Rotary phase converter sizing question

[Bill Dufour]

With a rotary converter does it need to be sized for the motor load like a static converter? Or will a 20 hp rotary run a 1hp motor at full power.
I do realize a larger rotary will draw more standby power at idle.
Bill D

[Jonathan Jung]

When I was doing all my shopping for one a couple years ago, the consensus was to double. So I got a 40hp to handle 20hp of machines. I do notice that when the WBS is running and I try to start my 5hp jointer, it starts with more of a strain than if the WBS is not running.

[Warren Lake]

talk to the manufacturer. The delta TME brand was 10HP Roto starts 10 HP machine and they gave three options of of Rotos at each HP rating. You get more gizmos on each level. Even on the heaviest model there were additional ballasts that could be added for some set ups. I got the middle choice 10 HP and it always started a heavy load 10 HP with no issues.

I was given a 3Hp that has no gizmos just some capacitors and it always worked fine to start even a 4 HP mortiser which is a low load.

[Larry Edgerton]

I run my whole shop on a 50 hp converter. No problem running from 1 1/2hp up to 11 hp, and several running at the same time.

[William Hodge]

I have a 20 hp rotary phase converter. It seems like what matters is the load. I run a few machines at a time. The pony motor is an electric drill with a nut driver in the chuck. I get the 20 hp spinning, pull the drill back, then throw the knife switch that runs it. I looked around and found a higher speed electric drill, probably 1500 rpm's.

[Warren Lake]

Rotos have some ballast affect where more machines the merrier. I ran five machines once at once off the roto and total draw was about 23 amps approx including the roto. Larry what does your roto draw on idle? I had a past measure of 17.6 amps on the 10 HP on idle.

[Bradley Gray]

I have a Kay 10hp. It will start 10bhp and run 20hp

[Andrew Hughes]

I also have a 10 hp Kay phasemaster. My only complaint it’s so quite I forgot to turn it off and leave it running all night long.
I would appreciate any ideas how to add a run light when its on.

[Bill Dufour]

You might add a wall switch that is a twist to turn on as used for bath fans. Turn itself off in one or two hours?
You can buy edison base led bulbs that are 120-240 volt. Just wire it in parallel to the input power.
Bill D

[Michael Schuch]

My 10hp rotary phase converter has no problems starting and running 7.5hp motors. It will also start and run the .5 hp 3ph motor on my stock feeder which is mounted to my single phase shaper. (I have the VFD for the stock feeder it just hasn't made it to the top of my project list yet).

A static phase converter is just a capacitor used to start a 3ph motor and bring it up to speed before a potential relay removes it from from the circuit. As such a static convertor needs to be sized to the motor it is starting... just like a starting capacitor needs to be sized to the single phase motor it is starting. If a starting capacitor is too large, for a single phase motor or as a static phase convertor for a 3 phase motor, it will push more current through the motor windings when starting... possibly enough current to fry the motor windings immediately or over time. A RPC has no such sizing requirement. A RPC just needs to be big enough to start and run the biggest motor that will be connected to it. For an RPC I have always gone by the RPC idler motor needing to be 1.5x larger than the biggest motor it will be starting and running... which has always worked for me. Part of the RPC idler sizing equation depends on how much load the 3ph motor will be under when starting.

[Bill Dufour]

I bet my 18" planer is a big starting load with the factory 7.5hp motor. Lots of mass to spin up to speed.
BillD

[Steve Jenkins]

When I moved away from where I had 3 phase I called Kay and told them the equipment I had and asked for their recommendation. I figured I’d get one answer and it would be right. Maybe conservative but I don’t have to worry.

[Aaron Inami]

A comment for those of you who are running "technically undersized" rotary phase converters. One fact to know is that many machine motors may not ever require the full amount of current rated on the motor (i.e. full load amps). This depends on what kind of machine it is and what you are trying to do with it. For example, a 5HP table saw that is rated at about 16 full load amps will only require about 1300 watts when just spinning the blade. A 16 amp full load would be about 3750 watts. But if you are pushing through some 2" dense hardwood, the current draw will definitely go up. Various machines machine pull different "actual current" depending on what kind of machine it is. One machine that will definitely pull "full load amps" is your dust collector when all blastgates are open.

[Bradley Gray]

I bet my 18" planer is a big starting load with the factory 7.5hp motor. Lots of mass to spin up to speed.
BillD

I start the 7.5 on this thing with my 10hp Kay
517524

[Robert Hayward]

I also have a 10 hp Kay phasemaster. My only complaint it’s so quite I forgot to turn it off and leave it running all night long.
I would appreciate any ideas how to add a run light when its on.
Not for 3 phase but my air compressor I put a pilot light on the circuit with HD parts. I moved my compressor from the shop to an out building and did not want it powered on all the time. It is on two three way switches, each with a pilot light.

Works great, I can turn it on or off from the shop or out building and know when the compressor is powered.

The major problem is I forget to look at the pilot light. I might not use air for two days and go over to turn on the compressor and the pilot light will be glowing red. Should have used a switch that uses a mallet to hit me instead of a pilot light.

[Warren Lake]

Id listen to the people who build the stuff I think the manual for the rotos I bought is over 10 pages long. A planer is not hard start compared to things they had to power. The company I had picked made Rotos for the mennonites and farm areas where they didn't have three phase. The three choices allowed you to pick what was best and you could do more over and above. Hard start 10HP started fine with 10HP roto and ran under full load fine. Each manufacturer is different. The old ones were massive heavy motors, the newer ones or some lighter higher efficiency motors.

[Andrew Hughes]

Id listen to the people who build the stuff I think the manual for the rotos I bought is over 10 pages long. A planer is not hard start compared to things they had to power. The company I had picked made Rotos for the mennonites and farm areas where they didn't have three phase. The three choices allowed you to pick what was best and you could do more over and above. Hard start 10HP started fine with 10HP roto and ran under full load fine. Each manufacturer is different. The old ones were massive heavy motors, the newer ones or some lighter higher efficiency motors.

Warren the roto kinda looks similar to a Kay Rpc. I would bet a box of Daniel Webster cigars they are made by Phasemaster. Or maybe it’s justbthe look of a U frame motor.
Good Luck

[Warren Lake]

Delta TME is gone now which is sad. Likely around 50 years and absolute pros. I was given one of their rotos a 3Hp roto from the wife of one of the cabinetmakers I knew years after buying some of his machines I took it in once and a lady changed out some caps. I think it had 25 years on it at the time. When I bought I bought the same company but with a few gizos, voltage regulation one of them I remember, it kicks in a bank of caps under load then clics out not needed.

[Larry Edgerton]

The caps on my 50 hp are scary! Would not want to get hit by one of those.

I never have checked draw at idle Warren. Its not on idle long because it makes an obnoxious growl at idle.

[Michael Schuch]

A comment for those of you who are running "technically undersized" rotary phase converters. One fact to know is that many machine motors may not ever require the full amount of current rated on the motor (i.e. full load amps). This depends on what kind of machine it is and what you are trying to do with it. For example, a 5HP table saw that is rated at about 16 full load amps will only require about 1300 watts when just spinning the blade. A 16 amp full load would be about 3750 watts. But if you are pushing through some 2" dense hardwood, the current draw will definitely go up. Various machines machine pull different "actual current" depending on what kind of machine it is. One machine that will definitely pull "full load amps" is your dust collector when all blastgates are open.

I agree. My 16" saws (2 radial arm saws [both 7.5hp] and 2 table saws [One 7.5hp and one 5hp]) come no where near pulling full current and start/run easily on my RPC.

When I think of a heavy starting load I think of an air compressor. Even a planer isn't doesn't really start under load.

I built my balanced 10hp idler rotary phase converter over 30 years ago specifically to run my 16" 1947 Redstar radial arm saw. It has handled my RAS admirably as well as every other 3 phase machine I have purchased since then. Most of my machines get converted to VFD's but all of them get plugged into my VFD and run while waiting for a VFD install.

[Warren Lake]

past the heavy duty models were higher than normal amps fof submersible pumps and sealed unit refrigeration. Agree the planer is not hard start the 3Hp roto with no gizmos started and ran the combo machine 3Hp easily and the shaft is a planer, a saw and a mortiser and still not hard start.