Help with automative relay choice

Discussion in 'Automotive Electronics' started by Hadaak, Jul 17, 2015.

  1. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    Hi guys. First poste here. I'm looking for an automotive relay to do the following:
    1. when ground signal is sensed on one pin the relay should switch between two connections (two +/- wires). I don't mean powering one connection or the other I mean switching between two wire connections only.
    Let's say you have a device which can be powered by a 12v source and you have two 12 sources which have different functions. You want to be able to switch between these two sources when needed. The trigger should be the detection of a ground signal on the relay pin. I'm thing of a relay with:
    1 Trigger pin (ground)
    2 pins for power (-/+) (to power the relay)
    2 pins for the connected device
    2 pins for the first power source device
    2 pins for the second power source
    which makes a 9 pin relay !!!!

    Any ideas how to achieve this please?
    Thanks.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you want a SPDT relay they come in automotive style, unless you want a SPDT with centre off, then you will need something non-automotive, or two separate relays.
    You need to be a little more explicit in your description as you may be able to use a DPDT type.
    Does the device power need to be separate to the relay coil power?
    Max..
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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  4. panic mode

    Senior Member

    Oct 10, 2011
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    if one relay does not do it, add another one (more contacts)
     
  5. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    the device is not powered by the relay. the relay will be there just to switch between the two power sources used to power the relay. I can do it with a dpdt manual switch but I'm looking into automating the task. And I don't know which relay to use.
    To be more more accurate I need to be able to unplug the device from power source 1 and plug it to power source 2. and this should be triggered by a condition: ground signal on relay pin.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I for one am still not clear on what you want, can you draft out a diagram of some kind?
    Max.
     
  7. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    how to edit a post? I made a mistake in my description here:
    the device is not powered by the relay. the relay will be there just to switch between the two power sources used to power the rela

    Instead it should read like this:
    the device is not powered by the relay. the relay will be there just to switch between the two power sources used to power the device.

    Imagine it like a phone usb plug and two usb sockets: on some condition (ground signal in my case on a separate wire) I have tu unplug the phone usb plug from socket one and plug it in socket 2. and these sockets have nothing to do with the relay power socket (+/- wires which power the relay).

    Is this helping :)
     
  8. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    ok now I see the edit button :) guess it is linked to a minimum number of posts before it appears !
     
  9. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    Ok I guess this is what I need: a DPDT relay like this one:

    [​IMG]
     
  10. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    and an example of the application (with some variations) I'm looking to achieve:

    [​IMG]
     
  11. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    the difference is the fan and the LED are the same device in my case. and the 5V and 9 volt are 12v both.
    What do you think?
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    DPDT relays are plentiful, you need to be aware when switching loads such as DC motors, the contact rating will need to be sufficient, most are rated for resistive loads.
    Max.
     
  13. Hadaak

    Thread Starter New Member

    Jul 17, 2015
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    yes. am I right in saying that my goal of switching only between the 9v and the 5v in this example and connecting the fan to both sources will do the job?
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Depends on the load presented by the DC motor.
    Max.
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Why can't you drive the LEDs from the same (9/12V) source that supplies the fan and motor?
    BTW, each LED should have a current-limiting resistor in series with it.
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    A single pole relay and appropriate resistor on each LED is enough. All can be done with just the 9 volt supply and power to your coil. I assumed 12v to the coil but you can also use your 9v supply for that as well. I hope your 9v supply is not a 9v battery. It won't last long.

    image.jpg



    image.jpg
     
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