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  1. #1
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    Default motor rpm

    getting ready to build a rpc and trying to decide on the rpm of the motor. have read i want to go with a 3600 if i can over a 1760, does it make that much of a difference, as of now it will be a 10hp 3600rpm, if that falls through it will be a 7.5hp 1760rpm, i will be just using for a doall band saw and a lathe in my home hobby shop,

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    Many suggest lower rpm with the idea that it may be quieter. That is possible, as the higher rpm can make more noise from the internal fan etc since it is running twice as fast. I have a 3600 rpm unit, and I do not find it annoying, but your mileage may vary....

    Either type will work just as well in terms of the output, which is the important factor..

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    I have a 1200rpm idler with my 15HP RPC, and find it to be ideal. I can hardly hear it running.

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    I too like the slower RPC motors, I have found not only are they quieter but the slower motors are easier to start. They also seem to preform as an RPC better than the faster ones but I haven't tested it to be certain. My RPC motor is 1160 RPM (1200 sync speed) Built or help build RPCs for friends, used the slower motors and they are all happy with them.

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    Before I learned how RPC's work and built my own, I foolishly bought a unit from a company on eBay that came with a 3,600 rpm motor. The second I started it up, I knew that I had made a mistake.

    That thing wailed like a Banshee! (I heard that Banshees were pretty loud. LOL) You literally couldn't hear yourself think. I had to turn it off each time I was finished using it. There was no way that I could let it run and just idle while doing some further setup on my mill. The result was that it blew a couple of start capacitors due to the frequent starts.

    I kept it until I was able to build my own unit. I used a 1,750 rpm Boston Gear motor from an eBay seller. You can hardly hear it run.

    The OP would be wise to consider a slower rpm motor as recommended by others above. He'll be glad that he did.

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    Do the lower (1200 RPM) motors require different run caps to balance them? Most of the converter plans and kits specify a 17XX or 35XX motor. I just bought an 1160 RPM 10 hp to use as an idler.

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    Quote Originally Posted by MushCreek View Post
    Do the lower (1200 RPM) motors require different run caps to balance them? Most of the converter plans and kits specify a 17XX or 35XX motor. I just bought an 1160 RPM 10 hp to use as an idler.
    I don't think motor rpm would make a difference in balancing caps. In fact, you probably should start out with no caps and take a reading. If it's close across L1-L3 and L2-L3, you are good to go. If not, trial and error will give some change. Regardless of motor rpm, the process would be the same.

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    Quote Originally Posted by MushCreek View Post
    Do the lower (1200 RPM) motors require different run caps to balance them? Most of the converter plans and kits specify a 17XX or 35XX motor. I just bought an 1160 RPM 10 hp to use as an idler.
    I don't know if it was the start or run capacitors that needed to be adjusted for my 1200rpm motor, but they were customized by the company that sold a panel to me when I mentioned that my idler would be a 1200rpm 15HP monster. I suspect it was the start cap, but I cannot say for sure.

    I guess you can discuss the issue directly with the company I bought the panel from, WNY: WNY Supply & Phase Converter Store :: Rotary Phase converter panel Incidentally, I'm very happy with the quality of their panel and the way they handled the transaction back then (no affiliation).

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    I'll write to WNY and ask them. Their website specifies 4 or 2 pole motors. An 11XX is a 6 pole. I did find another panel maker that told me to send the specs on the motor when I order, and that an 11XX is no problem. I'm going to buy a panel, because when I started adding up the components, it's cheaper to just buy one ready-made, plus I can start making chips sooner.

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    Quote Originally Posted by MushCreek View Post
    I'm going to buy a panel, because when I started adding up the components, it's cheaper to just buy one ready-made, plus I can start making chips sooner.
    These were my reasons too when I bought my panel. It's well and very accurately built and works flawlessly. At one point I added an LED to remind me to switch it off when I'm done (with a 6500rpm motor I wouldn't need this reminder.)


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