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Old 07-17-2016, 09:08 AM   #1
rlhinit
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Default '37 horn (12v)

I'm looking for somebody that can convert a 6v to a 12v original horn from a '37 ? Or perhaps can instruct me on how to do and where to get the parts.
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Old 07-17-2016, 12:19 PM   #2
Charlie Stephens
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Default Re: '37 horn (12v)

Quote:
Originally Posted by rlhinit View Post
I'm looking for somebody that can convert a 6v to a 12v original horn from a '37 ? Or perhaps can instruct me on how to do and where to get the parts.
All it should take is a resister in the line to the horn. My guess is that the major suppliers should have them. I didn't see anything in the on line catalogs so you will probably need to make a few phone calls. Definitely a "do-it-yourself" job.

Charlie Stephens

Last edited by Charlie Stephens; 07-17-2016 at 12:30 PM.
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Old 07-17-2016, 12:23 PM   #3
SofaKing
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Default Re: '37 horn (12v)

I would not expect there to be any need to convert. The 6v system will have heavier windings in the coil due to higher amp draw than 12v system. That and infrequent use I would expect it to work ok as is.
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Old 07-17-2016, 01:00 PM   #4
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Default Re: '37 horn (12v)

I have the original horns on my '40 and it is converted to 12v. It's been running for 12 years and 21k now and the horn still works great. I've never blown it for long periods of time but it's never acted like it was going to quit. It is very loud. I think you can wire yours' in just as I did to 12 volts. jhb
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Old 07-17-2016, 06:02 PM   #5
Jack E/NJ
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Default Re: '37 horn (12v)

>>>The 6v system will have heavier windings in the coil due to higher amp draw than 12v system. >>>

They in fact will have twice the amp draw and four times the power output (aka *very loud*) on 12v since their resistance doesn't change. To be safe, I isolated mine from ground and simply wired them in series for 12v. Cuz you never know when those special occasions arise when you just gotta blow your horns a lot without fear of them going hoarse. 8^)

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Old 07-17-2016, 06:52 PM   #6
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Default Re: '37 horn (12v)

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The Model A vendors sell a resistor with fins to go from 12v to 6v, around $20 but is a quality item. I run my 6v horns on 12v with no problem, sound slightly different though.
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Old 07-18-2016, 08:16 AM   #7
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Default Re: '37 horn (12v)

[QUOTE=Jack E/NJ;1325380]>>>The 6v system will have heavier windings in the coil due to higher amp draw than 12v system. >>>

They in fact will have twice the amp draw.

You are correct, I was thinking about the formula for power, P=IE. Thanks for being gentle.
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Old 07-18-2016, 09:26 AM   #8
19Fordy
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Default Re: '37 horn (12v)

rlhinit: Here is the 60 ohm resistor I think will work to reduce your 12V to 6 V. Read post #10 where I used the same resistor to reduce the voltage to my BATT gauge from 12V to 6 V. Very inexpensive so buy a couple.
https://www.fordbarn.com/forum/showth...940+BATT+gauge

Last edited by 19Fordy; 07-18-2016 at 10:43 AM.
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Old 07-18-2016, 07:17 PM   #9
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Default Re: '37 horn (12v)

19Fordy, I am sorry to say that a 60 ohm resistor will not work at all for powering a 6 volt horn or horns on 12 volts. It might work for gauges which only draw about one amp of current. A pair of 6 volt horns would draw approx. 15 amps or more current. One resistor does not suit all conditions. To work out the resistance value in ohms required one first has to establish the current draw of each horn. Many suppliers such as MACS do have available a resistor capable of 6 amps or more load which would be required for EACH horn. Some people as stated previously have connected the two horns in series which will have the desired effect to a point. I have tried this but the sound of the horns is just not as nice as it should be. The correct value resistor for each individual horn is the better way to go. Regards, Kevin.
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Old 07-18-2016, 08:00 PM   #10
rlhinit
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Default Re: '37 horn (12v)

O.K. Here's the problem - the first time I blew the 6v horn using 12volts - yes indeed it was LOUD -
later, like a month or so - I blew the horn again - this time it was weaker , the next time even more so weak - then it turned into a buzzer - and now its no blow ! Rayzor
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Old 07-18-2016, 08:20 PM   #11
koates
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Default Re: '37 horn (12v)

I would say the contacts inside the horn are burnt now and not passing current. This can happen sometimes because by running a 6 volt horn on 12 volts then twice the current (amps) is passing through those contacts (and winding) and causing excessive arching and burning. Regardless of what some others say that running a 6 volt horn on 12 volts is OK, it is not really OK as the horn was designed to operate on 6 volts efficiently and for a long life and a nice sounding tone. You can clean up the contacts somewhat by using a points file or similar. You may then have to adjust the adjustment screw on the contacts for the best sound. DONT RUN IT ON 12 VOLTS. Regards, Kevin.
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Old 07-21-2016, 09:52 AM   #12
COE Dan
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Default Re: '37 horn (12v)

This thread presents a couple potential misconceptions:

1) Running a 6V horn on 12V uses half the amperage
2) The heavier wiring will prevent damage/destruction of the horn

Both of these are not true. The first is only true when comparing a 6V horn against a horn designed for 12V. When you apply 12V to a 6V horn, the current is not halved, it is doubled.

Explanation: Let’s assume a 6V horn has a notional resistance of 12 ohms. Resistance remains essentially constant regardless of the voltage applied (there are some slight changes due to thermal/inductive properties that result from changing the voltage but they are negligible in our application).

Using Ohm’s Law, a 6V horn with 12 ohms resistance draws a current of 0.5A (A = V/R = 6/12 = 0.5A).

Taking the same 6V/12-ohm horn and applying 12V draws a current of 1A (A = V/R = 12V/12 ohms = 1A).

Therefore, you end up pushing about twice the current through your 6V horn if you hook it up to 12V. For short periods, you probably won’t overload the horn wiring and can get away with it. Eventually the horn contacts may burn (a parallel situation is removing the ignition resistor from your ignition circuit which increases voltage across the points – potentially burning them). It appears “rlhinit” may have encountered this. You’ll also observe the horn changes pitch as others have noted.

Solution: The only way to maintain proper operation of a 6V horn in a 12V circuit is to add a resistor in that drops the voltage to 6V across the horn.

Resistors have two important values in this case: resistance and wattage. To compute the resistance value needed, you need to know either: 1) the resistance of the horn or 2) current drawn during 6V operation.

If you know the resistance, compute current: Current = V/R
If you know the current draw, compute resistance: Resistance = V/Current


Besides resistance, the resistor must be rated with sufficient capacity to dissipate the power flowing through it otherwise it will burn up. Therefore, the resistor must have a wattage rating equal to or higher than the power consumed. To determine the wattage of the resistor, use the following Ohm’s Law relationship: Power = Current x Voltage.

To drop the 12V input to 6V across the horn, add a resistor equal to the resistance of the horn in series with the horn (Resistance is additive in a series circuit).

Thus, you now know the proper resistance and wattage values and can obtain the appropriate resistor. This maintains the correct operating conditions at the horn ensuring longer life and allows the horn to sound as it should.

One last note on dual horn cars: Some folks have taken their 2 horns wired in parallel (6V across each) and rewire them in series and apply the 12V across both. Seemingly, this is identical to adding a resistor in the circuit as outlined above. However, these Ford horns will likely not have identical resistances. Therefore, you are not guaranteed than the voltage drop across the two horns will be split evenly. One may see 3V, the other 9V – making the sound come out off-pitch. Best to keep the 2 horns in parallel and apply the same voltage to both for the best sound.
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