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Baldor 3-phase motor for RPC

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  • #61
    Originally posted by J Tiers View Post
    If the motor is turning under power, AND THE WINDINGS ARE GOOD, there is no alternative, it WILL produce "approximately" the same voltage across 1-2, 2-3 and 1-3 (3 is generated line), there is no choice, it is "baked-into" the way the motor works.

    Now, if there is a very heavy load on , say, 1-3, that may draw down the voltage and also pull a very large current.

    The first thing I would suggest (and I think I may already have done so) is to disconnect ALL the "run" capacitors. They are NOT required for generating voltage, they are for "tuning" it, if needed. So DISCONNECT the 2 and the other 5. Make sure the wires are not touching anything they should not.

    Make sure all loads of any sort are DISCONNECTED from the generated line output.


    The 40 HP motor will pull a bit over 100A if under full load, and on idle, it may pull as much as 40 or 50 A. I would NOT expect it to pull much over that just running with no run capacitors and no load.

    Power factor capacitors might help by reducing the no-load draw, but leave that until it is all working OK otherwise

    Okay, I just a little bit ago disconnected 3 run caps on L1&L3 and tried it. The motor wouldn't run on it's own.

    I'll try no run caps next.

    If it does run on it's own, what sequence should I start adding caps?

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    • #62
      Does the motor even try to start when the start capacitors are connected? I assume they are connected from T2 to T3 as shown in the schematic. You should be able to get a voltage reading approximately 150-220 VAC from T2 to T3 when trying to start, and a similar voltage from T1 to T3. Also, as I said before, the run capacitors should be on the same phases as the start capacitors. It would also be helpful to show voltage readings on all three phases with the Baldor motor disconnected.
      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

      Comment


      • #63
        Originally posted by PStechPaul View Post
        Does the motor even try to start when the start capacitors are connected? I assume they are connected from T2 to T3 as shown in the schematic. You should be able to get a voltage reading approximately 150-220 VAC from T2 to T3 when trying to start, and a similar voltage from T1 to T3. Also, as I said before, the run capacitors should be on the same phases as the start capacitors. It would also be helpful to show voltage readings on all three phases with the Baldor motor disconnected.
        The start caps are between T1&T3, I double checked to make sure I wrote that right on the schematic.

        The motor does not spin with the start caps alone.

        I tried many variations of disconnecting caps and nothing gets up to speed and steadily running except for 8 run caps on T1&T3. Even 7 caps wouldn't do it. I dropped from 4 caps from T2&T3 to 2 caps and it didn't really change the outcome.

        Comment


        • #64
          Well Fear ,I imagine you are pretty frustrated by now...take a deep breath..you need it.
          You are complicating the troubleshooting by having run Caps in the circuit..You do not need them !
          If the motor does not run without them, It is because there is a problem else ware .. Putting run caps in complicates the issue.
          Forget voltages ( for now)

          Three things I see
          Reading your schematic is a bit tough as control for the Start Relay looks to be a separate pushbutton. This can work
          if you hold down that button, then turn on power, and release the start button when up to speed.. Is this how you do it ?
          Your Start caps are too small. The general rule is 15 Mf per Hp , so your motor would need (15 x 40) 600 Mf at 370 V
          This formula is not cast in stone as motor characteristics can change this ,but you are at the low end.
          If you have all start caps installed and no run caps and the motor does not turn , Your relay or start control is not working or bad.

          Rich

          FYI
          There are 5 common methods to control Start caps on RPC's
          Separate Push Button engaging Start Cap when held
          Voltage sensing Relay
          Amperage Sensing Relay
          Timing Relay
          Centrifugal Switch
          Green Bay, WI

          Comment


          • #65
            Originally posted by Rich Carlstedt View Post
            Well Fear ,I imagine you are pretty frustrated by now...take a deep breath..you need it.
            You are complicating the troubleshooting by having run Caps in the circuit..You do not need them !
            If the motor does not run without them, It is because there is a problem else ware .. Putting run caps in complicates the issue.
            Forget voltages ( for now)

            Three things I see
            Reading your schematic is a bit tough as control for the Start Relay looks to be a separate pushbutton. This can work
            if you hold down that button, then turn on power, and release the start button when up to speed.. Is this how you do it ?
            Your Start caps are too small. The general rule is 15 Mf per Hp , so your motor would need (15 x 40) 600 Mf at 370 V
            This formula is not cast in stone as motor characteristics can change this ,but you are at the low end.
            If you have all start caps installed and no run caps and the motor does not turn , Your relay or start control is not working or bad.

            Rich

            FYI
            There are 5 common methods to control Start caps on RPC's
            Separate Push Button engaging Start Cap when held
            Voltage sensing Relay
            Amperage Sensing Relay
            Timing Relay
            Centrifugal Switch
            The start is doing something. I cut on power from L1&L2(1ph) to T1&T2(3ph) with the original momentary start button. The motor gets very loud without moving. I hit stop and it all goes dead. If I do it and hit the start button I put in place of the timer to engage the start contactor, it gets louder and scarier but doesn't spin. I hit stop and it goes dead. I spin it by hand and hit start on the run caps it gets loud, I then hit the start button on the start contactor and it spins up to a much higher speed and seems to behave until the breaker trips.

            I don't see how the start contactor isn't doing anything if it is spinning the motor faster when engaged.

            I am wondering about the speed. Most RPCs use a motor rated at under 2000rpm. This motor is rated twice as fast and I don't have a non-contact tachometer to verify, but it doesn't seem to be spinning all that fast when it stops accelerating while I'm holding the button down for the start contactor.

            I'm wondering if it running at half speed isn't what's tripping the breaker.

            I'm not getting the part about MFD. Each start cap is rated at 270-324MFD @ 330VAC and there's four of them. Since there's only 240VAC both single and three phase, 330VAC just seems like a happy max rating margin, 370VAC would be better like the run caps. Don't microfarads stack when run in parallel? (+/-1200MFD total?)
            Last edited by Fear; 06-07-2020, 08:22 PM.

            Comment


            • #66
              Fear
              Reading your schematic is a bit tough as control for the Start Relay looks to be a separate pushbutton. This can work
              if you hold down that Start button, then turn on power, and release the start button when up to speed.. Is this how you do it ?
              Rich
              Yes , Microfarads are additive when hooked in parallel
              Last edited by Rich Carlstedt; 06-07-2020, 09:30 PM.
              Green Bay, WI

              Comment


              • #67
                Originally posted by Fear View Post

                The start caps are between T1&T3, I double checked to make sure I wrote that right on the schematic.

                The motor does not spin with the start caps alone.

                I tried many variations of disconnecting caps and nothing gets up to speed and steadily running except for 8 run caps on T1&T3. Even 7 caps wouldn't do it. I dropped from 4 caps from T2&T3 to 2 caps and it didn't really change the outcome.
                OK, you need to be sure the start caps really ARE getting connected, and that they really DO get voltage when connected. If so, then you do not have enough of them, (although SOMETHING should be happening).

                One "rule of thumb" is about 100 uF per HP, which suggests 4000 uF, while you have only 1200 UF connected. Your 8 start caps if ALL between 1 & 3, would give you 2000 uF total, and you may need more than that much. But you do NOT want to have them always connected.

                I would, as a test, take ALL the RUN capacitors OUT, and re-connect them in parallel with the existing start capacitors. Start with 8 of them if that is what it takes. See if it starts. You should be able to replace those with the 300 uF start caps if you can get it running, so don't worry about the type for now.

                Your goal is to get the thing running, and NOT pulling a ton of current.

                MAKE CERTAIN that the contactor for the start caps closes when you want it to, AND OPENS when the button is released. If that does not happen right, stop and figure out what is wrong. The start caps HAVE TO BE out of circuit or they will nbe damaged, and the motor will draw a lot of current.

                See if that gets you running, and then after that the voltages can be adjusted if that is even needed (I forget what the eventual load will be, but I thought the 40 HP was more than needed)
                Last edited by J Tiers; 06-07-2020, 09:43 PM.
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #68
                  Here is a simplified schematic of what I think should be correct for this RPC. This is basically a single line diagram which shows logically how things should be connected, and not every physical connection or control wiring. The run capacitors should be on the same phase as those for the start. I still think the problem is that the start capacitors are on the phase opposite to where the run capacitors are connected, and thus the motor is trying to run both ways at once. No wonder it's grunting and growling!

                  Click image for larger version

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                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

                  Comment


                  • #69
                    Originally posted by J Tiers View Post

                    OK, you need to be sure the start caps really ARE getting connected, and that they really DO get voltage when connected. If so, then you do not have enough of them, (although SOMETHING should be happening).

                    One "rule of thumb" is about 100 uF per HP, which suggests 4000 uF, while you have only 1200 UF connected. Your 8 start caps if ALL between 1 & 3, would give you 2000 uF total, and you may need more than that much. But you do NOT want to have them always connected.

                    I would, as a test, take ALL the RUN capacitors OUT, and re-connect them in parallel with the existing start capacitors. Start with 8 of them if that is what it takes. See if it starts. You should be able to replace those with the 300 uF start caps if you can get it running, so don't worry about the type for now.

                    Your goal is to get the thing running, and NOT pulling a ton of current.

                    MAKE CERTAIN that the contactor for the start caps closes when you want it to, AND OPENS when the button is released. If that does not happen right, stop and figure out what is wrong. The start caps HAVE TO BE out of circuit or they will nbe damaged, and the motor will draw a lot of current.

                    ....................
                    My bad ...Thanks Jerry..yes,start are 100 Mf and run are 15Mf
                    Had my head up me you know where.
                    Rich


                    Green Bay, WI

                    Comment


                    • #70
                      Originally posted by Rich Carlstedt View Post

                      My bad ...Thanks Jerry..yes,start are 100 Mf and run are 15Mf
                      Had my head up me you know where.
                      Rich

                      [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

                      Comment


                      • #71
                        Originally posted by PStechPaul View Post

                        [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]
                        Sorry Paul , I can't get ,my head around that , it is too busy elseware ๐Ÿ˜€๐Ÿ˜€
                        Rich

                        appreciate the rant !
                        Green Bay, WI

                        Comment


                        • #72
                          I don't know how to type the upside-down lower case "h" for microfarad so I've just been using MFD.

                          How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?

                          Comment


                          • #73
                            Originally posted by Fear View Post
                            I don't know how to type the upside-down lower case "h" for microfarad so I've just been using MFD.

                            How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?
                            Dunno how to help with the rest of it, but you can use a lower case "u" instead of an upside-down lower case "h"

                            Comment


                            • #74
                              Originally posted by Fear View Post

                              How come most schematics for homemade RPCs show run caps between L1&L3 and L2&L3? Isn't it going to balance out (as in literally balance, like minimal vibration) if caps are spread more uniformly?
                              because the run caps are there to cancel motor inductance, they do not have to be from one line specifically the way start caps must be. There can be an imbalance of run caps on the two incoming lines to make adjustments to the phase, since the act of "almost fully" compensating for inductance still makes a bit of change to phase.

                              The motor itself produces correct phase even with NO "balance" capacitors. That is due to the location of the windings in the motor, which is acting as a generator for the "generated phase". They are already properly located mechanically to give the 120 degree phasing.

                              But you cannot make a total compensation for inductance or the voltage gets out of hand. That not-quite-complete compensation leaves some inductance uncompensated, which causes a slight phase lag of current. The extra capacitance to one or the other of the incoming lines "pulls" the phase slightly, so that it gives a good compromise overall. It is essentially a "final tweak" of the unit.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment


                              • #75
                                Originally posted by PStechPaul View Post

                                [rant] Microfarads are "uF", whereas "mF" is millifarads, so 1000 uF is 1 mF. And 100 Mf would be 100 Megafarads, which would be huge. Also, the abbreviation for Farads is a capital "F", for the proper name of Michael Faraday. [/rant]

                                Well, Paul, perhaps you haven't been dealing with old electronics - by "old" I mean from the twenties and thirties.

                                My first radio receiver was an RME (Radio Manufacturing Engineers) superhet, manufactured in '36 or thereabouts. The dial was calibrated in Kilocycles and the manual used MFD throughout. Tubes with grid caps on top. So MFD does have historical precedence.

                                BTW, for anyone who still cares about this, ยต is in the extended ASCII character set. Windows has it in the character map tool.

                                -js
                                There are no stupid questions. But there are lots of stupid answers. This is the internet.

                                Location: SF Bay Area

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