12 vdc Relay problem

Discussion in 'The Projects Forum' started by timc4444, Mar 13, 2008.

  1. timc4444

    Thread Starter New Member

    Mar 13, 2008
    Building a control circuit for turning on some lights on a remote building.
    The RF remote unit we are using is below.


    The unit allows the ability to toggle. (The mode we are using) Because the relay is only rated at 7A, we had it control another 12 volt relay with higher contact ratings. The unit switches fine except when we hook up another relay coil to the switch of the units relay in which it holds the relay closed and doesn't release it.

    Is there some sort of force (inductance, capacitance) stopping the relay from toggling?

  2. mik3

    Senior Member

    Feb 4, 2008
    I did not fully understand you but form the unit there are three output terminals as i can see. The one is the common , the other is a normally open contact and the other maybe is a normally closed contact . thus it supplies 12V all the time to the second relay. Check it
  3. timc4444

    Thread Starter New Member

    Mar 13, 2008
    The Rf unit has a relay on it. Though terminal labels are misleading, it is merely a
    toggle switch. There is no 12 vdc on those terminals.
  4. SgtWookie


    Jul 17, 2007
    Does the relay that you're controlling with your remotely-controllable relay have a reverse-EMF protection diode on it?

    And do you have a decent-sized capacitor connected in with your remotely-controllable relay power source?

    It could be that the pair of relays being turned on may be too much for your 12v power supply, or that your 12v power supply is located a significant distance away, and the surge of having both turn on or off at once is just too far out of tolerance for your remotely-controlled relay's control circuit.
  5. Haajee

    New Member

    Nov 9, 2007
    Voltage-converter ICs are in the market.

  6. timc4444

    Thread Starter New Member

    Mar 13, 2008
    There is no cap nor reverse EMF diode in the other relay. Initially I intended to use the same 12vdc source but ran in to the problem. I would rather use the same source.
    Can you comment on where to place the diode an cap if necessary ?
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    If the first relay is engaging and disengaging, and the second relay is only engaging, it may be that the second relay is a latching relay.

    Some latching relays hold until power is removed, but the more common type is put in one state by a "positive" pulse, and placed in the other state by another pulse where the polarity on the coil is reversed.
  8. Søren

    Senior Member

    Sep 2, 2006

  9. timc4444

    Thread Starter New Member

    Mar 13, 2008
    Thank you. It works great !

    Can you explain why the two are affecting each other even though they are mechanically separated ?