Phase Converter

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hamburgerpatty

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I have come across a 230 Volt "Roto-Phase" single phase to 3 phase converter on a service call. The customer didn't know if it worked, but asked me to get rid of it. So naturally, I took it home. When it starts up it makes a rumbling noise at start-up but after the start capacitors are done, and full rotation is met, the motor sounds fine. When it is hooked to a load, the Voltage is imbalanced. IE 250 volt A-B 220 volt B-C 190 volt C-A. My question is; If I bond one the the?phases - to make it a
"grounded B", will it get the voltage more in balance. Or does anybody have any input on the characteristics of a Rotary Phase Converter?
 
Re: Phase Converter

patty I have sold the arco rotophase in the past and they are a fine unit.You should read line voltage on 2 of the lines and 190 would be uncommon for the manufactured leg at no load. When a 3 phase load is applied to the unit the voltage will balance. Arco has a web site where you can get technical data on line. What model do you have? In any case donot under any cicumstances "bond" one of the phases. 2 of your "phases" are common to the input line of 230 volts and a bond there would of course result in dead grounding of your 230 volt line and trip the breaker. Grounding of C phase the manufactured leg will also result in tripping of the breaker as this leg comes from the winding of the rotophase with the capacitors in parralel as well.My recollection is that A./B will read line voltage and A/C or B/C will read slightly higher than the input voltage at no load. 190 volts seems to me to be too low. This may be because of one or more of the capcitors being bad.In any event Arco can help you with this by phone. I do not have thier # any longer but in my other life I sold several hundred of these units to be use with motors as large as 40 HP. Thes are one of the only units that will handle multiple motor applications. If you give them the nameplate info they can also send you the install info which is very important especially when it comes to wire size. If I can be of any further help just pm me. Joe

[ July 07, 2004, 10:33 PM: Message edited by: stew ]
 
Re: Phase Converter

Thank you very much. Is the rough sound during startup normal? It sounds similar, but not exctly as the same as a 3 phase motor single phasing during startup.
 
Re: Phase Converter

Is this a bearing noise you hear or is it electrical? If electrical my hunch is probably correct that one or more capacitors are bad. Check the caps for leakage of fluid. Also check with an analog meter if you have one to see if the capacitors will charge or if one or more check shorted or open. The capacitor bank needs to be ok for the unit to start properly and maintain the manufactured phase under load. If you do think you have an electrical growl then I would put my money on a bad cap or 2.I also have aquired a capacitor tester from Grainger that I use to check single phase motor starting and running capacitors. The ones that arco uses are 370 volt oval caps of about 30 or 35 mfd. Some in the larger units are square 440 volt caps about 25 to 40 mfd each.Check them closely because they are a bit spendy if you need to replace. Grainger stocks all the ones you would need if they are bad. What letter model do you have?

[ July 07, 2004, 11:19 PM: Message edited by: stew ]
 
Re: Phase Converter

The Nameplate is very illegible. It is a 7.5 HP. and it is not a bearing issue. It just growls on startup only, and the voltage imbalance is when I have it loaded with a 12 A load.
 
Re: Phase Converter

If the voltage will not stay up to at least line voltage the probability of bad caps is even more than a hunch. 7.5 hp unit would be a model A capable of running a largest motor of 7.5 hp with a total connected load of around 22 hp. This is type of unit that could be used to run a small machine shop very easily with several motors running at once. 12 amps of connected 3 phase load should not result in the voltage unbalance that you describe unless there is a problem with the caps. The caps are what helps keep th voltage stable as well as aiding in startup.I assume the load you are applying is a 3 phase load?

[ July 08, 2004, 01:05 AM: Message edited by: stew ]
 
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