How do I build a horn for my bike using a car horn?

I want to build a bike horn from a car horn, but need some help with the wiring.

In riding my bike from home to the train to commute in morning and back in the afternoon, I am having a series of incidents where I, or a vehicle, am causing a nuisance. I have a bell, but it just isn’t cutting it for the cars trying to get to the congested highway as fast as they can. The bell is perfect to alert pedestrians to my presence, but the cars just can’t hear it.

I want to get a horn for my bike, but the ones I have found online just don’t cut it. The AirZound looks good, but it looks rather bulky. I figure I could put the workings in a saddle bag that would just fit the items and run the switch wiring up to the handlebars. I figure I can get a cheap 12V horn from a wrecker.

  1. Could it be as simple as Batt(+) to Switch, Switch to Horn(+), Horn(-) to Batt(-)?
  2. Can I wire 8 AA batteries in series to provide enough juice to power the horn?
  3. If I use the 8AA batteries, how do I figure out how long the charge will last?
  4. Do I need a relay, or is a momentary switch sufficient?
  5. Does it complicate things a lot if I hook up 2 horns?
  6. I’ve got a couple of electronics surplus stores that I can pick up equipment from…what do I need to look for?

I’ve tried to find some sort of instruction for this, but my search skills are ineffective.

The voltage isn’t the only thing you have to think about. I don’t know how much current a car horn draws but I’ll bet it’s more than you think and I think you would need a sizable battery, not an array of AA’s, to deliver it.

You would probably need a car battery or at least a motorcycle battery. You probably also need a relay if the switch can’t handle the current (I think most car horns use a relay).

On a second look the AirZound looks great, and much simpler to implement than an electric horn.

For a real economical solution, use a referee’s whistle. Those things will pierce through a lot of background noise. Small, cheap, human powered.

Something like this might be better suited for what you need.

I’m not necessarily recommending this particular vendor. It’s just the first link that Google came up with. I think you can buy these at K-Mart or most sporting goods stores.

No help on the wiring, but my friend has a 9V horn (says “Mega Horn”) that is quite loud. If you missed that one online, it seems to be available for ~20$.

1) Could it be as simple as Batt(+) to Switch, Switch to Horn(+), Horn(-) to Batt(-)?
Yep.

2) Can I wire 8 AA batteries in series to provide enough juice to power the horn?
Enough voltage, yes. Enough amperage? I don’t know, but I have my doubts.

3) If I use the 8AA batteries, how do I figure out how long the charge will last?
Well, you could measure the amperage the horns draw, and get the ampere-hour specs on the batteries, and research at what voltage the batteries won’t deliver enough power. Or you could just try it and see.

4) Do I need a relay, or is a momentary switch sufficient?
A switch will do if it can handle the amperage. Most switches aren’t sturdy enough.

5) Does it complicate things a lot if I hook up 2 horns?
Not really. You just hook the horns in parallel. It asks a lot more of the batteries, though.

6) I’ve got a couple of electronics surplus stores that I can pick up equipment from…what do I need to look for?
Maybe a battery pack/holder for what you have in mind. Other than that, a better bet would be an auto parts store, a general electrical store, or a hardware store. Electronics are much fancier and more delicate than this, and I doubt an electronics store will have a robust enough switch (even with a relay) or a suitable relay. They might have big enough wire - I’d go for 14 gauge.

I’ve tried to find some sort of instruction for this, but my search skills are ineffective.
It may not be your search skills so much as that what you want to accomplish is almost certainly done more easily in some other way. Things that hardly anyone does aren’t going to have much written about them.

You need around 3-5 amps to get a car horn going. Far more than a string of AA batteries can supply for more than a quarter-second. At best, you’d get a very brief tick out of the horn.

A 12V cordless drill battery will be able to source enough juice, and is at least a lot smaller than a car or motorcycle battery.

A far more portable solution may be a Fox whistle. Much louder than the typical referee’s whistle. Not to mention lighter, simpler and less likely to be stolen or messed with while your bike is parked.

I’ve got an AirZound. That thing is LOUD.

And it’s not as bulky as you think. I’ve got the air supply tucked into one of my water bottle cages with the hose taped up the seat post and along the crosstube. Of course, I live in New York, so I’ve got a pipe clamp holding it into place, and a couple smaller clamps holding the horn in place.

Not according to Malacandra: Ni-MH Batteries - Discharge Current - R/C model - Factual Questions - Straight Dope Message Board, at least for NiMH rechargeables.

Assuming each NiMH AA battery is delivering 1.5Volts and is rated for 2200mah, you will get about 25 minutes at 5amp draw. Of course you can connect banks of 8AA’s in parallel to reduce current draw from each individual battery.

However, you can get a 6V lantern battery that isn’t too big that’s rated for 50000mah or more (for example Energizer 521). It’s not rechargable but two of those should last you for a really long time.

Maybe you could rig up a laptop lithium battery and a standalone charger? I don’t know how cheap or safe that is, but a laptop can draw in excess of 60W at 12V which is right about 5amps

You could use a thunder horn 110db as is it runs on a 9 volt battery.I commute often in busy traffic at night so I spliced a 12 volt lithium polymer 9000ma. This battery is about the size of 2 decks of cards and only weights 2lbs. I used 3.5mm splitter and connectors the type used in cctv setup I then hooked up signals and brake lights.
Tried to hook a car horn not enough amperage but this setup did provide me with more visibility and the thunder horn is even louder. Signals switch all generic motor cycle parts, battery cables and horn found on Ebay search. 6lbs of added weight worth the safety.:slight_smile:

But is it loud enough that the sound wave can travel back to 2006?

Is it even legal to use a warning device like a car horn - zombie or not - on a push-bike?

Funny. I opened this thread thinking that I had started one like this years ago. I read to OP without looking at the author and thought “This is a better post than I wrote.”

I ended up not implementing any of the suggested solutions as I didn’t want to leave the goods unattended at the commuter lot. My solution? Change my route. Since that time I have stopped riding to the train station due to family circumstances. I miss the ride.

Thanks all for the information. I may try something like the solution from Nightrider when my kids start riding their bikes to school…or at the very least the Fox40.

NiCads or NiMH AAs would do it. They have much lower internal resistance than dry cells, even low resistance alkaline. This is what allows those little lunch box sized jump starter packs to start a car.

The AirSound is a good solution, but be aware they may not work when extremely cold. I think it is an issue with the plastic diaphragm shrinking and becoming too tight for the air pressure to overcome. I haven’t figured out a non-destructive way to open mine up and investigate it though, so that is only a guess.

Hello bicycle car horn fans!
After extensive testing and using the method of try and error I finally came up with this pretty reliable setup. I do not mean to say it is the best but this one turns out to be the cheapest one for me . Ie drill or notebook battery is still pretty expensive. I therefore decided to use AA batteries. The advantage being that if you leave the project you can still use them to power digital camera etc.
Things you need:
1 ) 16 AA rechargeable batteries 2100 – 2500 mAh for the power source.
2) 2 x 8AA Battery Holders
3) Two switches - one used as a safety switch with ON and OFF to close and open the circuit and the other to trigger the horn.
4) Strong wires used in electro installation. If the wires are weak they wont carry the sufficient current. You need about two mm inner diameter.
5) The horn. The one I bought is not dual it is a simple single horn pretty reliable, loud as hell rating 110db 12v, bought at the local car accessories dealers - was about ten dollars.
6) soldering equipment to solder the circuit
Step ONE
Power source was the greatest challenge! You will need 16 AA batteries rating 2100 – 2500 mAh. (I am using 16 rechargeable tronic AA 1,2V 2100 mAh. I would strongly recommend rechargeable batteries. It is also relatively light weighs only 300 grams. The complete setup weighs about 450g.
From these batteries you create two power sources. Each of the power sources using 8 AA batteries connected in series This can be achieved by buying two 8AA Battery Holders which I bought at the local store. You can google the term “8AA Battery Holder” to see what it looks like. The bettery holder was cheap plus please remember to buy connectors for the battery holder. So now we have two power sources each giving you 12v and 2,5 Amps current. Now you want the voltage remain the same but you want to double the amperage to make the horn work . believe me it doesnt work with 12v and 2,5 Amps current. It is not enough amperage all you got was a slight beep…
Step TWO
Connect these two power sources in parallel. Parallel connections will double your current rating, but the voltage will stay the same. To join batteries in parallel, use a set of cables to connect both the positive terminals and another set of cables to connect both the negative terminals of both batteries to each other. Negative to negative and positive to positive.
With this power setup you can get about one to two monts of honking. Or you will get about 35 minutes o f continuous loud honking before it dies out. I reacherge every two months.
Step THREE
Test the horn before soldering. Cover the horn with a blanket and take your power source and put positive and negative cables to the connectors on the horn. REMEMBER TO COVER THE HORN WITH THE BLANKET OR A PIECE OF CLOTH otherwise you might go death for a while. If it honks, create the power circuit using your source, switch, safety switch and the horn.
The safety switch is optional. It is on and off button. I opted for it because it happened to me two or three times that I hit the horn button accidently when I was in my garage while manipulating the bike.
Step FOUR
Mount the circuit on the bike. I have it mounted on my handlebars and it is hardly visible. The batteries are strapped to the handlebars as well as the horn.

I wonder if this could be an application for supercaps.

Was thinking the same thing.

If the horn is not used very often, one idea is to use a small battery pack and a DC-to-DC voltage booster to charge an electrolytic cap. The same concept is used for camera flashes.

I’d kill for a horn that worked that well.

He’s deaf, Jim.