3 phase or not to 3 phase

masterofall99 · Aug 4, 2019

I am looking at putting together a home shop with several different pieces of equipment. The show will also have the ability to have a 320 amp main breaker. I currently have a large air compressor with two 7.5hp 3 phase motors and all the circuitry to run them. Eventually I am going to get more equipment to include: a monarch lathe running 5-7.5hp motor, a Bridgeport series 1 mill with power feed, and a surface grinder with power feed. Also will probably get a few smaller items later, but for the most part this is all the large machines. I am debating between getting a 20-40hp rotary phase convert or just replacing each motor with single phase 220v. Vfd and static phase converts are not really what I want to do. The problem with the RPC is the very high initial cost ($2500-4500). The motor swap depending on motor brand will cost about the same give or take as the RPC for motor and control circuitry. However I don't have to spend it all at once. If I had more than 5 heavy machines I would definitely go with the RPC.

If the motor change is recommended I have the options of Weg, Baldor, Leeson. The Weg is the cheapest. I haven't heard much bad things about the Weg but also haven't heard much good. The Weg vs Baldor debating comes down to American made or not.

Thanks for any advice.

medsar · Aug 4, 2019

I vote for 3ph using the RPC. Buy a good one and don't look back.

thermite · Aug 4, 2019

masterofall99 said:
I am looking at putting together a home shop with several different pieces of equipment. The show will also have the ability to have a 320 amp main breaker. I currently have a large air compressor with two 7.5hp 3 phase motors and all the circuitry to run them. Eventually I am going to get more equipment to include: a monarch lathe running 5-7.5hp motor, a Bridgeport series 1 mill with power feed, and a surface grinder with power feed. Also will probably get a few smaller items later, but for the most part this is all the large machines. I am debating between getting a 20-40hp rotary phase convert or just replacing each motor with single phase 220v. Vfd and static phase converts are not really what I want to do. The problem with the RPC is the very high initial cost ($2500-4500). The motor swap depending on motor brand will cost about the same give or take as the RPC for motor and control circuitry. However I don't have to spend it all at once. If I had more than 5 heavy machines I would definitely go with the RPC.

If the motor change is recommended I have the options of Weg, Baldor, Leeson. The Weg is the cheapest. I haven't heard much bad things about the Weg but also haven't heard much good. The Weg vs Baldor debating comes down to American made or not.

Thanks for any advice.

You ALREADY justify an RPC.

Might need only a 15 HP, or a 10 HP with drop-on 5 HP or 7.5 HP supplementary idler, though. Didn't hear a plan to hire staff, so how many machines will you run, same time?

Either way, I call nonsense on the $2500, let alone the $4500 for an RPC. DIY it, or at least buy just the control and scout an idler. Many, many here have done.

Several decent 15, 20, 30, 40 HP motors suitable for use as idlers are going cheap this week - new as well as used. I've been tripping over them for days trying to get good deals on 5 HP, 7.5 HP or 10 HP ones.

Figure Fastenal for shipping, pick an East Coast source, in-state or next-state may be possible and a same-day go-fetch.

Single-phase swaps? More work than you might expect. Not easily reversible, many have big, fat capacitor humps, and your case, you are too far into 3-P needs, already, especially with no missing motors mentioned. I wouldn't give it anther thought for what you have, or will have.

Reliance fan, here. Or Marathon. I do have a Weg. A 10 HP. Brazilian made by a firm founded by German expats. Decent value for money.

My most-recent new Baldor was made in Mexico. Back to Ft Smith or no more, on those.

Big B · Aug 4, 2019

When I started putting my shop together about 15 years ago I bought a 5hp rpc. My whole shop is being run off of a 60 amp 240 volt single phase breaker in my homes 100 amp panel. I have never had a breaker blow for overloading and am running around 14 3ph motors. The key is that I am usually only running three of them max at any one time. I upgraded to a 7.5 hp because I got a good deal on one but it is pretty amazing how much machinery you can run on a single 5hp rpc.

I have a cnc vmc that has a 7.5 hp spindle and I bought a 10 hp rpc to run it all on it's own so I don't have to worry about power surges from other machines starting and stopping. Smooth as silk. I wouldn't mind picking up a phase perfect to replace the 7.5 rpc but I missed my chance on that a year or so ago when thermite and a few others picked up three of them here.

thermite · Aug 4, 2019

Big B said:
...pretty amazing how much machinery you can run on a single 5hp rpc.

Even more so a 10 HP with a drop-in, drop-out supplementary idler to cover even fairly hard starting challenges.

Once the load-motor gets its water-skis up outta the water, few of us run ours at even half nameplate, let alone pegged.

MichaelP · Aug 5, 2019

15hp RPC will be more than sufficient for your needs. I have everything you listed plus more (my air compressor is 5HP though), and I run a 15HP RPC. The hardest load will be your 7.5HP compressor, but a 15HP RPC will provide a nice margin of error.

You can buy a low RPM motor (visit your local motor repair shops) and a panel (mine is by WNY Supply) for about $500 total or less.

Low RPM=low noise. This is important, IMO. My motor is a 15 HP 1200 RPM old monster bought for $150. You can hardly hear it running. At one point I used to play with a brand new 5HP 6500 RPM Baldor, and the shriek of a pig being slaughtered was unbearable.

JST · Aug 5, 2019

Yes RPC.

The only thing about WEG, is that IIRC, they have a bit of a reputation for being pigs as far as drawing a good deal of starting current. You seem to have plenty of power so that may not be an issue (and I may recall wrong anyhow).

rons · Aug 5, 2019

Weg is going to cost roughly 1/2 of a Baldor. Used ones that work can be cleaned up and painted. Here I mean motors for a RPC idler.
Changing all your machines to single phase is something I wouldn't do.

Ohio Mike · Aug 5, 2019

Buy a phase converter and be done with it. Why downgrade to crappy single phase motors

thermite · Aug 5, 2019

JST said:
Yes RPC.

The only thing about WEG, is that IIRC, they have a bit of a reputation for being pigs as far as drawing a good deal of starting current. You seem to have plenty of power so that may not be an issue (and I may recall wrong anyhow).

I thnk you are correct.

OTOH, "payback" is reflected in decent efficient running numbers for the modest spend.

Motor is too light overall for me to claim higher than average rotor inertia! My 10 HP Weg 3-P may weigh but ten or twenty percent what a FIVE HP Reliance RPM III Dinosaur-Current motor - same shaft size - weighs.

Part of that is the RPM clan's use of stacked laminations as FRAME vs the Weg's simple rolled sheet steel housing. The rest the gawdawful mass of Copper it takes to implement a straight-shunt-wound "Type T" at a mere 180 VDC target operating Voltage. Same frame size as 500 VDC RPM III of 20 HP.

Goods new is the 180 VDC RPM III's can use the cheaper KB DC Drives, need neither of ripple filter choke nor boost transformer.

Bad news is they are far too large to run inside a 10EE. Tried it. Would have needed an underslung mounting plate, casting cut-aways, ELSE countershaft run aft out of the former MG "garage", ELSE a "back porch", HS end, to park the porker.

markz528 · Aug 7, 2019

Industrial duty WEG motors are perfectly acceptable. WEG has the best NEMA motor product manager hands down. But you want a Brazilian made motor not a Mexican made motor. Big difference.

I have been to most of the major motor manufacturer factories all over the world - been to WEG in Brazil probably 30 times in the last 15 years. I know them very well.

JST · Aug 7, 2019

Nothing against the brand.

Motors have different design types, and within them, they have a variation in start current, which for NEMA motors, is designated by a code letter. A very good motor may be at the high end of the start current range, it is just a design choice, and not a sign of a crummy motor.

In fact, a high start current motor may be a good choice for an RPC, since the high start current may indicate a lower impedance, which will translate to the generated leg holding up better under load, even without fancy "balancing".

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3 phase or not to 3 phase

masterofall99

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MichaelP

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JST

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rons

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Ohio Mike

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