double latching relay?

Discussion in 'The Projects Forum' started by Rapidrob, Jan 2, 2009.

  1. Rapidrob

    Thread Starter New Member

    Dec 19, 2008
    I could use some help please. I need to build a resetting circuit that will do the following:
    an actuator will make a switch and close a 120 VAC relay that will start a linear actuator. The actuator will drive an arm to the max travel and then return to the start. The end of travel switch will have to unlatch the relay, engage a relay to reverse the travel of the arm back to the starting point. In other words, it needs to make one complete cycle...move out,and then return.
    The drive motor has four wires. Common,drive forward,drive backwards, and ground. The motor draws ten amps and is two horse power.
    The initial actuation will be done by gravity. The switch will "latch" the relay, drive forward, strike the second switch and drop out. A second relay or set of contacts will need to pull in to reverse the travel. Once to the starting point again, the motor needs to stop and stand by for the next cycle. The circuit must remain at rest until the gravity actuator makes the switch once again.
    I would prefer to not use a PC board, but rather hard wire the components. The unit will be outside in a dusty environment when in use. Not long term, just a few hours per month.
    Thank you for any help.
  2. eblc1388

    Senior Member

    Nov 28, 2008

    You have not mentioned the linear actuator will strike a limit switch at the start position.
    Last edited: Jan 3, 2009
  3. SgtWookie


    Jul 17, 2007
    Here's one approach:

    To reduce clutter, several wires were replaced by connector symbols labeled as 'NEUT', 'L1', etc. All like-named connectors are to be wired together.

    S1 is depressed to supply L1 (120vac, or hot) to energize the coil of RLY1 via S3, the extension limit switch. Once the N.O. contacts of the relay are closed, the coil is held energized (latched) via the lower set of contacts through S3.

    The upper set of N.O. contacts being made, power is applied to the motor in the FWD direction, until S3 is depressed by contact with the linear actuator.

    When S3 is depressed by the extended actuator, the coil of the relay is no longer energized, so the relay's contacts toggle to the N.C. position.

    Current is then supplied to the REV terminal of the motor via S2, until it is contacted by the returning actuator.

    One disadvantage is that S2 must be rated to carry the full motor load current. S2 could be used instead to energize another relay.
    Another shortcoming is that there is no delay between full speed forward and full speed reverse. If the actuator is not rated for it, short service life will result.

    If the actuator does not remove the object that depressed S1, or if S1 is held down, the actuator will oscillate FWD/REV rapidly at the extended position.
    Last edited: Jan 3, 2009
  4. Rapidrob

    Thread Starter New Member

    Dec 19, 2008
    Thank you Sgt. I'll try this out and let you know how it works.