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# How to use a bicycle dynamo to charge a battery pack?

## How to use a bicycle dynamo to charge a battery pack?

(OP)
I have a lot of electrical equipment on my bike, all of which uses batteries, some much more than others.

What I'd like to do is to use a dynamo to charge a battery pack, which all the equipment could then run off. I'd like the process to be continuous, the way that a car alternator charges the battery even while you're using it.

There are quite a lot of articles on the net about how to do this, but they all assume that you're using 6V lighting. Some also assume that when the dynamo output is sufficient, it can be routed directly to the 6V lights.

All my lighting is 3V DC.

So, I would like one central power source to run:
3V halogen headlight (2 x C cells, quite high drain);
3V front LED light (2, x AA, low drain);
2 x 3V LED rear lights (2 x AA, low drain);
cordless cycle computer speedo pickup (2 x LR44 watch battery, don't last long);

So all of these are 3V DC, so by my way of thinking, a 6V 3W dynamo should be easily capable of charging such a battery pack, the way a car alternator producing around 18V DC can be regulated to 14.5V to charge a car battery. (6V is at a moderate speed, eventual solution must allow for higher output of 8-9V when going downhill).

If you're talking electronics, speak slowly and I'll get there. I do know what a resistor, diode and capacitor is, but that's about it.

Now, the final crunch. The base station for the cycle computer (that picks up the two signals from the speedo and the cadence) uses 2 x CR2032 - or 6V. These don't last long either, but I'm sure it's consumption isn't disasterous, just small batteries. Could I use some sort of step-up circuit to power this?

This might seem back to front, but charging a 6V battery pack from 6V AC is pushing it a bit, hence my desire to use 3V to match the majority of my kit.

Sorry if this is a bit long, but hope it makes sense, even if you have to read it twice.

Cheers
Steve

### RE: How to use a bicycle dynamo to charge a battery pack?

Try your question over on Topica Bike Current.  Its full of DIY guys doing all kinds of stuff with dynamos, leds, Li batteries, etc, they are a good group and know how to explain all that stuff in plain English.

Good luck

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