knots Posted February 20, 2011 Share Posted February 20, 2011 I just completed wiring a 5 HP rotary phase converter . I now need to balance the voltage between L1, L2, & L3. My line voltage is 250 volts at the outlet. With my current capacitor configuration L1 to L2 = 250v, L1 to L3= 225v, L2 to L3 = 225v. I was hoping to balance the legs to within say 10 volts however before proceeding with the balancing I need to buy more capacitors. Has any one here built and balanced a RFD ? Any comments and observations will be appreciated since this is breaking new ground for me. For instance - is there a procedure used to balance or is random substitutions of capacitors until balance is achieved the usual approach ? Link to comment Share on other sites More sharing options...
arftist Posted February 20, 2011 Share Posted February 20, 2011 You can use a static phase converter to balance your homemade one. Link to comment Share on other sites More sharing options...
Fosterob Posted February 20, 2011 Share Posted February 20, 2011 Have you checked those readings under load, that is what matters, not just idling. Rob Link to comment Share on other sites More sharing options...
knots Posted February 20, 2011 Author Share Posted February 20, 2011 You can use a static phase converter to balance your homemade one. Artist - Thanks for your response. I never heard of that one before. How would they be wired - In parallel ? Is there literature - If so where ? Probably only academic, because additional capacitors are cheap, but I am interested anyway. Link to comment Share on other sites More sharing options...
knots Posted February 20, 2011 Author Share Posted February 20, 2011 Have you checked those readings under load, that is what matters, not just idling. Rob Actually I have not checked the readings under load. I was aiming to get the voltages a bit closer before connecting to and running my new/old mill . The voltage is within 8% so it will probably be OK. I have heard of others running their RPC's with no capacitors and no problems reported. I also expect just running the mill without a milling load will not tell me to much. Is that a correct assumption ? Thanks Link to comment Share on other sites More sharing options...
Fosterob Posted February 21, 2011 Share Posted February 21, 2011 If you could check with motor running under some kind of load that would be best. Like you said if it is just freespinning it is not the same as loaded but I would try it both ways and see what happens to the readings. If you have no autofeed set up a light cut and have someone turn the feed crank while you take your test readings. I am redoing mine now and will take some readings before changing it around but i am not trying to change anything except the location of switches. Rob Link to comment Share on other sites More sharing options...
BIGGUNDOCTOR Posted February 21, 2011 Share Posted February 21, 2011 I know certain transformers, and supply lines have one higher leg. I believe it is the Y configuration, as opposed to a delta wiring. Consult a local electrician, but you may be fine with what you have. Back home I just ran through another 3ph motor with no capacitors. My Monarch lathe, mill, and surface grinder ran fine even at 2/3rds output capacity. With this set up only 2 legs are hot. Link to comment Share on other sites More sharing options...
knots Posted February 21, 2011 Author Share Posted February 21, 2011 I played with it some more and got the L3 to L1 voltage to 240v (unloaded) . One more 50 mf cap should balance the RPC (unloaded) . Having gotten that far I started the machine up. The motor runs without excessive bearing noise. I had rewired the machine from 480v to 240v . That conversion seems to be ship shape Before I use the machine, or proceed further with balancing, I need to install a magnetic on/off switch. The mill is a Gorton MasterMill built in 1958/59. Built in oiler, mechanical quill power feed, x axis table power feed. NT 30 spindle. The power feed for the table is interesting in that the feed motor is 3 phase, with variable feed accomplished by introducing a variable DC current into the dive motor rotor winding. The DC current rectifier uses vacuum tubes. The table is a little rough but he ways are in really great shape. Link to comment Share on other sites More sharing options...
Steve Sells Posted February 21, 2011 Share Posted February 21, 2011 I know certain transformers, and supply lines have one higher leg. I believe it is the Y configuration, as opposed to a delta wiring. Consult a local electrician, but you may be fine with what you have. Back home I just ran through another 3ph motor with no capacitors. My Monarch lathe, mill, and surface grinder ran fine even at 2/3rds output capacity. With this set up only 2 legs are hot. Its the DELTA that has the high leg, and it has the neutral coming from the center tap off the high leg's coil. In a WYE the neutral is from the center connection point of the three. Also its normal that all three legs are not the exactly the same, especially with the artificially manufactured third leg. In real 3 phase, the AC waves are 120 degrees out of phase, in a house wiring single phase the two are 180 degrees apart. While this will run the machine its not as good as a true 3phase converter, because 2 of your legs are still 180 degrees apart, so your readings are going to be higher on one pair because of the phase differences as well as the fact that conversion is not 100% efficient. But these do cost less to purchase. Link to comment Share on other sites More sharing options...
arftist Posted February 22, 2011 Share Posted February 22, 2011 Artist - Thanks for your response. I never heard of that one before. How would they be wired - In parallel ? Is there literature - If so where ? Probably only academic, because additional capacitors are cheap, but I am interested anyway. When I bought a static phase converter to run my Bridgeport mill, it came with instuctions to use it to regulate a rotary phase converter or to be used as is. You may be able to get info from the manufacturer's website. Link to comment Share on other sites More sharing options...
knots Posted March 11, 2011 Author Share Posted March 11, 2011 When I bought a static phase converter to run my Bridgeport mill, it came with instuctions to use it to regulate a rotary phase converter or to be used as is. You may be able to get info from the manufacturer's website. My phase Converter is compete and balanced using a combination of motor run capacitors . I am now able to run my mill, evaluate, and work toward getting it fully operational. Having done so I thought that I would backtrack to the concept of using a static phase converter to balance voltage for of a rotary phase converter. The literature that I have found indicates that the performance of circuits, where the power is provided by static phase converters, can be improved if an unloaded idler motor is run along along with other motors which are loaded. Static phase converters provide about 70% of full power for 3 phase circuits. Apparently the idler motor enhances this performance. I found no literature suggesting of a static phase converter being used to balance voltage outputs between the three legs of a rotary phase converter. However this is a subject of interest so if there is a more complete explanation, or additional information please add whatever you can to this subject. Link to comment Share on other sites More sharing options...
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