rpc start circut problems
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  1. #1
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    Default rpc start circut problems

    I recently wired a 15 kva 240/600 to my FW RPC . To my surprise I learned that their had to be a switch between the rpc and transformer .

    I have dissconnected the transformer and now my rpc will not spin up to 1800 rpm . It just moans and rotates very slowly until it throws the breaker .

    Could that transformer have damaged the rpc start circut ? I tested the start caps ( 3 - 270uf ) with my multimeter and they act the same as a brand new one .

    leads of motor have 24-26 ohms between all phases .

    thanks
    Scott

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    What is motor voltage, and what are you actually giving it?

    If you NEEDED the 240-600V stepup, it's no wonder it will not work, you are giving it a fraction of normal voltage, so start torque is very low.

    If you did NOT need the transformer, what was it for?

    Obviously if you needed it as a step DOWN, you might have other problems, which you did not mention!!

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    i need 600 for a cnc mill but also need 240 3 phase for other machines . I am supplying rpc with 240vac single phase .

    my rpc has worked fine for years producing 240 3 phase .

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    My guess is that you are correct in that your starting circuit got over stressed, trying to start with your step up xformer connected during starts. Caps are know to overheat and fail with excessive starting currents. You said you checked the caps, did you check the running caps too? Running caps also contribute phase shift during starting as well as running modes.

    You mentioned the Fitch Williams design in use. Do you have a schematic that you used and some photos? That could certainly help, seeing what your working with. The Fitch design uses a start and run contactor, does both of these pull in while starting?

    Post up some details for better assistance.

    SAF Ω

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    I checked all caps with ohm meter . They all seem fine but I dont have the uf setting on my meter .

    Machine is reciving 240 vac , I tightened ever terminal inside rpc and both starters are pulling in .

    What are the chances the start caps are weakened by the overloading of the step up transformer ?


    Im going to track down a meter with a uf setting . .

    Thanks

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    I've tested all caps with a micro Farad meter. Everything checks out......... Run and start contractors are doing their jobs.

    I do however have another 270 start capacitor. What would be the worst thing that would happen if I added.it to the mix?


    The rpc currently has 3 of those 270 start caps on its start circuit.


    Thanks

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    I'm using the pdf download of the fw rpc schematic avaliable in this section.


    I know the wiring is a mess, was my first wiring job, I'll tidy er up though.
    Regards
    Scott

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    My fw ( ugly wiring job) rpc has ran for years. Worked really well, the start problems had only begun when I wired the transformer direct to rpc.
    Transformer is now disconnected, rpc will not start as it once had.

    What a drag........

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    The RPC will NOT start right with a load on it during start. Entirely possible that the added load caused damage due to excessive currents. So you will have to check everything again and make sure that it is all showing continuity when and where it should.

    I initially thought you had the transformer on the INPUT to the unit, and not on the load side.

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    The box below transformer has got the on delay relay and motor starter in it. It also controls pendent at 24vdc.

    I rounded up some new start caps today. They are half the size yet have the same numbers as my original.

    Problem solved..... Fw rpc running! Finally making 600 in my garage.

    Thanks pm


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