# My upgraded RPC is up and running



## Investigator (Nov 6, 2020)

Got it almost finished.  I now have a push-button start, 7.5hp RPC.  I have a couple more little things to finish up but I hooked it up and tested it and all is running well.  My voltage readings are:
L1-L2   250V
L1-L3   216V
L2-L3   208V
and that is totally unbalanced, no run capacitors at all.  I'm running this in order to use a 12" Logan lathe and a Bridgeport clone knee mll.  I have no electronics to run.

So, do I need to add caps?

Pics when I get it all done tomorrow.  I'm going to add some meters/displays so I can see the voltage and amps on each line.


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## Ulma Doctor (Nov 6, 2020)

these machines will operate just fine on the unbalanced RPC
just remember, don't use the generated leg to power a transformer.
only use the supplied single phase legs for transformer power


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## benmychree (Nov 6, 2020)

I would add some caps, they likely would make starts and reversals function better.


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## Investigator (Nov 6, 2020)

For the sake ok argument, if I wanted to balance it out, where do I start?


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## Canus (Nov 7, 2020)

I'm with Investigator here.  I built a 10 hp RPC and have partially balanced it using caps but would like to fine tune it to get the voltages closer to each other.  Any tips on selecting caps for final tuning would be greatly appreciated.


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## Ulma Doctor (Nov 7, 2020)

benmychree said:


> I would add some caps, they likely would make starts and reversals function better.


how much capacitance would you use and between which phases?


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## Weldingrod1 (Nov 7, 2020)

Add capacitance to the low leg. Total and complete swag: 10 uF.
Hopefully someone with a RPC will chime in.

Sent from my SM-G892A using Tapatalk


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## pontiac428 (Nov 7, 2020)

If those voltage readings are from a no-load condition, they won't mean anything.  What are they under load?


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## Investigator (Nov 7, 2020)

Canus said:


> I'm with Investigator here.  I built a 10 hp RPC and have partially balanced it using caps but would like to fine tune it to get the voltages closer to each other.  Any tips on selecting caps for final tuning would be greatly appreciated.





Ulma Doctor said:


> how much capacitance would you use and between which phases?





Weldingrod1 said:


> Add capacitance to the low leg. Total and complete swag: 10 uF.
> Hopefully someone with a RPC will chime in.
> 
> Sent from my SM-G892A using Tapatalk





pontiac428 said:


> If those voltage readings are from a no-load condition, they won't mean anything.  What are they under load?



Well, I'm not saying I want to, or that I even think I need to.  Fact is that same voltage setup has ran my Logan 12" for a couple of years. I'm more wondering about the academic argument of how really.
It's my understanding that you can never completely balance an RPC due to the various loads put on it normally. I've even read one opinion that it is a complete waste of time.

Pontiac, I haven't got everything finished yet. Still need to add 3 combo voltage and amperage meters, then I should be able to read it off the panel all at once.


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## zamboni2354 (Nov 7, 2020)

I think it's a little trial and error. For my 10hp converter I ended up with 100mf between L1 and L3 and 170mf between L2 and L3
.
Here's how mine turned out. 

Jeff
	

	
	
		
		

		
			








Sent from my LM-V405 using Tapatalk


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## Ulma Doctor (Nov 7, 2020)

i


Weldingrod1 said:


> Add capacitance to the low leg. Total and complete swag: 10 uF.
> Hopefully someone with a RPC will chime in.
> 
> Sent from my SM-G892A using Tapatalk


i build RPC's, 
the output of a balancing capacitor would go to the low leg but is completely unnecessary for what the OP whishes to accomplish
capacitance should be 10 to 15 UF per HP for phase balancing
i have played with this extensively


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## Investigator (Nov 7, 2020)

Just an update for what it's worth.  I got it all hooked up and ran my lathe, the mill is not where I can hook it up yet.  With the 12" Logan running, the voltage didnt change from what it was with just the idler motor.

I added some duel meters that show the voltages and had hall sensors to read the amps.  They were from China via the 'bay.  I'm not sure how accurate they are.  I know the voltage part is right because I checked it with my meter.  I dont have an amp meter so.....there's that.  I had a sensor on each leg, L1 showed 19 amps, L2 showed 17/18 fluctuations, and L3 showed 0 amps with just the idler and 3.2 with the lathe running.


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## Sblack (Nov 8, 2020)

I need to step up a rpc output from 220v to 600v. How balanced do the 3 legs have to be? The most powerful machine I have is rated at 3hp.


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## Ulma Doctor (Nov 8, 2020)

as long as you are around 15% between legs, you'll be ok


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## Investigator (Nov 20, 2020)

Up and mounted now.  Unbalanced, running the lathe fine.  Hopefully in the near future I will move this to my new shop.


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