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My dynamo charging system....and powering system for my bike - will it work?


Ben Lessani

Jan 1, 1970
Hi there,

I wonder if you can help me out with something. I am going on a
cycling trip for about 3 weeks in France this summer, but I have a few
problems. As I will be in the middle of nowhere, I decided I'm going
to take my GPS unit (Garmin GPS 12), it runs on 6v and consumes 1 watt
of power. I will also have my bike headlamp (which has 5 of these
Should I wire the bulbs in the light like this ?

+ve -----| |----- -ve
(6v) |-B-B-B-|

I also wish to charge 4 NiMH batteries whilst on the move. So far I've
made this.

Dynamo attached to the bike that produces any voltage, depending on
speed, its marked 6v and 3w, I'm guessing it produces 0.5 A of current
(P=VI). I made a full wave rectifier out of 4 Schoitty diodes (.5v
versions) and two capacitors (2x 220uF). The capacitors are in series
and are going to be used to 'smooth' the power, for when the lamp is
in use. I also bought a lead acid battery pack (mainly because they
can be charged virtually non stop - like in a car). The battery is 6v
4.5 Ah. In theory I should be able to charge the battery in around 8.5
hours. I also have a small battery pack that consists of 4 1800mAh
NiMH batteries, I also intend to charge this off the dynamo -
seperately from the lac, obviously.

To charge the batteries, do I need a Zener to lock the voltage at 6v,
or can I let it creep over to 9v +. I just want to know if the setup I
have is the best possible setup. I have a small transformer (2:1) that
I could use to raise the current to 1A.

Is the system I have efficient, or are there improvements that can be