Balancing rotary phase converter to run three phase VFD.

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I need to hook up a small CNC router table. I was hoping the spindle VFD could be run off single phase but it's a three phase only input. So I decided I'd use a small RPC I picked up to a while back. It's a small ARCO Roto-Phase model M. It's rated to start 3 HP max and a combined load of 9 HP, according to the nameplate. It should work. Everything appears to run as expected. It idles at 3 amps on L1 & L2. My capacitor bank consists of three caps and measures 13 amps. This all matches the manual.http://www.arco-electric.com/PDFs/IN...pdf?2021-04-17Does anyone have experience running a VFD off a RPC? How balanced do the voltages need to be?Unloadeed voltages between legs are:T1 & T2 247VT1 & T3 260VT2 & T3 275V
Reply:Cool thread - I'll be watching it to learn stuff

Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:The Arco use a 3 phase motor to generate rather third leg. If look close at one end the cut off the shaft. 40 years ago the would buy a a bell to cover up the cut shaft. They also add oil fill capacitors to increase the power but this make voltage unstable on third leg witch you see.Unloadeed voltages between legs are:T1 & T2 247VT1 & T3 260VT2 & T3 275V
Reply:I emailed Arco about a schematic and they this was the reply: "Because of the age of this unit, there is no internal schematic available. Pretty basic connection...T1 & T2 are the 1PH input to power the phase converter. T3 is the manufactured phase. Capacitors are wired and connected in parallel on the T2 & T3 connections."I have three 40 MFD caps in parallel with T2 and T3. No start cap. No balance caps between T1 and T3.I'm thinking I need some caps between T1 and T3 to balance all three legs. I really need to know how balanced the VFD is expecting the legs to be.




Reply:They are using the oil capacitors for starting. After the motor starts just turn off one or two capacitors the voltage will be right .If need more power later just turn on capacitor. Note You need all the capacitors to start the rotor phase . But do not need the capacitors after Starting. You can buy Starting relay witch is easier.  I have diagram on this part. Dave

Originally Posted by forhire

I emailed Arco about a schematic and they this was the reply: "Because of the age of this unit, there is no internal schematic available. Pretty basic connection...T1 & T2 are the 1PH input to power the phase converter. T3 is the manufactured phase. Capacitors are wired and connected in parallel on the T2 & T3 connections."I have three 40 MFD caps in parallel with T2 and T3. No start cap. No balance caps between T1 and T3.I'm thinking I need some caps between T1 and T3 to balance all three legs. I really need to know how balanced the VFD is expecting the legs to be.




Reply:

Originally Posted by smithdoor

They are using the oil capacitors for starting. After the motor starts just turn off one or two capacitors the voltage will be right .If need more power later just turn on capacitor. Note You need all the capacitors to start the rotor phase . But do not need the capacitors after Starting. You can buy Starting relay witch is easier.  I have diagram on this part. Dave
Reply:Later I goto computer log on  and send diagram Dave

Originally Posted by forhire

I added the jumper with the blue crimp connectors between T3 side of the lowest cap and the rest of the caps. The jumper was broken when I got it. I think this is an accurate schematic. Obviously a potential relay would be ideal for unload the start caps. I'd be interested in your schematic with the relay.


Reply:I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.
Reply:That about what should be if capacitors are balanced. No load should balanced with out any capacitor. Sound like yours has a start relay too. They run real big AC by balancing the capacitors at load using 3 phase on single phase. Dave

Originally Posted by M J D

I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.
Reply:

Originally Posted by M J D

I'm not running anything on a VFD but on my north American rotary 5hp my legs are much more balanced especially when under load. I'm within 10 volts unloaded and within 5 under load. On mine there are quite a few capacitors.
Reply:Log on to my laptop This is a simple way for three phase.I could not upload to book it is to big.note there are two page one is PDF file zipDave

Originally Posted by forhire

As originally configured, without the missing jumper, on just one 40 MFD capacitor, my unit ran fairly balanced. I added the jumper after Arco told me all three capacitors should be parallel to T2 and T3. It's quite possible the additional two caps would only be required to maintain balance under higher loads. The unit started and ran fine with one cap. With all three caps hooked up the amp measurement is 13 amps, the same value listed in the manual.Is it possible that there would have been a switch to enable the additional capacitors for startup in place of the jumper I made? There was a broken jumper in the enclosure. Of course I bought it from a guy that never used it so I'm thin on details.I would really prefer to get the voltages within 5 or 10 volts. I think it's definitely doable. I think I'll play around with the configuration and see if I can get it dialed in.I found this schematic that suggests using caps on each leg. I'll need to read through the whole page to wrap my head around the math later tonight. Is there a reason most schematics only show caps on T2 & T3?http://www.waterfront-woods.com/Arti...econverter.htm


Reply:I saw a series of good videos on YouTube about using different capacitors, adding more, etc. to even out the legs. The guys channel went by the name " sbirdranch". 3 parts I believe, where it shows how he did it. After watching I came to the conclusion that it's was way easier and probably in the long run cheaper, to simply buy an existing proven unit.