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  1. #1
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    Default Electrical help? Connecting a servo with surge suppressor

    Hi all so I got this picture in the Chinese manual for my servos that are going on my HM-46 mill:
    img upload

    Was hoping someone could help me select a contactor online I could buy. Looks like I need a contactor with surge suppression so I started looking.... 240v should do it with a 24V DC coil.
    I got 4000 to go through on RS Online - https://au.rs-online.com/web/c/autom...Term=contactor
    Not sure on the differences between them all but will this one do the job? It's the cheapest at 24V DC coil - https://au.rs-online.com/web/p/contactors/7061106/
    Datasheet says size "S00" and I looked for a surge suppressor and this one is for "3RT2" but size S2 - https://au.rs-online.com/web/p/conta...ories/1271495/
    I found some more here and was hoping someone could point me in the right direction it's a bit confusing with all the specs on voltage on the datasheets - https://au.rs-online.com/web/c/autom...434,4294639534

    My servos are three 3 750W and I also have one 1.8kw servo (spindle).
    Hoping the breaker is a fair bit easier to find.
    Thanks for any help.

    edit - The servos take single phase voltage (240v) as well as 3 phase - just connect two wires. And are surge suppressors just for the A1 A2 and to protect whatever controller you hook up to it?

  2. #2
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    Default

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  3. #3
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    Default

    Hi,

    Normally the "Median Filter" takes care of any spikes or other interference on the supply lines. Now whether any surge suppression is needed on the contactor coil or not depends upon whether the coil is fed with AC or DC. If it is AC then a simple capacitor across the coil, say 0.1uf would work, if it is DC then a snubber circuit, a "Resistance plus a Capacitor" in series across the switch contacts to reduce or prevent arcing. The component values would depend upon the current drawn through the switch. 0.1uf + 200 ohms would be a good start.

    Hope this helps.
    Best Regards:
    BaronJ.

  4. #4
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    Default

    Quote Originally Posted by BaronJ View Post
    Hi,

    Normally the "Median Filter" takes care of any spikes or other interference on the supply lines. Now whether any surge suppression is needed on the contactor coil or not depends upon whether the coil is fed with AC or DC. If it is AC then a simple capacitor across the coil, say 0.1uf would work, if it is DC then a snubber circuit, a "Resistance plus a Capacitor" in series across the switch contacts to reduce or prevent arcing. The component values would depend upon the current drawn through the switch. 0.1uf + 200 ohms would be a good start.

    Hope this helps.
    I will be using 24v control voltage contactors, main load is 240v AC.

    Are you able to show me an image of a suitable circuit? Thanks... [edited]

    Here is a circuit someone on the internet suggested would be suitable for the application:

    [/url]

    In my application as I don't know if I need overload protection (normal for servos?) I guess I'll need less poles on the contactor - but it was also suggested to me to use one contactor for all 3 axis servos.
    Is that -| |- sign to the left of M1 an electromagnet that closes M1, and M1 also closes the main voltage contactor? The Start/Stop are NO buttons/switches that are only on as long as you hold down the button? I am a bit confused by the above circuit, stared at it for a while.

    [edit 4] I am surprised a median filter could deal with a voltage spike caused by rapidly shutting off the big main load. Does a servo ever use a braking resistor btw? - saw a few circuits with VFDs that used braking resistors. Thanks again.

  5. #5
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    Hi J3dprints,

    In the circuit above the +positive line goes to point 53. This point is connected to one side of the start button and one side of a contact operated by the contactor. The other side of this contact numbered 54 is connected to the junction between the start and stop buttons.
    M1 is the contactor operating coil. A1 and A2 are the connections to the coil. 95 and 96 are the connections to a normally closed contact on the thermal overload.

    What happens is this: When the start button is pressed current flows from the +positive line, via the start button and via the stop button, via the points 96 and 95 to the coil at A1 and A2 into the -negative power line. The coil closes the contacts at 96 & 95, locking the contactor closed. In turn supplying power to the motor. Pressing the stop button or the thermal overload contacts opening breaking the circuit will cause the contactor to disengage.

    You mentioned earlier surge suppression ! A capacitor, sometimes built into the contactor is used to suppress any arc that may occur across points 53 - 54.
    A 0.1 uf capacitor of 100 volts or greater working voltage can be used for this purpose. Only because the DC voltage is quite low. Some systems may use much higher voltages including the 230 volt AC mains.

    If I were wiring that motor I would not bother using L3 - T3 and use T1 & T2 for the motor and L1 - L2 for the live and neutral power feed. This will take one set of contacts out of the circuit, increase reliability and give you a spare set of contacts should you need them in future.

    HTH.
    Best Regards:
    BaronJ.

  6. #6
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    Thanks, I think I was confused.... I just realised the surge suppression is for disconnecting the contactor coil, I thought you might some sort of protection for the main load itself as it is a motor + driver (servo/servo drive). So any sort of surge suppression will be built into the contactor itself and sized based on its own known coil characteristics... Should be simple shopping then.

  7. #7
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    Hi J3d,

    Yes the difference between surge suppressed contactors is just the capacitor, though sometimes there may be a resistor in there as well.
    Personally I would just stick a capacitor across the contacts. Might be cheaper as well.
    Best Regards:
    BaronJ.

  8. #8
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    And there wouldn't be any requirement for surge suppression on the main load? I thought their might be since the contactors could open rapidly if an e-stop was hit, or the breakers before the contactor could activate quickly. Since the servo motor is an inductive load (I guess?) I thought it would have the bigger requirement.
    The manufacturer in their pic above just wants it on the contactor coil?

  9. #9
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    Hi J3D,

    If you were that concerned you could add a capacitor across the main contactor points, but I wouldn't bother ! The driver circuitry should take care of any of those issues. Also you might find that adding a capacitor like that, disturbs the driver behaviour.
    Best Regards:
    BaronJ.

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