Rotary phase converter

So I've been looking into building a phase converter and I'm thinking about doing just a quick and dirty setup with just a motor, trip switch and a rip cord to spin it up. Some of my research says this is a great setup, while others say I need to set it up with start and balance capacitors to balance the load. Any help or advice?

what are you trying to power with it?

For now I have a power feeder with a 2hp motor on it, but I'm looking to add a wide belt sander 10 hp, not to be run at the same time. No electronics this is all older stuff. Otherwise I'd fork over the cash to bring it in 1/4 mile from the highway.

i have seen them done that way.i have also seen them use a little 110 motor with a rubber wheel that you could lever into the big motor to spin it up then throw the switch and pull the 110 motor away.ran a lathe and mill at the same time that way.

leon

Rotary phase converters are simple to build, and cheap if you use used parts.

If you are going to rope start a 10 hp 3 phase motor very often, then be sure to set aside some money for new shirts. Your biceps are going to grow :laugh:

I started off with a bare 5hp 3 phase motor, spin it up and flip the breaker on, if it wasn't spinning fat enough when I flipped the breaker on it would growl at me.

Used some stuff I had gotten in a box for $5 at an auction to build a self starting phase converter out of that same 5 hp motor. Works a treat, just flip on the breaker and away she goes. Got bored one day and built another one with big old meters to monitor voltage on each leg, never used it though.

The phase converter powers my mill and surface grinder, the lathe is powered by a VFD

I never bothered to balance the converter, it's a 5hp powering two 1 hp machines.

Oh yeah, a 10hp three phase motor is going to pull an awful lot of amps as inrush current when you start it, so you might think about using a 1/2 hp or so single phase motor with a belt and pulleys to spin it up. Leave the single phase motor hooked to the 3 phase motor permanently. Just shut the power off after the 3 phase is running. Won't hurt and it will actually help if you're starting a big load.

Practical Machinist has a whole forum on phase conversion.

One thing I haven't been able to figure out... Is the motor just rotating power from the other two legs out of phase, or does it actually generate the third leg power?

I do have several small pony motors around so I may just do that. If you're really loading the rpc would you need to turn it back on to act as a sort of run capacitor?

The way I understand it is the motor is generating the third phase using residual magnetism from the other two phases.

My self starting phase converter uses a potential relay hooked up to the third leg and controlling the start capacitor(s).
If the voltage on the 3rd leg drops below a certain point (I think 200V in my case), the potential relay connects the starting capacitors into the circuit. No volts at start up, so capacitors kick in, if I were to slow the motor to the point the voltage on the third leg dropped below 200, capacitors would kick in again to boost it back up. When I turn it off and the motor slows down, all at once the motor will "kick" as the capacitors kick in.

The more mass you have rotating, the more load it's going to take to slow the motor down. That's why I suggest leaving the pony motor connected via V belt full time. Max load normally happens at start up, and only lasts for a second or two.

Sounds like the relay and capacitors is easy enough to build, I already have an empty box to put it in I just don't know where to go to get them cheap. Locke is high, but I've been watching cl with no luck

just a thought

www.surpluscenter.com/sort.asp?catname=electric&keyword=EPPC

baldtires wrote:

just a thought

www.surpluscenter.com/sort.asp?catname=electric&keyword=EPPC

Yep, that's where a lot of guys are getting parts.

Potential relay is $9 - $13 or so at Grainger, and single purpose three phase relays are pretty cheap there also. Just be sure to get one with a 110V or 220V coil or you'll need a transformer to provide 12V or 24V .

Tell me what parts you need and I'll look around here.

Thanks for the help. The first thing I have to do is find an extra motor around here. My fater in-law works at a quarry, so I'm hoping he can scavange something for me. I was going to build something real simple at first with what I have around while I look for the extras. I guess what I will need for capacitors and will depend on what I can find for an idler motor. I'm hoping I can find a 10 to 15 hp, but for now I may have a trade worked out for a sander that has a 3 on it and I can rob that for the idler and convert it to single phase.

When you talk 10-15 hp you're also talking minimum 100 amp service to the garage/shop, not including what the house uses.

I'm not sure a 15 hp motor wouldn't trip a 100 amp breaker at start up :woohoo:

Your garage/shop have separate electrical service from house?

My understand is that idle motors can be ganged for greater hp. So you could use 3 5 hp motors in order to get your 15 hp.
Build a self starting 5 hp then start the other two one at a time off the 3 phase from the first one.

Lots of ways to skin a cat