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6 volt horn on 12 volt system

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DiverDownJames View Drop Down
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    Posted: 05 Mar. 2012 at 3:37pm
So I found a great condition 6 volt autolite horn (with the long trumpet) at a local antique shop.  The price is right, and I was wondering what strength of resistor would be necessary in order to run it on a 12 volt system?  Also, I would like to know what amperage the resistor should be.  Mainly I don't want to cook a horn that looks as though it may be NOS.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Carlsjeep Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar. 2012 at 6:18pm
You can measure the amp draw of the horn with a 6v battery and then measure the resistance of the horn coil and get a resistor that matches the ohms and the watts of the horn on 6v and be pretty close to a safe working system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar. 2012 at 7:02pm
When measuring amp draw, you will get about 1/2 of the actual amperage of the horn since the contacts are opening and closing, that is if the horn is properly adjusted. On original horn the reading while operating is about 5 amps. With the points closed it would draw about 10 amps.
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sean View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 05 Mar. 2012 at 8:09pm
Originally posted by DiverDownJames DiverDownJames wrote:

So I found a great condition 6 volt autolite horn (with the long trumpet) at a local antique shop.  The price is right, and I was wondering what strength of resistor would be necessary in order to run it on a 12 volt system?  Also, I would like to know what amperage the resistor should be...
If it's stock HA model horn, and based on Autolite specs, 0.7-.75 ohms  30 watts minimum (more is better).

Is there a model number stamp on the mating flanges?

Sean
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DiverDownJames View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DiverDownJames Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2012 at 2:16pm
Sean, I will inform when I pick up the horn.  Gotta wait until payday, but the shop owner is going to hold it for me until then.
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