Are 3 phase motors used for 3 phase converters?

[N2 Welding]

pretty good deal on 6x18 grinder.dayum!

I'm not a machinist so I don't know any thing about any thing when it comes to machines like that. I wouldn't know the first thing about what to use that grinder for and or how to use it. Could the grinder possibly be worn out and not repeating well enough to make good flat surfaced parts? $2500 seems like a lot of money for an old rusted out machine like that to me.

[Bluewelders]

The idea is to use a crappy static phase converter or a motor or a pull starter to spin a 3 phase motor up to speed.
They hardly use any power just idling ,so a induction motor phase converter of 10-20hp to run a few horsepower machine is not particularly wasteful.
Salvage yards and recycling places around here will often sell a motor for its scrap weight price.

[ronsii]

And... the scrap price/lb. on the larger motors is usually less than the smaller ones for the frames being the winding weight is a lot lower percentage.

[Willie B]

I own, then loaned a manufactured phase converter. It looks like a motor with a box full of capacitors, has three wires. It consumes the power of a 12 HP single phase, less when load is less. It powers a 7.5 HP three phase motor, or combined motor load of 10 HP. They are not efficient. They consume far more energy than a motor directly powered by three phase. They typically are used for home shops, or small commercial operations where three phase power is not available from the utility. They don't work as well for non inductive loads, as a motor will self excite to aid in the three phase load.

I've seen a single phase motor coupled to a three phase motor also serving the purpose.

Commercially made RPCs cost less than a good television.

For single machine applications a Variable Frequency Drive is cheaper still, and provides speed control They are fussy. They need clean climate controlled air, they don't play nice with more than one motor. Failure seems to be a common problem.

[walker]

I made one out of a 10 hp motor earlier this year. People make it sound like you just throw a few capacitors in a box, throw in some wire and you're off to the races. Its not that easy, but not that difficult either. I bought a kit on ebay for around a hundred bucks. It comes with everything you need except the motor. It took a bit less than two hours to plot it all out in the box, mount everything and make all the jumper wires. It worked very well and I enjoyed the project.

[el perro]

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.

[MinnesotaDave]

I made one out of a 10 hp motor earlier this year. People make it sound like you just throw a few capacitors in a box, throw in some wire and you're off to the races. Its not that easy, but not that difficult either. I bought a kit on ebay for around a hundred bucks. It comes with everything you need except the motor. It took a bit less than two hours to plot it all out in the box, mount everything and make all the jumper wires. It worked very well and I enjoyed the project.

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.

I read all the posts, these two agree with the research I did for my upcoming build.

I got a 7.5 hp 3 phase motor used for $100 to do the rpc.

[el perro]

My 7.5 hp 3 phase Northfield shaper pulls 100 amps at startup.

[MinnesotaDave]

My 7.5 hp 3 phase Northfield shaper pulls 100 amps at startup.

I wonder what it pulls during a cut? Must be fairly high if the feed rate is quick enough.

[danielplace]

I made one out of a 10 hp motor earlier this year. People make it sound like you just throw a few capacitors in a box, throw in some wire and you're off to the races. Its not that easy, but not that difficult either. I bought a kit on ebay for around a hundred bucks. It comes with everything you need except the motor. It took a bit less than two hours to plot it all out in the box, mount everything and make all the jumper wires. It worked very well and I enjoyed the project.

Here is link to those kits if anyone interested.

https://www.ebay.com/sch/i.html?_fro...r+kit&_sacat=0

[Willie B]

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.

Most of the people here don't have two phase power. Two posts can support 1 clothesline. Adding another post to form a triangle offers the opportunity to support three clotheslines. Three phase is three poles, (power lines) The loads connected like three clotheslines would be Delta.

If you tied three ropes together at one end, and the other end to a pole, that'd be WYE connected.

A three pole motor has at least three windings. (a magnetic coil on an iron core) each has two ends. They are configured in different ways, some windings are two part so they can be arranged dual voltage.

If power comes from two wires it is single phase. If from three, it could be connected as three phase. Three separate transformer windings can be used to supply. It makes motors that work more efficiently. Similar to a two cylinder engine, or a six. This does NOT triple potential wattage. A three phase increases power potential by a factor of the square root of three (1.73).

When we manage to persuade a three phase motor to run on single phase, it has little mechanical power, but does generate other phases though they are weak. Add another motor, It will start, and run stronger, a third, even better. When we add a machine that does work, it has considerable torque, but not what it would on "clean" three phase.

When capacitors are correctly calculated, and included, it gets to be functional.

[Country Metals]

Most of the people here don't have two phase power. Two posts can support 1 clothesline. Adding another post to form a triangle offers the opportunity to support three clotheslines. Three phase is three poles, (power lines) The loads connected like three clotheslines would be Delta.

If you tied three ropes together at one end, and the other end to a pole, that'd be WYE connected.

A three pole motor has at least three windings. (a magnetic coil on an iron core) each has two ends. They are configured in different ways, some windings are two part so they can be arranged dual voltage.

If power comes from two wires it is single phase. If from three, it could be connected as three phase. Three separate transformer windings can be used to supply. It makes motors that work more efficiently. Similar to a two cylinder engine, or a six. This does NOT triple potential wattage. A three phase increases power potential by a factor of the square root of three (1.73).

When we manage to persuade a three phase motor to run on single phase, it has little mechanical power, but does generate other phases though they are weak. Add another motor, It will start, and run stronger, a third, even better. When we add a machine that does work, it has considerable torque, but not what it would on "clean" three phase.

When capacitors are correctly calculated, and included, it gets to be functional.

Actually, there is actually 2 phase. There is only 1 place in the world that has it. Can you guess where?

Hint.... It is 1 city in the USA

I found this out from people buying 2 phase motors at an auction. All they are is scrap.

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[Virgil5]

Actually, there is actually 2 phase. There is only 1 place in the world that has it. Can you guess where?

Hint.... It is 1 city in the USA

I found this out from people buying 2 phase motors at an auction. All they are is scrap.

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There is still, last I knew, true 2 phase in use in the backwaters of Philly.

The nomenclature "2 phase" as currently used in some regions including Central Maine and REA companies in Montana for open Delta transformer banks. The reasoning behind the nomenclature is that only 2 phases are taken from Primary and the derived 3rd or "wildcat" is not truly a phase.

[metalman21]

When we manage to persuade a three phase motor to run on single phase, it has little mechanical power, but does generate other phases though they are weak. Add another motor, It will start, and run stronger, a third, even better. When we add a machine that does work, it has considerable torque, but not what it would on "clean" three phase.

When capacitors are correctly calculated, and included, it gets to be functional.

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.

[N2 Welding]

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.

There are videos about how to build a RPC.

[Country Metals]

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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[Willie B]

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!!!"

[Bluewelders]

The simple answer is that an RPC is the best that you can do for the price/performance.

[Country Metals]

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!!!"

That's true. I should have said, basic and dirty (being delta)

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[N2 Welding]

That's true. I should have said, basic and dirty (being delta)

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And the capacitors help level and equalize out each phase so you get a consistent 240v on each leg?

[Country Metals]

And the capacitors help level and equalize out each phase so you get a consistent 240v on each leg?

The capacitors only help start the rpc

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[Boostinjdm]

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.

[el perro]

Most of the people here don't have two phase power. Two posts can support ........

Thanks for the corrections Willie B.

[Willie B]

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.

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.

[Willie B]

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.