Rotary Phase Converters - revisited

[WinterDeere]

Repulsion Induction. They have absolutely massive startup torque, for their size and draw.

It's basically running as a universal motor on startup, usually with very large brushes (each the size of a Zippo lighter) on a commutator that usually looks like a large dinner plate, rather than the more typical drum commutators you see today. The brushes lift off the commutator when you reach some fraction of synchronous speed, just like a regular capacitor start single phase induction motor will often use a mechanical switch to de-energize the start windings. Many of the older RI motors I've seen have a setting where you can adjust the speed at which the brushes lift off or set back down, as well as shift the brushes a few degrees to change the motor direction.

So, on startup, it's operating as a universal motor, but then at speed it's acting as a normal induction motor.

So, "what's a universal motor?", asks the next guy. They're the torquey little monsters found in every handheld drill and woodworking router, as well as vacuum cleaners and anything else where you need big torque in a small package. They're also called "DC" motors, because this is the same motor type used for DC current, although I think the ones made for operation on AC are optimized somewhat differently.

Most larger machinery (table saws, band saws, vintage planers) do not use universal motors, but instead use induction motors, although you can find universals in some compact modern versions of each. The most common motor used in machinery you're going to find in a personal or cabinet shop is the capacitor start induction motor.

 

[dstig1]

Yeah I know Induction (w/start and or run caps). I know Universal. But RI was a new one to me. Thanks!

 

[WinterDeere]

There are so many motor types! Because of cost optimization and competition, what we see in our consumer products is such a narrow slice of what's out there. When you get into vintage stuff, many more interesting variants pop up, as older manufacturers were then just experimenting with different types to leverage one advantage over another, and manufacturing costs were still so high on all fronts, that shaving pennies was not yet a big concern.

Old cities like Philadelphia had a lot of 2-phase systems, in fact I think Philly might be the only one left, last I heard. That brings out even other options for motor arrangements, which I know nothing about.

What I see most on machinery today is of course universal (always-engaged commutator), cap start induction run, cap start cap run, split phase, and repulsion-induction. But even each of the last four have multiple variants, as each can have mechanical switches (centrifugal), potential relays, or current inrush relays, to switch out the starting circuit.

 

[CalG]

There are so many motor types! Because of cost optimization and competition, what we see in our consumer products is such a narrow slice of what's out there. When you get into vintage stuff, many more interesting variants pop up, as older manufacturers were then just experimenting with different types to leverage one advantage over another, and manufacturing costs were still so high on all fronts, that shaving pennies was not yet a big concern.

Old cities like Philadelphia had a lot of 2-phase systems, in fact I think Philly might be the only one left, last I heard. That brings out even other options for motor arrangements, which I know nothing about.

What I see most on machinery today is of course universal (always-engaged commutator), cap start induction run, cap start cap run, split phase, and repulsion-induction. But even each of the last four have multiple variants, as each can have mechanical switches (centrifugal), potential relays, or current inrush relays, to switch out the starting circuit.

All that variety is why a straight 3phase motor is so desirable. They are heavy for the HP though. Can't imagine one replacing an AC?DC universal in a hand tool. Heck, I like the permanent type like in the Rockwell 1/2 inch drill motor.

 

[rlrsk8r]

I have a three-phase Bridgeport milling machine and hooked up a one horse motor to generate my own three phase. Since the Bridgeport is one and a half horsepower, my rotary converter was not big enough to run the mill properly, but since I was not pushing the mill to its capacity, it worked for me. I was able to spin the first motor by hand to get it up to speed to generate my three phase. Eventually, I picked up a five horse three phase motor, but could not spin it fast enough by hand to get it running. I mounted it on a plate And lined up a 1/4 horse motor on a homemade bracket with the two shafts in line. I connected the two shafts with a piece of hydraulic hose. I turned on the quarter horse motor and when the big motor got up to speed, I shut the power off to the quarter horse, and applied power to the big motor. What I found was I had to shut off the quarter horse before powering up the big motor or I would blow a fuse. I have since picked up a solid state converter, but have not hooked it up yet. It’s one of those rainy day projects.

 

[WinterDeere]

You'd do well to learn about how to start a three-phase motor on single phase, with a few start capacitors to the third leg, and then how to switch them out. Also, you can balance the other two phases with that supplied by the utility, using run capacitors. This may give you better success in running loads closer to the size of your idler motor.

 

[ultrarunner]

I have a three-phase Bridgeport milling machine and hooked up a one horse motor to generate my own three phase. Since the Bridgeport is one and a half horsepower, my rotary converter was not big enough to run the mill properly, but since I was not pushing the mill to its capacity, it worked for me. I was able to spin the first motor by hand to get it up to speed to generate my three phase. Eventually, I picked up a five horse three phase motor, but could not spin it fast enough by hand to get it running. I mounted it on a plate And lined up a 1/4 horse motor on a homemade bracket with the two shafts in line. I connected the two shafts with a piece of hydraulic hose. I turned on the quarter horse motor and when the big motor got up to speed, I shut the power off to the quarter horse, and applied power to the big motor. What I found was I had to shut off the quarter horse before powering up the big motor or I would blow a fuse. I have since picked up a solid state converter, but have not hooked it up yet. It’s one of those rainy day projects.

I do the exact same for 25 years and have at times run 8-10 hours on the NC mill...

Turning the shaft is as easy as snapping my thumb and index finger and plugging in the power cord...

 

[Williy]

dadohead
You ever go duck hunting or fishing in horicon marsh?

willy

 

[rlrsk8r]

I do the exact same for 25 years and have at times run 8-10 hours on the NC mill...

Turning the shaft is as easy as snapping my thumb and index finger and plugging in the power cord...

I tried to start the motor but it's not one of those newer, 'compact' designs with less steel but couldn't spin it fast enough. I prolly could have used a pulley with a lawnmower-type pull rope but having it (I've used it for the last 10 years this way and I'm happy with it) 'hidden' behind the Bridgey, next to the wall, I dint want to contort my (then) 65 year old body to do that so I opted to add my pony motor. Besides, it's always a challenge to design and build something like we all do.

 

[WinterDeere]

I have a rotary phase converter panel that I no longer use, with a compact 7.5 hp idler. If you need one, send me a PM. I'll probably end up selling it way lower than the cost of the parts alone, just because I want my shop space back.