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IndustryArena Forum > CNC Electronics > Phase Converters > Building a 20HP RPC, have questions
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  1. #1
    Join Date
    Sep 2011

    Building a 20HP RPC, have questions

    I have finally rounded up all the components to get my 20HP Rotary converter built. I went a bit overboard and picked up two 120amp contactors, one each for the main and start contactors. I also picked up various other parts needed to get it going. Below are some pictures of what I have so far.

    My first question is do PRC's generate any heat while they are in use. The reason I ask is that I have a small 120v AC fan I saved from the scrapper. I can mount it on the side of the cabinet very easily. If it doesn't need it then I will leave it out. It can be seen in the pictures.

    I have calculated from various sources that for a 20HP converter I will need approximately 1600uf worth of Capacitors to start it and about 300uf per phase relation for balancing, about 2200uf total. Is this correct or is it too much.

    I picked up a bunch of capacitors for this build and after sorting out the calculated amount I thought to myself, where am I going to put all of these. I can fit 3/4 of the caps across the bottom of the enclosure but I am going to have to come up with something to mount the rest. Perhaps a shelf or something? Any ideas?

    The enclosure I picked up came with some components in it when I bought it, namely 2 sets of 3 phase fuse holders, with 30amp fuses already in them. The fuses are time delay fuses. I thought about using these as my 2 outputs from the converter that go to my machinery. Should I use standard fast burn 30amp fuses or are time delay OK? I ask because I bought two sets of holders for class H fuses and then a week later bought the enclosure which had the holders in it with time delay fuses installed. They are both in the pictures as well.


  2. #2
    Join Date
    Sep 2011
    Well I made a little more progress today. My original plan was to use all run capacitors in my converter. Mainly because I got a great deal on a box of new capacitors. After trying to fit the required amount in the enclosure I realized pretty quick that it was not going to work. I talked to a couple friends of mine and decided that going with start capacitors instead of run capacitors for the starting circuit would be best. I started looking around and found some 330v 300-360uf capacitors on eBay. I tried to find them locally and was about to give up when I finally found them. Now I have 5 of them and should hopefully have the assembly done tomorrow.

    All I have to do now is get the sub panel in my shop finished up and wire it all in. I am beginning to see the light at the end of the tunnel.


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