12v battery

[Martin Bush]

Hi all

Before I embark on a simple project I wanted to ask if you think it is possible to make a rechargeable battery capable of powering a car horn.

The proviso is that it should be smallish - it is to go on a bicycle so a car battery is out.

Simple is the key. If it involves dismantled a laptop battery it's probably out the question for me.

Martin

[paulsherwin]

10 AAA NiMH cells in holders would probably do it, though the power requirements of car horns vary a lot.

This is probably the wrong technology to be using though. A hand held air horn of the type used on boats would be a better idea if you want a really loud bike horn.

[Martin Bush]

Thanks Paul. I wasn't sure if those would drain too quickly.

By the wrong technology do you mean legally or practically? There are both air and car type horns for cycles commercially available now but they seem to have class or be costly. I thought making my own would be a fun experiment that wouldn't cost too much.

[paulsherwin]

As far as I know, there are no legal restrictions on bike horns, though you may be very unpopular with pedestrians and other cyclists if you use a loud aggressive horn.

You can build quite a loud horn with a conventional speaker and some sort of oscillator. Most simple personal attack alarms are built like this. On a larger scale, emergency services vehicle sirens generate the sound electronically and replay it through a transducer.

[Martin Bush]

The horn would be used appropriately if I build it. It's more for road use in instances where I know someone pulling out hasn't seen me. I have a bell too for normal use.

[Refugee]

Emergency vehicles have a square wave generator driving a hard cone speaker/sounder and are very efficient.
You used to be able to buy the chips for making your own toy police cars.
4 FETS in bridge would be common on a full size unit.

[kellys_eye]

I don't have much sympathy for 'horn users'. When learning to drive I was taught that using the brakes was preferable to using the horn.

Can't recall EVER using a horn on a vehicle or bike in my entire life!

[Martin Bush]

At the risk of going off topic, many drivers now fail to use their eyes, or at least they don't register anything that isn't running on petrol or diesel.

However I think I have my answer about the power side and some extra info about other ideas. So I am happy.

[MrBungle]

I had a modified rape alarm on my bicycle. Highly recommended and cheap solution. At the risk of going off topic, there is definitely a use case for this if you are a cyclist. I've given up cycling now after I was wiped out by a taxi in 2005 but it does indeed keep the cars away and the pedestrians on the pavement.

[paulsherwin]

There are also small units designed as window and door alarms which could be adapted.

[Boater Sam]

How about a hand powered Klaxon? They get pedestrians airborne!

[paulsherwin]

Martin wants a horn to alert motorists who aren't paying attention and haven't seen him. Using a loud horn to frighten pedestrians out of the way is antisocial and likely to result in confrontation and violence. A traditional bike bell is appropriate in those circumstances.

[russell_w_b]

Originally Posted by Boater Sam

How about a hand powered Klaxon?

That's exactly what I had as a teenager on my orange Dawes racer! Dad 'rescued' it for me from a scrap mine-car at Haig Pit. They're still obtainable - RS had them at one time - but quite expensive. I had mine years, and it mounted satisfactorily on the angled lamp-bracket on the front fork.

[TonyDuell]

Going back to the original question.

In my experience a car horn takes a surprising current (10A-15A sort of order), although it is obviously only used for short periods. So you do need a battery with a low internal resistance.

What about a sealed lead-acid battery? There are 12V ones made, and I would think something around 1Ah-2Ah would be small enough to carry on a bicycle. I know nothing about bicycles, but a friend used to use such batteries to power his cycle lamps. You do need a special constant-voltage charger for them (traditional car battery chargers will wreck such batteries), but they are not hard to build.

[Martin Bush]

Well I have just done a bit of a bike ride - 2.5 miles - and I've not had any need to beep anyone. But that may change as I increase fitness and get to where I am hoping to get to (the local park and ride).

Anyway, it's just a project rather than a necessity. I've got the helmet and day glo t shirt that make me look a proper Berk in the interests of safety.

Tony - can you link to an example of the type of battery you mean?

There's various 'instructables' online, but all seem to be by people with even less skill than me. One involves carrying a car battery in a basket! Another I think uses a drill battery but with lots of electrical tape rather than conventional connections.

The car horns I think I I can mount unobtrusively. The power needs to be mountable as you might affix a pump or bottle and removable. AAA or AA batteries would be ideal, but perhaps would drain very quickly?

For anyone wondering about the wisdom of a horn over any other safety features, I can confirm that I have serviced the bike and invested in some good lights (it's a second hand bike).

[paulsherwin]

I do think horns etc. will do little to protect you on the open road, as by the time you sound the horn it will probably be too late, and the sort of clueless driver that pulls out in front of a bike is unlikely to notice the horn anyway. All you can do is read the road and ride defensively. Remember that the cyclist always comes off worst in a collision, regardless of who is legally or morally to blame.

Speaking as both a driver and cyclist, it's quite easy to fail to see cyclists if they're not highly visible, and especially to misjudge their speed if riding fast. A flashing LED front lamp is probably more useful than a loud horn.

A flashing LED front lamp is probably more useful than a loud horn

Some are annoyingly bright, good thing in my book, good drivers will realise why they are annoying, bad ones see them (most of the time). I wish they where allowed on motorcycles.

Apparently a blonde wig helps https://www.eta.co.uk/2011/04/01/saf...-built-in-wig/

And as Paul said "read the road and ride defensively" plus control the road, don't hide in the gutter, stick out and be seen.

[Martin Bush]

Very true Paul. I drive, bus and walk... And now I am trying a bit of cycling.

Still, I am curious about this. I suppose the thing to do is give it a try. As long as it doesn't cost the earth (like the product I am trying to replicate) I won't lose much.

[Boater Sam]

Sense of humour failure suspected here. I was joking.
Seems lycra louts have no sense of humour either, they race on the towpath, no bells, no manners, no consideration.
I would welcome them using anything less than a fog horn having been pushed into the canal once by a speeding idiot when I was cycling slowly.

[TonyDuell]

Here's a link to one of the lead acid batteries that RS stock :

http://uk.rs-online.com/web/p/lead-a...eries/1287028/

Maplin do them too, I think. They are not hard to get.