Someone want to check my work?

I want to build a 5 hp rotary phase converter.
Last week I picked up a 7 1/2 hp 208-230/440 3 ph motor. Free is good!
I will connect it on the lower voltage.
Only problem is it turns at 3450 rpm.
I'm thinking it will still work as a rpc but I'll have more parasitic loss due to the faster idle speed.
Is that correct? I don't know how much loss. Any guesses?
I am looking at buying this kit.

7.5Hp Rotary phase converter kit 230vac

Have others here used their products? Are they reliable?
Is there a better brand of kit I should consider?
Where do I buy a metal box to put the components in?
I have 100 amp 220V (1 ph) power in my garage with plenty of spaces left. How big of a breaker do I want to power this?
If you guys are kind enough to guide me here I'll reward you with some more questions.
Such a deal huh?

I ordered from Phase Craft when I made my 10hp phase converter so I don't know about this particular kit. I also have a 3450rpm motor and have run a 18" planer with a 5hp motor on it with heavy load and it is fine. I would use that motor. Mine I setup to plug into a 50amp 220v outlet for my welders. Depending on where you are in MN, you can get a used box from Next Day Automation pretty inexpensively.

The biggest drawback to using a 3600 rpm motor, is the extra noise level.Not a big deal in my book.

Yeah, the speed is not an issue as to function, although yes there are complaints of noise from some.

Beware of what looks like a great deal and will solve all your problems. Get yourself a design and then get quality parts piece by piece.
Not from some website that has pictures so small that you can't identify cheap ass ChiComm parts.

Look in the design section here.

The 3450 speed rating (it's a 2-pole motor, so it actually sees synchronous speed as 3600, but when fully loaded, it sees max load/slip as 3450, which won't happen on an RPC idler...

but yeah, noise and vibration are the biggest detraction, and an 1800 or 1200rpm motor of same power rating will usually have more rotating mass (higher polar moment). You could nix the idler's cooling fan and put a constant speed fan on it instead, as the idler will NOT be generating nearly as much heat as it would if it were actually pulling a mechanical load. Put good bearings in it, and it'll be mouse-quiet.

Parasitic load... most of the idler's parasitic energy loss is the result of what's happening with capacative and inductive reactance between the 'generated' leg, and your load, which is a very complex equation with several variables. You really can't do much about it that will yield a reduction of parasitic losses, but the good news is, they occur regardless of how fast the idler is rotating.

So the only part that really would have any substantial effect, is the noise/vibration. I know guys that take an old doghouse, set it on bricks outside the shop wall, and put the idler in there... and call it 'quiet' in the shop. I know some guys that mount 'em to the wall and let it transmit the vibration into the wall like a loudspeaker, as a reminder to shut the RPC off when they're done with the Lodge and Shipley... and some guys put the idler on a pair of well-rotted 4x4 blocks on the concrete floor, and enjoy the natural vibration-suppressive effects of the punky fungus-filled wood.

Don't overthink it too much, DO take Ron's advice and just build it with quality parts you acquire on your own, and once built, use it a while, and make incremental improvements, because the more you do, the more you'll understand how, and why it works, and it'll be easier for you in the future, to operate and maintain.

Oh, and your other questions ('ll TRY to answer all, but I may miss)

If you're running a 7.5hp, that suggests you're planning on feeding a machine about-equal to that, which is in the realm of a 50A range-plug... on three phase, 30A per leg or so. I'd probably use a 50-60A n HACR-type breaker from your single-phase to power it... but depending on how your RPC starts, and the load you're feeding it, you may need to make some adjustments after a few tries.

I would use TWO boxes, probably mount them back-to-back. One box I'd have a piece of DIN rail for contactors, terminal blocks, control relays and a single (input) and three phase (output) circuit breaker...

And I'd mount another box to it (back to back, or aside) specifically for housing the run and start capacitors.

Reason: When a capacitor decides to retire, it oftentimes throws itself a party... a slightly pyrotechnic celebration, complete will aluminum foil and gooey bits of party favors everywhere. Having THEM in a dedicated box, keeps it from disturbing the socially-intolerant electrical church service occurring next door.

DaveKamp said:

The 3450 speed rating (it's a 2-pole motor, so it actually sees synchronous speed as 3600, but when fully loaded, it sees max load/slip as 3450, which won't happen on an RPC idler...

but yeah, noise and vibration are the biggest detraction, and an 1800 or 1200rpm motor of same power rating will usually have more rotating mass (higher polar moment). ...........

Click to expand...

That polar moment is likely outpaced by the 4x rpm factor. Neither motor stores enough energy to do much toward getting the load motor started. Not really an issue.

The RPC has to provide approximately 1/3 of the idler power in the perfect world. In the real world, it usually does not do that well. So the idler does OK even though that can be a very significant load on starting.

Inout load is therefore about 1/3 of motor power, plus losses (and magnetizing current, which is large).

rons said:

Beware of what looks like a great deal and will solve all your problems. Get your self a design and then get quality parts piece by piece.
Not from some website that has pictures so small that you can't identify cheap ass ChiComm parts.

Click to expand...

Ha,
I'm not smart enough for that.
I've wired a bunch of houses and I can wire old tractors and can make a convincing argument why a 12V conversion w/alternator is way better than a 6V ststem w/generator and Vreg. But to pick one capacitor over another or even size it properly is well above my pay grade.
I do understand the noise issue. The motor I have is an end/flange mount. It was mounted vertically in a large cyclone dust collector. I was thinking about using it vertically again. Set it on (or hang it from?) 4 coil springs of some sort. Do something to deal with the torque of course.
Any thoughts about that?

There are many motors that are built specifically to be upright, and if yours is one of those, I encourage you to mount it vertically, and frankly, vertical mounting can be convenient in terms of taking up floor space.

I wouldn't go with coil springs. If you're just setting it on the floor, wood blocks with rubber pads will give it all the isolation you'd need, without it wanting to wander or rattle on the floor. An HVAC supplier has rubber cushion feet used for supporting air handlers and such, and they work nicely... you do need to know the weight of what you're supporting, and select the feet accordingly. There will be a little torque reaction when it starts, but it won't be aggressive enough to warrant concern... just keep the base circle of your machine's feet out far enough so that the idler, and the control box isn't extremely top-heavy.

Ultradog MN said:

Ha,
I'm not smart enough for that.
I've wired a bunch of houses and I can wire old tractors and can make a convincing argument why a 12V conversion w/alternator is way better than a 6V ststem w/generator and Vreg. But to pick one capacitor over another or even size it properly is well above my pay grade.
I do understand the noise issue. The motor I have is an end/flange mount. It was mounted vertically in a large cyclone dust collector. I was thinking about using it vertically again. Set it on (or hang it from?) 4 coil springs of some sort. Do something to deal with the torque of course.
Any thoughts about that?

Click to expand...

My motor I used is a face mount and I put it face down on the top shelf of a pallet rack with a hole for the shaft and bolted right to the 2x4s on the shelf. There is only going to be a small amount of starting torque, so I dont think it needs to be too elaborate.

Ultradog MN,

This is a decent thread subject but the title does not reflect what it is s about, so others could search and find information. I'm Just saying in the future you might try to title your started thread with the likes of
"5 hp rotary phase converter build questions..".

No, I'm not a moderator

Idler motor at 7.5 hp will be just adequate to run a 5 hp load motor - but you will need to be mindful of balancing the voltages on it (with balance capacitors), under the actual load, to get them within ten percent or so. You can test the operation of the idler by starting it across the line once it has been spun up to speed using a smaller single phase motor (aka pony motor).

Also a good idea to test line to line continuity and rough ground isolation on the windings to catch a motor problem before you get too deep into the project.

Bob-J-H said:

The biggest drawback to using a 3600 rpm motor, is the extra noise level.Not a big deal in my book.

Click to expand...

You can say that again. I bought an RPC on eBay once just to get my mill going when I first got it. It was made with a 3,450 motor that had been over-rated by the manufacturer. It was so loud I couldn't stand it. I built my own 5 hp RPC with plans and help from this site and sold the noisy one cheap with full disclosure. 3,450 rpm is a no-no for an RPC in my estimation.

DaveKamp said:

There are many motors that are built specifically to be upright, and if yours is one of those, I encourage you to mount it vertically, and frankly, vertical mounting can be convenient in terms of taking up floor space.

I wouldn't go with coil springs. If you're just setting it on the floor, wood blocks with rubber pads will give it all the isolation you'd need, without it wanting to wander or rattle on the floor. An HVAC supplier has rubber cushion feet used for supporting air handlers and such, and they work nicely... you do need to know the weight of what you're supporting, and select the feet accordingly. There will be a little torque reaction when it starts, but it won't be aggressive enough to warrant concern... just keep the base circle of your machine's feet out far enough so that the idler, and the control box isn't extremely top-heavy.

Click to expand...

Small shop here so floor space is a big issue.
I have 9'4" walls though so was thinking vertically... Hang it from the ceiling. 4 chains with springs
running up from the 19" dia mounting plate it is bolted to .
Something similar to these.

https://www.homedepot.com/p/Barton-Kramer-Storm-Door-Crash-Chain-7/205929788

Mount the box on the wall about eye level.
Am thinking the springs would act as a vibration and noise damper.
Wish I could figure out posting photos here.


https://www.yesterdaystractors.com/cvphotos/cvphoto70221.jpg

https://www.yesterdaystractors.com/cvphotos/cvphoto70222.jpg

It will likely twist itself all up if it is hung by chains. Just make a shelf near the ceiling to mount it.

Ultradog MN said:

I want to build a 5 hp rotary phase converter.
Last week I picked up a 7 1/2 hp 208-230/440 3 ph motor. Free is good!
I will connect it on the lower voltage.
Only problem is it turns at 3450 rpm.
I'm thinking it will still work as a rpc but I'll have more parasitic loss due to the faster idle speed.
Is that correct? I don't know how much loss. Any guesses?
I am looking at buying this kit.

7.5Hp Rotary phase converter kit 230vac

Have others here used their products? Are they reliable?
Is there a better brand of kit I should consider?
Where do I buy a metal box to put the components in?
I have 100 amp 220V (1 ph) power in my garage with plenty of spaces left. How big of a breaker do I want to power this?
If you guys are kind enough to guide me here I'll reward you with some more questions.
Such a deal huh?

Click to expand...

why not pick up a unit already designed and assembled like the ones from north american phase converter. a 10HP system ready to go with switches and all in a box is only $300.
Motor Control Panels | Rotary Phase Converter Control Panels

also a 10HP reccomends at least a 50A single phase double pole breaker to run it. as they are about 30A 3ph x1.82 is about 12.5KVA and 50A is about the same.

Ultradog MN said:

Ha,
I'm not smart enough for that.
I've wired a bunch of houses and I can wire old tractors and can make a convincing argument why a 12V conversion w/alternator is way better than a 6V ststem w/generator and Vreg. But to pick one capacitor over another or even size it properly is well above my pay grade.
I do understand the noise issue. The motor I have is an end/flange mount. It was mounted vertically in a large cyclone dust collector. I was thinking about using it vertically again. Set it on (or hang it from?) 4 coil springs of some sort. Do something to deal with the torque of course.
Any thoughts about that?

Click to expand...

A 3450rpm versus a 1725rpm motor will have a different pitch. But either one can be annoying in terms of db. I say it depends.

All you need to start:
- a start capacitor 150-200uf
- contactor
- push button switch

Later on you can add:
- fuses
- run capacitors
- thermal overload
- metal box
- red/green lights

Any RPC comes down to this. Starting capacitor to the left and two run capacitors on the right. You can even get by without the run capacitors to begin with.