Rotary Phase Converter

[matthewsx]

That's one of the advantages of the pony set up. If you are a scrounger, or just can't afford the cost of buying the set up, you can do the entire thing pretty for cheap. All depends on where you are in life.

I continue to maintain that good work can be done safely, fun and affordably.

Daryl
MN

Would definitely be interested in the pony setup. I have an unused 1phase motor lying around too.

John

 

[MikeInOr]

A pony motor setup does not use a start capacitor to get the idler motor moving. A 1ph pony motor is linked to the 3ph idler motor (usually) by a belt.

The pony motor is started and used to start the idler motor turning. Once the idler motor is up to speed power is applied to the idler motor which keeps it turning at its rated speed. The pony motor is then shut off and the belt is usually removed so the idler motor isn't spinning the non-powered pony motor.

The pony motor RPC I saw used a 30hp idler motor and a 5hp pony motor. The pony motor was mounted on a hinge. When the idler motor was up to speed and powered the pony motor was pushed forwards slacking the belt causing the belt to shoot out into the shop some where. This wasn't my design but it was effective! The capacitance and inrush current needed to start a 30hp idler motor probably would have been more than the service could handle. This RPC was in a production shop that made rat poison that was extruded into pellets by a big 3 phase pellet mill.

I think I might have tried a couple rubber wheels, one on the pony motor and one on the idler motor to get the idler motor up to speed without a belt.

 

[Uglydog]

A pony motor setup does not use a start capacitor to get the idler motor moving. A 1ph pony motor is linked to the 3ph idler motor (usually) by a belt.

The pony motor is started and used to start the idler motor turning. Once the idler motor is up to speed power is applied to the idler motor which keeps it turning at its rated speed. The pony motor is then shut off and the belt is usually removed so the idler motor isn't spinning the non-powered pony motor.

The pony motor RPC I saw used a 30hp idler motor and a 5hp pony motor. The pony motor was mounted on a hinge. When the idler motor was up to speed and powered the pony motor was pushed forwards slacking the belt causing the belt to shoot out into the shop some where. This wasn't my design but it was effective! The capacitance and inrush current needed to start a 30hp idler motor probably would have been more than the service could handle. This RPC was in a production shop that made rat poison that was extruded into pellets by a big 3 phase pellet mill.

I think I might have tried a couple rubber wheels, one on the pony motor and one on the idler motor to get the idler motor up to speed without a belt.

MikeInOr: Very well done write up!!

I thought the hinge mechanism dangerous and wasn't even gonna mention it. I've also heard of set ups wherein a notch was cut in the pulley of the 3ph RPC and a rope with a wooden handle was wound around the pulley like an old fashioned lawn mower with out a spring retracted pull rope.

On mine the motor RPM is the same for both motors and the pulley size is the same. The belt is positioned over both pulleys and always runs. Make a belt cover! Both motors need to run the same direction. The 1ph pony uses a motor rated 120v switch to turn on the pony. Once it is turning the 3ph motor the magnetic starter is engaged the RPC powers up and I manual turn off the pony. As the low hp pony doesn't run for more than a few moments I didn't put it on a manual or mag starter. UlmaDoc taught me the value of run caps many years ago. I'd recommend them. Be sure that your cordage, plugs, electrical wiring and circuit breakers are all rated appropriately and everything is grounded. I run the pony RPC in the wood shop. Let me know if a sketch would be helpful. Additionally, as always, if anyone has input on how this can should be done differently I look forward to redirection.

In the metal shop I have a commercial 20hp RPC wired with a fused knife switch, a mag starter and a used commercial panel. All of this was well used or salvage stuff. It took a second trip by the Minnesota State Electrical Inspector as I needed to correct an error I had made. My point is that this is all doable, affordable, safe and fun.

Daryl
MN

 

[rabler]

FWIW, My 20HP RPC, I measured a peak startup current of 209 amps on the 245V line, using a Fluke clamp amp meter set on peak detect. Obviously that peak was fairly short, it is a 200a service.

Edited to add: This is on a WNY control panel that I bought maybe a year ago, used in conjunction with a 3ph motor I had. Timed capacitor start with a bank of run caps.

 

[Uglydog]

FWIW, My 20HP RPC, I measured a peak startup current of 209 amps on the 245V line, using a Fluke clamp amp meter set on peak detect. Obviously that peak was fairly short, it is a 200a service.

This is critical for us all to think about!
Start up demand on large RPCs is huge!
Even small ones can ask for more than a circuit was wired for.

Daryl
MN

 

[MikeInOr]

FWIW, My 20HP RPC, I measured a peak startup current of 209 amps on the 245V line, using a Fluke clamp amp meter set on peak detect. Obviously that peak was fairly short, it is a 200a service.

Edited to add: This is on a WNY control panel that I bought maybe a year ago, used in conjunction with a 3ph motor I had. Timed capacitor start with a bank of run caps.

When I was building my 10hp RPC I found that the higher the capacitance of the start capacitor the quicker the idler would come up to speed and the higher the peak inrush current... as well as the peak voltage. I ended up removing a couple capacitors from starting capacitor bank for a slower start and lower current peak and voltage peak.

When my 7.5hp 3ph RAS starts from the RPC the peak current read between the 1ph mains and the RPC is much lower.

One of the BIG advantages to a VFD is the soft start really lowers the starting current a lot which I would also assume would be much easier on the motor windings to noit have to carry so much current.

 

[rabler]

As a comparison, it was 209A peak on startup, and 9.2A with the idler motor running and no load on the RPC.
It's wired on 2/0 aluminum on a 100A breaker. The break doesn't blow so that is presumably a very short peak.
I'm using it to power a lathe that has three motors, the main motor, a rapids feed motor, and a hydraulic/lubricant pump motor. Not practical to convert that to a VFD.

 

[rabler]

One of the BIG advantages to a VFD is the soft start really lowers the starting current a lot which I would also assume would be much easier on the motor windings to noit have to carry so much current.

I don't think peak starting current is that hard on the windings. That peak current is so short that it doesn't generate any significant heat.

 

[rabler]

Please disregard. I deleted a brain fart.

 

[Ultradog MN]

Some random thoughts.
I hemmed and hawed about going with a VFD or RPC. What decided it for me was I got a 7.5 hp 3 ph motor for free. I spent $100 for a capacitor kit' $20 for an enclosure on CL plus maybe $50 for conduit, wire, a breaker, etc.
I now have four 3 ph machines and didn't need to keep buying VFDs for each one.
I put the idler outside. Quiet.
Another thing is I my lathe is a big, hefty old gal with 16 speeds so I haven't felt a need for variable speed. And I actually enjoy handling her knobs to change gears.
A friend of mine has a home built rpc set on the floor that he hits the switch then starts it rotating with his foot. Utterly simple, inexpensive and effective.