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Unsticking electromechanical relays

Discussion in 'Troubleshooting and Repair' started by Kardo22, Jan 15, 2015.

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  1. Kardo22

    Kardo22

    35
    0
    Mar 7, 2014
    Is there a good way to unstick em relays?
    I have this relay board:
    http://sine.ni.com/nips/cds/view/p/lang/en/nid/13538

    The relay tend to stick sometimes and I've gotten them to unstick by tapping on them with a rubber hammer. But that might damage the board and I'm wondering if there is a better way?
    Someone suggested putting AC current through the coil but that would probably damage the other components? Even if I took off the sticking relay and unstuck it with AC and put it back, would it last long? imo the contacts would still be quite dirty and this would be a short term solution with a lot of work.

    Is there a better way?

    thanks
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    What do you mean by "unstick"?

    If the relay contacts stick due to overload (welded contacts), you're better off replacing the defect relays and ensuring operation within specs for the future. A relay contact, once welded, will never again operate reliably.

    If you refer to the contacts staying in the "on" position instead of switching "off" when the board is de-energized, this is a feature of the relays used. The board uses "latching relays" where the contact mechanism is held in either "on" or "off" position by permanent magnets. Therefore these relays require energy only during the switching phase, not permanently. Otherwise 100 relays on a PCB this size would require too much energy and develop too much heat.

    Using AC in the relay's coil is no remedy for either of these cases. Latching relays either have two coils or a single coil where the polarity of the current determines the switch direction.
    The correct way is to de-energize all relays in software before turning power off. Look at the relays, on top of the case there is the manufacturer and type (these could be DSP-relays from NAIS aka. Panasonic) and check the datasheet for tge single relay for more information about the relays.
     
    KrisBlueNZ likes this.
  3. Kardo22

    Kardo22

    35
    0
    Mar 7, 2014
    The contacts stick and won't switch anymore.
    By knocking on the relays, the problem was solved for about 2-3 months (previously over 1,5 years of no problems). What I wanted to know if there is a way to get the same result (a couple of months extra working time) until I order replacements (I don't want to buy in advance) that is easier than knocking on the relays. The knocking takes delicate work, I had to do it 3 times (every time increasing the force a little) until all of them stopped sticking (if I didn't use enough force then the relay would stick again soon).
     
  4. shrtrnd

    shrtrnd

    3,736
    478
    Jan 15, 2010
    This was a common problem in the 1960's through the early 1980's when these relays were in common usage. I've still got my kits for servicing relays. Burnishers, alignment tools, leaf straighteners.
    Harald pointed-out causes to be aware of. Servicing these relays is a lost art-form anymore, with only the old guys familiar with how to service them. (If Harald's input doesn't apply to you).
    If this is an issue you believe you're going to have to deal with for some time (no plans to replace the electro-mechanical relay board with something else), you might consider a few tools, or invest in a relay tool kit.
    At the least, I'd buy a burnishing tool and a can of spray contact cleaner. Open the relay, burnish the contacts, and spray them off with contact cleaner.
    You'll probably get other following posts from people convinced your problem will be solved electrically. I don't know your circuit. I do know sticking relays.
    Good luck. Maybe this is a problem caused by your circuit driving the relay, and someone will have a solution that solves your issue.
     
    Harald Kapp likes this.
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