need help with rotary phase convertor wiring / plans
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  1. #1
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    Default need help with rotary phase convertor wiring / plans

    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 3 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.
    Attached Thumbnails Attached Thumbnails 20190816_120701.jpg  

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    Quote Originally Posted by Shadycreek007 View Post
    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.
    Hmmmm, not sure about your diagram. A 120V start capacitor won't last long in an RPC. You need the correct value of capacitance with at least 240-250V rating.

    There are numerous plans and schematics for RPC's in the sticky thread at the top of this section. I used that section to build two RPC's: a 5.0 and 7.5 hp. with success.

    Hope this helps. Good luck.

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    I think that is the issue too. That's what I will try next. I will also look at other plans. thanks...

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    You might consider buying a phase converter box for your 7.5 hp motor, they are reasonably priced and have the correctly rated parts.

    7.5Hp Rotary phase converter control panel 230vac

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    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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    Quote Originally Posted by Shadycreek007 View Post
    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.
    Are you certain that the potential relay is opening to remove the start capacitor from the circuit after the proper voltage is achieved?

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    I will be getting another capacitor and change the relay. Maybe I got a bad one. I have another relay in stock but only have 110v capacitor like the plans called for in the first place.

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    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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    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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    Quote Originally Posted by Shadycreek007 View Post
    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.

    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.

    rotary-phase-converter-miller.jpg

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    The 270-324 Mfd 220/250V jobs I keep in stock have lasted 10 years without issue in starting this 15HP

    How To Make An Old 15HP 3 Phase Go

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    Quote Originally Posted by Newman109 View Post
    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.

    rotary-phase-converter-miller.jpg
    Thanks Newman, I have run it a couple hours now on that high frequency pvc welder and has held up so far, not to say it will continue. From what I can tell, the start capacitor just has 110v going to it for the most part. On the relay, #1 has 110v infeed, #5 has the other leg. when the motor excites #2 it energizes the coil and takes the capacitor out of the start process. I could see that as m3 starts to excite the PR, there could be a moment that the volts climb for a millisecond as the coil energizes. I don't think this is great for the capacitor and will be replacing it. Mainly used it because that's what I had. For $10, it can ease my mind a little. The run capacitors are my next to learn to balance...

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    Quote Originally Posted by Froneck View Post
    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!
    Yes on the identifications...
    Trying to understand, If I don't run a line voltage to the starting capacitor, Your saying connect one side of the capacitor to M3/T3? What does the other side of the capacitor connect to? Also, does it not get dropped out? Does it continue to be connected to M3/T3 for as long as motor runs? I tried to start the motor on single phase 220, it wont start, trip 50 amp breaker. With it wired as I have it, It starts instantly and I have ran for hours. Started and stopped on numerous counts. Although I'd like it to continue for years which is why I am here. Feel free to show me how you would connect what I have.
    The initial reason for me posting is the first relay was bad, that has been replaced.
    Thanks in advance.


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