Using 2-SPST switches to control a linear actuator

Discussion in 'The Projects Forum' started by Racer189, Feb 5, 2013.

  1. Racer189

    Thread Starter New Member

    Feb 5, 2013
    2
    0
    I'm a newbie here and have searched to no avail for the answer to my question. First off, my knowledge of electronics is limited so I apologize in advance if there's a simple answer to my problem. This is going to be in a marine endurance racing application so my goal is to keep things as simple and reliable as possible. Some of my fellow competitors are using a reversing solenoid commonly found in winches but I'm not a big fan of solenoids and hope there's another way other than going with a single dpdt (on)-off-(on) switch which I've used before..

    This actuator is used to control my front wings or Canards for lift as you can see in the attached picture. . I would like to run this actuator in both directions using 2 separate and simple spst off-(on) push button switches. One button would extend the actuator and the other would retract it.

    components:
    1- 12vdc linear actuator, max 3 amps. http://www.lectrotab.com/products/standard-actuators.php
    Note: the actuator doesn't have limit switches and it will be visually operated so we don't use them.

    Thanks in advance. :)
     
  2. chuckey

    Well-Known Member

    Jun 4, 2007
    75
    10
    You need two 12V relays as well. Take the "up" switch wire it to the coil of one relay, the switch then goes to +12 V and the other side of the coil goes to earth. When you push "UP", the relay pulls in. So take your two wires from the actuator and connect them to two moving contacts (rated at 3 A). Find which contacts are made to the previous moveable ones when the relay is energised, wire these to +12 and earth. When the "UP" button is pushed make sure the actuator goes UP. Copy all the wiring to the other relay/switch, making sure that the +12/earth wires are crossed over to their contacts. Test push "down", "down" relay should pull in, motor should run downwards. Sit down and have a beer. :)
    Frank
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I agree with Chuyckey, but would make a major addition. You should place a normally closed (NC) contact of the UP relay in series with the DOWN switch and a NC contact of the DOWN relay in series with the UP switch. Otherwise, an accidental push of both switches at the same time will produce a major short circuit.

    Or, try this.....
     
    Last edited: Feb 6, 2013
  4. Racer189

    Thread Starter New Member

    Feb 5, 2013
    2
    0
    Thank you for your response, but wouldn't using relays be the same as using a solenoid which I'm trying to avoid? Or are relays more reliable then solenoids?

    Thanks again.
     
  5. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    you could use fets if you want to go solid state.....
     
  6. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    Automotive type relays should be pretty reliable as long as they don't get soaked.

    But you could use a MOSFET bridge to drive the actuator if you want to go solid state.
     
  7. chuckey

    Well-Known Member

    Jun 4, 2007
    75
    10
    As far as I can see using MOS FETs, very neat but requires, 4 power FETs, 4 resistors and 4 diodes as a minimum. - Look up "H bridge "output stages. This would suffer the "short across the battery" syndrome if both switches were pressed. To overcome this, would complicate it quite a bit, say 4 more transistors + additional resistors.
    Frank
     
  8. williamj

    Active Member

    Sep 3, 2009
    180
    32
    Racer189

    For the actuator to function as you described I would suggest using a single on-off-on appropriately sized and rated toggle switch or as BillB3857 correctly stated there is a definite possibility of an accidental dead short.

    I would also recommend the use of limits. If what I have seen about these boats is correct, that they take a LOT of bounce and slam abuse. If that is correct then there is the possibility over extension or over retraction the Canards. This over extension or retraction could result in damage to the actuator, the Canards or the boat itself. Limits would be cheap insurance.

    williamj
     
  9. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    BillB3857's posted circuit will not short if both buttons are pushed. You don't even need to cross wire the relay coils as shown, since if both relays are actuated at the same time, it just connects both motor terminals to ground.

    Edit: It doesn't make a big difference but I would wire the relay contacts so the NC contacts go to ground and the NO contacts go to 12V. That way there is no voltage on the motor terminals when neither button is pressed.
     
    Last edited: Feb 8, 2013
    williamj likes this.
  10. williamj

    Active Member

    Sep 3, 2009
    180
    32
    I stand corrected, thanks for the wake up call Crutscnow

    williamj
     
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