# Rpc simple design unbalanced



## Ulma Doctor (Feb 23, 2013)

*Rpc simple design*

Here's a simple plan for an unbalanced 220/240 v single to 3 phase converter.
this design will start ANY 3 phase motor of ANY horsepower with a change of start capacitors!
keep in mind,the contactor coil is 220v in this design, adjust coil voltage for high voltage use(480v)
thanks for looking!




enjoy!


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## Rbeckett (Feb 23, 2013)

Mike,
Can you help me understand the difference between ballanced and unballanced 3 phase and what difference it could make if any.  I understand the very basic concept of three phase power from my electronics course but am at a complete loss beyond that.  So a quick primer would probably be a good idea so I can fathom all of the foibles that go along with multi phase power.  Thanks for the great looking  diagram too.
Bob


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## Ulma Doctor (Feb 24, 2013)

Rbeckett said:


> Mike,
> Can you help me understand the difference between ballanced and unballanced 3 phase and what difference it could make if any.  I understand the very basic concept of three phase power from my electronics course but am at a complete loss beyond that.  So a quick primer would probably be a good idea so I can fathom all of the foibles that go along with multi phase power.  Thanks for the great looking  diagram too.
> Bob



Thank You Bob, it's my pleasure to help out.

A balanced 3 phase circuit is a simple enough concept, all three power legs have equal voltages.
When you run a three phase motor on single phase input, the third leg is being induced(generated) rather than supplied.
this causes the third legs' voltage to be less than the voltage in the supplied legs, causing the unbalance... you can hear this in the buzz of a unloaded RPC. To balance the outputs between phases, we add RUN CAPACITORS between phases to add voltage to the circuit that is low, adding balance to the circuit, therefore operating the intended motor more efficiently , and saving money through a greater motor power factor. 
In a perfect world we could 100% balance a 3 phase motor/converter, but since our incoming power is not constant, our loads are not usually constant, and internal motor conditions change literally every second of operation. Adding capacitors are kinda like adding shock absorbing batteries to a circuit, they take low input , store it for a length of time until the capacitor fills to it's rated charge, then discharges into the circuit, raising the voltage temporarily until it empties, the capacitor fills and discharges, 60 times a second here in the US, 50 times a second in Europe and some other countries. 
Here's something interesting most do not know... A capacitor can only store DC voltage, even when used in an AC circuit.
so when we add capacitors, we are actually boosting an AC circuit with DC power to achieve an end.

I hope i have made the use of capacitors a little more clear, but if you have further questions i'm all to happy too share my knowledge. 
Drop me a message, i'll be happy to help out the best way i know how.
mike)


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## raross61 (Jul 19, 2013)

*Re: Rpc simple design*



Ulma Doctor said:


> Here's a simple plan for an unbalanced 220/240 v single to 3 phase converter.
> this design will start ANY 3 phase motor of ANY horsepower with a change of start capacitors!
> keep in mind,the contactor coil is 220v in this design, adjust coil voltage for high voltage use(480v)
> thanks for looking!
> ...



Ok couple questions here, on this drawing I have to assume that the start button (DPST switch) is a locking type and remains closed during running operation right? So I also would assume that the stop button is momentary to stop operation right? Are these switches linked together (mechanical link), like some of the start stop switches I have seen in the past? Also do you have any formulas, for how big the capacitor mfd, needs to be?


                                            Thanks Bob in Oregon


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## Ulma Doctor (Jul 19, 2013)

hi bob,
both switches are momentary
the holding circuit is provided by the contactor.
this type of wiring is used to latch the contactor until power is broken by the stop switch.
the start capacitor is operated by the momentary start switch and drops out of circuit when the start switch is opened.
it is receiving line voltage to recharge in it's off cycle.

about 30 to 50 UF per hp is sufficient to start any motor,
 i like to stay to the higher end just to get the cap out of circuit quicker!
 i have put  500UF to start 7.5 hp and 10 hp motors on single phase with this very same design

i hope the info better explains the system.
mike)


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## raross61 (Jul 19, 2013)

Ulma Doctor said:


> hi bob,
> both switches are momentary
> the holding circuit is provided by the contactor.
> this type of wiring is used to latch the contactor until power is broken by the stop switch.
> ...



Mike,

     Thanks I don't want to be a pain to you, and I very much appreciate all your information on these "static converters" !

                                 Bob in Oregon


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## Philco (Jul 19, 2013)

Mike can you show a simple diagram of how to wire the balance capacitors into the circuit. I built my RPC several years ago with limited electrical knowledge.i was so happy about getting it working & being able to run my lathe & mill that I never finished fine tuning it.
Another question is, what is the breaking point or the voltage difference between the three legs that it makes a difference if they are balanced or not.
Phil


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## Ulma Doctor (Jul 19, 2013)

Philco said:


> Mike can you show a simple diagram of how to wire the balance capacitors into the circuit. I built my RPC several years ago with limited electrical knowledge.i was so happy about getting it working & being able to run my lathe & mill that I never finished fine tuning it.
> Another question is, what is the breaking point or the voltage difference between the three legs that it makes a difference if they are balanced or not.
> Phil




Sure Phil, i can help out!!
i have seen the balance difference between legs to be 50 volts +/- the other 2 legs or a 20% difference if you want to look at it like that.
A RPC to be considered electrically balanced has only 10% difference between legs.
 i have been able to realize less than 2% for sensitive units.

Balance is important for a few reasons:
an unbalanced RPC will run hotter than balanced unit
an unbalanced RPC will run louder than a balanced unit
an unbalanced RPC will consume more energy than a balanced unit
an unbalanced RPC will have a shortened life expectancy of a balanced unit.

Phil, if you can send a PM or post a picture of you RPC i'll be happy to advise you as to how to proceed.
i'm just going to need some information from you to start.
I'm happy to help out..
mike)


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## Ulma Doctor (Jul 19, 2013)

raross61 said:


> Mike,
> 
> Thanks I don't want to be a pain to you, and I very much appreciate all your information on these "static converters" !
> 
> Bob in Oregon



Hi Bob,
 it's always a pleasure to share information whenever i can!!
mike)


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## Ulma Doctor (Aug 12, 2013)

i have pictures of a working model made from 90% recycled parts.
i purchased a new 400 UF starting capacitor and took a couple momentary switches out of my work stock, other than that everything else was recovered from other machinery, just to prove it can be done very cheaply and easily.
here's some pictures of the control box...




The enclosure was rendered from an old electric water heater timer.







thanks for looking

mike


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## rgray (Aug 13, 2013)

I had an rpc in the past that was so quiet that I had to remember to shut it down. I now have a 3 hp phoenix phase converter and it is very loud. Is it just poor quality? should I add caps to the run circuit? I actualy don't think it has a seperate start and run circuit. 
Have you had any dealings with these? Did they just compromise on capacitors using start caps full time?
It has no contactor or relays.


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## Ulma Doctor (Aug 13, 2013)

rgray said:


> I had an rpc in the past that was so quiet that I had to remember to shut it down. I now have a 3 hp phoenix phase converter and it is very loud. Is it just poor quality?
> No, it's not poor quality. the converter is just not balanced
> should I add caps to the run circuit?  I actualy don't think it has a seperate start and run circuit.
> Correct, In 3 phase motors the circuits are not separate. it is the same circuit!
> ...



We add run capacitors between all 3 phases.  as a result the generated legs power increases in proportion to the value of the added capacitors.  different capacitor values are used for different size motors and balancing requirements.
Capacitors are not one size fits all, simple calculations can be made after the loaded voltage difference between legs has been established.
Ideally all 3 legs would equal in a perfect world, but we don't live there so we strive for 10% difference between legs to be considered balanced. i personally try to be closer to 5% difference and have achieved 2% for sensitive customer units.

if there are other questions, please don't hesitate to ask. i'm happy to help out.
mike)


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## randyjaco (Aug 14, 2013)

I have  a 5hp Phoenix RPC that runs very quiet. You might want to check with Phoenix

Randy


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## Ulma Doctor (Mar 8, 2014)

randyjaco said:


> I have  a 5hp Phoenix RPC that runs very quiet. You might want to check with Phoenix
> 
> Randy





I would never buy a converter from anyone, when i can build a superior balanced converter myself and way cheaper.


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## Uglydog (Mar 9, 2014)

Ulma Doc,
As soon as schools out this spring I'm hoping to actually balance my RPC, instead of merely changing the leads around like I did last summer. Changing the leads actually seems to improve  performance, as I'm no longer blowing thermals on my 20hp 3phase lathe. But, following the direction of another thread on HM, I'd like to add a third leg thermal on all my 3phase old iron and balance the RPC.  

Sounds like the place to start is with the assessment of amperage output on all legs coming out of the RPC using a clamp ampmeter. Does a 3phase machine need to be tuurned on in order to get an accurate reading? Does it matter which machine?

How do I best know where which capacitor to add, where to put it and how to connect it? If I can do this myself I believe I'd learn great heaps of stuff However, I don't want to trouble all of you with questions for which answers are obvious to all except us noobs.   

Daryl
MN



Ulma Doctor said:


> Sure Phil, i can help out!!
> i have seen the balance difference between legs to be 50 volts +/- the other 2 legs or a 20% difference if you want to look at it like that.
> A RPC to be considered electrically balanced has only 10% difference between legs.
> i have been able to realize less than 2% for sensitive units.
> ...


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## Ulma Doctor (Mar 9, 2014)

Sounds like the place to start is with the assessment of amperage output on all legs coming out of the RPC using a clamp ampmeter. Does a 3phase machine need to be tuurned on in order to get an accurate reading? Does it matter which machine?

*Hi Daryl,
I would place a typical load on the machines you would intend to use on the RPC for the most accurate balancing.
**
if you intend on using multiple machines at the same time, make sure that you start them one at a time.
*
do I best know where which capacitor to add, where to put it and how to connect it? If I can do this myself I believe I'd learn great heaps of stuff However, I don't want to trouble all of you with questions for which answers are obvious to all except us noobs.   
*
Daryl,
i'm always happy to lend a hand wherever i can, you would not be bothering me in the least by asking questions.
**​when you are ready to start tackling the balancing procedure,  drop me a line i'll be glad to assist you*


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## Uglydog (Mar 9, 2014)

Thank you.
Come May please expect long and tedious interrogatory.
Would this be best as a forum item or as a series of PMs?
Will my endless questions be helpful to others?

Daryl
MN




Ulma Doctor said:


> Sounds like the place to start is with the assessment of amperage output on all legs coming out of the RPC using a clamp ampmeter. Does a 3phase machine need to be tuurned on in order to get an accurate reading? Does it matter which machine?
> 
> *Hi Daryl,
> I would place a typical load on the machines you would intend to use on the RPC for the most accurate balancing.
> ...


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## Ulma Doctor (Mar 10, 2014)

Uglydog said:


> Thank you.
> Come May please expect long and tedious interrogatory.
> Would this be best as a forum item or as a series of PMs?
> Will my endless questions be helpful to others?
> ...



I'm happy to reply either way is best for you, i'm sure others will have questions that may be answered by our correspondences


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## Ulma Doctor (Aug 31, 2015)

if you need more help or i can even help make one for you, let me know
i'm happy to help out


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## Uglydog (Aug 31, 2015)

I've picked up a used commercially made 20hp RPC several years ago as my Gisholt is 10hp. 
I was thinking about a static converter as then I wouldn't need to run 3ph to my wood machine area.... and ..... here's the best part.... my daughter is asking/requesting all the vintage wood machines as she plans her shop. Granted it's a few years out as she finishes up her academic work. 
I thought that a static would work well in this application. But, maybe it's not worth the trouble and going directly to a RPC makes more sense?

Daryl
MN


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## John Hasler (Aug 31, 2015)

Ulma Doctor said:


> i have pictures of a working model made from 90% recycled parts.


I have a "static converter" on my Avey made from 100% recycled parts.  Air conditioners and well controllers are good sources of potential relays and start capacitors.  I got some nice 660VAC oil-filled capacitors for run caps out of an obsolete power conditioner.  The cabinet once held lighting controls for a microwave tower, which also supplied some terminal strips.  No photos, though.


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## Uglydog (Aug 31, 2015)

I've so much to learn!

Daryl
MN


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## railfancwb (Sep 14, 2015)

A number of how-tos on the web explaining the whys as well as the hows of home brew converters. 

This one has additional links within it. 

http://www.nojolt.com/how-to-build-a-rotary-phase-converter.shtml




Sent from my iPhone using Tapatalk


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## Firestopper (Sep 14, 2015)

Another good source of information on RPC can be found on metal web news. I used this back in 2001 to build my first system.


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## Ulma Doctor (Jun 18, 2016)

I made this motor starter for HM supporter, Bamban's Bridgeport Milling Machine
6/16/2016






the box is very simple to hook up to any motor.
you simply hook the box up to your idler motor and distribute the 3 phase circuit from the idler motor to whatever you'd like to run.
in my home shop, i have a 5 hp and a 7.5 hp RPC's wired in & ready to go at the push of a button.
i use the 5 hp most of the time,
but when i want to fire up my 300 amp POWCON 3 pahse welder- it needs a bit more juice, so i run the 7.5 for that or anytime i need to run larger capacity motors.

on your BP,
this box, as configured, only has the capacity to start the motor in one direction.
because the start capacitor in the box is starting the motor with a strong bias in one direction of rotation.
a 3 phase motor is happy running forward or reverse, they truly are bi-directional the efficiency and power output is equal, regardless of direction of rotation.
but since we are tricking the motor on start up to believe it has 3 phases( but one of the phases is a burst of 120VDC @ 200UF momentarily)
after the motor is running, it creates it's own 3rd phase, the start capacitor is no longer in the motor circuit after you let up off the green(start) button.
you'll wire the output of the box to your BP's drum switch, then the drum switch to motor.

sequence of operations:
after the box is wired in, to start the BP you'll pick a direction on your drum switch F or R- then push the green button- the mill will run in that direction.
you will push the red (stop) button on the box, power is cut to the BP's motor.
if you'd like to restart in the same rotation, simply push the green button again and then the red button to stop once again.
to reverse the motors' rotation select the other direction on the drum switch and push the green box button, the motor will run in reverse until the stop button is actuated.

one point of information, the drum switches are normally open center switches.
that is that they don't conduct electricity between poles in the center position and are isolated.
that being said, there is potential for possible motor damage if you were to mistakenly switch directions on the drum switch before the motor came to a complete stop.
get into the habit of stopping the mill with the red box button.


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## quickcut (Jul 5, 2016)

Is their any sort best practice (rule of thumb) for determining a cap value per horsepower for running. I read about 50 mf for starting. not sure about the run side of things though. Thanks in advance. 

charles


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## Ulma Doctor (Jul 5, 2016)

Hi Charles,
generally speaking for normal service, somewhere around 20 uf per hp of running capacitance is all that's required, unless you are running very heavy loads.


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## quickcut (Jul 11, 2016)

Thanks, Missed your reply.


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## killswitch505 (Aug 20, 2017)

Sweet thanks for the post I will be doing this soon


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## Ulma Doctor (Aug 20, 2017)

killswitch505 said:


> Sweet thanks for the post I will be doing this soon


i hope the information is useful.
let me know if i can assist you in any way


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## Rev. Mike (Dec 10, 2018)

Hello Mike
If I would build this exact setup what size would the fuse's need to be and the Amp for the coil need to be? I guess I need to let you know my motor is 208 V as well as you said this was for. Thanks


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## Ulma Doctor (Dec 10, 2018)

the motor fuses would depend on the hp rating of the motor
but as a rule of thumb is fusing is about 10 amps per hp 
the control fuses are 1 amp


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## Rev. Mike (Dec 10, 2018)

Ulma Doctor said:


> the motor fuses would depend on the hp rating of the motor
> but as a rule of thumb is fusing is about 10 amps per hp
> the control fuses are 1 amp


the motor is 1/3 hp


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## rwm (Dec 10, 2018)

Basic question: I don't understand how this is "rotary"? It looks like you box starts and runs 3 phase motors with no moving parts? What is the idler motor? 
Robert


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## Ulma Doctor (Dec 10, 2018)

rwm said:


> Basic question: I don't understand how this is "rotary"? It looks like you box starts and runs 3 phase motors with no moving parts? What is the idler motor?
> Robert


Hi Robert,
technically it is a static converter, but few would understand the difference.
the rotary part comes when you couple the starting box, with an idler motor.
when the idler motor is running, it provides the 3rd leg of power that is lacking in most residential service
this 3rd leg, in conjunction with the 2 power company supplied legs, can be used to run 3 phase motors

my stater box, just gets the 3 phase motor spinning, quickly


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## Ulma Doctor (Dec 10, 2018)

Rev. Mike said:


> the motor is 1/3 hp


10 amp fuses would suffice, for the motor fuses


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## Rev. Mike (Dec 11, 2018)

Ulma Doctor said:


> 10 amp fuses would suffice, for the motor fuses


Would this Contactor "AC Contactor AC220V Coil 12A 3 Pole Phase NO Normal Open +1 NO Switch CJX2-D1210" work for a 208 V 1/3 hp 3 ph motor to make this setup and with his setup do I still need a idler motor also? Thanks


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## Ulma Doctor (Dec 11, 2018)

Rev. Mike said:


> Would this Contactor "AC Contactor AC220V Coil 12A 3 Pole Phase NO Normal Open +1 NO Switch CJX2-D1210" work for a 208 V 1/3 hp 3 ph motor to make this setup and with his setup do I still need a idler motor also? Thanks


You can start a 3 phase motor with this set up.
An idler motor would increase the potential of the 3 phase circuit.
Without an idler you lose a portion of the motors hp rating


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## markba633csi (Dec 12, 2018)

I think it would be good to point out that a static phase converter and a rotary phase converter are both methods of running 3-phase equipment (motors) from a single phase power line.  The static method usually allows only about 2/3 horsepower with any given motor load. In other words, a 1 hp motor running on a static phase converter will only deliver about 2/3 horsepower. 
The rotary phase converter is more efficient but of course it is more expensive.
mark


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## tjmlack (Jan 24, 2019)

Hi Mike,
Would you tell me where you bought the momentary start button (DPST switch) with both contacts NO that you show in your wiring schematic?
Thanks,
Tony


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## Ulma Doctor (Jun 5, 2019)

tjmlack said:


> Hi Mike,
> Would you tell me where you bought the momentary start button (DPST switch) with both contacts NO that you show in your wiring schematic?
> Thanks,
> Tony


i got the square d NO contact blocks on ebay and assembled the switch


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