Switch Poles and Throws Banging head of wall

Discussion in 'The Projects Forum' started by bowlingo, Mar 25, 2012.

  1. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    Hi all,

    As of the below picture this is how you would change a motors direction using a DPDT switch.

    [​IMG]

    If the switch is in the centre position nothing happens and it is off. If the switch is in the forward direction it makes the motor to go in one direction and if you move the switch backwards it makes the switch go in the other direction.

    Here is what I am trying to acheive and have been drawing things for 3 hours now and its driving me potty

    I have a perm -, perm + and a switched +

    When the switch is in the middle position I would like it to make the switched + only so the device controling it can switch the motor in a reverse direction on command

    When the switch is in the forward direction I would like it to make the perm + only and cause the motor to go in forward direction

    When the switch is in the backwards position I would like it to make the perm + only and make the motor go into reverse

    In effect if I wire it as of the above drawing but have the perm - also going to the - of the motor directly and have the switched + also going to the + of motor this would work but when I move the switch into the forward or backwards positions it would cause a dead short between + and - if the switched + is on at the same time.

    I would like the switch to flick back to the centre point when I let go of it after holding it in the forward or backwards positions.

    Can anyone point me in the right direction of a suitable switch please. The perm +, switched + and permanent - is all the wires I have and I dont want to add more cores.

    The motor load (8 x 12V motors plugged into a junction box) is 1.8A per motor = 14.4A so I will need a 15A rated switch

    Thanks
     
    Last edited: Mar 25, 2012
  2. P-MONKE

    Member

    Mar 14, 2012
    83
    5
    Hi there,

    You need to think in reverse (pun intended!) connect the motor to the poles and the power to the outside connections.
    Excuse my poor scribble - I'm still learning Ltspice and this is still a lot quicker. :)
     
  3. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    Thanks for the quick reply....

    How would I add the switched + and - so if in the centre position the item controlling it can turn the motors on and off?

    If I were to add the switched + directly to the motor and the perm - directly to the motor when the switch is moved forward or backwards it would cause a dead short ....please help :)
     
    Last edited: Mar 25, 2012
  4. P-MONKE

    Member

    Mar 14, 2012
    83
    5
    I'm glad to be of help - I'm new here and while my electronics knowledge is better than Joe public's, it's certainly not up to an engineers standard, so I'm being very circumspect about what I answer for fear of getting it all wrong ;)

    What you need to search for is a dual pole dual throw (dpdt) centre off switch. This has three positions, up and down are the same as a normal dpdt, but in addition there is a centre position where the poles are not connected to anything. This kind of switch is actually designed for controlling motors in this way.

    Good luck!
     
  5. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    Thanks again :)

    Anyone any other ideas?

    I am now thinking I maybe need to put a relay in somewhere but will have to be a 15A of which are pretty big
     
  6. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    I dont seem to be able to find anything as of dual pole dual throw
     
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,815
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    Google "DPDT center off reversing" and you will find a wealth of information on how to wire up a switch. This is a common circuit and once you understand it, it is fairly simple. For example, here is a you tube video on wiring up a DPDT center off as a reversing switch for a DC motor.

    Just Google "DPDT center off" for sources...
     
  8. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0

    I fully understand how to do a DPDP center off switch.....

    I have another switched + to add into the mix so when it is in the centre position the switch can still be turned on and off from the control source and when I switch the switch forward or backwards I need it to disengage the switching + from the control source then move the motor forwards and backwards manually
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Will the control source also move the motor forward and backward? Are you trying to control a motor - forward, backward and off - from two locations?
     
  10. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    ok...I am having problems explaning what I need to do...

    [​IMG]

    As of the picture you can see I can add a DPDP centre off switch using the permanent + that I have added and the common - of which will overide the motor and allow me to operate it in the forward and backwards directions.

    I need to deal with the original switching + that is controlled by the application (GSM controller) This need to fully disengage when I move the overide switch in the forward or backwards directions but wiring the switching + and common - direct to the motor terminals and adding the DPDP centre off overide switch would cause a dead short between + and - / - and +
     
  11. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    The control source moves the motor in one direction only via text command

    The overide switch will have to make sure the control source cant be on at the same time as the user uses the local overide switch to move the motors forward or backwards.

    I think I need a 3 position switch...

    when in the middle position it makes the control source switching +

    when in the forward position it picks up the permanant + and moves the motor in one direction (reversing the load side + and - if need be)

    when in the backwards position it picks up the permanant + and moves the motor in the other direction (reversing the load side + and - if need be)
     
  12. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    You mean like a DP3T switch? where you have two poles (which you need since you are reversing the motor) and three throws or selections (forward, from controller and reverse). I have attached a picture to see if this is what you mean. Note that since your negative supply is common, I wired it from one of the other contacts.
    [​IMG]
     
  13. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    Thanks for that...

    I am not sure if the diagram is correct..I believe it would need to have 3 poles....

    centre position would have the switching + from the application on one side and the motor + on the other in the made position until you move the switch forward or backwards

    Forward position would disconnect from the centre position completely and engage common - and perm + on one side and connect to the motor + and - on the load side

    Backwards position would disconnect from the centre position completely and engage common - and perm + on one side and connect to the motor + and - on the load side but in reverse

    So a triple pole double throw switch would work I believe....Any ideas where I might get a central spring back type one?
     
  14. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    The below scribble is what I am trying to say

    [​IMG]

    Thanks
     
    Last edited: Mar 25, 2012
  15. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Are you confusing poles and throws? A "throw" is the number of positions- controlled by the control source +, forward manual override and reverse manual override. Three positions hence three throws. "Poles" are the number of circuits, and you need two for the motor leads.
     
  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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  17. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
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    Thanks for your help...

    I will need a 15A rated switch which is prooving to be a bit of a problem
     
  18. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
    0
    So the centre position isnt another throw? i.e triple pole 3 throw?
     
  19. bowlingo

    Thread Starter Member

    Jun 29, 2011
    162
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    It would appear these DP3T switches are incredibly rare and the chances of a 15A one are pretty much zero...Any ideas on what else will do the job?
     
  20. CDRIVE

    Senior Member

    Jul 1, 2008
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    This is an extremely confusing thread. On the up side this fact makes this topic fairly typical of what we get here. :rolleyes:

    You have not given any pertinent information on the constructs of the existing control circuit in question. You say the motor's ON - OFF & Direction are controlled by key stroke commands...

    Is this computer controlled?
    How does the controller interface to the computer, USB, RS232, ParPort, etc?
    Does the existing controller employ a control relay or H Bridge?


    Thus far it would appear more logical to control the existing controller but that's only because we have such miniscule information. The more detailed your information is the more pertinent and accurate the replies will be.

    EDIT: For clarity I replaced the words "current" with "existing".
     
    Last edited: Mar 25, 2012
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