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  1. #1
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    Default 6V car horns on a 12V car

    I have a pair of 85yo 6v car horns on that I need to run on 12V without stressing the 85yo internals.

    The resistance across the horn terminals is 3Ω. According to my rudimentary electrical knowledge, if I put a 3Ω resistor in the 12V supply that will suffice?

  2. #2
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    Hi Bob,

    Yes it will work ! Although your resistor will need to be able to handle 12 Watts as heat.

    V squared divide by R

    6 X 6 = 36 / 3 = 12

    So I would use a 15 or 20 watt rated resistor of 3.0 Ohms. 3.3 is the nearest preferred value.

    HTH.

    Last thought, could you put them in series ?
    Last edited by BaronJ; 14th Jan 2021 at 12:32 AM. Reason: Misread values
    Best Regards:
    Baron J.

  3. #3
    BobL is offline Member: Blue and white apron brigade
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    Yep just put the 2 , 6V horns in series across the 12V and you will be sweet!
    They will of course have to both sound off at the same time

  4. #4
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    Hi Guys,

    Apart from being very deaf, I'm also struggling with cataracts. So sorry about the multiple edits !

    One last thought. Its likely that the horn bodies are one of the two terminals, so they both cannot be bolted to the chassis. You will have to insulate one of them to get a series connection.
    Best Regards:
    Baron J.

  5. #5
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    Default

    Or just use one of these.

    https://www.ebay.com.au/itm/12V-to-6...Cclp%3A2334524


    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  6. #6
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    Very common on motorbikes which are converted from 6v to 12v... leave the 6v hooter there, it'll just be louder!

  7. #7
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    Good Morning Bob,
    Are the horns "Klaxon" types with a motor?

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    I had 12V Klaxon on 6V VW Beetle and it sounded like a drunk toad.

    If you run one on 6V and one on 12V you will get two frequencies and two sound volumes. a couple more and some different voltage converter and you could play a tune.

  9. #9
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    Drunken Toads like double the Veees rather than half the Vees obviously.

  10. #10
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    Thanks guys, 3.3Ω 20W resistors it shall be.

    The horns are Klaxon brand made by Delco Remy but they aren't 'aooogha' motor driven klaxons. US car makers had pretty much moved away from the traditional motor driven klaxon in favour of the cheaper vibrating membrane variety by the mid 1920s.

    Trumpet horns, 1935 Hudson, very commonly used as decoration on the front of cars by all US car makers in the mid 30s.

    IMG_3753.jpg

  11. #11
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    I have restored a couple of cars that were 6 volt and in the process converted them to 12 volt, both have 6 volt horns operating on 12 volt, as the horn is only used in short bursts it works with no problem, in fact one of these cars has been on the road for over 18 years and the horn still works fine.
    These are English cars with Lucas horns and all I did was tune them to get a better sound.
    I have changed the starter motors on my cars, but 6 volt starters will work fine on 12 volts as well, as long as you don't keep cranking when they do not want to start.
    On my latest restoration, completed about 12 months ago, I have had issues with the fuel gauge operating on 12 volt, I seem to have overcome that by putting a resister in series with the tank sender unit.
    Regards
    Bradford

  12. #12
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    If I had a pair of 85 year old genuine Klaxon brand horns, there’s no way I would risk damaging them by applying double their rated voltage. Doubling the voltage means they are consuming four times the power. I think Bob is wise to use resistors.
    Chris

  13. #13
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    Quote Originally Posted by jack620 View Post
    Doubling the voltage means they are consuming four times the power. I think Bob is wise to use resistors.
    If the horns are in good condition the risk is minimal to the point of almost non existent , and in the case of horns they are only used infrequently and then only for a few seconds.
    I would have no issue using them on 12 volts, however if the OP has concerns about that then resistors could be one way to go, or 12 to 6 volt converter would be better, then you would have a regulated 6 volt supply.

    If you use 12 volt, how do you figure four times the power?
    Regards
    Bradford

  14. #14
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    Quote Originally Posted by BRADFORD View Post
    If you use 12 volt, how do you figure four times the power?
    P=V^2/R, so if you double the voltage the power increases by a factor of four.
    Chris

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