How to find polarity of nonlatching relay?

Discussion in 'General Electronics Chat' started by geratheg, Aug 6, 2014.

  1. geratheg

    Thread Starter Member

    Jul 11, 2014
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    I have the datasheet for a relay I'm using, and I know what the polarity is.

    However, what if the datasheet was not available, I can find out which contacts are supposed to by powered from a supply just by the resistance. But how would be able to find out which way current is supposed to go?

    Here is the relay I'm referring to: http://www.futurlec.com/Relays/HFD31-12.shtml
     
  2. Brevor

    Active Member

    Apr 9, 2011
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    Connect it to a DC supply and see which way(s) works.
     
  3. geratheg

    Thread Starter Member

    Jul 11, 2014
    107
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    Ok, that's easy. I thought maybe there was a method of doing this with just maybe a multimeter and without a power supply.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Most non-latching relays are not polarity sensitive.
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    It would be interesting to know for the relay in question if the coil is actually polarized for correct operation. I wouldn't be surprised if the DC could be applied to the coil in either direction without any loss of functionality.
     
  6. Ramussons

    Active Member

    May 3, 2013
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    Some relays have an In Built Surge Suppressor using a Diode. These relays have a polarity. I have quite a few DPDT 12 Volt relays in TO-18 package that have polarity marked.

    Ramesh
     
  7. geratheg

    Thread Starter Member

    Jul 11, 2014
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    Checked it, polarity matters. Otherwise it won't switch the connection.
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    According the the pin-out diagram in your link...if polarity mattered...pin #1 is (+). But that is probably of a consequence only in the single coil, latching versions. Yours can go either way.

    Ken
     
  9. geratheg

    Thread Starter Member

    Jul 11, 2014
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    Mines is non-latching and polarity does matter. It would make sense for polarity to not matter, hmmm but it does matter for me. Otherwise the switch doesn't switch if I reverse the polarity. It only switches with the correct polarity.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is the exact part No? there are three versions of your relay?
    pin 1=+v 10=-v even for the non latching, per the spec sheet.
    Max.
     
  11. Alberto

    Active Member

    Nov 7, 2008
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    It only switches with the correct polarity.

    Then as already mentioned in post #6 your relay has a diode across the coil. So you must respect the polarity.

    Alberto
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The spec shows it is a polarized relay, and no diode is shown in the diagram, just that it will not operate unless correct polarity, if a diode was present, it would most likely have blown open by now if connected wrong.
    Max.
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Odd too! On the non-latching and single-coil latching relays they show the coil polarity. But on the two-coil latching they show polarity for the Set coil, but not for the Reset coil.

    Ken
     
  14. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Read "Notice 1)...." on the last page of the data sheet. ;)

    Ken
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see it on the spec sheet as 1+ 5- for latch and 10+ 6- unlatch?
    Max.
     
  16. KMoffett

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    Dec 19, 2007
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    I was looking at the right most image on page "59" of the spec sheet in his link. Where did you see it?

    Ken
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    On P55 PDF.
    Max.
     
  18. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Ah! A different link. I went by the one in Post#1

    Ken
     
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