Introduction: Power Adapter for Bike Generator.

Good morning.

This is about an adapter (one more) for electrical power supplied by a bike generator.

First of all, what is a ‘bike generator’? It’s an electrical power generator that takes movement from wheels and pedals of a bike; in fact, it converts the power of your legs into electrical power (for free!!).

Here are some examples:





The need at the origin of this model of adapter is to get power at 5Vdc (for nomad device recharging) and 12Vdc (for lighting, especially when the generator is used open air: during winter here the dark falls early…).

Step 1: Overall Schema

This is the overall schema of the adapter:

From the left, the generator is a permanent magnet motor, salvaged from a dismissed installation;

Step 2: The Generator

In this case is a 3-phase brushless motor, but a brushed dc motor will also be good: just, there will be only 2 wires instead of 3.

Please note: the Reddish wires are the 'star center' connection, I don't use it in this project (wire is left unconnected).

Step 3: Installation.

As a redresser, I used an integrated 3-phases diode bridge, salvaged from a frequency converter; of course it’s possible to make one with 6 diodes connected as in the schema. (for a DC brushed motor with 2 wires, you will need only 4 diodes, following the well-known ‘Graetz bridge’ configuration).

The smoothing capacitor is soldered directly on the output of the diode bridge, just in order to not to add 2 more wires to the already messy wiring...

Step 4: Redressed Voltage.

I added a volt-meter, in order to display the relationship between the speed of the movement and the electrical tension generated.

As my voltmeter was an old panel galvanometer with 100µA end-of-scale (here also, salvaged from an old dismissed installation), I added a 500K potentiometer in order to get a 40V end-of-scale (the real needed resistance value is about 400K).

Why 40V? Because the DC-to-DC converter just after can accept an input of 40V maximum.

Of course, if your motor delivers a higher voltage, you will have to find a DC-to-DC converter that can accept that voltage; for example, if your generator delivers a voltage between 80V and 240V, you maybe could use a wall-plug converter for portable PC.

The 1st DC-DC converter (12V):

I did my own because I didn’t have one that was strong enough (about 6 amps) and readily available; to do it, I used the 34063A integrated circuit: it supplies 1A max, but in its Datasheet (from or websites, for example) you will find an application schema for higher current, using a PNP external transistor (I used a BDX54c). For the freewheeling diode, I used a ‘Fast Recovery’ double diode salvaged from an old Desktop PC power supply. The coil is handmade, with enough copper wire to achieve 220 µH induction value, as indicated in the Datasheet.

After this first DC-DC converter, I put an Ampère-meter (in series), in order to display the power consumed by all the devices you can connect (12V lamps, phone charger,…); once again, this is not necessary but it can be useful for any eventual pedagogic purpose.

This 12Vdc tension obtained is then used to supply a spring-connector (just like the ones used to connect speaker to low-power home Hi-Fi sets), in order to make those 12V easily available for any use; I think that in my case it will be for low-voltage LED lighting.

Step 5: 5V Outlets

A little further downstream, a 2nd DC-DC converter to get a 5Vdc output; this time I had one already made, salvaged from an old thermal printer.

To get this 5V supply externally available, I made a simple board with some USB connector; this is a DIY, but you could maybe salvage a similar one from some old Desktop PC: often they have 2- , 4- or even 6- USB connectors in the rear side.

Step 6: Testing

The last photos are about the final test; I used an 18Vdc power supply, because the bike installation haven’t been realized (yet).

The second picture shows the 12Vdc outlet, the last is about the 5Vdc USB outlet testing.

Next improvement:

About the energy stocking, many way are possible; for example:

a) with 2 wires, make available outside the tension at the terminals of the smoothing capacitors; it will then possible to supply a charge controller for 12V lead-acid batteries (as used for cars).

b) connect an USB power bank to the 5V USB outlets.


Thanks for your attention, I hope it wll be of any utility.

And, of course, thanks to Instructable website for this (free!) space.