Technical Horn relay

Ok...I hope this is a simple one to figure out. I have an entire 12v system on my 47 chevy. I have the original horns wired up with a 3 pin relay just like the picture. It works great as is but, I wanted to keep the horns at operating at 6v. Would a 12v to 6v reducer do the trick? and if so, where would it go? The 12v wire going in to the relay or the wire going out to the horn?

 

If it works, why fix it?

 

what kind of voltage reducer are you planning to use? You kind of need to know how much current the horns draw.

But like he said, as seldom as I use a horn on an old car, I'd not worry about it ever having longevity issues at 12v. If the sound is better at 6v, then maybe it would be worth doing.

If you can isolate one of them so it's not grounded, and run the power through it on it's way to the other horn, it will drop the voltage to each to about 6v.

 

Your horn should be quite loud. That's not necessarily a bad thing. As long as you don't "lay" on the horn for an extended period of time it shouldn't damage it. But to answer your question, I would wire the reducer into the line leaving the relay and going to the horn(s).

 

The wire going out to the horn, the relay needs the full +12 Volts to stay energized.

 

Thanks for the replies. Another route I thought about was getting a 6v relay and reduce the hot wire going in. But as mentioned above, If it ain't broke......

 

They'll work. They'll be very loud. They may also blow a fuse depending on what the fuse amperage is. Six volt horns on 12 volts will draw twice their usual current. My 52 horns work well on 12 volts and they have blown a 30 amp fuse at times.

 

I think that's backwards. P = E * I, or power = volts x amps. If the volts are doubled, the amps have to be halved.

 

6v horns on 12v will draw twice the usual current of 12v horns.

I think is what he meant to say.

 

Maybe, maybe not. There's a CEMF (counter electromotive force) involved that may reduce current draw. Any electrical device that converts electricity to mechanical motion is considered as a 'motor' so there's inductive reactance to deal with. Magnetic saturation also enters into it.

 

Ohms law would be E over I x R. If the resistance of the horn is 6 ohms, and the voltage is 6 volts, the amperage, 6 ohms divided into the 6 volts would be 1 amp. When the resistance is the same 6 ohms, divided into 12 volts. That would be 2 amps or twice the current.

 

Your talking Wattage not amperage with P=ExI

 

Thanks for clearing that up.

 

squirrel, you are correct as the 12 volt horns designed for 12 volts will draw less current. What I'm showing is the 6 volt horns designed for 6 volts will draw twice the amperage when the voltage is doubled. The resistance of the device will be constant and draw different current ratings related to the voltage introduced.

 

Blues 4U, you need to talk of the amperage of the device. It is directly related to its resistance to the flow of voltage. Wattage is not important here. When the voltage is doubled and the resistance stays the same, the amperage or resistance to the voltage will double. A 6 ohm horn on 6 volts will draw 1 amp in current. A 6 ohm horn on 12 volts will draw 2 amps in current.

Amps calculations. The current I in amps (A) is equal to the voltage V in volts (V) divided by the resistance R in ohms (Ω): ...

 

SO, I had to back up here and reconsider this. I was starting at the power output and working back from there, and yeah, you cant do that. The power produced is a consequence of the voltage & amperage. So yes, I agree with you. Following Ohms Law, if the voltage is doubled, the amperage is doubled, and the power output is quadrupled.

But as Crazy Steve pointed out, you're dealing with a motor that has reactance, so the actual outcome of the above would depend on the reactance of the horn, and as he also pointed out possible saturation of the voice coil.

So yes, I was wrong in my initial post; but that doesn't necessarily mean you're calculations are correct. Throw a 1 ohm resistor in series with one of the leads and measure the voltage drop across it, that will tell you the actual current draw.

 

I just like to simplify things. No need to complicate this. The horn is most likely a large coil with a vibrating device that makes the sound. A big old resister to me. It will work and very loudly at that. I did this in my 52 and probably have the same horns as Country Joe has in his 47. I also wired my car for 12 volts and did have a fuse issue with my horns. It did blow at times. Not every time I blew the horns but occasionally. If I were to put my amp probe around the wire to the horns, I probably would get fluctuating amperage readings. As long as the over current protection is protecting the circuit, I'm fine. I just wanted to give Country Joe him a heads up with what might happen and why.

 

Again, not always true. It's true for a pure resistance circuit, but when you add changing magnetic fields to the circuit you now have inductive reactance, another form of 'resistance' AKA as 'impedance'.

A 6V horn will draw more on 12V than it would on 6V, but the current draw probably won't double because of reactance.

Reactance is why speakers are rated at some ohm value 'nominal impedance'. A '8 ohm' speaker can vary from as little as .5 ohm to as much as 30+ ohms depending on the frequency going into it.

 

There's no place like Ohms.

 

I put a pair of 6 Volt trumpets in my (12 Volt) 1956 Ford Victoria. They were LOUD! They wouldn't exactly raise the dead, but very deaf drivers could hear them well. In as much as the purpose of a horn is to attract attention, they really got that job done.

 

Did you happen to work in the Prop Department of that Ghost Busters movie by any chance?

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Has anybody suggested just putting in a freakin' 12v horn?
..

 

That is genius! Not sure the OP picked up on that comment, but it is a perfect solution. Isolate the horn's normal ground and wire it to the second one.
1

 

Yes, wire them up in series. Or, wire them in parallel with a resistor in the horn feed wire. Or, for a more "manly" sound, wire them in parallel without a resistor.

 

I'd be curious to see how well (or even if) that would work. On the face of it you'd think it would, but will it?

Most horns are a rapidly-switched on-off circuit. Apply power, the diaphragm moves until it opens a contact cutting power, the diaphragm return to it's 'at rest' position and the contact closes, and the cycle repeats. The many cycles-per-second of the vibrating diaphragm is what produces the sound and how many per second it does this determines it's 'tone'. Faster, higher pitch, slower it's lower. The amount it moves determines sound volume.

So you have two horns in series. Most horn pairs are two tone, so they operate at different cycles-per-second. But because they're in series, when either horn contact opens, both lose power. So at the least, one or both horns will sound 'funny' because of the dueling cycles. I would expect reduced sound volume too.

Edit: I had a brain fart, current doesn't double... But you still have the above issues.

 

Yes I agree with what Steve is saying. Wiring in series is not worth it. These horns have one wire available while the body of the horn is grounded to the car. It would be crazy to try and isolate the horns from the car just to wire them in series. Keep it simple. As I get older, my patience is getting thin and this is how I like to go about things. Just put the 12 volts to them, get ear plugs and keep a stock of fuses available!!

 

I love these theoretical discussions, which are resolved by resorting to the KISS principle.

 

You can do all sorts of cool stuff with electricity, but you do have to jump through it's hoops....

 

Yeh, I'm tired of it though. Been doing it since 1972. I don't want to do it any more.