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What is the meaning of "110V AC / 24 DC relay"?

  1. Mar 23, 2017 #1
    I have seen some relays mentioned as 110V AC/ 24V DC relay. Is this means, can I use both 24DC and 110V AC to the coil of relay?
  2. jcsd
  3. Mar 23, 2017 #2
    Could you please give us a link for one such relay?

    Regarding the coil, the AC and DC requirements are usually the same. So a relay designed for 24V AC should be OK for 24V DC.

    However: regarding the poles the AC and DC ratings are different. It's less stressing to switch AC voltage, so the limit for AC is always higher.
    To switch off DC voltage is the most stressing. I think that 110V AC/ 24V DC will be about this, but without further input I cannot be sure.
  4. Mar 23, 2017 #3


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    and to expand of Rive's good response, there will usually be a current rating in amps along with the voltage for the relay contacts
  5. Mar 23, 2017 #4
  6. Mar 23, 2017 #5
    That's not for a single relay, but for a family. Within the family the contact rating is '10 Amps contact rating at 24V DC or 230V AC', and the coil ratings are 'from 6volts to 110V DC and upto 230V AC with phenolic cover'.

    This family consists of 10-20 different relays with various coil ratings, contact arrangement and chasing options.

    Ps.: and yes, on the contacts for 10A these relays will bear 24V DC or 230V AC. The limit for DC is far lower than for AC.
  7. Mar 23, 2017 #6
    I have to make chattering relay with above spec. I was using the below circuit for relay chattering. Now with the above relay if I connect 110V AC instead of 12V DC, it will work as same right?
  8. Mar 23, 2017 #7
    Not likely. If that relay coil works at 12V then 110V AC will most likely break/burn it within seconds.

    The contacts might survive, if that's any help :angel:
  9. Mar 23, 2017 #8
    Let me take the first relay spec, they have given the relay work either in 24V DC or 240V AC, so in the above circuit, if I am connecting 240V AC with the first relay, the chattering circuit should work right?
  10. Mar 23, 2017 #9
    In a relay you have the coil and you have the contacts. These are different things.
    For that relay the rating for the coil is 12V (or something in this caliber, since it works at this voltage).
    For the contacts, the rating is 24V DC//240V AC (for 10A at most).

    Don't mix the different ratings. If you try to apply 240V AC for the coil, then it'll be far out of it's rating.
  11. Mar 23, 2017 #10
    Just see this product info. It has mentioed the coil DC volage range and AC voltage ranges. For this relay, will it work in both AC and DC volages?
    http://oenindia.com/uploads/products/58_20160601032651.pdf [Broken]
    Last edited by a moderator: May 8, 2017
  12. Mar 23, 2017 #11
    That product info sheet is also about a whole family.
    The 24V AC version will ~ work as the 12V DC version, but for this family this kind of operation is out of spec. I do not recommend it. Buy the right tool for the job.
  13. Mar 23, 2017 #12

    jim hardy

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    Not so at all.

    A DC relay coil has enough resistance to limit the current through it to whatever the designer wanted it to be.

    An AC relay coil has far less resistance, instead depends on its inductive reactance to limit coil current.
    When first energized it draws several times its rated current and does so until the armature plunger moves into position reducing the air gap which raises inductance, pushing coil current back down to design value. Inrush might be 10X steady state current.
    AC relays also have ,magnetic shading on the pole to prevent buzzing when closed , DC poles don't need it because there are no zero crossings.

    Panasonic says about relay coils:
    Apply 24 volts DC to a 24 volt AC relay coil and you'll probably let the smoke out of it in just minutes.
    Here's a snip from the datasheet of that relay
    http://oenindia.com/uploads/products/58_20160601032651.pdf [Broken]

    Calculate the power in each with 24 volts DC applied , E2/R , to convince yourself .
    Last edited by a moderator: May 8, 2017
  14. Mar 23, 2017 #13
    I have this relay with me. My doubt is whether can I use AC across coil and make a chattering circuit>?
    Last edited by a moderator: May 8, 2017
  15. Mar 23, 2017 #14

    jim hardy

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    What is rated voltage and frequency of is coil?
    A 24 VAC coil will be ruint by application of 24 VDC.
    A 24 VDC coil will not be harmed by application of 24 VAC . But it might not pull in its armature to close the contacts, either.

    One experiment is worth a thousand expert opinions.
  16. Mar 23, 2017 #15
    Yep. It seems I messed up that part.

    I won't try it above 24V AC without measuring the actual current through the coil.
    And I won't try it above 30V AC at all.
  17. Mar 23, 2017 #16
    By this specification what it means? I have a Eagleman relay, their website showing these details only.
  18. Mar 23, 2017 #17


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    not mains AC

    the pic of the one you have shown is a 12V coil

    As Rive said many posts ago .....................

    so if you put anything significantly higher than 12V across it, it will fail

  19. Mar 23, 2017 #18

    jim hardy

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    you have to work with what information you have, or find a better spec sheet.

    I see no direct statement whether that coil is for AC or DC voltage.

    If coil power is as they stated 1.5 to 1.2 VA , at 12 volts (as written on the side of the relay ) that would mean 0.125 to 0.100 amps

    which at 12 volts would be 96 to 120 ohms of impedance. Is that impedance all resistance or is it the sum of resistance and reactance?
    What does your ohm meter show for resistance of the coil ?
    If it's much less than 96 ohms you'd better not apply very much DC to it.
  20. Mar 25, 2017 #19
    No it means the relay is operated by a 24V DC voltage to control a 110AC source.
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