12 Volt Conversion with 6 Volt Horn

A

A-Man

Senior Member
Well I went and done it. I converted my 1930 Model A Ford Closed Cab Pickup to a 12 volt system with an alternator. Main reason was to provide halogen headlights and a good turn signal system.

However, I do not a functional Ahooga horn. In the conversion process, I did install a voltage reducer on the horn. The horn is not the problem, as it worked as it should before the conversion. In reading the forum threads, I see a horn resistor is mentioned.

So I have some questions. Does the alternator need to be "charging" for the horn to properly function? Is it safe to use a 6 volt horn, with a 12 volt system, or is it better to have a voltage reducer? Would a resistor to the horn be in order?

Thanks.
 
I use 6 volt horns on my cars with 12v systems. I do NOT blow the horn for long periods. I use them as signaling devices only. No problems in many years.
 
There should be not difference between using the horn with the alternator charging or not (electricity goes both way in the wire at that point.)

There will be a slight "raise" in the voltage when you're alternating. for a 12v battery expect about 14.7 volts while charging - and 13.2 volts (perhaps) when not charging. Maybe less on that second voltage if your battery is run down a bit.

Most advocate a resistor. This more to protect your horn motor from high amperage at higher voltage. But as Art says, use the horn with care and you should have no problem (aside from the "active" sound - but that is what a klaxon is supposed to be isn't it?)

Joe K
 
Usually the old 6V horns are so worn out that a couple of extra volts helps them out.

I use a 6V horn with my 12V setup with a load resistor in series, tucked out of sight between the radiator and shell. Around 1 ohm resistance gets you in the ball park. You can calculate more exactly using Ohm's Law,

voltage = current x resistance or R = voltage/current

"voltage" is the voltage DROP you want the resistor to accomplish: 6 if you want to get down to 6V for the horn, or, say, 4 if you want the horn to see around 8V. "Current" is a little trickier because it depends on the voltage applied to the horn, which, in turn, depends on whether the generator is charging and, if not, how much the battery's voltage drops under load: You want the value when the horn is functioning properly. in the neighborhood of 6 to 10 amps, probably. Model A ammeters are notoriously inaccurate, but whatever yours reads with the horn on the 6V battery will probably be close enough.

So, for example, a 6V drop for a 6 amp current requires a 1 ohm resistor.

The other issue will be the power rating of the resistor. This is the rate at which the resistor can safely dispose of the heat that is generated from the electrical energy, and is calculated as

watts = current-squared x resistance.

So, 6 amps of current thru a 1 ohm resistor requires a 36 watt resistor. Anything larger will be fine, but you could probably get away with a lower rating for short, intermittent use--depending on ventilation, etc.

Steve
 
I used a 1.5 ohm 35 watt resistor for a customer and it sounds fine. I wouldn't run a 6 volt horn (especially an original) on 12 volts, as you risk throwing the commutator segments from excess RPM.
 
A-Man
Did you go with the positive ground or switch to negative ground?
I bought car with 12v positive ground but think I'd prefer what I always had;
namely 1v neg ground.
Thanks, Dick
oops, guess newbe goofrf the to.
 
I use one of these, works great:

HORN VOLTAGE REDUCER- inside cover 1928-31

Allows you to use the 6-volt horn with a 12-volt system. Made just for the Model A. This unit fits inside the horn motor cover. 1928-1931. 21A P.176
 

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On one my "A"s that has a 12 volt system,I found that a rotary sliding type heater fan resistor that controls the fan speed on old heaters works very well. I can adjust this rotary switch until I get the original horn sound by reducing the voltage as needed. I have found that sometimes my horn will not work after setting for a long period of time. If driving and this happens, I can just reach down and momentarily increase the voltage with this setup until the horn works. Then I reset it for the original sound again. I like this setup. Saves me running out to adjust the horn adjustment on the horn. I also found that in heavy city traffic, I can adjust the voltage a little higher to get a much louder horn for safety's sake.
 
Did it involve connecting batt negative to frame, reversing ammeter connections ? What connections to coil & distributor? Anything done for alternater connections?

Concerned about damaging a working system..
Thanks, Dick
 
I give up on the resistor setup! I bought one just like the pic posted in earlier post from Bratton's. It sucks... just no other explanation. I have a new 12V system and barely winds up to a weak ahoga not AHOOOGA! Get maybe 2 toots and then the resistor is too hot and no more horn!

So IMHO save your money. So I am looking for a good 12Volt Ahooga horn to replace the 12V Spartan I have now. It worked fine on 6 volts.
 
I just rewound the field coils. I counted the turns as I unwound each of them and replaced them with twice as many turns of 24ga magnet wire. Took me about 1-1/2 hours and it sounds great.
Also did the same thing to my electric wiper motor.
 
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barkleydave said:
I give up on the resistor setup! I bought one just like the pic posted in earlier post from Bratton's. It sucks... just no other explanation. I have a new 12V system and barely winds up to a weak ahoga not AHOOOGA! Get maybe 2 toots and then the resistor is too hot and no more horn!

So IMHO save your money. So I am looking for a good 12Volt Ahooga horn to replace the 12V Spartan I have now. It worked fine on 6 volts.
Click to expand...

Snyders has one that sits in the chassis rail out of sight where it should also be way less inclined to overheat.
 

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Someone, here, used an old coil, hidden in the frame rail, as a horn resistor!!
6 volt or 12 volt??? I DON'T REMEMBER, WHUT DO YOU THINK I AM? A walking MEMORY bank ur sumpthing??? I kin jist barely master tipin' my furst NAME, but I can remember thet yesterday wuz the 13th uf sum MONTH??
Bill W.
 
I've used this little jewel for the last 5 years and it works great. Lots of use in parades. Came from Sacramento Vintage, fits inside the horn.
 

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Then why did the same resistor work in yours and not mine?

Gurrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

Now rewinding... that might be worth a go...
Now to find the darn wire! A picture of your work would be great.
 
I pulled the resistor today. Same as CarlG is using. It reached the point where it would not even turn the motor with the adjusting screw relieved! It was hot. I tested with OHM meter and read 0.001. Looking at the coils seems pretty straight forward to rewind them.
 
I messed around a bit with resistors, but it spoiled the sound of the horn, so now I'm operating the 6v horn on the 12v system. No issues, but I'm careful not to overuse the horn :)
 
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