DIY bike lights

Introduction

A lot of people have made their own bike lights to save money when riding at night. I did the same. Here's what I did. In total this cost around $100-$120 NZD. That seems like a lot, but this got me two batteries, 3 lights, and several bulbs of different wattages.

Required items

• 12V lead acid battery (or equivalent 12V battery pack)
• ~14V ~500 mA power supply (to charge the lead acid battery)
• Battery terminal connectors
• 3A fuses
• Fuse holder
• MR11 bulbs (5W, 10W, 20W, etc), narrow beam bulbs are best for trail riding (< 15 degrees)!
• MR11 bulb sockets (I used some floppy drive power cable connectors from an old PC)
• 38 mm PVC pipe
• 38 mm PVC end cap
• 38 mm PVC open-ended cap (fits perfectly over the bulb)
• Some wire (I used spare wire I found lying around)
• RC cable connectors
• Small switches
• 16 cm strips of inner tube (used to attach the lights to your helmet)
• Soldering iron and solder (if you want the connections solid)

Procedure

First I set up the circuit so the lights worked. I didn't solder anything, I just wired it up.

Here are the bulbs mounted in the floppy drive power cable connectors. I cut off the unneeded wires and the bulbs fit well. They aren't designed for this, however, especially with respect to the heat produced by the bulbs, so be careful. I have also broken some pins off of the back of cheaper bulbs by forcing them into the connector. What can I say, I'm cheap.

It's a good idea to put a fuse inline so you don't destroy your battery or bulbs if there is a short. And I have shorted this thing many times and had to replace the fuses. Fuses are really cheap! Use them! I used 3A fuses, for no particular reason other than a recommendation from the dude at the electronics store.

This is the lead acid battery I used. It cost about $25 NZD at a car battery depot. They're simple, cheap, easy to charge, and they last. However, they are heavier and don't have as many Amp-hours as say a battery pack made of 10 AA NiMH batteries. Note the battery terminals. It just so happened that I had an old junk PC with a switch that had some terminal connectors. These fit the battery perfectly. Alternatively, you could solder the wires directly to the battery.

With a 20W bulb, this battery lasts roughly one hour. Two hours at 10W, and four hours at 5W.

Charging these batteries is really simple. I have an old voltage adjustable power supply that can put out about 14V and about 500 mA of current. This is all you really need to charge these batteries. They take about 8-10 hours to charge, so I do it at night.

I also wired up this spare battery from my crappy cordless drill. I soldered the wire onto the contacts inside the pack and cut a small hole for a wire to go through. This battery sucks and doesn't last very long at all. So I just use it as a backup.

Here's the kit. I wired it so I can have two bulbs at once. Sometimes you want a high watt bulb (fast singletrack at night) and sometimes you just want a low watt bulb (street riding for visibility). Note the terminal connectors in the foreground. These attach to the battery terminals.

These are the finished lights. Switches are installed on the back and as you can see the male connector is on the lights, not the battery. If you put the male connectors on the battery you risk shorting out and blowing your fuse (if you installed one).

Here's how I built each light.

1. Cut the 38 mm PVC pipe to desired length. Mine was about 10-12 cm.
2. Drill two holes in the end cap (one for the switch, one for the wire)
3. Solder the bulb socket. One lead goes to the switch, one lead goes to the RC connector. The other lead of the RC connector goes to the other lead on the switch. Check that it works before you solder.
4. Install the bulb in the socket, place the bulb into the PVC and put the 38 mm open-ended cap overtop. This will keep the bulb in place.

Note: The bulbs get hot. Mine got warm enough that they softened the PVC and deformed it slightly. I used some electrical tape to keep the open-ended cap in place.

I used strips of inner tube tied around the holes of the helmet to provide a cheap, fast, and flexible method of attaching and removing the lights. I leave the strips on my helmet at all times so when I want the lights I just tuck them under and go. It looks kinda ghetto but if you tuck the knot down into the helmet it's not so bad. Some people use zip ties, which is okay but you have to cut them when you want to take your lights off.

The other helmet.

The finished setup.

Written by Donn Morrison, March 10, 2006

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