phase converters

Iggy sez: "Thank you. I am reading an article at

A good article. If you read it in detail, moreover, understand it in detail you will be on your way to making great RPCs.

Bob Swinney

I have not yet been able to find a shipping deal under $200 or so... Jerry's offer is most appreciated!

Would that be a better deal than one of Jerry's hand picked free motors, if you paid shipping on each>

Advise you take a close look at the starting capacitor arrangement used in the wood working article you cited. A momentary push button to start and some free caps is a lot better than a klunky pony moror.

I think of a rotary phase converter consisting of a three phase motor as a motor generator. Of course I think of a single phase motor as a motor generator too. Works for me, but apparently not for a lot of people. If you did not have the back EMF generated in a motor, the motor would draw a huge amount of current.

Dan

jim rozen wrote:

You might want to consider that a induction motor that is driven acts as a induction generator. Jim Pentagrid has posted some very accurate information about induction generators. To summarize, they are very load sensitive if they are used as a stand alone generator. But if they are connected to the power grid, they work very well.

So you can make a motor generator using a single phase motor driving a three phase motor which has one phase connected to the same single phase that drives the single phase motor. Nota Bene In order to actually be driving the three phase motor, you have to drive it faster than the rpm that it would run at when running on single phase as a idler. The way to do this is with a belt drive. One pulley should be a variable pulley. So one can measure the current drawn by the single phase motor and adjust the pulley so the single phase motor draws its nameplate current or somewhat less.

This is the way to make a phase converter for driving something as a surface grinder that is sensitive to variations in torque.

I made one like this some twenty years ago to run a centerless sander. Worked slick. The single phase motor worked as a pony motor to start the three phase motor and then drove the three phase motor to produce a better three phase than most rotary three phase converters.

Dan

Robert Sw> What Grant said . . . a single phase motor driving a generator would, in

Dan,

This is a really interesting suggestion. What size motors did you use? I can get a 2.5 hp three phase motor free, and a 3/4 hp single phase motor for little money. How do you think this would work? From what I've read phase convertors are pretty forgiving about the size of motors used.

Many thanks,

Chris

I've seen better....

Jim

Dan,

That's a really interesting suggestion. What size motors did you use? I can get a 2.5 hp three phase motor free, and a 3/4 hp single phase motor for little money. How do you think these would perform in a phase convertor? From what I've read phase convertors seem quite forgiving when it comes to the size of motors used.

Many thanks,

Chris

The motors I used were a 7.5 hp three phase motor and a 2 hp single phase motor. My motor picks were dictated by what I had available, but seemed to work well. The centerless sander had a 5 hp main drive motor and a couple of smaller three phase motors.

I think a 3/4 hp single phase and a 2.5 hp three phase motor should also work well.

If you do a' little googling on induction generators, you will find they are not uncommon. But mostly used on things as street cars when braking.

Dan

Thanks very much for the opinion. I'll probably make a trip soon to get the 2.5 hp motor and start experimenting. Will let everyone know how it goes.

Many thanks,

Chris

I resemble that remark!!

Jim