Rpc simple design unbalanced

Ulma Doctor

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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!

RPC.jpg

enjoy!

RPC.jpg RPC.jpg
 
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Rbeckett

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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
 

Ulma Doctor

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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

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Re: 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!

View attachment 48836

enjoy!
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
 

Ulma Doctor

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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:))
 

raross61

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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:))
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
 

Philco

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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
 

Ulma Doctor

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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

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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:))
 

Ulma Doctor

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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...

RPC 1.JPG

The enclosure was rendered from an old electric water heater timer.
RPC 2.JPG RPC 3.JPG
RPC 4.JPG


thanks for looking

mike

RPC 1.JPG RPC 2.JPG RPC 3.JPG RPC 4.JPG
 

rgray

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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.RPC.jpg

RPC.jpg
 

Ulma Doctor

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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!
Have you had any dealings with these? Did they just compromise on capacitors using start caps full time?
​I have not actually worked with that brand, but you can think of it as a 3 phase motor starting device.
The capacitor is used to start the idler motor and drops out of circuit after the motor has started. no other capacitors are used it appears in this design. this is an unbalanced converter design.
if you were to leave a start capacitor in circuit like you would a run capacitor it would quickly overheat and fail.
start caps are not equipped to dissipate heat like a run capacitor. run capacitors are usually oil filled and can dissipate heat a lot easier and can stay in circuit constantly.

View attachment 58880
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
:))
 

randyjaco

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

Randy
 

Ulma Doctor

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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.
 

Uglydog

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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

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:))
 

Ulma Doctor

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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

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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


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
 

Ulma Doctor

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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
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
 

Ulma Doctor

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

Uglydog

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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
 

John Hasler

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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.
 

Uglydog

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I've so much to learn!

Daryl
MN
 
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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.
 

Ulma Doctor

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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

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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
 

Ulma Doctor

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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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