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

The first of 2 parts covering the entire process of building a rotary phase converter. RPC theory( How electric motors work, the difference between single phase and three phase motors, why phase converters are necessary, and how a rotary phase converter works), idler motor examination and testing, mobile base build, and automatic start sequence design and testing.

The plans referred to in the video can be found here:

[AM-dnlk]

This was an excellent theoretical overview of how motors, 3 phase and, 1 phase and rotary phase converters work. Thank you.

[ecvolt]

Very knowledgeable !! gives a good understanding of the inter-relationship of the three phase motor acting as a motor and also as a generator. I like how you moved on to the starting capacitor and the relay well done. thank you for sharing your knowledge

[ssnoc]

This is Excellent! - I have been searching a long time for a basic understanding of windings and phase induction. I’m trying to teach myself how to re-wind a motor, but there is nothing in English on YouTube. Your excellent video is helping me understand and I Thank You 🙏

[propertypaul]

The drill start part reminded me of my first converter ; I used a rope to start it. That was the 'temporary' method that I used for about five years.

[keithgibbons]

Thank you for taking the time and effort to make this VERY informative video. It is a big help to us DIY with limited electrical knowledge!

[paolo]

I thought i knew how induction motors worked for years but i learned It only After this video and some sperimentation

[chadjsaul]

I learned a lot from your build. Great job explaining along the way. Thankful for the knowledge!

[MrWaalkman]

Excellent video!

Small point, but what the Buildist refers to as a "Time delay" is usually referred to as "phase shift". You need that phase shift to get a motor (any AC motor) to start to rotate on its own. You can do this with capacitors as shown, but it can be done with inductors (coils) as well. The inductor option is heavy and expensive which is why caps are the go-to option for starting.

For instance, small AC motors such as the ones powering bathroom fans are what's called "Shaded pole" motors. This is the copper bar that goes across part of the motor. This is inefficient since shorting out part of your core robs the motor of power. But no capacitor is required to start the motor, and it's fine for small motors.

BTW, a relay with an AC coil will have the same phase shifting setup.

[richardyantz]

Great video.Answered alot of questions i had

[BadKarmaFab]

Great video! Did you scrap out an elevator roller guide to build your motor dolly?

[PeterTremonti]

I have a question about your diagram at the 9 second mark. I'm wondering if the Countdown DPDT Relay is drawn correctly in the deactivated position or if I'm just misunderstanding it. It looks like when the timer comes on (as drawn) that the start capacitors would be disconnected instead of connected. My other question is, what's the benefit of using 24VDC instead of just straight 120V to power a countdown relay and solid state relay?

[bradsmith]

I apologize if I missed it but could you provide any sources I might get a 1200uF start capacitor from? Also what breaker size was your 20hp idler drawing from? Thank for the excellent video and very clear process description you have provided.

[RichardKandarian]

Is your idler motor configured as wye or delta? Your schematic shows wye but I want to double check.

[ICBOY]

Hey Thanks so much!!!! Great video!! 👍👍👍

[garthkennedy]

A question; If the the 220 single phase, is fed into a 3 phase transformer producing 380 volts, having a capacitor on the third leg on the 220 input so 3 phase power comming out of the transformer, then fed into the idler produce greater torque?

[ForCheapTimeS]

Excelent video! The motor being used is a three phase idle motor correct?

[victoryfirst]

Can you build a phase converter that is perfectly balanced between the phases ???? How close can the voltage balance be between legs ??? Nice video with lots of information on the subject. VF

[joemancino]

Do you think it would hurt to use a starter capacitor value above what it should be rated? My motor is a 5HP 230/460 motor, so if it is approximately 70uF per HP, then 360uF would do the job, but I am finding ones cheaper in the 750uF range. Do you think that the extra capacitance would hurt or do you think it might make the startup even more efficient? I'd imagine the extra capacitance would definitely take more time to charge up and thus it would need to be in the circuit a little bit longer. My gears are turning lol. Great video by the way!

[mrmattable]

Hey I got my 15hp Baldor motor phase converter wired up, everything works great, but just idling it uses 42amps on 240v!! Start running my milling machine with a 7.5 hp motor and it’s drawing 50+ amps!!
The 42 amps at an idle seems like a bit much? Did I wire something wrong??

[GAJT]

For breaking loose rusted nuts, bolts, etc., I like using a mixture of 50% acetone and 50% Automatic Transmission Fluid (ATF). I load it up into a syringe or a pistol pump oiler... It works great! If I get a wild hair... I'll replace 10% of total volume with Marvel Mystery Oil... shake before every use