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idler motor sizing for rotary phase converter.

arse_sidewards

Contrary to everything
Joined
May 19, 2020
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I'm gonna build a rotary phase converter. How much motor do I need if I want 15hp start and 25hp run capacity?

Can I get away with less if I stick a big fuckin flywheel on the idler motor?
 
Too bad there’s not a shop tool section, oh wait...
 
Depends on what you are starting. Go to America rotary and use the sizing guide.
 
Depends on what you are starting. Go to America rotary and use the sizing guide.

Neither they nor anyone else tells you the nameplate horsepower of the idlers they use. They just tell you what it's good to start
 
Are you sure? I will need to look. I needed to start a 20hp clutched lathe and I needed a 40hp.
 
I have a 10 hp idler and American rotary panel. It will start my 1440 7.5 hp in low but not on high. It has a 2 speed motor. It starts my 5 hp hbm just fine.if it starts it it will run it. If your starting 25hp better put a 40 or 50 on the idler. A flywheel might help but it’s the wire size of the motor you need to watch. Running 100 startup amps through a 25 hp idler might burn a wire off.

You have 100+ amps of 220 available for the phase converter? I put a dedicaded 200 amp drop into my machine shop.
 
I have a 10 hp idler and American rotary panel. It will start my 1440 7.5 hp in low but not on high. It has a 2 speed motor. It starts my 5 hp hbm just fine.if it starts it it will run it. If your starting 25hp better put a 40 or 50 on the idler. A flywheel might help but it’s the wire size of the motor you need to watch. Running 100 startup amps through a 25 hp idler might burn a wire off.

You have 100+ amps of 220 available for the phase converter? I put a dedicaded 200 amp drop into my machine shop.

What's the start rating and load rating for your converter?

I have 60a but I could make it 100+ with nothing more than 25ft of fat wire. 25hp load is worst case with me on the lathe and a buddy on the mill. The largest thing I need to start is 15hp.
 
The tag says 40HP and I bought a AD40

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I have a 320a single phase service and a 30hp American Rotary and another 20hp idler of my own hacking so I'm speaking from some experience, whatever that's worth on the internet. I run a 13hp and 15hp spindle on a couple CNC machines at the same time on the 30hp without any trouble, but I don't max them out, probably 75% loaded at times. The CNC stuff is all soft-starting though, and that's the hard part. I think a 30hp will start your 15hp and run 20-25hp of it, but that's pushing it if you really load it up. I would look for a 30-50hp setup, but you're getting out of what single phase service can support. You probably don't have more than 200a. I have one of those, too. lol.
 
What's the start rating and load rating for your converter?

I have 60a but I could make it 100+ with nothing more than 25ft of fat wire. 25hp load is worst case with me on the lathe and a buddy on the mill. The largest thing I need to start is 15hp.

I have never measured the startup amperage of my phase converter. My gut says that 15 hp is gonna pull 65-80 amps on startup. Startup is all you have to really worry about. If you can get it rolling it will stay running under a full load.

25 hp is like 86amps in a perfect world of 220 single phase.

my little 10hp can run my 1440 lathe Bridgeport and 5hp bandsaw simultaneously with no issue.

You can cheat to start bigger stuff by starting the Bridgeport and bandsaw then start larger load using them as the rotary helpers. The big thing is it will work fine as long as the voltage drop from the single phase doesn’t go too low. This means huge wires from panel to convertor.
 
I'm gonna build a rotary phase converter. How much motor do I need if I want 15hp start and 25hp run capacity?

Can I get away with less if I stick a big fuckin flywheel on the idler motor?

You do not want a flywheel on the idler. That needs to start up as fast as possible.
 
I have never measured the startup amperage of my phase converter. My gut says that 15 hp is gonna pull 65-80 amps on startup. Startup is all you have to really worry about. If you can get it rolling it will stay running under a full load.

25 hp is like 86amps in a perfect world of 220 single phase.

my little 10hp can run my 1440 lathe Bridgeport and 5hp bandsaw simultaneously with no issue.

You can cheat to start bigger stuff by starting the Bridgeport and bandsaw then start larger load using them as the rotary helpers. The big thing is it will work fine as long as the voltage drop from the single phase doesn’t go too low. This means huge wires from panel to convertor.

I's got a 6ga wire now for the 5hp/15hp converter which is why I said 60a. I can put whatever wire I want in when I build a big converter.
 
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