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Contactors on my mill question

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  • #31
    Good decision from the engineering point of view. But if your children are anything like mine were/are, you better rethink the no feeding thing.

    A caution would be to look up the amount of current that/those 24 Volt control outputs can supply and compare it to the current the 24 V contactor coils will need. If there is not enough you would need to put a relay between them which uses a higher current rated source.

    As for all the worry about E-Stop, I personally do not like any kind of software or logic circuit based generation of such signals. In my mind an E-Stop is an EMERGENCY stop and should be used only in cases where life or limb is at stake. And in those cases, any damage to the machine or the electronic controls is of far less consequence. Thus an E-Stop should consist of the very simplest and MOST RELIABLE circuitry possible. I favor a NORMAL stop system for all other uses. If I design a control, like the one on my lathe, then the two can often be combined into one stop system. On my lathe any one of many switches in the open state if enough to stop it. If the relay/contactor 24V power supply goes bad, it stops. If the wiring breaks, it stops. Etc. Unfortunately my simple control circuit will not work with most VFDs.

    With a CNC system designed by others you may be forced to work with their limitations. Unfortunately, all to often the designs where price is often a big issue, rely on a number of components and/or software features. Failures in any of that can leave the machine running and unstoppable without pulling the power cord or switching the breaker in the building's breaker panel off.

    For better or worse, the designers of that system, are the best source for information on how to do wire it.



    Originally posted by Black Forest View Post
    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!
    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

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    • #32
      Out of interest, Google "24vdc control circuits in industrial equipment" 😉

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