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[newbie] Powering car horn?

Winfried

Dec 11, 2013
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Hello

I know nothing about electricity/electronics and would like to hook up a car horn on my bicycle.

I bought this pair of car horns + relay combo on eBay, and now need to buy a battery, a switch, and cables to connect the whole thing.

I read that a 12V li-po battery could be enough to power the horns, or at least one of them, but am stuck at what to buy and how to get to a working solution.

Any help appreciated.

---
Edit: What about something lighter such as this 20W horn?
 
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(*steve*)

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Jan 21, 2010
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Your first consideration is the current required to operate the horn. From that you can determine the switching and wiring requirements (which will also determine if you need a relay). After this you need to figure out how long the horn needs to operate between battery charges. This will feed into your decision as to the battery you will require.
 

Winfried

Dec 11, 2013
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Thanks Steve.

The relay mentions 30A. I read elsewhere that a device can need more amps when started.

Since it's a horn for bike use, I'll only need it to run less than a second a few times a day max.

I'll bring it to an electronics store and see what people recommend I buy.

BTW, I understand that a device must be provided with the right tension (voltage), but what happens if I provide less current (amps) that it expects? Will the horn simply work less loud or not at all?
 
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(*steve*)

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The relay mentions 30A. I read elsewhere that a device can need more amps when started.

That's not important at the moment. That is simply how much it can switch.

You need to find the current draw of the horn.

Since it's a horn for bike use, I'll only need it to run less than a second a few times a day max.

That's what I assumed. You need a battery that can supply the current though.

I'll bring it to an electronics store and see what people recommend I buy.

If you're lucky, they'll have people in there that know something about electronics. That used to be the case. No so much any more.

BTW, I understand that a device must be provided with the right tension (voltage)

The horn may operate from a range of voltages, but that range is likely to be relatively small. (say 10 to 14V)

, but what happens if I provide less current (amps) that it expects? Will the horn simply work less loud or not at all?

You kinda can't. The current is determined by the voltage.

If your battery can't supply the current, the voltage will fall to a point at which the battery can supply the current. The horn may sound strange, not at all, and the battery or wires may get hot and even fail (sometimes spectacularly)
 

shrtrnd

Jan 15, 2010
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My input, is to get a small (loud) piezo siren or buzzer.
They're loud, and lower voltage and current.
 

Winfried

Dec 11, 2013
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Thanks for the infos.

I went to a store sellings RC toys. It turns out that a 12V lead battery to power just one of the horns is way too big and heavy for use on a bicycle, but an 11V li-ion battery is about €150 and provides about 3,000mAh. The salesman mentioned that I could pair two 7V li-ion batteries but it might be too much voltage, and it's still pricey.

So it looks like a piezo siren/buzzer is indeed a better option.

I saw some 20W/12V/1.6A sirens:

- They're supposed to be about 120dB, which is way too loud: Is there a way (electronics?) to lower the level?

- Do they sound close to a car horn, so that it sounds like what car drivers expect to hear? Otherwise, it'll likely not be effective.

Thank you.
 

(*steve*)

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There are smaller lead acid batteries. I'd probably try a 2.4AH battery. Assuming it can handle the load for a short time, it shouldn't be too heavy and it will be cheap.

A charger will cost more than the battery!
 

shrtrnd

Jan 15, 2010
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And there are smaller peizo sirens and buzzers, .... but they don't sound like car horns.
 

BobK

Jan 5, 2010
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Thanks for the infos.

I went to a store sellings RC toys. It turns out that a 12V lead battery to power just one of the horns is way too big and heavy for use on a bicycle, but an 11V li-ion battery is about €150 and provides about 3,000mAh. The salesman mentioned that I could pair two 7V li-ion batteries but it might be too much voltage, and it's still pricey.

So it looks like a piezo siren/buzzer is indeed a better option.

I saw some 20W/12V/1.6A sirens:

- They're supposed to be about 120dB, which is way too loud: Is there a way (electronics?) to lower the level?

- Do they sound close to a car horn, so that it sounds like what car drivers expect to hear? Otherwise, it'll likely not be effective.

Thank you.
Using a siren is illegal if you are in the U.S. and probably elsewhere.

Bob
 

mursal

Dec 13, 2013
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This drill has a rechargeable 12Volt battery and charger
http://bit.ly/1b3iCkS

You will have to make a holder to connect the two wires from the horn circuit to the battery. There is little information on the battery capacity, so I'm not sure how long it will run the horn for you. Obviously if you use two horns, when in use, it will go flat at a faster rate.
If you have a ohmmeter, measure the resistance across the connections to the horn. Then divide 12Volts by this number to calculate the current required. V/R= I

Small push button switch rated around 5Amps should be OK for one horn, leave the relay to one side until you go for two horns in the circuit
 
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Winfried

Dec 11, 2013
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Incidently, what makes a car horn sound different than a siren?

IOW, is it possible for a 20W/12V solution to sound like a car horn without using as much power and weighing less?
 

Six_Shooter

Nov 16, 2012
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The physical construction and in some cases the control circuitry is what makes each horn sound differently.

How often are you using the horn on a daily basis that you need to worry about how long a charge will last? A small battery in the 5 Ah or less rating should be enough to sound the horn(s) for an hour or so of constant on, which will lasts days depending on just how much you use it.
 

Winfried

Dec 11, 2013
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I'll see if I can find a 20W device that sounds as close to a car horn as possible.

Thank you.
 

Winfried

Dec 11, 2013
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I went to a couple of electronics stores and they recommended I use a lead battery instead of a li-ion/nimh battery because of the amps the horns need... but lead batteries are just too heavy.

As a lighter alternative, I was thinking of feeding an MP3 to a compact megaphone with an amplifier between the audio source and the megaphone.

If all else fails, there's the hand air pump solution :)
 

Winfried

Dec 11, 2013
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Thanks for the tip. I already bought an AirZound, but it doesn't work when it's cold/rainy and it stopped working altogether after a few months :-/

Some li-po/ion battery + Arduino/RaspberyPi to play an MP3 + amplifier + mini-horn sounds like a cool project.
 

BobK

Jan 5, 2010
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Maybe you could pull a trailer with your batteries and equipment on it.

Bob
 
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