# Video of 7.5 hp Rotary Phase Converter



## marcaap (Apr 9, 2013)

Well, here's another successful story for 'custom built' rotary phase converters:
Attached is a video of a 7.5hp Rotary Phase Converter that I built using a combination of 4-5 different plans.


[video=youtube;Y5TGZThIy38]https://www.youtube.com/watch?v=Y5TGZThIy38&amp;feature=youtube_gdata_player [/video]

I want to take the time to say thanks for the fabulous information on this site!

Paul​


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## Nightshift (Apr 13, 2013)

marcaap said:


> Well, here's another successful story for 'custom built' rotary phase converters:
> Attached is a video of a 7.5hp Rotary Phase Converter that I built using a combination of 4-5 different plans.
> 
> 
> ...


Paul, an excellent vid of your RPC. Thanks for sharing. I am thinking about building one similar and am wondering if you have put together the list of parts needed (especially cap sizes and relays). Also do you have the wiring diagram that you've used? I really like your idea of powering the contactor coil via your shop lights. Very clever especially when you have the idler motor outside where you can't hear it running. I've also see some RPC that have added three 0-300v analog panel meters to the control box so you can see if each of the 3 legs of power is balanced. I'm not sure how one goes about balancing those legs, but assume it is by changing the size of the run caps? Bill


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## Daver (Apr 13, 2013)

Great video! Be carefull poking around in that box with a screw driver, those are some pretty hefty capacitors.

On you light switch for the 24v transformer; I would be worried that someone, someday will inadvertently throw that switch while you are using one of the machines!  My wife for instance, will flip one bank of lights to get my attention if it is noisy in the shop and I can't hear her call me. I think I would wire up the transformer with its own switch on the converter panel, and wire up a 24v red indicator light on the face of the panel, or maybe up the wall a ways where it would be seen from anywhere in the shop.  Then a quick glance back on the way out will remind you...or if its after dark,the red lighting in the shop will remind you...  Not trying to be a safety nancy or start a flame fest or anything, just not the way I would do it...

p.s. I'm jealousy of your shop space and equipment!


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## marcaap (Apr 13, 2013)

Yeah Daver, you're right about the 'juice' in that box and that's the reason I have the power source unplugged while I was filming for the video.  

I understand your concerns about the light switch and no offense taken at all!


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## marcaap (Apr 14, 2013)

Bill,
I sent you a PM regarding your questions.


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## marcaap (Apr 17, 2013)

Nightshift said:


> Paul, an excellent vid of your RPC. Thanks for sharing. I am thinking about building one similar and am wondering if you have put together the list of parts needed (especially cap sizes and relays). Also do you have the wiring diagram that you've used? I really like your idea of powering the contactor coil via your shop lights. Very clever especially when you have the idler motor outside where you can't hear it running. I've also see some RPC that have added three 0-300v analog panel meters to the control box so you can see if each of the 3 legs of power is balanced. I'm not sure how one goes about balancing those legs, but assume it is by changing the size of the run caps? Bill



Bill,
Attached is the list of the items from Grainger, as well as the main schematic that I used.  Important to remember that the potential relay should be oriented in the 'up' position.  Let me know if you have any other questions, I'll be glad to help.

You'll have to click the link to download, then open in browser.

https://dl.dropboxusercontent.com/u/24231093/Rotary Phase Converter parts @ Grainger.webarchive


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## Nightshift (Apr 17, 2013)

Paul, thanks for the wiring diagram and the parts list. I just printed them both out so I now need to study and digest your stuff here. I'll be back if I have questions. Thanks again for sharing. Cheers, Bill


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## Jkassis (Apr 20, 2013)

Hi Paul, Thanks for the info on this converter. Curious as to the RPM (1725 or 3450) of the 3-ph motor you used and where to get one at a reasonable price. Thanks! Jerry


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## marcaap (Apr 21, 2013)

I'm not certain on the rpm of the motor as there are no tags on the motor at all, in fact I had to ohm the 6 leads to determine how to terminate the wiring.  As for where to purchase a motor, a salvage/scrap yard would be a good start. 



Jkassis said:


> Hi Paul, Thanks for the info on this converter. Curious as to the RPM (1725 or 3450) of the 3-ph motor you used and where to get one at a reasonable price. Thanks! Jerry


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## 7thKahuna (Dec 17, 2016)

Hello Paul. Thanks for posting the video. I discovered it several months ago but it took a bit of additional research before I understood what you had put together. I think I've got a pretty good handle on it now. Two questions, you mention a parts list above. I'm wondering if that is still available. I'm trying to match yours and though I think I have found the right contactor, a part number would be helpful. Same would be true for the capacitors. Second, you mentioned somewhere that this was originally designed for a 10hp motor. Are the capacitors then tailored to the hp or perhaps even to the individual motor? Somewhere there was a mention of a capacitor value that didn't match the plan. Perhaps I misunderstood but, and I suppose this is the hearth of the question, are the capacitor values in the plan just the starting point and tailored to each installation?

I just received the Steveco relay yesterday. Time to pull the rest of the parts together. Thank you for your time.


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## 4GSR (Dec 17, 2016)

For starting your "pony motor" on your RPC it doesn't take a lot of starting capacitors as it would on a static converter.  That shown in the diagram in the above post is sufficient in my opinion.  If by chance the motor is sluggish when getting up to RPM, add another capacitor in parallel to the starting circuit. You won't hurt the system by having too many capacitors.  But it will be obvious if too many are in the system.  Motor will over run on one of the legs momentary.   Ken


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## Keith Foor (Dec 18, 2016)

Nice job. Only thing I saw that I questioned was using the white wire on your power cable as a line source.  220 single phase wired by code would use the black and red as the hot legs and the white as neutral.  
Other than that, I was never a fan of direct wiring a potential relay for start caps.  The current rating can be easily exceeded causing the contacts to stick and hold the start caps in the circuit causing a high 3rd leg voltage and then failure of the start caps (blowing up).  Personally I use a timer relay set for the amount of time required to spin up the idler motor and it controls a heavy duty contactor that switches the start caps in and out of the circuit. 

Other than those small things I saw the build quality is great.  Good wire management, heat shrink on all the crimp terminals good mounting of the start and run caps.  Looks as good as any I have ever seen or built and much better than a number of them I have worked on in the past.


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## Smithdoor (Dec 18, 2016)

Here a drawing I have used
Simple and low cost around $25.00 for all parts from Amazon

The lowest cost was a I think was 5HP 3phase motor and a rope a lawn mower and pulley 


I was how it worked by throwing switch and pulling the rope at same time. I did work good too.
Dave


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## 7thKahuna (Dec 19, 2016)

4gsr said:


> For starting your "pony motor" on your RPC it doesn't take a lot of starting capacitors as it would on a static converter.  That shown in the diagram in the above post is sufficient in my opinion.  If by chance the motor is sluggish when getting up to RPM, add another capacitor in parallel to the starting circuit. You won't hurt the system by having too many capacitors.  But it will be obvious if too many are in the system.  Motor will over run on one of the legs momentary.   Ken



Thanks Ken, for the input. I very much appreciate it. I know enough about electricity to keep myself out of trouble but not so much as to feel comfortable changing the plan without asking questions first. From your comments and others I have read, it sounds as though the capacitors are pretty straight forward to adjust. Obviously, just don't short a charged capacitor. You'll be in for a bit of a surprise.



Keith Foor said:


> ...  Other than that, I was never a fan of direct wiring a potential relay for start caps.  The current rating can be easily exceeded causing the contacts to stick and hold the start caps in the circuit causing a high 3rd leg voltage and then failure of the start caps (blowing up).  Personally I use a timer relay set for the amount of time required to spin up the idler motor and it controls a heavy duty contactor that switches the start caps in and out of the circuit.



Interesting thought Keith. The Steeveco relay seems to be popular in this application. Do you have first hand knowledge of sticking contacts or is this more of a theoretical concern? It makes sense but I find myself wondering if the issue is the design or an underrated relay for the application. I would be interested in knowing more about your design. You then have two contactors in your system?

Paul, if you happen to see this, I'd still be interested in your parts list.


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## Keith Foor (Dec 19, 2016)

Yes, I do have first hand knowledge.  I build and repair RPC's to pay for my machining addiction.  I have seen a number of them that the potential relay had failed closed and blown the capacitors.  The contacts are typically not rated for the amount of current required to start a 3 phase motor off single phase power.  If you look at the expected full load start current and then double it that's about what it takes to spin one up.  a 15 HP motor can easily draw 90 amps starting because you are forcing it to start in a manner that it's not designed to.  The 15 or 20 amp rated contacts in a potential relay are just not suited for that sort of power being run across them and it can over time weld the contacts.  That pops the start caps in very short order.  There are a couple easy ways to get past it.  First is to use the start button (momentary) contacts to close a contactor that controls the start caps.  You just hold the start button until the motor spins up.  Now this only will work if you have a double momentary open set of contacts on the start button.  Of course the other set closes the input contactor. 
I actually run three contactors in most of my setups.  One controls the input power, it sets between the motor and the single phase power feed. The second is a single or dual pole that controls the start caps. and the third connects to the output and the run caps.  That way I am not fighting the L2 to L3 capacitors against the start caps and I always have positive control of the output.  I also ALWAYS use pushbutton start that will fail off when the power is interrupted.   It's safer that way so I don't have a machine spinning down and all of a sudden restart or have a power failure and the RPC restart when the utility comes back on.  

Is the third contactor necessary, probably not.  One thing I do with my design is build them to be expandable.  Say you wanted a 100HP RPC.  There are a couple ways to do that.  One is a huge cabinet and 800 amps of start current.  It frankly sucks just wiring it because the you need welding cable in the start circuit and connecting it to 1/4 spade lugs, which you can't really do, so you would run a bunch of wires to the multitude of start caps and have a HUGE contactor to deal with the current load.  Same thing for the input power feed.  The cool thing with RPC's is you can stack them in parallel and they become bigger.  so 2 10 HP RPC's in parallel is a 20 HP unit.  And you can start a 40 HP idler with a 15 HP RPC if it's built right from the get go.  Now 40 is the largest I have ever started with my 15 but it does it without any issue and no motor starter.... just a disconnect in line.  SO if you design timer circuits to start in steps, doing a full start on a 15 or 20 HP RPC, you can eliminate all the rest of the start caps for the other motors.  Once the first one is started, you connect the second idler motor to it and it spins up, then via a 3 line contactor you connect it's run capacitors, the HP rating has just increased by the size of that idler motor.  So a 20, a 30 and a 50 (the 20 and the 30 together start the 50) you reach 100HP load ability with start caps only required for a 20 HP idler.  The timing circuits for each individual motor in the string rely on the coupling contactor from the previous idler to apply power to it starting the timer count down.  Once the last motor in the string starts and has it's coupling to the output bus in place a final contactor closes and connects the 3 phase power output to the panel for distribution to the connected equipment.


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## Keith Foor (Dec 19, 2016)

On a side note, the one 100 HP unit I built took about 10 seconds to come all the way up and apply power to the panel so it's not a real long process for all this to happen.


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## 4GSR (Dec 19, 2016)

As Keith mentioned above using a push button with two sets normally open contacts, Like a Allen Bradly 800T type where you can stack multitudes of contacts on one push button, is all I've ever used on most of the static converters I've ever built.  I've never put an potential relay in the starting circuit.  Just hold the "start" push button in until the motor got up to speed and let go of the button.   The first one I built between my dad and I way back in the 1970's used to power a 3HP motor on a old Avey drill press we bought.  Like Keith said, once you get one motor started and running, the next one was easy to start.  We would start the drill press and once it was running, we could start the two speed motor on the Gorton mill we had back then.  So one static converter was used to power two motors the way I had it set up.

Later in life when I had my 20" Lodge & Shipley, I rigged it up with a static converter with a bank of four starting capacitors, like 375 mfd a piece if I recall and two oil filled capacitors to balance L2 and L3.  I installed a control relay that had contacts rated for about 40 amps for each contact. So I split the four starting caps between two of the contacts on the control relay..  This way I wasn't pulling all of that current thru the start button on the pendant control on front of the lathe.  Worked out pretty nice!  I've also connected time delay relays in the circuit that would keep the starting circuit energized for about 1 to 2 seconds before kicking out.  That works pretty good, too.  Ken


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## 7thKahuna (Jan 21, 2017)

Ken, Keith, 
Sorry about the delay in expressing my thanks. The holidays got a hold of me. I do appreciate your time. I am simultaneously excited to give it a go and confused by the new information. I think I am going to need to start my own thread for this project. I look forward to continuing this conversation.


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