Need a little help with my RPC build.
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  1. #1
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    Default Need a little help with my RPC build.

    So I finally made the time to assemble my RPC.

    I used an old 7.5HP General Electric motor that I scrounged from a friend many years ago in plans for this build. Here is a photo of the tag,

    I had a hard time figuring the necessary heaters for the AB Overload Relay 592-BOV16 that I used. They make that part very confusing to someone new to that aspect. Anyway I ended up figuring that I needed W43's.

    Now that the unit is running I can hear that the motor bearings are very noisy! Too loud to tolerate for very long in the shop. But I am having an issue with the Overload Relay getting hot and popping the circuit.

    I can feel the heat in the W43's and they get too hot to touch. But cool down and I can start up the unit again after. So I was able to run the RPC long enough to take some measurements.

    My line in is 241V.

    My 3 phase voltages are,

    A-B = 242V
    A-C= 240V
    B-C= 262V

    So it seems that I need to do some balancing on the run caps. Not surprised at that.

    So how do I get the Overload Relay to cool down? Is it a problem with the heaters that I choose? An issue with the motor itself? Windings? Or the bearings?

    I did take the motor apart for a good cleaning and cleaned out the bearings and fresh grease today after my first test yesterday. Reassembled and still noisy bearings, and got the test results posted.

    So I don't know how to proceed. I hate to spend money on bearings if the motor is just bad. Not sure of the heaters that I spec'd. Maybe they are too "small" for the load.

    Any pointers on how to move on this? Would balancing the output have any affect on the heaters?

    Can I check the windings?
    Attached Thumbnails Attached Thumbnails cropped.jpg  

  2. #2
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    Thought I'd add a bit more info that I just found.

    So I wired the motor based on the labels that were on the wires from the previous user. I did a search to determine if that was correct. It seems that it is correctly wired for my use. It is a 9 wire motor, wired as a Lower Voltage (230V) Wye start motor. Here is a copy of what I found.

    "Three-phase motors with 9 leads are nearly always dual-voltage motors. Connecting these is a bit more complicated, and mistakes are actually common. Typically, these motors don’t permit a wye start with delta run; you can usually wire them only for a delta start. But there are exceptions (IEC motors, for example).

    For the wye start, dual voltage nine lead motor on the lower voltage, connect 1 and 7 to L1, 2 and 8 to L2, and 3 and 9 to L3. Connect the remaining leads (4, 5, and 6) together. For the higher voltage, connect 1 to L1, 2 to L2, and 3 to L3. Connect 4 to 7, 5 to 8, and 6 to 9.

    For the delta start, dual voltage nine lead motor on the lower voltage, connect 1, 6, and 7 to L1. Connect 2, 4, and 8 to L2. Connect 3, 5, and 9 to L3. For the higher voltage, connect 1 to L1, 2 to L2, and 3 to L3. Connect 4 to 7, 5 to 8, and 6 to 9."

    I also checked the amperage going from the Overload Relay to the motor.

    A= 7.0A
    B= 16.5A
    C=13.3A

    Seems odd that they are so different, but still below the 21.6A on the plate. Although there is no load on the motor, not sure if that matters in this instance.

  3. #3
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    My internet search shows W43 heaters are reated for 4 amps. So I would expect them to trip. That makes me ask what size starter do you have. It should be at least a #1.

    As far as the noise goes, RPCs do not run quiet. The imbalaced loads cause vibration. I recommend that the idler not be in the shop.

  4. #4
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    Quote Originally Posted by Bill Simmons View Post
    My internet search shows W43 heaters are reated for 4 amps. So I would expect them to trip. That makes me ask what size starter do you have. It should be at least a #1.

    As far as the noise goes, RPCs do not run quiet. The imbalaced loads cause vibration. I recommend that the idler not be in the shop.
    Thank you Bill.

    I appreciate the help, so don't want to sound rude but what did you search to find that W43 is rated for 4 amps? I ask because when I started to figure out the parts list I was totally confused by the way they spec out the heaters. It's been over 1 year now, but as memory serves me part of my confusion was that my old motor has a 1.0 Service Factor where as newer motors are 1.15 SF and the charts are all based off of the newer SF ratings.

    Not sure what you are asking about a size starter. I am using Start Capacitors to start the motor. 2 caps rated @ 216-259MFD Start Caps 220-250VAC.

    I think/hope that new bearings will help the noise issue. Although I am surprised that it is so loud after cleaning the bearings of the old grease they seemed to be OK. I didn't expect them to be this loud. You are probably correct on the imbalance issue.

    Frustrating being so close after all this time. Almost feel that I should have just bought one, but where is the fun in that.

  5. #5
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    Heaters are rated based on motor current. A good starting point is the full load current on the data plate. For a 7.5 hp motor it will be about 21 amps. Allen bradley says that w type heaters should be sized at 115% of FLA. I just googled w43 heater and several vendors popped up and clicked on Rexelusa and one other and got similar ratings. To find the proper heater you should use a manufacturers chart. The chart should be based on current, not motor parameters.

    The chart you want is available at rockwell automation.

    The starter is the combination of your heaters and the contactor they are attached to. This is what I believe you are calling an overload relay. They come in sizes like shoes. Yours is either a size 0 or size 1 as that is what a w43 will fit. The size should be on a label on the starter (contactor). According to the chart a w60 is rated for 23.8 amps and should only be used in a size 1.

  6. #6
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    Well I got the heater issue sorted, kinda. In my recent research I remembered/found this thread that I had started last year when I was working on gathering up parts.

    Sizing Overload Heaters?

    I never did really decide if I need W59, or W60 heaters. But at some point I had received a set of W59's. No idea how I came up with the W43's probably installed in something I bought along the way.

    So the W59 seems to be working so far. YAY!

    Now I got it running and have done my best to balance the phases. I'll start another thread to see how well that has gone.

    Thanks for the help, again on this. That 1.0 SF still has me twisted. But I think that I got it close.


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