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Did I screw up - Ronk Roto-Con?

beeser

Cast Iron
Joined
Jan 3, 2015
I just purchased a used Ronk Roto-Con rotary phase converter with the following specs.
Converter size - 20 KVA
Largest single 3 phase motor - 10hp
Total 3 phase motors - 20 hp
Single phase input - 96 A

Mainly what concerns me is the minimum motor load of 3 KVA. My goal is to power a 2hp Bridgeport mill and a 3hp, 2 speed Victor lathe. Will this rotary phase converter work or did I just purchase a boat anchor? If it makes any difference the motor is a Baldor ODP.
 
Sounds fine.... Definitely is NOT a boat anchor. The basic converter puts out just what you want, and does not care about the load, it would run a 1/20 HP 3 phase motor, if there was such a thing connected. The problem arises when they "compensate" the converter with a lot of "balance capacitors". That raises the loaded voltage. But it REALLY raises the un-loaded voltage, if it is over-done. Too much "balance" capacitor will raise the unloaded voltage to a really high voltage on the "generated leg" vs the others. It then might take a fairly heqvy load to pull that voltage down within the normal range. If you will not have that much load, you can disconnect some balance capacitors, which will "de-tune" it a bit so that the unloaded voltage does not start out so high. Then the "loaded voltage" may be a bit lower, as it common with RPCs, but it will work fine. BUT... first check to see if the un-loaded voltage really IS too high. It might be OK, in which case you do not need to do anything.
 
Thanks JST! After thinking about it a little more and looking more closely at the control panel I wondered what is done in a shop with machinery having both large and small motors. I suspect a rotary converter is sized for the largest load or combined loads, probably not unlike my setup but without the large loads. The panel contains 8 capacitors in 2 banks. But 3 of the capacitors in one bank are not connected and shorted out. It appears the previous owner has already done what Bob-J-H suggested. There are other modifications too that have me confused. I plan to start another thread with pics with hopes of getting some help to get everything hooked up correctly. I watched a few videos last night on home built rotary phase converters to get me started. Until then, thanks again for giving some hope on this project.
 
It will probably be just fine. I had an Arco phase converter, largest motor 25 hp. I ran 1/3 hp gear motor on it with no problems. Once you are around the thing for awhile, you will figure out how to experiment with capacitors hooked in between magnetic starter and the load motor to balance voltages. Don't get too hung up on balanced voltage. I have motors bought at auction 30 years ago for $17 that are still doing what they did.
 
Tell us what the no-load voltage is between each line pair. It ideally is no more than 10% higher on any pair vs the incoming line. If it is within that range, and incoming line itself is not abnormally high, then you may not need to worry at all.
 








 
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