Building a Rotary Phase Converter. Part 1: Theory, initial testing and proof of concept 

Same here. And changing phase rotation was a piece of cake. :)

Glad it was helpful!

I bought one of these: www.ebay.com/itm/223030502520 I only had my idler hooked up to a double 30 for testing, but best I recall it would need to be higher if I intended to pull anywhere near its full capacity. It's at least the sum of the amperage of all your motors that you'll run simultaneously.

Good catch! Not everybody would recognize that piece.😁

It's hard to say for sure, but it is generally fairly forgiving. My GUESS is that it would work. But I wouldn't bet much money on it...

I think it's possible in theory... but there are two problems that I know of: 1. Capacitors are not infinitely variable, so you'll always have to use a capacitor whose value is an approximation of perfect. You could only get "perfect" if you had the perfect size capacitor. and 2. The capacitance for perfect balance is dependent on the load. So you have to shoot for an approximated load when you're doing the balancing step. The more perfect your approximation of load, the better your balance can be achieved. But if you need to support differing loads (2 or more different machines) then your "perfect" balance can only be for one of them. THE GOOD NEWS IS that it makes very little difference whether the balance is "perfect". Anything beyond the steps in this video is only going to produce tiny increments of efficiency. My understanding is that this method produces something that's about 97% efficient, and if you went to extreme measures you might achieve 98.5% efficiency. A very small benefit.

@@TheBuildist Thank you so much for clearing up my thinking on balancing the legs of the phase converter and the limit of efficiency that can be achieved. Good day to you Mr, The Buildist. Look forward to more great videos to come from you Sir. VF

I had another question for you Sir ??? Would using an electronic phase converter have efficiency closer to 99 plus percent ?? Just an idea The Buildist. Thanks VF

I'm not certain that I drew it correctly. But if you follow the link to the plans (in the description) you'll find on the righthand side a detailed step through of the start sequence. The step through is accurate as to what I built. I've since been convinced that a single on/off button was a mistake. That it should have a master "on/off" switch and a separate momentary push button to initiate the start sequence. It's safer in the long run. I'm not losing sleep over this one, but the other config is superior. Lastly, no, the 24v dc is not required. It happened that I had spare 24v control devices, so I converted to that in order to utilize them and be able to make use of the solid state relay. It could all conceivably be 240 or 120ac relays, but I don't know if you'll find ac-triggered solid state relays. And I wasn't confident that the response timing for the start capacitor was going to be precise enough using a mechanical relay. Not saying it can't work, but I had more confidence in the solid state route.

I'm not qualified to answer. But it sounds like you're thinking of using a transformer as a phase converter. I'm not aware of that being possible.

At the moment, I have the 220 running the 3 phase idler motor ( as you have described) giving me 3 phases of 220. These are attached to the the 3 phase 220-380 transformer and the result is 3 phases of 380. Drives a post drill and other gear....but they don't have a great deal of torque........ Many thanks for your reply!

Ok, now I understand. My only input is to point out that when you step up in voltage, you step down in amperage. So if a 10HP phase converter can support a 6.6hp motor at 240 volts, it can only support a ((220/380)*6.6)=3.82 HP motor at 380 volts. And that's if your transformer were 100% efficient, which it's not. I'd guess your rotary phase converter may be too small.

@@TheBuildist The idler motor is 6 HP and the moters it is driving are no more than 3 HP. I hadn't realized about the loss of power, with increase of voltage. Thanks once more!

Sound like a bad bearing in my opinion . If it had a bent shaft, the motor would be vibrating. It is not vibrating, hence I’d bet it just needs two 25.00 bearings. Simple fix for a 20hp motor. And…. Excellent video. Subscribed.

my take on it too, bearing, it should be almost silent

@@stuarth43 I'm using a 15hp motor for my RPC, and it would run fine for a while but start to howl and make whiny noises. After a $450 bearing replacement and lube it's working very silently now. I think the grease had hardened after sitting idle too long.

The does strike me as pretty high. It's impossible to say why from here. Could it be that the idler motor has a bad bearing and is drawing a lot of current just to stay on speed? Or did you do the full capacitor balance procedure? I know that the capacitor balancing reduces the current meaningfully but I'm not sure how much. I will say that the jump and current from 42 amps to 50 to run your milling machine motor is about right. All the current for both motors is going through your phase converter. So going up by 8 amps to run that extra motor is about right. But the 42 amp baseline is definitely higher than what my 20 horsepower idler was drawing.

@@TheBuildist ok thanks for the reply!, the motor spins freely. I’ll have to go through and check my wiring. I haven’t capacitor Balanced the output yet, nor do I have that capacitor on the input side of the motor yet either.... I had a start capacitor explode so I’m waiting for more capacitors off amazon. I’ll get back to you when I balance it :)

That's a bummer. Could it be that I found a 400V version? It's been a while for mine so I don't recall the precise details. But it never gave me the slightest trouble.

@@TheBuildist Weird. Ended up buying four "270-324uF" caps, 330V. and it's running! Playlist of three videos... ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9vopNRoZM_Q.html Thanks for your videos, they were helpful!

@@turbo2ltr That's fantastic news! Your build looks great so far. Nicely done.

The RPC pony motor needs to be at least 33% bigger than the biggest motor you'll use. In your case a 15hp pony would work, but if you can do 20, it gives you more margin of error. The RPM of the pony motor doesn't matter. Good questions!

I was told the higher the voltage of the start capacitors is better. I am interested in the micro farads it is rated. Is this true?

@@maryjaneeclipsemendozaport1109 You're looking for voltage rating at least as high as what you need, the higher the better. For my 230 volt motor I bought an affordable 250Volt capacitor, which is adequate, but I would have bought a 350 or 400V rated if it were similarly priced. More than enough headroom is a good thing. Then the guideline is you need about 70MF capacitance per horsepower of motor. So for my 20HP motor, 1400MF is ideal. I found an attractively priced 1200 MF cap and decided to give it a try, and it worked just fine. So at least enough voltage rating for what you'll be sending through it, the higher the better, and about 70MF capacitance per horsepower motor that you intend to start with it. I'm no expert, but it has worked for me on two different builds so far.

Thank you very much, this is my husband's project just so you know, I will continue on my project

Yes, you can run a 3 phase welder off of a rotary phase converter. But I don't know how to get the voltage up to the 408 you need.

What if you could wire two and one together 220x220 ,I do not know how to come motor probably have come off another 220circuit then add a leg from motor very confusing.

@@Apollo1van I don't think that would work. I don't think the voltages would add up like that. There would have to be some kind of transformer involved, but I don't know the specifics.

The more precise statement would be three times the torque. And it's not violation of conservation of energy it's simply efficiency. Three phase are three times as efficient of turning electrical current into rotation as single phase. To be clear: I'm neither a professor nor an engineer. So I could conceivably be wrong. But I'm 100% confident that three phase are profoundly more efficient even if not fully three times as efficient. But Google could tell you for sure.

And also I'm from the US and how do you get 240 volts from one wire here I have two wires 120 each

@@louiehostetler7327 Louie, I'm also in the US. The RPC is fed by two wires that are 120 v each. They add up to 240 in relation to each other. if you go through the video you'll see that I do have the third wire, the neutral, wired into the controls of my RPC. But it's only because I have some internal components that need 120 volts to operate. if every part of my components were 240 volts, then I wouldn't even need the neutral wire to be fed into my RPC. As far as 480 volts, to my understanding you would have to get a transformer to step up from 240 to 480 and then feed the output of that transformer into your rotary phase converter.

@@TheBuildist okay yes I just saw part to where you explain two wires coming in and I understand 240 measures between the two but I am dealing with 480 volts I think I understand how to build a rotary phase converter that I don't understand how to get 480 volt without interfering with my house I guess I need to get some kind of Transformer

@@louiehostetler7327 You're right, you definitely need a transformer. But most 480Volt transformers will be three phase. I don't know what you'll get out of a 3 phase 240-to-480 transformer if you feed it single phase 240. If it DOES spit out 480 single phase, then you'll feed that into your 480V RPC (Made from the 480V motor) and you'll then have 3phase 480V. HOWEVER If you don't need 480V, then there's a good chance your motor can be rewired for 240V. There are a lot of 240/480 motors whose voltage just depends on how they're wired. Do you need 480? If not, see if your motor's data plate has a 240 configuration.

@@TheBuildist I have a brand new 4 sided wood planter 4 Motors 7 & 5 and two 4 horsepower motors 480 straight 1 horsepower Drive motor is the only one that has 240 / 480 I know I have a problem and you are the only one that shows a Transformer before you go to the rotary phase converter motor And I just wondered what that was and how much it cost

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AMONG many other things... I do reveal my fondness for the ONE, the ORIGINAL, THE LIQUID WRENCH. 🤣