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Relay Testing

Discussion in 'Troubleshooting and Repair' started by biglar, Aug 11, 2013.

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  1. biglar


    Aug 11, 2013
    Hi- This is my first post; sorry if a newbie question...

    I'm trying to test 2 relays on a board. (The board is for a life fitness treadmill that stopped working). Both relays are 5 pin "CO" type. (one leg is open while the other is closed when de-energized- if energized the opposite occurs: with the first leg getting closed and the second getting open). The first relay tests out fine with "1" or infinity on the resistance scale of my multimeter while de-energized and near 0 when energized. The second relay shows a resistance of about 10 with the multimeter in the "20k" range. This drops to near zero when energized. The other leg does the same thing (in reverse of course). My question: Is the relay good or bad? (Is this adequate resistance for a "closed" leg?)

    Relay : siemens T7CS5D-09

  2. Elecbegginner


    Mar 24, 2013
    When you energize them , the contact goes from the initial leg to the second leg , this means you should read low resistance near zero on the second leg and high resistance near infinity on the initial leg , when de-energized the opposite happens .
  3. biglar


    Aug 11, 2013
    This is precisely my question- when I view you tube videos on relay testing (and when I tested relay #1 on my board) I get a 1 (infinity) when the leg is open. How do I interpret a value of 10 (on the 20k resistance range)? - Is this "high enough" resistance or is there a fault in the relay?

  4. Elecbegginner


    Mar 24, 2013
    No its ok once you get 1 "infinity" it mean that the leg is open , you can tell also by hearing the sound of it when you energize .
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Unconnected (open) contacts should read infinite resistance on every resistance range. This is the same indication you get when the probes aren't connected to anything.

    Connected (closed) contacts should read close to 0 on every resistance range. This is the same indication you get when you touch the probes together. On the lowest resistance range (often 200 ohms), you may see a small amount of resistance (should be less than one ohm); this is probably the resistance of the probes, wires, and plug-and-socket contacts. The actual resistance between closed contacts should be extremely low; much less than one ohm.
  6. duke37


    Jan 9, 2011
    Your first post says that you are trying to test relays on a board.

    If this is true, then the resistances that you see could have nothing to do with the relays but due to resistances in the board. As has been said, the resistance should either be zero or infinity. I have seen poor contacts and welded contacts.

    You may be able to open the relay and see the trouble.
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