Help! I need more current!

[GasPassLass]

Hey,

OK, so this isn't a flashlight query (sorry!) but it is a battery query.

I'm trying to modify an old car horn to go on my bike (was knocked off by a man on his mobile phone recently so finding ways to draw attention to myself!). I've made a few simple electronic devices in the past, but nothing that's required any more power than can be supplied by 2 AA batteries.

It's a 12V 1.0A horn. I bought a load of 12V A23 batteries, not realising how little power they actually delivered. Needless to say, they didn't work.

Do any of you have any suggestions as to how to produce a battery setup that might deliver enough power without me having to strap a car battery to my bike (If that's the only option, I'll just have to settle for a plain old bell.) It needs to be as small and lightweight as possible.

Thanks everyone!

Amy

 

[Mr Happy]

That's a tricky one. Rechargeable NiMH batteries in the AA size would deliver enough current, but you'd need ten of them in series and that makes it not so simple to mount them and charge them.

Have you looked into the possibility of an air horn? Sometimes you can run those off a compressed air "dust buster" type can and the whole assembly is lighter and easier to work with.

 

[HKJ]

One possibility is to buy a 3 cell LiIon/LIPO battery pack (See RC shops) and a charger. They can easily deliverer the current.

 

[alpg88]

get yourself sealed lead acid battery aka sla, 12v 1ah should be relatively small and light. pbly like 10-15 bucks.
or get 2 4AA, and 1 2AA holders at radio shack, connect them parallel, and load them with 12 nimh AA, not from radio shack, their cells are crap and others there are too expensive.
or you can use a 12v battery pack from cordless tools.

there are many options, just don't use alkaline cells, AA wont have enough power, and D cells will, but you'll need 10, big and heavy pack.

 

[arek98]

Maybe you should use this or little more power

 

[Linger]

Small 3s lipo pack, almost the same size as a 2AA set-up but with 4x the voltage.
Available in a range of capacities (~460ma -> 5000mah), these hold up remarkably well under draw.
http://www.hobbyking.com/hobbyking/...&Product_Name=ZIPPY_Flightmax_500mAh_3S1P_15C
I have a 3s ~560mah pack that I use as the worlds smallest show-off light, plugging a Hikari JC5607 6v20w into the pack (12v= +4A draw), and a battery monitor. Sure with the tiny pack I could watch the voltage fall on the battery monitor as the bulb kicked out massive lumens, on disconnecting the bulb each cell only recovered .02v (e.g. stopped at 3.92/cell, recovered to 3.94 almost immediately and held constant 5 minutes later).

Point being, the 1A draw is nothing.
Best,
Linger

P.s., I'd go with a bell...I have one on all bikes but my racing bike.

 

[louie]

The Delta Airzound is the first-call choice of many cyclists, requiring no electricity at all (pump it yourself):
http://deltacycle.com/Airzound-Bike-Horn

I have not tried it myself.

 

[fivemega]

It's a 12V 1.0A horn.

Are you sure it draws 1 Amp off of a 12 volt car battery?
Most of car horns draw much more than that.
However, using 4 IMR connected in serial will safely deliver enough current.

 

[Mr Happy]

With someone new to the forum, are we sure all these exotic battery and charger recommendations are the best answer?

In terms of convenience and power to weight ratio, compressed air does much better than electricity. Some of the air horn recommendations above, like the Airzound for example, seem much more likely to deliver a practical solution.

 

[fivemega]

With someone new to the forum, are we sure all these exotic battery and charger recommendations are the best answer?

No, not BEST answer but yes that's some answer of OP.
OP's question is about solution of more electrical current.
I am sure whistling might be cheaper and safer solution for him but it won't be answer of his question.
Everybody must read and understand Causion, warning, attention and danger of every product before they attempt to buy, weather they are newbe or old master.

 

[Mr Happy]

...for him...

(Actually, for her. )

 

[KiwiMark]

Are you sure it draws 1 Amp off of a 12 volt car battery?
Most of car horns draw much more than that.
However, using 4 IMR connected in serial will safely deliver enough current.

It could be worth testing with 3 IMR cells if going this way. Fully charged 3 x 4.2V = 12.6, after dropping to the nominal voltage of 3.7V you would still have 3 x 3.7V = 11.1V which would probably power the airhorn fine. However auto horns have to cope with batteries that are being charged off the alternator so they should be able to cope with the voltage of 4 cells as well. It couldn't hurt to test with 3 or 4 cells and seeing how well they work.

But I also agree that compressed air can powered horns may be easier. I guess it depends if the OP wants to have fun setting up an electric powered horn rather than just going the simplest way possible.

 

[hoongern]

To be honest, if we're talking about things like 4xIMR cells, I would also suggest getting a pre-assembled 600-800mAh 12.8V LiFePO4 pack (they go for ~$20-$30) which can handle 5-7A of current. A 12.8V LiFePO4 charger will be needed (~$30).

I wouldn't think you need a WHOLE lot of capacity unless your horn is on all the time....

Then it'll be as easy as hooking up the + and - wires from the pack directly to the horn, and LiFePO4 is a pretty safe battery chemistry. (Plus the pre-assembled packs should have built-in overcharge/overdischarge/overcurrent/shortcircuit protection - make sure of it, of course, when buying)