Supco potental relay in rpc.
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  1. #1
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    Default Supco potental relay in rpc.

    Ive used this rpc for some 15 years with few problems. A couple days ago it popped the start caps during heavy use of the air compressor. I found that the ge 6x550 relay contacts stuck. That relay is no longer made replaced with the supco supr.
    The problem is when replacing the relay and caps I lost track of the wiring connections, i know dumb ass.
    So i believe this is pretty close, the #5 pin out on the relay probably goes to L2?
    The r line is the developed leg.

    Does this look right? img_0727.jpg
    Thanks jeff

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    Your diagram looks good. Potential relay should go between either of the lines L1 and L2 to L3.

    This diagram shows that the rotational direction of the motor will change depending upon whether you use L1 or L2. Not an issue with a capacitor start, of course.

    Sorry about the small diagram.
    Attached Thumbnails Attached Thumbnails rotary-phase-converter-miller.jpg  

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    So Pin 5 to L2 thats what i thought. Thanks.
    The rest looked ok?

    Thanks. Jeff

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    Quote Originally Posted by 4miller1 View Post
    So Pin 5 to L2 thats what i thought. Thanks.
    The rest looked ok?

    Thanks. Jeff
    I think so. Check against the diagram that I sent as well. I've used that to build up two RPC's with good success.

    Note also the suggestions for capacitor size. (If you can read it. LOL.)

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    Here is the relay line drawing and specs.
    Still having difficulty with this.
    I cant make out the drawing you sent maybe to small.



    img_0731.jpgimg_0730.jpg

    Took the motor to the shop checked out fine.
    Thanks jeff

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    Here is another diagram that is clearer. It's one that I used on my 5 hp RPC.
    The potential relay shown in the sense section is a Steveco/White Rogers 90-66 (no longer made) but the Supco is a replacement for it.

    Cap values are roughly 100 mf per hp for start caps for 240 volt service and 10 mf per hp for run caps for 240 volt service.

    Hope this helps.
    Attached Thumbnails Attached Thumbnails rotary-phase-converter-schematic.jpg  

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    Thanks Newman.
    Ok sorted it out. I had a hidden load on start up. Not usefull.
    Not sure why the capicitors are connected like that looks different.
    The motor on the compressor is a 2speed 1 winding 10-5 hp. If i use the low speed will i have the same torque? Reasion im asking is that on high speed its slow start 5-8 seconds. Maybe thats not to bad.
    Also i switched to a steveco relay.
    Last edited by 4miller1; 01-04-2020 at 09:27 AM. Reason: Added info.

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    In that drawing looks like you have pin 5 on the generated leg?

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    Quote Originally Posted by 4miller1 View Post
    In that drawing looks like you have pin 5 on the generated leg?
    Yes , pin 5 is indeed connected to the generated lag, L3 in the diagram. Pin 5 is one side of the relay coil. The relay, being a potential relay and normally closed, will open when it senses the generated leg has risen above 208 VAC. That removes the start capacitor or capacitors from the circuit.

    By the way, this diagram is courtesy of and re-drawn from one given to me by Peter Haas, a member here. (The Haas of Haas-Kamp) He very kindly communicated with me on several occasions and explained the mysterious inner workings of rotary phase converters. He's a great guy!

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    Ok I see your using the relay for a contactor.
    Again thanks a million for your patience and help.
    Thanks. Jeff

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    Quote Originally Posted by 4miller1 View Post
    Ok I see your using the relay for a contactor.
    Again thanks a million for your patience and help.
    Thanks. Jeff

    Yes, that's correct. The contactor was used in the schematic shown to control more than one start capacitor. Two are shown. The contactor will close when power is initially supplied to it by the normally-closed points of the potential relay at startup. When the proper voltage is achieved on L3, the potential relay will pull open cutting off the current to the start contactor, thus dropping the start capacitors out of the circuit. In practice, this will occur almost instantaneously during the auto-start process.

    This setup is very reliable and minimizes the current carried by the points in the potential relay.


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