[How do I?] My 2017 Rotary Phase Converter Build

[British Steel]

Usually you'd oversize it a bit! I'm building mine around a 9kVA (roughly 12 HP?) autotransformer (the dual-voltage primary on a big oil-cooled welder) to get to 415v ("default" voltage for UK 3-phase machinery), followed up by a 5.5 kw / 7.5 HP idler motor, and have a second 3 kw (4 HP) motor I may add, complete with its balancing caps, as a switchable-in reserve should I need the full 9 kw / 12 HP - although I think it's unlikely I'll need to! My lathe's double-VFD-ed, mill runs near-as-dammit 4 HP at full chat. I hope it's going to work as well as I expect...

Note that it's often recommended that the idler motor in the convertor's rated 1.5 times the load power for reliable starting, difficult loads (starting lathes without a clutch but with e.g. a 12" 4-jaw in highest gear, big compressors f'rinstance) may need an idler motor up to 2 x...

Cap selection: Depends... RPCs can work fine without balancing (running) caps, but the differing voltages from the three phases may be difficult for the load - more so if the attached machine has electronics / has a transformer for control relays etc.. Static convertors often have switches to select the caps according to the load, there's no reason you shouldn't do this on a rotary (or if you really enjoy the work, no reason you couldn't put together an auto-balance system with caps switched in by relays/contactors).

The Practical Machinist forum (http://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/) has a lot of material to work through, describing / advising on convertors from the simplest rope-start, cap-less to clever stuff with potential relays, auto-balancing (within limits) etc., very educational but not the friendliest place in the world though...

Dave H. (the other one)

 

[scsmith42]

I'd like to resurrect this old thread with a new question. For starters, many thanks to Keith and others who have shared some very insightful information.

I've recently replaced a 30hp Phase-a-matic converter that I've had running in my shop with a 40 hp converter. I started with a 1075 rpm Lincoln motor and bought a converter kit from Croman Converters in California. I'm having two problems with my converter.

First, the voltage on the generated leg is only 190VAC, whereas the voltage across L1 and L2 is around 220. So it looks like my generated leg is 30V low. Presumably I need to add some run cap's to the system?

Second, the converter output is different from my former converter, in that all of my equipment is now running backwards. My shop is set up to run off of either a 225KW Kohler generator (480VAC output), or I can flip a transfer switch and run my 240VAC 3 phase equipment off of the converter w/o having to fire up the generator. Because of this, I don't want to rewire all of my equipment motors to reverse direction, because then they will run backwards when I'm using the generator.

Is there a way to change the converter wiring so that my equipment motors run in the correct direction?

Thanks much.

Scott

 

[Eddyde]

I'd like to resurrect this old thread with a new question. For starters, many thanks to Keith and others who have shared some very insightful information.

I've recently replaced a 30hp Phase-a-matic converter that I've had running in my shop with a 40 hp converter. I started with a 1075 rpm Lincoln motor and bought a converter kit from Croman Converters in California. I'm having two problems with my converter.

First, the voltage on the generated leg is only 190VAC, whereas the voltage across L1 and L2 is around 220. So it looks like my generated leg is 30V low. Presumably I need to add some run cap's to the system?

Second, the converter output is different from my former converter, in that all of my equipment is now running backwards. My shop is set up to run off of either a 225KW Kohler generator (480VAC output), or I can flip a transfer switch and run my 240VAC 3 phase equipment off of the converter w/o having to fire up the generator. Because of this, I don't want to rewire all of my equipment motors to reverse direction, because then they will run backwards when I'm using the generator.

Is there a way to change the converter wiring so that my equipment motors run in the correct direction?

Thanks much.

Scott

Just swap any two output leads and the direction will reverse.

Also, dig around in this thread you will find useful info and links to more on balancing the output voltage.

Rotary Phase Converter Rebuild / Build

Hi all, I just hooked up a used, Snyder brand, Rotary Phase Converter to my newly acquired lathe (more on that soon). It works but makes excessive noise & vibration, especially when running under no load condition. It sounds like its vibrating at 60hz so my thought is its electrical in nature...

www.hobby-machinist.com

 

[Datum1M]

Hi Everyone,

My first post on this forum and this old thread.

I am buying old 3 phase machines and like many only have a single phase supply to my shed, having read a lot online I think the flexibility of a Rotary Converter would work best for me, because some machines have more than one 3 phase motor of different HP outputs.

So I was thinking of buying a secondhand 15/20 HP slave/ideal motor for around $200/400 AUD (could buy new if old type of motors are not compatible), the largest HP requirement I have is a Ingersoll Rand T30 air compressor at 7.5 HP. My understanding is the slave motor will produce 3 phase electricity but not at its full HP rating and capacitors are needed to both start the slave motor and once running balance the ghost leg.

I was wondering if it would be possible to use a VFD to start and run the slave motor (it would need to be a large one so maybe would cost around $1000/1500 AUD), I am thinking that this would eliminate the need for all these capacitors, with the electronics inside the VFD sorting out a balanced 3 phase supply to the slave motor. The slave motor could be set by the VDF to run at is optimum RPM to both keep it cool and produce a good amount of balanced 3 phase power to run my old machines.

I have also seen a YouTube video where a VFD was powered by Solar panels and where I like in Australia we have good sun light for most of the year, so if the above would work, I would then look at powering it up using Solar where it switches to single phase when there is not enough sun light.

 

[Eddyde]

Hi Everyone,

My first post on this forum and this old thread.

I am buying old 3 phase machines and like many only have a single phase supply to my shed, having read a lot online I think the flexibility of a Rotary Converter would work best for me, because some machines have more than one 3 phase motor of different HP outputs.

So I was thinking of buying a secondhand 15/20 HP slave/ideal motor for around $200/400 AUD (could buy new if old type of motors are not compatible), the largest HP requirement I have is a Ingersoll Rand T30 air compressor at 7.5 HP. My understanding is the slave motor will produce 3 phase electricity but not at its full HP rating and capacitors are needed to both start the slave motor and once running balance the ghost leg.

I was wondering if it would be possible to use a VFD to start and run the slave motor (it would need to be a large one so maybe would cost around $1000/1500 AUD), I am thinking that this would eliminate the need for all these capacitors, with the electronics inside the VFD sorting out a balanced 3 phase supply to the slave motor. The slave motor could be set by the VDF to run at is optimum RPM to both keep it cool and produce a good amount of balanced 3 phase power to run my old machines.

I have also seen a YouTube video where a VFD was powered by Solar panels and where I like in Australia we have good sun light for most of the year, so if the above would work, I would then look at powering it up using Solar where it switches to single phase when there is not enough sun light.

You may be able to use a VFD to start the idler motor then disengage it, you couldn't leave it in the loop, it won't "sort out" the phase imbalance, capacitors do that. Besides, the capacitors work fine, a fraction of the cost of a VFD and are very reliable. Also the RPC's sine wave output will be cleaner. To start a 7.5 hp motor you should have around a 10 hp motor, 15 will be more than enough. Once going, a 15 hp idler will give you roughly 45 hp total motor load. It may seem a bit daunting at first but RPC's are fairly easy to build. Here's a link to my build, there are further links in that thread to other builds as well.

 

[Datum1M]

Hi Eddy,

Thanks for your response, I have read your thread, but your Converter build/ wiring diagram seems not to take the Neutral into account and is also a USA type build where you have L1 and L2 coming in from the street. In Australia we are more akin to the UK system where we get 240V from the street made up of only one Live, Neutral and Earth, so we really need to make 2 ghost legs. I also want to keep the Neutral at the Star point and not a floating Neutral like what is produced with many RPC's, this is important to me for the following two reasons. 1) The insulation on my old machine motors is poor (made out of cotton) and having a floating Neutral could/will over time cause the motors to fail. 2) Some of my machines also have a Single phase requirement e.g. 240V task light or small Single phase motor. So having a Neutral within the RPC build means I can tap into just one of the 3 phases and the Neutral to power up these Single phase elements, thus not having to change the switch gear on my machines and run more wires back to the consumer board to another breaker.

I was hoping a VFD would work because it takes the 240V Single phase and first turns it into DC and then back to 3 phase which I thought it would do in a balanced way therefore not requiring capacitors to balance each new additional leg, however having read more I see that once the Idle motor is running (the RPC generator of electricity) it will still be constantly monitored by the VFD which means any machine which I turn on will add load which in turn will effect how the VFD performs.

I am still researching and due to another constraint of limited AMP's to domestic supplies in Australia (I only have about 40 AMP's to my shed to play with) I am looking to use a Single phase 4 pole (running at approx. 1500 RPM) motor to get the large 3 phase motor rotating before adding power to get it started/running, this would do away with the need for Starting Capacitors and the AMP's they would require to get the RPC motor running

 

[Eddyde]

Hi Eddy,

Thanks for your response, I have read your thread, but your Converter build/ wiring diagram seems not to take the Neutral into account and is also a USA type build where you have L1 and L2 coming in from the street. In Australia we are more akin to the UK system where we get 240V from the street made up of only one Live, Neutral and Earth, so we really need to make 2 ghost legs. I also want to keep the Neutral at the Star point and not a floating Neutral like what is produced with many RPC's, this is important to me for the following two reasons. 1) The insulation on my old machine motors is poor (made out of cotton) and having a floating Neutral could/will over time cause the motors to fail. 2) Some of my machines also have a Single phase requirement e.g. 240V task light or small Single phase motor. So having a Neutral within the RPC build means I can tap into just one of the 3 phases and the Neutral to power up these Single phase elements, thus not having to change the switch gear on my machines and run more wires back to the consumer board to another breaker.

I was hoping a VFD would work because it takes the 240V Single phase and first turns it into DC and then back to 3 phase which I thought it would do in a balanced way therefore not requiring capacitors to balance each new additional leg, however having read more I see that once the Idle motor is running (the RPC generator of electricity) it will still be constantly monitored by the VFD which means any machine which I turn on will add load which in turn will effect how the VFD performs.

I am still researching and due to another constraint of limited AMP's to domestic supplies in Australia (I only have about 40 AMP's to my shed to play with) I am looking to use a Single phase 4 pole (running at approx. 1500 RPM) motor to get the large 3 phase motor rotating before adding power to get it started/running, this would do away with the need for Starting Capacitors and the AMP's they would require to get the RPC motor running

You are welcome,
Though I only know a little about foreign power distribution, I'm pretty sure three phase motors don't ever require a neutral? I do get the need for the neutral for ancillary components, in my design I did bring in a neutral for the control circuit. Although in contradiction to my final schematic drawing, I brought in a separate 120v line for that circuit and did not tap off one of the incoming legs. I suppose you might be able to get a transformer to split the single phase into two "legs" (as is done here before the mains enter the home). Such a transformer will provide a centre tapped neutral. Then you could use my or similar RPC design to provide 240v three phase power. I don't know if you can generate two "ghost legs"to run a RPC, have you seen such designs?

Yes, In my opinion, you cannot use a VFD to "regulate" a RPC. VFDs are very sensitive to dynamic conditions, interruptions, etc. They are meant to control only one motor (or group of identical motors) at a time. You cannot have any switches or other such devices between the VFD and the motor, they must be wired directly, all control is done from the VFD, thus the need to rewire all the machines controls. I actually went through the same thought process when I initially was looking into creating three phase power, I never saw any such designs and upon learning the requirements of VFDs, I abandoned the pursuit. However, you can use multiple VFD's to convert single to three phase for each motor you have but as mentioned, it will require rewiring the machines controls, but it may be the easiest way out in the log run. I currently have 5 VFDs on various machines, in addition to the RPC, they offer several advantages, speed control, reversing, breaking, current & torque limiting etc. There must be people in your country with the same problem, what are they doing?

Good luck with your endeavor.

Eddy

 

[mksj]

An RPC just generates the 3rd phase, and uses the existing 2 legs. Not sure how RPC's would be setup in Australia since your 240VAC is N to 230VAC, so the RPC design would be different. Might be worth looking into systems for your power grid.
https://phasechanger.com.au/

A VFD generates all 3 legs but the output is PWM and typically is only designed to be directly connected to the motor, not switch gear or control systems. You are also limited as to how the VFD can deliver short term power increases, so the locked rotor startup current would be too high when switching in downstream motors. Parameters for VFD's a motor/application specific.

As Eddy outlined it is possible to use a VFD for each specific machine, but the operation controls need to be rewired to use the low voltage control inputs of the VFD. You typically cannot use them as a power source for the machine and use the high voltage switch gear in the machine to control the motor. It can damage the VFD and/or trip an error code. The other major problem is that you have a 40 Amp service, which limits you to around a 3 Hp motor, possibly a 5Hp motor with a soft start. A 5 Hp single phase motor has a running current of around 28-32A. A 3.7kW (5 Hp) single phase input VFD might be able to run off of a 40-50A circuit breaker.

 

[Datum1M]

You are welcome,
Though I only know a little about foreign power distribution, I'm pretty sure three phase motors don't ever require a neutral? I do get the need for the neutral for ancillary components, in my design I did bring in a neutral for the control circuit. Although in contradiction to my final schematic drawing, I brought in a separate 120v line for that circuit and did not tap off one of the incoming legs. I suppose you might be able to get a transformer to split the single phase into two "legs" (as is done here before the mains enter the home). Such a transformer will provide a centre tapped neutral. Then you could use my or similar RPC design to provide 240v three phase power. I don't know if you can generate two "ghost legs"to run a RPC, have you seen such designs?

Yes, In my opinion, you cannot use a VFD to "regulate" a RPC. VFDs are very sensitive to dynamic conditions, interruptions, etc. They are meant to control only one motor (or group of identical motors) at a time. You cannot have any switches or other such devices between the VFD and the motor, they must be wired directly, all control is done from the VFD, thus the need to rewire all the machines controls. I actually went through the same thought process when I initially was looking into creating three phase power, I never saw any such designs and upon learning the requirements of VFDs, I abandoned the pursuit. However, you can use multiple VFD's to convert single to three phase for each motor you have but as mentioned, it will require rewiring the machines controls, but it may be the easiest way out in the log run. I currently have 5 VFDs on various machines, in addition to the RPC, they offer several advantages, speed control, reversing, breaking, current & torque limiting etc. There must be people in your country with the same problem, what are they doing?

Good luck with your endeavor.

Eddy

I have seen one rough drawn design and I have used it for the attached PDF (not sure if the symbols I have drawn are correct), I have limited AMP's to my shed so was looking at using a 240V "Pony" motor to spin the Idle motor up to speed thus saving the large current required with the Starting Capacitors. I would look to use "V" belts on the Pony, but need a way to engage/disengage them once the Idler is up to speed, also I am looking at a 20/30HP Idle motor.

I have not found anything online for Australia RPC's apart from companies that make them for sale and they start at $3K for just a low HP Converter, so better to build my own, if possible.

I am looking to use a 50/60's old style Brook motor for the Idle motor because again I have read they are more forgiving within a RPC build, but finding one in Australia is quite hard.

 

[Datum1M]

An RPC just generates the 3rd phase, and uses the existing 2 legs. Not sure how RPC's would be setup in Australia since your 240VAC is N to 230VAC, so the RPC design would be different. Might be worth looking into systems for your power grid.
https://phasechanger.com.au/

A VFD generates all 3 legs but the output is PWM and typically is only designed to be directly connected to the motor, not switch gear or control systems. You are also limited as to how the VFD can deliver short term power increases, so the locked rotor startup current would be too high when switching in downstream motors. Parameters for VFD's a motor/application specific.

As Eddy outlined it is possible to use a VFD for each specific machine, but the operation controls need to be rewired to use the low voltage control inputs of the VFD. You typically cannot use them as a power source for the machine and use the high voltage switch gear in the machine to control the motor. It can damage the VFD and/or trip an error code. The other major problem is that you have a 40 Amp service, which limits you to around a 3 Hp motor, possibly a 5Hp motor with a soft start. A 5 Hp single phase motor has a running current of around 28-32A. A 3.7kW (5 Hp) single phase input VFD might be able to run off of a 40-50A circuit breaker.

mksj Thanks for your reply.

I really don't want to use multiple VFD's, because they would all need to be wired back to the consumer board taking up more space and AMP's than just one large RPC, (plus I am not sure if they are good for old motors with poor insulation), which I have also read can become self generating (if that's the right terminology) in that the more machines that are turned on (large to small) the more generated electric is produced.

Thanks for the link, I am aware of the company mentioned within the link, but their RPC's are more than I want to spend for the size that I want to achieve.

With regards to your comments regarding AMP's, my understanding is that I need to take into account the Line Voltage of the 3 phase motor within my RPC build, so looking at the attached chart the Line Voltage requirement in AMP's from any one Leg to Neutral is 39 AMP's for a 30HP (22kw) motor. It is this one leg (lets call it L1) that I need to fire up to get the Idle motor spinning, once spinning the 450V Capacitors will balance the 2 ghost legs (L2 & L3).

I have based my design ideas on the following link (a series of 4 YouTube videos) it is a guy in the UK that builds a RPC with a 17.5HP Idle motor using just a 20AMP breaker