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  • Need help with rotart converter-PICTS

    I have a friend, Bill Cogger (BigBoy1) in Elizabeth City, NC who built a rotary converter using the circuit I put together. The circuit is shown in my old thread
    http://bbs.homeshopmachinist.net/showthread.php?t=33353
    and works fine for me.

    He has built it and the start circuit works fine, but the motor will not start.

    The motor will turn slowly, hum and heats up. We have not run it for more than 10 seconds at a time, not wanting to harm anything.

    Some things I have noted:
    Bill used the size capacitors as I specificed for a 5 hp motor, but he has a 2 hp motor. He has 50 mf on the run capacitors, and a 250-324 mf on the start. To eliminate some questions, I disconnected the run capacitors, no change. I changed the start capacitor for the run capacitor, no change.

    I took his motor, a 2hp 3450rpm motor, and tried it with my rotary converter. It started and ran fine.

    I took the start capacitor from my converter, and wired it in to Bills box, no change.

    Some voltage readings:

    Across the start capacitor: buildup to 110VAC, then no more. Shut down after 10 seconds.

    T3 to T1 or T2: 110 VAC

    T! to T2: 240VAC

    The start relay never opens when attampting to start. Presumably not high enough voltage to open the switch.

    Here are some pictures of his unit:








    See next post for more picts...

    Steve

  • #2
    More picts...

    Here are a few more picts...









    Anyone got any ideas on what is wrong? I can't figgure it out.

    Remember, the start circuit works fine, the run caps are out of the circuit for simplicity (and it didn't work with them in either).

    The start cap size is a bit big, but it should still work.

    Steve

    Comment


    • #3
      Later, with more data...

      I completly dismantled what Bill had wired, and re wired it, testing as I went.

      The start circuit worked fine.

      I wired up the start capacitor and the start relay with nothing else in the circuit, it started correctly. Only tried it one time, tho.

      Wired in both run capacitors, would not start. Disconnected the run capacitors, ran once, then DID NOT START. Ran a test sequence of six starts in sucession, got 4 out of 6 good starts with 2 no-starts.

      Right now I am thinking the too-large capacitors might be the problem.

      Any thoughts on this?

      Steve

      Comment


      • #4
        If it's for an RPC on a 2hp motor the cap should be 160mf,no more than 200mf.The run cap isn't even needed except to correct power factor.
        I just need one more tool,just one!

        Comment


        • #5
          I am not a fan of having two run caps, coming from each side of the line.
          I know there are those who bless it, but I have found that they sometimes interfer with each other. I suggest you drop one Cap permanently.
          I also believe that 3400 motors are more difficult to start, based on my experience

          1. If you use a run cap, make sure it is on the SAME LINE side that the start cap is .
          2. 100 MF for run is way too high for a 2 HP motor. You want 10-15 MF per HP---MAX.
          3. You did not define your start relay ?? it sounds like the relay is dropping too fast. This is common with 3400 RPM motors.
          You want a Relay with 185 to 200 drop out voltage rating.
          MF on the START is not as critical as RUN. if you over do it(START) , the voltage rises faster and the voltage relay accomodates it. I like 100 MF per HP, but your 250 should work fine.
          4. If you intend to start the convertor in rapid sucession, make sure you have bleeder resistors accross the caps to save your relay


          Rich
          Green Bay, WI

          Comment


          • #6
            I am personally in favor of two run caps, but they are never the same size. I choose the run caps to balance out the voltages dependent upon load. For example, with a 5 HP RPC, I have found that 60 uF on one leg (same side as start cap per Rich's point), and 25 on the other works best. Two 50's are no good for a 2 hp, try 25 and 10, for example as a starting point.

            I just tried to look up the relay on Grainger; but the site is down for maintenance. You either drew your schematic incorrectly, or you are using the wrong relay; the relay (and schematic) should be NC. Check this out; if you drew your schematic according to the relay schematic, then you have the wrong relay.

            Comment


            • #7
              Suggest you take out the run caps, and then work with it that way until it is reliable. Then you can mess with run caps if you want. They are not required.

              If the start cap is TOO BIG, it will essentially connect the drop-out relay across the incoming line and give it too much voltage too early, so it might drop out before the motor gets going...... try moving toward the lower end of the range, closer to 50 uF per HP, and see whether it starts easier.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Good comments, I will suggest to Bill that he get a smaller start cap, not connect the run caps, and see what happens.

                Yes, I did draw the start relay wrong, it is a NC type with a 150-180 pull- voltage rating. It is the one recommended by several web sites I had visited.

                I had noticed relay arcing when I tried to restart several times in quick succesion, I will try bleed resistors on the caps.

                Thanks for all the comments, its a great help!

                Steve

                Comment


                • #9
                  I'm just curious. In the line drawing, it appears that the Neutral has been tied to L2 from the 240 VAC source. Is that OK? I thought that L1, L2 and Neutral were to be kept separate on a single phase system.

                  It's possible that my converter is wired the same way but the company that built mine doesn't like to give out their specs. They only give a wiring diagram for hookup so it might be similar to yours inside and I wouldn't know it.

                  Just wondering.......
                  Last edited by gnm109; 05-10-2009, 04:58 PM.

                  Comment


                  • #10
                    Voltage ratings:
                    Check your run cap voltages.
                    I just noticed you have 270V and they should be 370v

                    Relays:
                    Lower voltage <180 relays require a bit more Mfd
                    180-200 volt pull in respond to lesser Mfd ( like 100/hp).
                    Having Run relays means their Mfd must be used in the calculations
                    Modern motors with little Copper and lots of Aluminum do change the characteristics of a start circut and make it more difficult.

                    Just my opinion but:
                    For balancing legs, try to use amperage instead of voltage.
                    I have used both.
                    Voltage is "potential", while amperage is "power" and more closely reflects true performance, as the wave form is not a sine wave

                    Rich
                    Green Bay, WI

                    Comment


                    • #11
                      Gmn 109
                      Technically the wiring diagram is in violation of (NEC and many Local) code.
                      Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
                      Correct application is to add a 240 / 120 stepdown transformer and use that for control circuts, OR , you can use a 240 volt control circut ( but that is not legal in some localities)
                      I admit, I have done all of the above, but it is a good idea to always fuse the control circut seperately whether you use the unbalanced method or the transformer

                      it may also explain why the company will not provide you the info ???

                      Rich

                      Why the worry ?
                      Even the NEC and the Insurance Industry are wrong in some instances.
                      I worked for a company that had 2 boiler explosions caused by a 240 control circut. What was embarassing was that after the first explosion (200 HP Boiler !) about 6 inspectors( State, Insurance etc) did not pick up the cause which resulted in the second explosion 6 months later.
                      The 240 volt water control relays when exposed to dampness leaked voltage to ??? - ground. ( 120 potential)
                      Happens that only one side of the 240 leg was shut off during failsafe operation, but the other leg, leaking to ground, held the relays in--depriving the water pumps from turning on>> BOOM is the result
                      No one was killed luckily in either case, but lots and lots of damage

                      The solution was a isolation transformer and all new 120 volt controls..3 million dollars later
                      Green Bay, WI

                      Comment


                      • #12
                        Originally posted by Rich Carlstedt
                        Gmn 109
                        Technically the wiring diagram is in violation of (NEC and many Local) code.
                        Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
                        Rich
                        Someone had better tell that to the stove manufacturers....... they often have 220 in but 120V lights and timers etc.

                        In fact, there are special 4 wire plugs for those appliances so that the neutral is able to be supplied..... a change from earlier NEC which allowed the neutral to double as an equipment grounding conductor for stoves........

                        For an incidental load like that relay, the imbalance is below negligible.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          Originally posted by Rich Carlstedt
                          Gmn 109
                          Technically the wiring diagram is in violation of (NEC and many Local) code.
                          Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
                          Correct application is to add a 240 / 120 stepdown transformer and use that for control circuts, OR , you can use a 240 volt control circut ( but that is not legal in some localities)
                          I admit, I have done all of the above, but it is a good idea to always fuse the control circut seperately whether you use the unbalanced method or the transformer

                          it may also explain why the company will not provide you the info ???

                          Rich

                          Why the worry ?
                          Even the NEC and the Insurance Industry are wrong in some instances.
                          I worked for a company that had 2 boiler explosions caused by a 240 control circut. What was embarassing was that after the first explosion (200 HP Boiler !) about 6 inspectors( State, Insurance etc) did not pick up the cause which resulted in the second explosion 6 months later.
                          The 240 volt water control relays when exposed to dampness leaked voltage to ??? - ground. ( 120 potential)
                          Happens that only one side of the 240 leg was shut off during failsafe operation, but the other leg, leaking to ground, held the relays in--depriving the water pumps from turning on>> BOOM is the result
                          No one was killed luckily in either case, but lots and lots of damage

                          The solution was a isolation transformer and all new 120 volt controls..3 million dollars later


                          It's possible that the company that built my RPC did the same thing with the neutral, but it's more likely that they don't want aoyone building them from their drawings.

                          My RPC does have a start relay but it could be that it operates from the 240 VAC for all I know. We shall see.

                          All I really needed is the hookup drawing that was supplied with the unit. If it ever breaks down, I'll figure out how it was wired as I rip it apart. LOL
                          Last edited by gnm109; 05-10-2009, 09:12 PM.

                          Comment


                          • #14
                            J
                            The stove people have their own lobbiests for the code.
                            It's even specifically covered in the NEC, unlike other home stuff
                            Yes, they now do use a 4 wire for new installs.
                            They may have transformers too..but I don't know about that
                            Check local codes fellows. Here in Green bay, it is not legal to use the neutral on your 220 lathes or mills, or for rotary convertors.
                            they are classified as appliances/tools
                            Fires have started from mere neglible loads.

                            GMN 109
                            Take the control box apart and record the wire runs.

                            Rich
                            Green Bay, WI

                            Comment


                            • #15
                              There are a number of other items that also use the neutral..... those plugs are used on other things as well, I believe dryers, etc. The application is common enough that a class of plug is sold at any big-box store (type L14-20, IIRC) which includes both hot wires, NEUTRAL, and equipment grounding conductor. Nominally, they are for generators, but.......

                              30 and 50 amp 4 wire plugs are also sold, similar to the old stove/dryer plugs, but including 4 prongs, for the new stoves and dryers.

                              Yes the stove people do strange things.

                              Yes, it is a better idea to use 220 or a transformer, even if simply on the basis of deriving control from the same source as the power, so that it is less likely to fail independently. That is sufficient to account for it being frowned upon without any spurious notions about unbalance.

                              However, I don't think there is any justification whatever for demanding it on the basis of balance..... That is basically BS.

                              When any person can plug in 1200W of heater on any 120V circuit, which is an unbalanced load by definition, there is no rational or sane reason for suggesting that a hundred milliamps of unbalance is dangerous and likely to cause a fire. Not unless the neutral is undersized.

                              While there are some failure modes which could impose 220V on that 120V coil, those failure modes will also smoke at least half of the 120V devices in the structure, so even those reasons are BS.

                              The transformer is the better choice overall, code notwithstanding.
                              Last edited by J Tiers; 05-10-2009, 10:01 PM.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment

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