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…build a bike light… July 4, 2007

Posted by Chief in Bicycle, Biking, build, Equipment, homebrew, Websites.
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For less than $50(US), you can easily build yourself a custom high-Watt bicycle light.

[NOTE: I have edited this post based on extremely useful information and feedback I received from BikeForums.net]

Parts List:

  • Reflector or Lamp :: $2.99
  • Halogen bulb :: $2.99 (for two)
  • Housing :: $1.55
  • Battery Pack :: $28.99
  • Switch (using the connector)
  • Charger :: (comes with battery pack)
  • Wire :: $3.60
  • Connectors :: $3.69
  • TOTAL: $43.81(us)!

For the reflector/lamp, the popular ones are the MR-11 and the MR-16. The MR-11 is smaller and easier to find, while the MR-16 is larger but more efficient, producing more Lumens per Watt. For this project, I’m going with the MR-11. Another thing to think about here is the type of beam. You can get them in varying degrees such as 10° to 40°. For riding a bike to commute, I’ll go with the 12° beam lamp.

MR11 Halogen LampMR11 Dimensions

MR-11 :: 6V :: 20W :: 12° beam :: 3000 hour life :: $2.95(US)

For the bulb, the reflector mentioned above takes the G4 bi-pin bulb. You can get them in varying Watts, with 10W and 20W being the most common for bike light purposes. Worth noting is that you want to pick the power of your bulb based on your battery pack capacity. If you have a 12V 1500mAh battery pack, you won’t want to go with the 20W bulb, as you will end up with only enough light for an hour. Since we are going with a 6V setup, and none of our riding will be high speed off-road, we’re going with the 9W bulb.

G4 Halogen bi-pin bulb

G4 :: bi-pin :: 9W :: 6V :: Halogen :: 2000 hour life :: $2.99(US) for two

The housing is where things get really creative. There is no easy choice here. This really depends on your ingenuity, spare parts, keen powers of observation, and history of pack-ratting. If you are taking the same route I am, by undervolting the bulb to extend battery and bulb life, then you will have more options for a housing since your 6V 9W light will be generating less heat than a 12V 20W light. In fact I’ll be using a PVC fitting. The lamp reflector is just over an inch in diameter, and will work nicely with the PVC section. Again, use your imagination, but I’m going to try and fit my lamp to a 1.25in x 1in PVC reducing coupler.

PVC reducing coupler

PVC reducing coupler :: 1.25 in x 1 in :: $1.55(US)

The battery pack is where you can have as much, or as little, “fun” as you want. You can buy a ready built battery pack with charger, or you can buy the pieces/parts and build one. Since my goal with this project is inexpensive and easy, I’m going with a ready-made setup. For my light, since I’m undervolting the bulb, I can get away with a smaller capacity battery pack. In fact, a 6V 2100mAh pack will do nicely, while being incredibly inexpensive compared to slightly larger capacity packs.

6V battery pack and charger

6V :: 2100mAh :: 5 AA cells :: NiMH :: 50mm x 15mm x 75mm :: with charger :: $28.99(US)

When deciding how to wire your lamp to your battery pack, you have to pay attention to the connection on your battery charger. If you have a favorite connector, then simply cut off the stock one on the charger, and wire it all up with whatever ones you want. For simplicity, I want to get a connector that works with the charger, which is a BEC connector, based on the information on the battery charger website. What I can’t tell from the picture is whether it is a male or female connector. When you are ready to build, however, you will see that it doesn’t matter. You will need to buy a male and a female connector. You simply solder or crimp the connector that mates with the charger to the wires going to the battery pack. That will leave the opposite connector for the wires going to the lamp.

BEC connector maleBEC connector female

BEC connectors :: 12in wire leads :: 5A :: 22AWG :: $1.25 each :: $2.50(US) total

Another connector you may want to get is a prewired ceramic connector for the bulb. This will make changing out the bulb easier, and at $1.19, is cheap enough to pay for the convenience.

prewired ceramic G4 bulb connector

Also in keeping with the design of the battery pack, is the wire I’ll be using. I’m going with a red/black, two conductor wire. This stuff is inexpensive, and I can order it from the same place I order the connectors.

22AWG :: red/black :: 2 lead :: $0.45 per foot :: $3.60(US) total

Having said all that about the connectors and wires, if you don’t mind spending just a little more money, you can go with slightly heavier gauge wire (such as 14AWG). The 22AWG in my project is almost too small. I am using it merely due to expense and convenience. Other recommended connectors are Anderson Power Pole’s, and Dean’s Ultra Connectors.

There are all kinds of ways you can hook up a cool switch on this project. You can wire up a handlebar mounted thumb switch. You can mount a push-button switch on the back of the housing. You can even wire up a small light detecting circuit for an auto-on headlight. However, since I am looking to do this easy and inexpensive, I’ll be disconnecting the battery to turn the light off. A little velcro strip will hold the wires out of the way, and I’ll have a simple way to turn the light on – just connect it.

The construction is fairly straightforward.

Some final thoughts:

Make sure you use high-temp silicone when mounting the lamp in the housing.
Your bulb will eventually fail, don’t make your mounting too permanent.
Make sure you have a vent hole for heated air to escape.
If you paint your housing, paint it with high-temp paint.
Make sure your red wire is connected to the (+) on the battery pack connector.
Di-electric grease on the connections will make them weather-proof, and improve conductivity.
Shrink wrap hides ugly solder, and protects the connection.
Other useful accessories: [HERE]
Rough equation to estimate run-time:

(Battery Pack Voltage * AmpHours) / Bulb Wattage = hours
( 6VDC * 2.1Ah ) / 9W = 1.4 hours

Well, enjoy, and leave me some feedback if you build this.

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Comments»

1. Carl - October 25, 2007

What about water-proofing? Is that an issue at all?


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