Phase convertors

Dieseltech

Well-known Member
Location
Akron, Indiana
School me on phase convertors. Looking at a machine that has a 5 or 7.5 hp three phase motor, need to recheck the size. 230V 60 cycle on tag. How critical is convertor size, should the convertor be the same size as motor or slightly larger for full motor hp rating? Have been told rotary type is best for least power loss. Thanks in advance.
 
Slightly larger if the machine is an easy starter, if it is a hard starter then 2 - 3 times the size. You could also go the VFD route, that can get you variable speed too. What kind of machine are we talking about? Lots of info on the web and doesn't necessarily cost a ton of money. I made my father in law a convertor for his Bridgeport milling machine for under $300 and run a couple of them myself. JB
 
Google phase converts. Rotary converter is better than static. Some say static may only be 60% efficient, so a 10 hp 3 phase motor will only produce 6 hp. The bigger the rotor motor, the more efficient it will be, but under load they could be as low as 70%. So a 10 hp motor will only produce 7 hp. The efficiency varies with load. It may be cheaper to get a 5 hp 230v single phase motor than to buy a rotary phaser then buy a bigger 3 phase motor.

When I was a kid, my dad built many phasers, both static and rotary, for farmers who had no choice, they had to use 3 phase motors, because of the motor size.
 
Machine is an older injection pump test stand. Would be easy start up with the pump set at no fuel position, just concerned about holding the full motor rating with a small loss as possible. Still need to see what the motor tag shows power wise, the machine tag shows 5 HP but some were 7.5. Sounds like the rotor type is what it needs, looks like static type would not handle the load as well. Some pumps can pull pretty hard at full fuel capacity and it doesn't have much to start with. Friend has two machines with the static box setup, but the motors are small an a lathe and Enco mill.
 

I built one for my milling machine years ago, now I wouldn't bother with it, just buy a VFD that will convert single phase to three phase, much easier and more options with most drives, torque values will be much better as well, look at www.automationdirect.com or www.factorymation.com and see what they have, I usually purchase a lot from automation direct, they have a great selection of everything you are looking for, just upgraded 25 machines in an ammo plant, everything but the enclosures came from automation direct, start the next 25 on Monday.

Good luck.
 
There are numerous ways to convert from 1phase to 3 phase. Each one has good and bad points. The most accurate is the digital phase converter. They are at phaseperfect.com ,their lit.will give you the good and "bad" points of each. 480ElecCase
 
I have a rotary phase converter and while it works I can't stand it. You run a machine once or twice a day and you have to go turn the phase converter on first, run the machine and then turn the phase converter off when your done. If I had to do it over I would get a VFD. If you do get a rotary phase converter, the converter should always have a idler motor larger than the machine motor.
 
(quoted from post at 19:44:43 06/17/15) I have a rotary phase converter and while it works I can't stand it. You run a machine once or twice a day and you have to go turn the phase converter on first, run the machine and then turn the phase converter off when your done. If I had to do it over I would get a VFD. If you do get a rotary phase converter, the converter should always have a idler motor larger than the machine motor.
have a 7.5 rotary converter to run my lathe with a 5 hp 3 ph motor on it.
I have the converter mounted next to the lathe so there is no walking involved to turn it on and off.
 
What no one has said so far is that both the VFD and static converter are pretty much limited to running one machine at a time, while the rotary converter can run multiple machines. Too, as others have said, the static basically does nothing but provide a third leg to start the motor and it's then kept running, basically on single phase at around 2/3 of it's rated HP.

The good thing about a rotary is that if your running multiple motors, as each one is started it acts as an idler also, and basically boosts the 'systems' ability to run a larger motor. In other words say you have a 7.5 HP motor that you need to start, but the converter doesn't have quite enough power to do it by itself. So, you start one of the other motors that draws off the converter and with it also acting as an idler, the larger motor will now start. We used to do that all the time with the converter in Dad's shop. During the winter, on really cold days, the 7.5 HP motor on his compressor would pull enough amps to trip the breaker if we tried to start it first. However if we started the 5HP motor on the lathe first and let it act as an idler also, the compressor would come to life like it was a summer day.

All it takes is a 3 phase motor about twice as large as the one you want to run to make your own. With the motor, a few capacitors, and a couple of motor starters, you can make a nice converter for a couple of hundred dollars at the most, IF you can source the starters, etc for a decent price. I got mine from a place that does municipal wells, etc. They often replace pump control boxes that usually have a couple of starters, and capacitors in them. I got mine free because my Dad works there, but given that most of those places would throw the controllers in the scrap anyways, you can probably get a couple of them from someone local to you, for cheap, if you ask.

I now run a 5HP mill, and a 5HP lathe with mine. The only issue I have is I have to use the lathe as an idler to get the horizontal spindle on the mill to run. The vertical runs fine, but the way the horizontal is geared it creates a huge load if it's on one of the higher gears. Like I said though, reach right behind me and hit the button and let the lathe motor idle, and the mill fires right up.
 
I made my own phase converter, used a 1 hp single phase motor to spin a 5 hp 3 ph motor. Had the motors, just had to buy a switch box and wire. No capacitors involved.
 
If you use a static convertor sizing is crucial. Rotary just get one a bit bigger than the largest motor you are using.

If you are working with a two speed motor only one speed will likely work with a static. BTDT and have a rotary now. Would also suggest mounting a rotary on a solid surface. Mine is mounted on a wood attic floor and gets kinda noisy.

JM2CW

jt
 
ncwayne, can you run a 3 phase welder off a rotary converter? i have a couple 460 amp 3 ph wire feed welders, but no 3ph in the barn where they are located.
 
(quoted from post at 16:07:42 06/18/15) ncwayne, can you run a 3 phase welder off a rotary converter? i have a couple 460 amp 3 ph wire feed welders, but no 3ph in the barn where they are located.

Few 480V and 600V welders are actually three phase. Most are single phase. A simple single phase stepup transformer is all that is required.
 
I've never tried that myself, so I honestly don't know. I've always heard it is possible, but I guess it would depend on the exact way the welder was wired. About the only way to know 100% for sure would be to call the mfg and ask them.
 
I think that's what the Hartridge 400, 700, and 2500 stands used as there is no variable speed pulley-belt drive like the older stands used. The older drive I'm looking at is simple and works, has up to 450 RPM in low range, up to 4500 in high range. I've seen a 2500 Hartridge that had trouble holding the correct speed when the thyrister drive went bad and was very expensive to repair.
 
I picked up a Cedarberg on craigslist a few years ago, and it's great! It runs my bandsaw, surface grinder, and bridgeport. All at once or one at a time. Money well spent.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top