Omron Relay Misbahaving

Discussion in 'General Electronics Chat' started by srinivasarao.beera, Dec 1, 2015.

  1. srinivasarao.beera

    Thread Starter New Member

    Dec 1, 2015
    This is regarding Omron relay ........circuit is attached here

    When I am turning off "Switch" , Relay will Switch off and 24V to will go to Tp131 through NC.
    When turning on "Switch" Relay will switch on and NO contact in floating mode. 24V off to TP131. This is actual working scenario.

    Actual scenario is happening 10 times out of 12 times. But 2 times "Relay is in NC mode when Switch is on also. ( both Switch on and off conditions, 24V is going to TP131.

    If I am using TE connectivity (TSC124H3L) relay , Actual scenario is happening 12 times out of 12 times.

    Plz help me what will be the issue.
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    The issue may be because you are trying to limit current into the base of the transistor - I see only about 700 uA into the base. Your Omron relay draws 7 mA as constant hold current but may take much more than that to switch. Make sure your other relay does not draw much more current.

    I would get rid of the 2700 ohm resistor and replace with a 470 ohm resistor. really give it some current to slam the relay closed. The 6200 resistor on the voltage divider will limit current to base of transistor to 3 to 5 mA, no need to worry so much - the BC transistor can handle much more base current. Also, you can eliminate the 10k resistor from base to emitter. There is no concern with floating on BJT bases. If you are really concerned, you can add a 1M instead.
    Last edited: Dec 1, 2015
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    The drive current looks a bit low but I have no idea what the relay actually needs. If the collector voltage is more than say 0.5 v then you probably have a drive issue. Removing R73 will give you more base current to get a good saturation of Q12.

    I disagree on leaving the base float as the Icbo current needs a path to ground that does not include the B to E path. 10K should be fine but 100K would be slightly better.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    From experience.. Omron relays are NEVER the problem..
    As stated the drive circuit is not sufficient.
    ErnieM likes this.
  5. #12


    Nov 30, 2010
    I have experience in this kind of design. 5uA @ 150C requires 100k or less from base to emitter. You can calculate that the junction temperature will never approach its design limit of 150C or you can assume Murphy's Law prevails and use 47K.;)
    GopherT likes this.