bicycle audio system

[fltchr]

Quick search found nothing on this subject.

I am looking to build a bicycle audio system powered by a dynamo hub and a rechargeable battery.

My knowledge of audio tech does not extend past tonight's research on the internet so forgive the ignorance.

I want to install an audio system on my bike. Headphones won't do, too dangerous (and not as cool or publicly accessible) . The audio input would come from a headphone jack plugged into something like an ipod (for now running off its own power).

The energy for the system after the jack would come from a Shimano DH-3D71 hub. It claims 6V, 0.6W of AC power (volts and watts make don't 'power', do they.) at speed. (an aside, why aren't amps included in the specs?) In use 'speed' will vary from slower to faster. I think the hub and battery combo is the way to go. Going from that to the audio system is still undetermined.

Bike frames are designed to absorb vibration. Suggestions on mounting drivers to the frame and material selection would be helpful.

Lastly, choice of components. What speakers to use, the necessity of amplifiers and resistance to weather (I am prepared to make weather shielding if I use 'indoor' components.) It'd be cool if I could rig a 3-way system. (i.e. better quality of sound = better setup)

On a different subject, suggestion about where to post this query would be great.

[Nigel Goodwin]

Originally posted by fltchr
The energy for the system after the jack would come from a Shimano DH-3D71 hub. It claims 6V, 0.6W of AC power (volts and watts make don't 'power', do they.) at speed. (an aside, why aren't amps included in the specs?)

You don't need to list amps, it's dead simple to calculate - W=VxI, so I=W/V, so 'amps' equals 100mA.

But in your case amps don't matter, power (0.6W) is all you need to know - specifically that's it's a puny amount of power, and you could only get about 400mW of audio from it. This is about what you get from the tiniest cheap radios, and is probably enough to feed a pair of headphones - NOT external speakers on a bike!.

You would need a LOT more power to do that!.

[neutron7]

Most bicycle dynamo hubs can put out 5 watts, that would be plenty for music power, but they are usually 6 volts AC, thats good, you can use 2 diodes to make 6 volts into 12v DC which would power most TDA chip amps. or a medium sized ghetto-blaster.

[neutron7]

i think that shimano spec is a mistake. 0.6 w of power would not be much use for even LED lights. they must mean amps, then you would have 3.6 watts, should still be enough.

edit:

ok i just looked at this
shimano pdf

look at the compatible bulbs, it says 0.6 watts for the rear and 2.4 for the front, or just 3 for the front so that is a rather weak 3 watts total. 3 watts can be quite loud though if you use the right speakers. many older factory car systems are only 4 watts per channel.

also remember , they want you to have light when you are going quite slow, so the generator might be able to put out more once you get going faster.

[Richard Ellis]

Yes the concept is very doable, the battery" storage" is the proper way to do it, perhaps an aluminum casing that rides below the top tube towards the steering stem. Said casing would house a small sealed wet-cell @ twelve volts, the amp would be integrated inside & the speakers would be mounted to the handlebars....... weatherproof drivers wouldn't work as all of them are physically too large to be any good.
Good idea, First you wil have to rundown to a specialty battery store to find a SMALL wet-cell @ 12V. Second you would have to find someone who will fabricate an aluminum enclosure, esthetically pleasing(AN artist type fabricater will do). Said enclosure will need a stout clamping system for attaching to the top horizontal tube. The enclosure needs to be servicable (Openable). Enough extra room inside for the amplifier(Not much).
Two more identical preferablely aluminum enclosures for the two channels again with a suitable mechanism to clamp onto the handelbars. Obtaining the electronics(Amp & speakers) is the easy part, making these "enclosures" is the tuffy....a tour of a local large artisans market....the types most big cities have, will turn up an "artist" who will most likely jump at the chance to create a masterpiece in metal for you.
______________________________________Rick........

[thomas997]

You can either diy, or buy a prebuilt water-bottle battery. It can be sealed well to prevent any water from entering.

You could even mount a speaker in a water bottle top but then you'd only have mono sound.

[vitalstates]

am intrigued by the shimano bumf.....it says beware an extremely high voltage is produced at high speed....one wonders what that voltage is.......sounds like a buffer battery is a must.....or heavy duty VR at least

[kevinkr]

Amplifier could probably be any number of the smaller inexpensive tripath amps you see advertised on eBay. Efficiency will be high enough to make very good use of the energy stored in your battery.

You can get a small 12V gel cell on eBay as well. Something with a rating of 1 - 2AH ought to be adequate provided that you can also charge it externally. (I wouldn't count on the bike dynamo to do much more than provide a considerable boost in run time.)

The most important thing will probably be how to effectively charge the battery with the hub dynamo. You can use a voltage doubler and a LDO with some means of current limiting.

[CBS240]

Hmm

Wonder if the input voltage could be rectified across a filter cap, then use a simple boost-buck converter to maintain a constant output voltage for the battery and amp as the speed increases/decreases and dynamo output voltage spikes above/below the battery voltage. This way it won't waste the extra energy at faster speeds in a resistor and overload the dynamo trying to supply overvoltage to the battery, and still charge at lower speeds.

http://www.edn.com/contents/images/90403di.pdf (at bottom of the page)

[kevinkr]

hi CBS240,
I think that would definitely be one way to do it, and a good one at that. I remember reading an article somewhere on the web about constant voltage and constant power for led lighting on a bike that used a boost/buck converter as one of the more deluxe and ambitious options..