1. #1
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    Adam07003's Avatar
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    Default Problem Wiring Horn/Siren

    I didn't know where to ask this but hopefully someone here can help me. Maybe someone who has experience wiring various things in a vehicle. Im a pretty handy guy wiring things, wired my entire truck all the accessories/stereo stuff/gos, but im having a lil trouble here.

    I have a whelen electronic air horn that I have hooked up to my horn ring (press horn, sends power to air horn PS and the air horn sounds). The whelen air horn has 2 wires going to the speaker. This works fine.

    I recently added a small able/sho-me siren. I have the siren output on the able/sho-me system tapping into my speaker wires. Problem is this... when I turn the siren on, it turns on for a few seconds, then cuts out. Both fuses on the sho-me siren and the whelen air horn get blown. Yesterday only the air horn fuse was blown, today though both were blown.

    Anybody have any idea why? My guess is that when i turn the siren on, it sends the signal through the speaker wires to the speaker, but it also routes the signal back to the air horn since the wires are connected, thus going backwards into the air horn thus blowing the fuse, and vice versa.

    CAN I use a diode? Will this work? Im not sure if i could being its a speaker, but thats what a dioe would be used for correct?

    Any help is most appreciative, iv'e attached a small diagram showing how its setup. Each system has 2 wires going to the speaker.

    Adam, EMT-B

  2. #2
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    You've got 100 watts backfeeding into whichever unit you're not using.Won't work,and you're lucky you haven't blown the finals(output transistors)out of the opposing unit.I don't know of any diodes that will stand 100 watts,they might exist,I don't know.Your options,as I see it are:Get another speaker and run separate systems or trade it all in for an all in one amplifier such as a Whelen 295,Federal Pa300,or other equivalent. T.C.

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    O.K. - it's kind of a Kludge of a fix, but what about routing the Positive Speaker Out's of the Horn & Siren Units to a relay.

    - The Siren would go to the Normally Closed Contact (allowing it to *have* the speaker all the time)
    - The Horn to the Normally Open Contact (allowing it to *have* the speaker only when the relay is active)
    - And the Speaker Positive to the common contact.

    Then you can rig an activation circuit to the coil through the horn ring also.

    Then Siren runs through the speaker all the time, then when you activate the horn ring, the relay opens the circuit between the siren & the speaker and closes the one between the horn & speaker (which should prevent any back-feeding) and it also activates the horn unit.

    FWIW - I like the idea of getting purpose built all-in-one unit better but if you're stuck on a budget this may get you by.

    DISCLAIMER - I am NOT an electronics type person. Perform this and any other operation at your own risk.
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    Use a DPDT relay so you can switch the + & - of both speaker outputs instead of leaving the - common. That will work fine.
    Even the burger-flippers at McDonald's probably have some McWackers.

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    yeah seems like its a pain and easiest method is to get another speaker, which im opting at.

    If i find a friend who wants the siren i'll sell it to him, but if i can't find anybody i think im just gonna buy a seperate speaker.

    But i have the big whelen rectangle one, spent $150 on it, woulda been nice to use that... for both units... i thought about just putting a switch in, when its in the up position it powers up the siren, when its in the down position it powers up the regular horn (and it would always stay in down)... that way its easier to wire and i use one thing at a time... makes most sense right and cheapest solution?
    Adam, EMT-B

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    It doesn't matter if one of them is turned off. You can't have two devices in parallel hooked to one speaker. One device must be totally disconnected using the DPDT relay or you need two speakers.
    Even the burger-flippers at McDonald's probably have some McWackers.

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    They do make diodes that big, some are used in musical instrument amps, others are used in charging systems for boats and RV's. Problem is that they are expensive and will reduce the performance of the siren (due to voltage drop).

    I don't know if I'd go wih the relay either, if your siren is pumping out 100 watts and you hit the horn you're disconnecting the speaker from the amplifer while its at full power, generally considered a bad thing to do. You could very easily fry the siren's final amplifiers.

    I agree with the others, a 2nd speaker or an all-in-one siren.
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    I ended up ordering another speaker on ebay. Or I might sell the siren and the speaker from ebay to a friend of mine. It was an impulse buy that i realize i have no use for, i just like gadgets and it was pay day, lol
    Adam, EMT-B

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