24VDC Relay Driver switching 240VAC 10A Load

Discussion in 'Electronic Projects' started by Ben Halicki, Apr 20, 2017 at 11:59 PM.

  1. Ben Halicki

    Ben Halicki

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    Hi Guys,

    I need someone to help me design a schematic for a basic relay driver (24VDC feed from PLC into optocoupler, which drives a relay). Pretty basic, but my main question is around the relay.

    The relay needs to switch 240VAC loads (up to 2400W / 10A). Is it possible / safe to have the relay mounted on PCB and be able to handle this sort of current, or would I be better off using an externally mounted relay?

    Thanks in advance,

    Ben.
     
    Ben Halicki, Apr 20, 2017 at 11:59 PM
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  2. Ben Halicki

    davenn Moderator

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    Hi Ben

    there are proper SSR ( Solid State Relays) available for this sort of thing. I would strongly suggest you get one of those
    It will simplify your project and be a hell of a lot safer :)

    google 240V switching SSR's

    Dave
     
    davenn, Apr 21, 2017 at 3:25 AM
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  3. Ben Halicki

    Minder

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    Another solution is to use a contactor, these are traditionally a large form of a relay so it would be mounted separate to any PCCT board.
    M.
     
    Minder, Apr 21, 2017 at 4:21 AM
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  4. Ben Halicki

    AnalogKid

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    With proper attention to trace width and copper thickness (weight), a pc board design can handle your voltage and current easily. After all, they are common in many power supplies.

    Since a relay has true galvanic isolation, why do you have an optocoupler between it and the PLC? Very few optos can move the current needed by the coil of a relay with those contact ratings.

    ak
     
    AnalogKid, Apr 21, 2017 at 5:27 AM
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    hevans1944 likes this.
  5. Ben Halicki

    Tha fios agaibh

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    Why not just buy relays with 24vdc coil?

    Btw, If your plc output card has common terminals for internal contacts, you can feed it with other than 24vdc.
    Example; feed common terminal with 120v so it outputs 120v. Of course you need to observe its rating.
     
    Tha fios agaibh, Apr 21, 2017 at 5:35 AM
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  6. Ben Halicki

    davenn Moderator

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    he's dealing with higher voltage and significant current

    SSR's are a very way to handle that
     
    davenn, Apr 21, 2017 at 7:15 AM
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  7. Ben Halicki

    Tha fios agaibh

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    I agree, but SSR's can get expensive and they tend to fail more often than a mechanical relay.
    A relay or contactor (coil) that matches the PLC output voltage is usually the best plan.

    I wasn't suggesting attaching the load directly to the PLC output card. I was merely noting that a PLC can often be rewired to suit the output voltage desired for a relay that one might already have on hand.
     
    Tha fios agaibh, Apr 22, 2017 at 6:52 AM
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