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  • Contactors on my mill question

    For educational purposes why is it a bad idea to use only one contactor to supply voltage to both the 3 motor drives and the spindle VFD? I was trying to think of a scenario where you wouldn't want one or the other killed in an emergency stop situation. It would be a simple wiring situation where the output of the contactor went to jumpered terminal blocks that would distribute the power to their destinations. I am only trying to understand the why's of the electronics. On the Centroid forum they tell me to use two contactors, one for the VFD and one for the motor drives power. I asked over there but no one answered. They also told me I should use 24v coils on the contactors. I have a bunch of contactors that came out of the mill and they all use 220v for the coils. It would be easy to wire them up but if 24v is better I will buy 24v coil contactors. I understand why to use 24v external homing/limit switches and 24v push buttons, etc. but don't see the harm in using the 220v coils inside the cabinet. So why is that?
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Because the switches to control the coils have 220 V on them and they are all over the place.
    ...lew...

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    • #3
      Originally posted by Lew Hartswick View Post
      Because the switches to control the coils have 220 V on them and they are all over the place.
      ...lew...
      NO there are no switches to control the coils. The coils are controlled by the motion controller board inside the cabinet. The only switch outside of the cabinet is the E-stop manual switch and that is 24v.
      Location: The Black Forest in Germany

      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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      • #4
        24v controls with 220v coils means you’ll be transforming down, then back up to run the coil. Would need a transformer for each contactor-becomes messy with multiple contactors.

        My understanding has been you don’t put switches between motor and VFD. I don’t see a problem with one master contactor.

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        • #5
          I'm talking about the "COIL" of the Contactor. . It has to be operated by one or more switches somewhere and they will have to be at the high voltage rather than 24 volts. Any voltage above 30V has to be wired the same as all your other "house wiring" .
          ...lew...

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          • #6
            VFDs and Servo drives have big DC capacitors
            and therefor a large inrush current. My buddy
            has a large 20hp VFD that he runs on single phase.
            He split up the capacitors on the DC buss, half
            and half. The first half comes in right away, but the
            second lot of caps comes in via a time delay relay,
            set for one second delay. That way the circuit
            breaker does not trip from the high inrush current.

            --Doozer
            Last edited by Doozer; 05-04-2022, 08:40 AM.
            DZER

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            • #7
              Originally posted by Black Forest View Post

              NO there are no switches to control the coils. The coils are controlled by the motion controller board inside the cabinet. The only switch outside of the cabinet is the E-stop manual switch and that is 24v.
              There would be the problem with using 240V coil contactors, your new motion control board is almost certainly not rated for such voltages on its I/O pins.

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              • #8
                The 'standard' recommended control voltage is now 24v DC, including contactor coils and solenoids etc.
                As to the contactor for the motors and VFD, in some cases you may want a controlled E-Stop for the VFD as allowed under NEC/NFPA79. To avoid dropping power when the motor is active.
                In order to do this, what can be done is use a E-stop contact in the VFD PLC stop input and then using a dedicated VFD contactor on the supply input, program one of the outputs on the VFD set for 'At Zero Speed' this output is then wired into the VFD contactor coil circuit.
                This enables a controlled stop, and prevents any likely damage to the VFD.
                Edit: You may need a e-stop N.C. contact across the VFD output relay in order to keep the relay contactor on when no E-stop present.
                There are other ways.
                Last edited by MaxHeadRoom; 05-04-2022, 10:05 AM.

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                • #9
                  Originally posted by Sparky_NY View Post

                  There would be the problem with using 240V coil contactors, your new motion control board is almost certainly not rated for such voltages on its I/O pins.
                  This is a direct copy and paste from the Acorn website. "The 8 relay module contains eight SPDT (Single Pole Double Throw) high current relays (10 AMPS at 250 VAC,and 10 amps at 30 VDC) which can directly control any device rated at or below the maximum rating of the relays."

                  The relays would only be controlling the 220v to the coil that activates the contactor. As I wrote before I am only trying to understand what is going on. I am not rejecting any of your input.
                  Location: The Black Forest in Germany

                  How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                  Comment


                  • #10
                    Originally posted by Lew Hartswick View Post
                    I'm talking about the "COIL" of the Contactor. . It has to be operated by one or more switches somewhere and they will have to be at the high voltage rather than 24 volts. Any voltage above 30V has to be wired the same as all your other "house wiring" .
                    ...lew...
                    The Coil of the contactor (or relay) can be any voltage, they sell 24, 120 and 240 volt ones. Someone said DC is also available?
                    Retired - Journeyman Refrigeration Pipefitter - Master Electrician

                    Comment


                    • #11
                      Originally posted by Black Forest View Post

                      This is a direct copy and paste from the Acorn website. "The 8 relay module contains eight SPDT (Single Pole Double Throw) high current relays (10 AMPS at 250 VAC,and 10 amps at 30 VDC) which can directly control any device rated at or below the maximum rating of the relays."

                      The relays would only be controlling the 220v to the coil that activates the contactor. As I wrote before I am only trying to understand what is going on. I am not rejecting any of your input.
                      I would never run 240 - 220 volts on those circuit board relays.
                      Retired - Journeyman Refrigeration Pipefitter - Master Electrician

                      Comment


                      • #12
                        Originally posted by MaxHeadRoom View Post
                        The 'standard' recommended control voltage is now 24v DC, including contactor coils and solenoids etc.
                        As to the contactor for the motors and VFD, in some cases you may want a controlled E-Stop for the VFD as allowed under NEC/NFPA79. To avoid dropping power when the motor is active.
                        In order to do this, what can be done is use a E-stop contact in the VFD PLC stop input and then using a dedicated VFD contactor on the supply input, program one of the outputs on the VFD set for 'At Zero Speed' this output is then wired into the VFD contactor coil circuit.
                        This enables a controlled stop, and prevents any likely damage to the VFD.
                        Edit: You may need a e-stop N.C. contact across the VFD output relay in order to keep the relay contactor on when no E-stop present.
                        There are other ways.
                        Wow, I think I actually understand this concept! I am shocked. You too probably. I am going to use a Hitachi Wl200 4kw VFD to run my 3kw spindle motor. Now I have to look at the manual and try to understand how to set this all up.
                        Last edited by Black Forest; 05-04-2022, 10:28 AM.
                        Location: The Black Forest in Germany

                        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                        Comment


                        • #13
                          OK I will ditch the 220v coil contactors and order 24v coil contactors. I was just trying to save money so I could feed my children. They are going to have to tuff it up now!
                          Location: The Black Forest in Germany

                          How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                          Comment


                          • #14
                            For an E-stop, there are options. A contactor in the VFD output is generally NOT going to fry a VFD. But it can allow the machine to continue moving by inertia. Either using the VFD to stop it, or cutting power and using a brake, would stop the moving parts.

                            If that is not a concern, many VFDs are rated as motor controllers, and may have "safe torque off" (STO) capability. That is low voltage DC connection to the output drive. If that is opened, the drive stops immediately, without requiring a contactor in the output, if you are concerned about (very unlikely) damage.

                            The combination of STO, power shutdown, and a brake can be very effective. The brake needs to be normally applied, and released by applied power.

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                            • #15
                              There is a brake on the spindle motor. It is a 220v brake and yes applying power releases the brake.
                              Location: The Black Forest in Germany

                              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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