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
 
Last edited:

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:))
 
Last edited:

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:))
 
Last edited:

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
 
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