Portable USB Battery Pack Bike Light (with a Luxeon III Conversion)




You've probably seen how handy it can be to have a portable USB power supply for charging iPods, PSP, cellphones etc. I decided to make one but it needed to be multipurpose to justify carrying around the extra weight.

I wanted to make it as simple a possible so I decided to use 4 AA sized NiMH batteries rated at 1.2v (or 1.25v) Which can provide the needed 5v without regulation. This also makes it possible to more quickly charge PSP's which can draw almost 1A when charging.

To extend the functionality I decided it should also be a flashlight. But a quick search of the local stores showed that most AA flashlights are generally 1 or 3 cells. Fortunately for me I decided to check the bike aisle at Wal-Mart and found that many of the bicycle headlights are 4AA cell!

So using a bicycle headlight we'll end up having a:

1. portable USB power
2. flashlight
3. bicycle headlight

Not only that but I happened to have a Luxeon III star and optics laying around the house so, why not improve this project by switching out the bulb for the Luxeon?

Expandable Capacity Bicycle Headlight
The most interesting part for me is that if you decide to make a second battery pack and connect them together via USB you'll double the burn time of the flashlight! How cool is that when being used as a bicycle headlight?!?

How about connecting it to a USB power generator such as the Hand Crank Lego USB charger set up so it's turned by a tire?

Multipurpose enough? I think so.

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Step 1: Parts

You'll need:

-1 Bicycle headlight (4xAA type)
-4 rechargable NiMH AA batteries
-1 Luxeon III star
-1 Luxeon Optics
-1 Heatsink for Luxeon (I used a copper pipe cap)
-1 Resistor ( Luxeon resistor calculator )
-1 USB motherboard adapter

Where to find parts

I didn't have to buy a headlight but they can be had at the bicycle section of most stores.

NiMH batteries. Again I had these as well as a charger. I got them from Walmart. They are 2500mAH generic, $5 at in the electronics section. I think they had it also availible with a wall charger for a bit over $10. Either way they're half the price of the brand names.

I don't remember where I got the Luxeon III, somewhere online with the optics and resistor. I believe everything cost about $10 shipped. I would suggest using either 5 or 10 degree lens.

The USB motherboard adapter I got from ebay for $2 plus $2 shipping

Step 2: Add the USB Port

I didn't take many pictures of this step. It basically consists of stripping one of the male USB ports down to the bare essentials -leaving just the red and black power wires attached.

Once that's done you need to decide on the best placement for the usb port withing the light housing. I chose to place the port on the bottom in the space left by removing the original reflector.

Just mark the location you can fit the USB port in and use a drill several holes to make the rough opening. A small file is then used to make the opening the right size and shape. I used the original USB adapter hardware for mounting, with a little hot glue to serve as strain relief.

In the final picture you can see how it's attached to the battery pack.

Step 3: Make the Light Assembly

The steps for this are pretty well explained by the pictures.

Attach the heatsink and Luxeon III using thermal compound and screws. Since the Luxeon came from a different project this was already done.

Then attach the optics to the Luxeon, with glue, hot glue, etc. Just be aware that if the hot glue is touching the heatsink it may get hot enough to melt and cause the optics to seperate from the LED. For this reason I usually apply some hot glue to the inside of the optics secure it to the star board.

Due to some clearance issues some cuts had to be made to the bottom of the flashlight lens, the heatsink, and the original lens face. Once that was done everything was glued together and the relay was soldered in.

Step 4: Replacing the Switch

This whole circuit board is just a complex switch. We don't know the tolerances so it'll have to go. In order to avoid a future failure it is best to just replace it with a simple switch.

Step 5: Putting It Together.

Pretty simple here, just solder everything together.

-The usb is connected directly to the batteries. red (+) black (-)

-The Luxeon III is connected (+) to the switch and then the battery; (-) directly to the battery.

Test with a multimeter before using shows 5.2v @ the USB port and 3.4v @ the light. Yay!


Voltage regulation can be added to the USB port if you desire

A buckpuck or other type of led driver can be added

More heatsinking for the Luxeon III

An additional battery pack such as this one can be connected via the USB port in order to double the burn time of the LED. Quite easy to do since the USB motherboard adapter comes with 2 USB ports.

Thank you for reading, hope you enjoyed my first instructable!

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    19 Discussions

    can this be easily be put in a box with a bike generator so I can plug in the usb port and charge my mp4 player and use speakers to amp the sound

    i have thought of making something similar to this, but i cant find the motherboard USB port. i've searched on ebay, found some, but i dont have a creditcard nor do i trust the sellers by mailing money TT__TT

    3 replies
    n0ukfSadam and Osama

    Reply 10 years ago on Introduction

    How are your desoldering skills? Get a cheap (or damaged) USB hub, or a non-functioning computer and scavenge the USB ports. Some of these will be a dual port, others (the thinner hubs) will be single. Look at whether they're stacked or not.


    Reply 10 years ago on Introduction

    Don't breathe the fumes then. Your work area should have at least the capability of being well ventilated, whether you're burning plastic, soldering, etching, gluing, painting or whatever.


    12 years ago on Introduction

    I love the idea of making portable power a liquid commodity that just follows me around, usable with any of my devices. My personal cloud of electricity. For a biker like me, the bike light is a perfect candidate - It's cheap and I already carry it around everywhere, so why not have it do some work when I get to where I'm going? Great photos and instructions, by the way.

    1 reply

    Reply 12 years ago on Introduction


    If you look at the second picture you'll see the light is on and the PSP's screen shows Power = External.

    It'd a good feature if you have a bike mounted GPS that uses USB to charge (like the TomTom) So you could use and charge your GPS at night with the headlight running, LOL.


    Reply 11 years ago on Introduction

    put a dymo on the wheel, attach with hot glue, and instant power, you'll need to use a variable voltage regulator


    12 years ago on Introduction

    This is cool. I'm thinking about making something similar myself. I'd use 4 AA batteries. Sometimes rechargeable, sometimes not. Would you advise using a voltage regulator? Would the volt reg provide a constant 5v even when the batteries are low? Been looking all over but can't find these answers

    4 replies

    Reply 11 years ago on Introduction

    If you want to be able to swap back and forth between different types of batteries then you do need to use a voltage regulator...especially to protect whatever you decide to plug into your USB charger. You'll still get better results by just using 4 NiMH batteries though.


    Reply 12 years ago on Introduction

    The voltage of 4 NiMH batteries is almost 5.3v on a fresh charge (off the top of my head) but quickly drops to around 5v. Of course for alkaline batteries you'd end up with over 6v. If you wish to be able to use any type of AA battery on hand you'd want to add a voltage regulator. You can download the .pdf for the particular voltage regulator to see it's specs. On most 5v regulators you do need about 5.15v input (+/-) to output the rated 5v.


    Reply 12 years ago on Introduction

    I'm sorry, I meant to say that the voltage of 4 freshly charged AA batteries is >5.3v