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[How do I?] Combining two rotary phase convertors ...

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FOMOGO

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#1
I have an existing 5hp RPC, and just picked up a 15hp 3 phase motor. The 5hp is a 220v idler, and the 15hp is 208v. Can I combine the two to get 20hp, and can I set them up so they could be run independently, or combined? Thanks, Mike
 

Bob Korves

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#2
I am not any kind of expert on this, Mike, but since you can use running machines to increase your three phase capacity beyond the phase converter, then I see no reason why RPCs cannot do the same. Iron shorts <ON> :eek 2:
 

bill70j

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#3
I have an existing 5hp RPC, and just picked up a 15hp 3 phase motor. The 5hp is a 220v idler, and the 15hp is 208v. Can I combine the two to get 20hp, and can I set them up so they could be run independently, or combined? Thanks, Mike
I also have a 5HP RPC which turned out to be too small for my new 3HP lathe. So I called North American Rotary and they fixed me right up by paralleling my idler with an additional motor and modifying the panel.

You might consider calling North American to get their opinion. These guys are very customer-friendly and know their business. Ask for Jay or Dave. You can also email them through their website. They will get back to you right away.
 
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JohnG

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#4
I did this for a while with a pair of 7 1/2 HP motors. One started up with a standard starter circuit. After it ran for a few seconds, it started up the second idler motor. The voltages were better balanced with 2 idlers, and my 5 HP air compressor started smoother with less voltage drop. The main breaker and trunk wiring to the RPC and 3 phase distribution panel was a 50 amp circuit, which leads to my question about your setup. I don't think you can run the 2 RPCs independently in parallel and then combine the outputs to run 20 HP supplied by one circuit wired and fused for 15 HP and one wired and fused for 5 HP. If you combine them as I did, the one trunk circuit would need to be fused to protect the 15 HP RPC with a branch circuit fused for the 5 HP auxiliary. You'd still have a 15 HP circuit that would be overloaded by a 20 HP motor. I did a lot of factory wiring in my time, but I'm not an electrical engineer.
 

Smithdoor

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#5
Just add a 10hp 3 phase motor star wound
This is motor the converter companies use
They will not tell any about being so simple to do.

Dave
 

ttabbal

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#6
I don't see any reason you couldn't run the independently, assuming a big enough driven motor to power them. So you would have 2 separate 3 phase outputs, sounds like different voltages. Unless one can be rewired so you get the same voltage.

Running them on the same circuit I don't think can work. The voltages are different and the phasing won't match. The power grid goes to great lengths to ensure that all the generators run with the same phase angle so they don't cause voltage fluctuations.

I'm not an expert in RPCs, perhaps they sync themselves up somehow. Just coming from what I know about AC power generation and electrical theory classes. If I were to try it, I'd connect an oscilloscope first to see if they do manage to sync.
 

FOMOGO

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#7
Thanks for all the input. From what I've read online, the idler motors are supposed to be the same hp rating. It's also my understanding from what I've read here, that the generated leg is always going to be 208V, but I may have misinterpreted that. My new to me Gorton mill has a 10hp spindle motor along with a 3hp motor for the XYZ axis drives. I'm thinking that a 15hp RPC would be adequate for that, but they seem to generally recommend double the RPC output of the motors to be driven. If I can't combine them, I will probably run the 5 & 15hp RPC's independently, and run the big one for the Gorton exclusively. If neccessary, I guess I could run the 7.5 hp lathe simutaneously to up the power available. Bob K, that was my thinking also, but I have no empherical evidence to substantiate that. Maybe Mark, or someone else better versed in 3 phase generation could enlighten us. I don't mind a little experimentation, but I would hate to let the magic smoke out. Mike
 

Karl_T

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#8
My big phase converter has a 10Hp then a 15 hp bought in ten seconds later for a total of 25 HP. I use it to run am Mazak M4 CNC lathe with a 20 hp spindle.

I built one for a my son with a 5 hp and bringing in a 20 hp ten seconds later. He uses it to run his big matsuura CNC mill.
 

rgray

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#9
I run a 10hp compressor with a 15hp rpc. It didn't start great so I geared it down with a smaller motor pulley and shorter belts.
Mill might start and run fine with the 15hp. I'd probably run the feed motors off a vfd to get by.
If things are close to each other maybe you could run the feeds from the existing 5hp rpc.

I have a 3, 10, 15, & 30hp rpc's. None are combined.
The 3 is hooked to 3 machines. The 10 to 2 machines. The 15 to an air compressor. And the 30 runs my 20hp cnc lathe with no problems so far (knock on wood).
 

JimDawson

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#10
The voltage difference of the motors might be a problem, but in general each motor you add to the system, whether it be an idler or a machine, adds to the motor starting capability of the system. I suspect you can run the 208V motor at 230V without any problems.
 

FOMOGO

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#11
Karl, is there a timer/switch used between the motors? Any chance you could do a quick schematic for the wiring? I could probably figure it out, but like they say "a picture is worth a thousand words". Thanks, Mike

Jim, That was what I was hoping. The 15HP motor was on a compressor, and appears to be pretty robust. I'm thinking the winding's wont be phased (pun intended) by the extra 32V. I was pretty confident you guys would get me pointed in the right direction. Cheers, Mike
 

Karl_T

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#12
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