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Bicycle Dynamo iPhone Charger

J

Jesse Hattabaugh

Jan 1, 1970
0
I have a bicycle with a Sturmey Archer 6v AC 3.5w front dynamo hub.
It's currently not hooked up to anything, and I'd like to fix that. A
headlight would be nice, but something that could charge my many USB
powered devices would be ideal. Here is a schematic that some kids
developed to accomplish this task; http://www.instructables.com/id/S0A88K9F3KLNUIQ/
However I have some concerns. Their system regulates a 6v DC down to
USB's 5v DC and runs it to a capacitor. My dynamo is AC, and will
likely be more complicated therefore. Can anyone point me in the right
directions for this?
 
L

linnix

Jan 1, 1970
0
I have a bicycle with a Sturmey Archer 6v AC 3.5w front dynamo hub.
It's currently not hooked up to anything, and I'd like to fix that. A
headlight would be nice, but something that could charge my many USB
powered devices would be ideal. Here is a schematic that some kids
developed to accomplish this task;http://www.instructables.com/id/S0A88K9F3KLNUIQ/
However I have some concerns. Their system regulates a 6v DC down to
USB's 5v DC and runs it to a capacitor. My dynamo is AC, and will
likely be more complicated therefore. Can anyone point me in the right
directions for this?

Actually, it's easier. Just use a small transformer to boost the
voltage, then switching regulate it down.
 
J

Jesse Hattabaugh

Jan 1, 1970
0
Actually, it's easier.  Just use a small transformer to boost the
voltage, then switching regulate it down.

Do I need to rectify to get all the current possible?
 
R

Rich Grise

Jan 1, 1970
0
I have a bicycle with a Sturmey Archer 6v AC 3.5w front dynamo hub.
It's currently not hooked up to anything, and I'd like to fix that. A
headlight would be nice, but something that could charge my many USB
powered devices would be ideal. Here is a schematic that some kids
developed to accomplish this task; http://www.instructables.com/id/S0A88K9F3KLNUIQ/
However I have some concerns. Their system regulates a 6v DC down to
USB's 5v DC and runs it to a capacitor. My dynamo is AC, and will
likely be more complicated therefore. Can anyone point me in the right
directions for this?

An ordinary bridge rectifier (4x 1N400x or a bridge in one package)
should give you what you need for power - then for a charger, all
you need is a regulator. IOW, you can copy their circuit, but interpose
a regulator or dedicated battery charger chip, and you should be good
to go!

Good Luck!
Rich
 
T

terryc

Jan 1, 1970
0
I have a bicycle with a Sturmey Archer 6v AC 3.5w front dynamo hub.
It's currently not hooked up to anything, and I'd like to fix that. A
headlight would be nice, but something that could charge my many USB
powered devices would be ideal. Here is a schematic that some kids
developed to accomplish this task; http://www.instructables.com/id/S0A88K9F3KLNUIQ/
However I have some concerns. Their system regulates a 6v DC down to
USB's 5v DC and runs it to a capacitor. My dynamo is AC, and will
likely be more complicated therefore. Can anyone point me in the right
directions for this?

First point is that unless you consistently ride faster than 10mph,
preferrably 15mph, then battery lights are far easier.

AFAIK, all bicycle generators are AC and when supplied straight to older
lights (aka not leds), then this isn't a problem.

If you want to store power from the generator, then you need to convert
it to DC. this is easiest and simply done by using a diode.

If you want to collect maximum power, then a bridge rectifier (4 diodes)
and something like a super cap would be simple and easy to do. When you
start riding, the super cap just collects the excess power and stores it
until you stop (say lights)when it takes over supplying the light until
the dynamo kicks back in(you gain enough speed for the dynamo to be
putting out a higher voltage than the level on the supercap.).

Only gotchas are; riding too slow and sudden or long descents when your
speed picks up, when you might need to consider some form of voltage
regulation, aka clipping zener(s) and large wattage resistors. the 6Volt
output is really nominal. Too slow and you get nothing. Too fast and as
many peeps can tell you you had a bulb popping moment and everything went
dark.

Now, if you want to use this excess power to recharge some device, the
device needs to accept DC and have the ability to regulate the provided
voltage down to its needs. Depending on the device, you might not event
need the supercap, just ttake the output from the cynamo , run it through
4 diodes in bridge formation and then plug it into the device.

Keep in mind that 3Watts isn't that much to play around with, so stuff
like Ac transformers and voltage regulators (lm39?? 7805, etc) are going
to waste a significant proportion of that 3watts.

I'd suggest building a basic 4 diode bridge recitifier, adding a super cap
and then connecting this to an old bulb light, plus a cheap multimeter set
on voltage and mounted on the handlebars (GPS caddy?). Ride around with
the light on and not the voltages sitting on the super cap. The idea is to
work out what power your personal riding style puts out, then you can
design from there. (I found that I ride so slowly, that I need a voltage
doubler, sucks).
 
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