 3 phase in a wye (can be delta, but why at this point), then phase correct it so all 3 phases are equal.

But at the end of the day, if you really need good 3p electric, you need to get 3p brought in to your building.

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You are very close.There is no cheap three phase!!!!!!!!!!!!! In single phase, there is no delta, or Wye. Commercially built rotary phase converters are best in the quality of power, and versatility of the power they provide.

There are alternatives. Each time I have been tempted to buy for my at home needs, something has stopped me. If I had one lathe, a dry warm, not hot space to run a VFD, I might buy one. VFDs are sensitive to heat, and cold. If the air has dust, it might get hot. they need fans to cool, but the air must be dust free. They don't start compressors well. There are more reasons to not use VFDs than to use. Yet, there are happy users. I don't own any, but I do get calls: "Five VFDs have failed!!!"
 
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#44 ·
Willie B said:
You are very close.There is no cheap three phase!!!!!!!!!!!!! In single phase, there is no delta, or Wye. Commercially built rotary phase converters are best in the quality of power, and versatility of the power they provide.

There are alternatives. Each time I have been tempted to buy for my at home needs, something has stopped me. If I had one lathe, a dry warm, not hot space to run a VFD, I might buy one. VFDs are sensitive to heat, and cold. If the air has dust, it might get hot. they need fans to cool, but the air must be dust free. They don't start compressors well. There are more reasons to not use VFDs than to use. Yet, there are happy users. I don't own any, but I do get calls: "Five VFDs have failed!!!"
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That's true. I should have said, basic and dirty (being delta)

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#47 ·
Country Metals said:
The capacitors only help start the rpc

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I'm pretty sure capacitors are also used to stabilize and balance the three legs as the generated leg can be quite a bit higher than the other two. The "wild" leg. Careful not to hook it up to anything critical. I burnt a work light the first time I hooked my lathe up. Paid a bit more attention after that.
 
#49 ·
metalman21 said:
Does this mean running 3 phase motors on rotary phase converters (from single phase power) is never as good or powerful as from a real 3 phase service?
I know running 3 phase motors from static phase converters results in a loss of power. It works/runs but at reduced HP and torque.

I'm lucky to have a 3 phase service because my shop used be a machine shop. But if the day comes where I have to work with single phase I would like to understand these phase converters to run my mill and lathe.
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I believe a well designed phase converter will give good quality power. Jury rigged homemade units will use a lot of single phase power, and still underpower a needed motor.

While good units whether manufactured, or homemade, are more efficient they still yield less power than they consume. A good one will consume 10,000 watts producing 6000 watts.
 
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#50 ·
Country Metals said:
That's true. I should have said, basic and dirty (being delta)

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Nothing dirty about Delta. In 240 volt, I strongly prefer delta power. It delivers 240 volts single, or three phase, 120, or 208 volt single phase.

WYE offers 208 volt in three phase, or single phase, or 120 to center.

Many motors are primarily designed for 230 volt, but will run in a make do manner on 208. As long circuits lose voltage A 230 volt motor might be under powered at the far end of a cable with 208 volt power. Office buildings typically have 208 volt wye power. Most of their load is single phase 120 volt. When 230 volt machines are used they must be fed with very large cables, or hard starting will be a problem. I hate powering expensive heat pumps with 208 volt power.
 
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#51 · (Edited)
Willie B said:
Nothing dirty about Delta. In 240 volt, I strongly prefer delta power. It delivers 240 volts single, or three phase, 120, or 208 volt single phase.

WYE offers 208 volt in three phase, or single phase, or 120 to center.

Many motors are primarily designed for 230 volt, but will run in a make do manner on 208. As long circuits lose voltage A 230 volt motor might be under powered at the far end of a cable with 208 volt power. Office buildings typically have 208 volt wye power. Most of their load is single phase 120 volt. When 230 volt machines are used they must be fed with very large cables, or hard starting will be a problem. I hate powering expensive heat pumps with 208 volt power.
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I wouldn't worry about a heat pump as probably better than 95% of heat pumps made today are 208/230 volt rated. They are not at all like powering straight 230 volt motor that is underpowered on 208. They are designed to run on 208 without being underpowered for the job at all. Any motor/compressor with a 208/230 volt rating has been tested and proven to function at voltages as low as 186 volt at rated load without overheating. They are tested to 10% under and 10% over.
But yes of course a straight 230 rated anything isn't going to like 208 especially if you aren't really getting all 208 when loaded. If all 208 is there while it will be lower torque/rpm it will usually work fine depending on the load it is powering.

That is something to consider when sourcing a motor for these phase converters. You don't want to buy 208 motor to make one with as there are plenty of those out there that will not work nearly as well as a 230 volt motor will.
 
Discussion starter · #52 ·
Boostinjdm said:
I'm pretty sure capacitors are also used to stabilize and balance the three legs as the generated leg can be quite a bit higher than the other two. The "wild" leg. Careful not to hook it up to anything critical. I burnt a work light the first time I hooked my lathe up. Paid a bit more attention after that.
Click to expand...
View attachment 1694863

danielplace said:
I wouldn't worry about a heat pump as probably better than 95% of heat pumps made today are 208/230 volt rated. They are not at all like powering straight 230 volt motor that is underpowered on 208. They are designed to run on 208 without being underpowered for the job at all. Any motor/compressor with a 208/230 volt rating has been tested and proven to function at voltages as low as 186 volt at rated load without overheating. They are tested to 10% under and 10% over.
But yes of course a straight 230 rated anything isn't going to like 208 especially if you aren't really getting all 208 when loaded. If all 208 is there while it will be lower torque/rpm it will usually work fine depending on the load it is powering.

That is something to consider when sourcing a motor for these phase converters. You don't want to buy 208 motor to make one with as there are plenty of those out there that will not work nearly as well as a 230 volt motor will.
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Check: Look for a motor that is rated at 230V not 208/230 so the outputs will be in the higher ranges like 230/240 when designed and built properly.
 
#55 ·
el perro said:
A RPC is a three phase motor run on two phase. The third leg is run as a generator, producing you third leg for your 3 phase equipment. There are start capacitors to help it get going and run capacitors to help with heavy loads. A RPC only produces that 3rd leg. The other two come from you panel. My 7.5 hp RPC runs my 5 hp 3ph table saw very well. Same with my 5 hp planer. 7.5 hp shaper, not so much.
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No such a thing as 2 phase power, either single, split single or three phase.
 
#56 ·
walker said:
No such a thing as 2 phase power, either single, split single or three phase.
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Actually there is such a thing as 2 phase power, but it was never widely used other than a few locations in the NE USA. It’s a 4 wire system and was still used in Philly as late as the 1950’s.

The original power station at Niagara Falls produced it back in the early part of the 20th century.
 
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#58 ·
walker said:
No such a thing as 2 phase power, either single, split single or three phase.
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No it exists. I've never seen it. I can think of no reason to have it. The books show it, explain it. I can't say anyone has correctly ever used the term. To me, it isn't logical to have a power supply that has no advantages, no machines are built to utilize. Two phase theoretically could exist. It'd use three wires, but only two transformer windings.

Split phase, I believe can be either single, or three phase. It only means windings are in two parts, They are connected in series for high voltage, or parallel for low. Most common are 115/230 single phase and 230/460 three phase.

Motor manufacturers association has agreed that motors sold in USA will tolerate a 10% plus or minus voltage. A 230 volt motor should function at 207-253 volts. At 207 it will produce slightly less speed, sharply less torque, and alarmingly more heat internally.
 
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#59 ·
scsmith42 said:
Actually there is such a thing as 2 phase power, but it was never widely used other than a few locations in the NE USA. It’s a 4 wire system and was still used in Philly as late as the 1950’s.

The original power station at Niagara Falls produced it back in the early part of the 20th century.
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That plant produced 25hz power. 25hz was pretty much the standard back then at least across NY State. Bebee Station in Rochester was originally 25hz and those machines remained in place driving rotary converters to 60hz until plant closure. Later machines installed in the 40s produced 60hz.
 
#60 ·
scsmith42 said:
Actually there is such a thing as 2 phase power, but it was never widely used other than a few locations in the NE USA. It’s a 4 wire system and was still used in Philly as late as the 1950’s.

The original power station at Niagara Falls produced it back in the early part of the 20th century.
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Gee, I'm not denying your statement, but the book Empires of Light by Jill Joness, stated that in the power wars between Edison with DC, and Westinghouse/Tesla with AC, those dynamos were designed by Tesla as three phase. Somebody is mistaken. I am not confident that Ms. Joness knew what she was talking about. I've always marveled that many educated people call everything painted yellow a bulldozer.

I will note that Tesla invented the three phase motor. I don't know which came first.
 
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