need help with rotary phase convertor wiring / plans

Shadycreek007 said:

Thanks in advance for any help. I have a 7.5hp 3ph motor that I am trying to make into rpc. I found a youtube video of a 7.5hp that the man says works great and it appeared simple. I figure I can balance later if needed. Attached are my hand drawn plans of what he used and I duplicated. I however blow the top out of the capacitor about 30 seconds after motor starts. It starts quick and smooth and continued to run until I got to my breaker box. As he shows using a 110v start capacitor, so did I. Should this be a 220v? I am thinking the PR is allowing back voltage to the capacitor. If you are familiar with this or know the issue, please enlighten me.

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Shadycreek007 said:

Well, tried the 250v 600mfd start capacitor and same story. Started up smooth, 10 seconds later, let the smoke out of the capacitor. ( I assume that's what they operate on ) Motor continues to run fine.
I agree their not expensive to buy, but I have all the parts in my garage except capacitor and this one is built. Just like to learn along the way instead of always wondering what was wrong.

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Shadycreek007 said:

That was it, I changed relay and went back with a 110v capacitor since that's what I had in my pile. Now to balance. I did a quick check, 219volts on legs 3&1 and 214 volts on 1&2.
What is a good start on run capacitors? I seen something like 15 mfd per horse power. I know this wont be a standard but maybe a starting spot..
Note: I am building my own for learning although complete kits can be bought cheap enough. I had a 10hp factory balanced that I bought on a pallet with 8 three phase motors.(using to build rpc's) Nobody at the auction knew what it was and I got the whole pallet for $30.. It got sold with a 25 ton clicker press I sold, the buyer just had to have the rpc. So with me having from auction, new contactors, relays, switches, box's, etc. Figure why not build rpc with them.

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Newman109 said:

I can't imagine a 110V capacitor lasting very long a a start capacitor in an RPC running on 240V.

Here is a schematic that I used a few years ago to build my RPC's. (5.0 and 7.5 HP). It has the suggested values for capacitors at different voltages and hp's. If running on 240 VAC single phase, all capacitors should be rated for 240 VAC or higher.

View attachment 263816

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Froneck said:

I don't understand the schematic. Is L1 and L2 input single phase? M1, 2 and 3 the motor? T1, 2 and 3 phase output? T3-M3 the created phase? If so you are wired wrong! I'm surprised the motor started but some will if connected only to single phase. The capacitor should be connected to the created phase which I assume is T3/M3 and not to L2. Also if your Cap. burns up after the motor is running means that the potential relay is not working or wired incorrectly!

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