Make It Rechargeable! Bike Lights Hack

I tried to make my cheap bike lights work with an old power bank to avoid using disposable batteries.

The experiment was more complicated than expected, but in the end I found 3 solutions to make our bike lights more sustainable!

The cost of the project is very low, less than 2€, and also very easy to make.

If you want to see the whole process on video, you can go to my channel.

Happy reading!

Materials:

Cheap bike light (you can find them in any store in your town for less than 2€)

Potentiometer RM-065 or resistors

Wires

Micro usb connector

Old powerbank or DC DC step-up boost converter

Bike inner tube

Heat shrink tube

Tools:

T12 soldering iron

Hot Glue Gun

Hot Air Gun

3d Printer

Multimeter

First I disassembled the light.

Nothing can be seen on the circuit, all components are hidden by a white resin....

Since the 2 CR2032 batteries in series supply 6 volts, I first connected the light circuit directly to the bench power supply set at 6v.

This was not a good idea... In fact, after about a second, the power supply reached a current of more than 300mA and the light stopped working permanently.

To avoid making the same mistake, I started doing some tests.

I analyzed the current of the light by putting the multimeter in ammeter mode between the battery and the light circuit.

I noticed that when the light is turned on in fixed mode, there is a current spike to about 70 milliamps and then it slowly drops to about 20-25 mA.

Also, since I want to power this light with a 5V power bank, I tried powering the circuit with different voltages limited to 20 mA.

I noticed that the light starts to turn on at 2V with a very dim light.

From 4 to 6V the light is bright and stable, so perfect for our powerbank!

Now that we know that we need to limit the current to 20mA to properly power our bike light, we can think about the circuit.

The easiest way to limit the current and thus power our light properly is to use a resistor between the power supply and the circuit.

So I connected the circuit to the 5V power supply and an RM-065 potentiometer between the power supply and the circuit. The code "101" means that the potentiometer is a maximum of one kilo ohm.

After turning on the light, I was able to find the correct setting by turning the potentiometer with the screwdriver to get a current of 20 mA.

The resistance is 115 ohms.

Of course, we can also use an ordinary resistor...

However, I suggest you do some tests with the multimeter and a potentiometer before selecting the resistor.

I will try to describe the assembly as clearly as possible...

I suggest you watch the assembly video, it will be much clearer!

I soldered 2 wires to the circuit (red positive and black negative).

On the red wire I soldered the correctly adjusted potentiometer.

I protected all the contacts with heat shrink.

To help with the assembly, I drew and printed a small object that you can find on thingiverse.

This print is very small, it took me about 20 minutes to print it.

The object fits perfectly into the battery case and we will need it to secure the micro usb connector and maintain the curvature of the light shell.  

Now we gently press the wires and the potentiometer inside the battery housing and use some hot glue to seal everything. I used the micro-USB connector as a cap.  

Now I soldered the black wire to the "ground" pin of the connector and the red wire to the "v-bus" pin.

As a last step, I took a piece of rubber from a used inner tube to make a round seal.

This is used both to keep the light in place on the bike and to protect the contacts on the USB connector.

I secure everything with hot glue.

Now that we have completed the assembly of our light, we can finally do a test.

I take my old power bank and a micro usb cable and connect everything to the light we just modified.

On the surface, everything seems to work very well. The light is bright and works well in all modes.

Unfortunately, after a few seconds the light stops working!

Doing some research on the web, I found out that almost all power banks automatically shut down when the connected load is too low.

Each power bank has a different minimum threshold of up to 100 mA.

So our light went out because the power bank I was using definitely had a threshold higher than the 20 milliamps that our little light was consuming.

Of course, there are several solutions to our problem!

The first solution I suggest is to try different power banks!

In fact, after some testing, I found an old power bank that does not have an automatic shutdown!

Another solution is to use a simple 4.2V lithium battery.

As you can see in the picture, I used a 18650 battery from an old laptop, a battery holder and a DC step-up boost converter with usb connector.

Of course you can avoid the voltage regulator, but remember to adjust the circuit resistance properly...

Finally, I suggest you watch this video by creator GreatScott in which he explains very well the problem we ran into and provides very elegant solutions.

Despite the technical problems, I had a lot of fun and learned a lot of new things making this project.

I hope this article will be an inspiration for all of you makers to convert small everyday devices that use disposable batteries to rechargeable ones. So that we can make our hobby a little more sustainable....

I hope you enjoyed this project.

If you want, you can see the full video of the project on my channel.

Thanks for your attention, and if you want to support my work, check out my links!