# How important is tuning an RPC?



## Investigator (Apr 27, 2017)

I am getting closer to getting things going.  I started looking for a 5hp idler motor.  I have ended up with a 7.5hp instead.  Found a new Marathon 208-230/460V for $125.

My specific question is this; considering I am using an RPC to power a 40's Southbend 16", and a 50's Logan 12", how important is it to have the RPC tuned?  I'm trying to get an idea of is it better to buy a box, or build my own.  I have no issues building, just wondering where the break over is in terms of money saved verses time to wire it all up.  I really don't have the test equipment to properly tune between legs.  

If as a practical matter the older equipment I am using is mostly unaffected by the legs being 'untuned' to each other, then building is definitely in order.  On the other hand if it will make a somewhat significant difference, I would buy a panel ready built and 'pre-tuned'. 

Open for suggestions and thoughts. Thanks


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## rgray (Apr 27, 2017)

After purchasing a panel the first time, I thought I'd just build my own for the second. I couldn't buy the parts for what they were selling the completed panel for so it made no sense.
http://www.ebay.com/itm/7-5-Hp-phas...hash=item2c973b19da:m:mwV9U3knllGMqu9KrsNvyUA

$174.00 and free shipping. If you have the resources to buy the parts cheaper and build your own ...go for it.
I have 2 from that company and 1 from phase craft. Both work very well. I have no cnc equipment needing better phase balance.


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## Karl_T (Apr 27, 2017)

I've built several 3 phase converters...

I agree, the above deal is about the same as buying components, I'd go with this this in a second.

re tuning: the above offer would be good for your equipment, just be sure the "wild leg" does not power any 1 phase accessories


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## Ulma Doctor (Apr 27, 2017)

you'll be able to run your equipment without tuning the RPC.
as Karl said, don't power accessories, transformers, or control circuits form the output of the (generated) 3rd leg.
i built a 5hp 20 years ago, (and 2 others 7.5 & 10 hp for my home shop)
the 5hp RPC that runs small loads, is not balanced between legs and fires off everything without incident- the RPC runs a little warmer but no ill effects even after 20 years of operation


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## Silverbullet (Apr 27, 2017)

From what I understand the tuning only balances the current on the third leg , that's accomplished with run capacitors. I may not be right but from everything I found out , that's about it. Unless you need some resistors for electronic protection? ???


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## randyjaco (Apr 27, 2017)

Wow, I am going to start looking for a 7.5hp 3phase motor. That is a great deal. 

Randy


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## Silverbullet (Apr 27, 2017)

Just got an email for a motor guy has a ten HP weg in box new he wants $180.00 delivered to my shop. He's local near me he knows I in a wheelchair. If anyone wants it let me  know.


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## Keith Foor (Apr 29, 2017)

As far as tuning an RPC and how critical it is, the answer depends on what are you using it with.
Now you should CHECK your RPC under a no load condition to verify that the generated leg is not abnormally high or low but if you are running gear that has no electronics in it and the voltages are reasonable then it's gonna work fine. 

Tuning does two things.  If first protects sensitive electronics from damage.
Second is that it make s the RPC more efficient when running and gets you the maximum performance out of it.
Mine that I tuned and run L1 to L# and L2 to L3 run cap banks on is built on a 15HP motor.  I have started 40HP motors with in that were not under load and sitting free.  That being said.  With the gear you listed, I don't see a need to go to the lengths of fully tuning the RPC if you are not comfortable with doing it.
Just make sure that you check the leg to leg voltages and none are below 205 or above 245.

On a side note.  The "pre-tuned" boxes are not tuned.  If they of any quality at all they will come with a number of installed run caps and a bag of jumpers that you would use to 'tune' the box to the motor.  Reason for this is that not every motor is the same.  This is due to changes in manufacturing methods over the years (age of the motor) and different types of motors but in speed and design.  A 10 HP open frame motor is going to have a different weight armature in it than a 10 HP fully sealed class 1 explosion proof pump motor rated for explosive gas environments.  My 15HP RPC is built with one of these motors.  It is the size of an open frame 100HP motor and has a 2 inch output shaft.  So the boxes available on the web do work well and most I have seen are well built but you would need to do a final tuning on them.


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## Reeltor (Apr 29, 2017)

I have a question----

How do you measure the voltage at each leg?  I have been using my RPC-15hp locally sourced motor and box from WNY phase converts for almost 10 years now with out any problems.  But I've never checked to see how balanced the legs are.

http://phaseconverterusa.com/Standard-Series_c_27.html
I agree 100% with previous posts, unless you have a lot of the parts already laying around, I don't see how you can build one for less than buying a control box.  Don't make the mistake of buying a Static Converter Box, you do want a Rotary Phase Converter box.

here is the guts of a 7.5 hp unit $179 with free shipping











*7.5Hp Rotary phase converter control panel 230vac *

Your Price:$179.00


*Availability:*
In Stock

Free Shipping.

Quantity

More Details






Mike


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## 4GSR (Apr 29, 2017)

In the box posted above, check the voltages at the terminal block where the wires are marked "C", "A", "B".

Over the years, I've built several static style converters with using a couple of starting capacitors, one run capacitor, a double pole momentary closed push button and a motor starter.  Never had an issue of stalling a motor while cutting! On any of the machines we put them on.  I've also used a running motor on one machine to jump start another motor on another machine, too.  Amazing what you can do with a hand full of components. 

Now, I put VFD's on my machines! Ken


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## Reeltor (Apr 29, 2017)

Ken,

So check voltage at C-A, C-B, B-A?

Thank you for the response

Mike


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## Keith Foor (Apr 29, 2017)

Yea test L1 to L2 L1 to L3 and L2 to L3. Mind you mine are all built with the generated leg being L3. The L1 to L2 reading is always gonna be the line voltage and it's not going to vary because it would require the voltage from the pole transformer to change.  So the two that you need to balance or 'tune' is those two legs to the generated leg.  

Sent from my SPH-L720 using Tapatalk


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## 4GSR (Apr 29, 2017)

With what Keith is saying, looking at the "phaseconverter-usa" unit, L1= A, L2= B, L3= C.  And follow the sequence Keith mentioned checking voltages.  As Keith said L3 or C is the generated leg and that voltage is the "wild" leg as some call it.  And make sure it doesn't get connected to any other circuit than T3 on the motor.  And don't check it against a neutral or ground, it will not give you a constant reading of any value to you, and can be dangerous to you if not careful.  Ken


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## Keith Foor (May 5, 2017)

Mike is right on buying parts as opposed to buying a completed cabinet if you are gonna buy it all new.
That being said , I source my parts from various places including ebay.  Start caps I would buy new unless you get a killer deal on them, like a buck or two each.  They have more of a chance of being bad than run caps.

If you are gonna get serious about it, buy a meter with a capacitor checker function in it.  I take mine with me when I buy used caps so I can check them.  Anything over a 10% variance in the labeled value and they are probably no good.


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