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Thread: Fire siren project, relay help needed.

  1. #1
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    Default Fire siren project, relay help needed.

    I'm a vol. emt and fire fighter, I have two identical sirens that I've been running paralell to each other with a dual throw toggle switch, I need to redo these. I dont have room for the dual throw switches, theyre too bulky. so I thought I'd try relays. what I had in mind was, in the first pic. if they make such a thing, using a dual throw relay. i'm not sure if this will work.
    relay design.jpg (56.4 KB)relay design.jpg
    In the second set up, running two relays, one after the other, using the coil side of the relays in a bridged set up. power wire into relay 1 pos, thenfrom relay 1 neg. to relay 2 pos. then from relay 2 neg. back to the battery.

    relay design 2.jpg (45.7 KB) relay design 2.jpg

    in the third, I'm illistrating the idea of using one sirent to trigger the relay to start the other siren.

    relay design4.jpg (31.6 KB)relay design4.jpg



    what do you guys think would be the easiest, what relays would you reccomend?
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    I would go with the two single pole relays in your second example.
    The relays should be in parallel instead of in series as in your example.
    With the relay coils in series, you would need 6 volt relays as the 12 volts would be divided between the two relays.
    Wire the +12 volts from the switch to the + side of both relay coils and the negative side of both relay coils to ground.

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    Are these electronic sirens or the old motor driven ones?
    I think the old style motors used a lot of power, so you will need to size the relays to handle the current load.

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    yeah theyre electrical sirens are you sure I only need 6 volts if I spit the power wires and run them seperately from one switch?
    86 Thunderbird TurboCoupe, 66 289 HI-PO, auto.
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    so it would be more like this, are you sure it would split into 6 volts per relay, or would it stay 12 volts per relay?


    relay design 5.jpg
    86 Thunderbird TurboCoupe, 66 289 HI-PO, auto.
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    i'm pretty sure the voltage will stay 12v, but the amperage will drop
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    Quote Originally Posted by shameless View Post
    so it would be more like this, are you sure it would split into 6 volts per relay, or would it stay 12 volts per relay?


    relay design 5.jpg
    Use 12 volt relays in this example. You have the relays wired in parallel.

    Your previous example had them in series.

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    Relays in series use 6 volt relays.
    Attached Images Attached Images

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    Relays in parallel use 12 volt relays. This is the way to go.
    You will have 12 volts applied to both relays. Not 6 volts as shown.
    Attached Images Attached Images

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    Quote Originally Posted by softtouch View Post
    Relays in parallel use 12 volt relays. This is the way to go.
    You will have 12 volts applied to both relays. Not 6 volts as shown.
    12v at both relays with a drop in amperage, compared to running a single relay, correct?
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