Introduction: Bright Rechargable Headlight for Your Bike!

About: I'm an environmentally conscious experimenter who loves to bring people together, build things, and when possible...blow things up! See us on YouTube too!
 Bike headlights generally fall into one of two classes. To see, or to be seen. My mountianbike group cares a lot more about seeing since we tend to ride in places where hazards like cars do not and cannot go.
Here's what we came up with. 10 watts (between 150-200 lumens is our guess), $34.00 including light, battery pack and charger. Using disposable batteries can bring this project into the sub $15.00 range real quick.
The light burns bright. It's completely waterproof and the PVC holds up to the heat the lamp produces without issue.

Step 1: Materials & Tools

Before we begin
We believe in making use of available materials. If you have something laying around that you think will work as a suitable substitute for any of these materials, by all means, use that instead. Beyond that, the 1¼" compression fitting found at my Home Depot may not be the same as the one at your Home Depot. When we ran the workshop, we ran in to this very issue. This is a very versitile project. Here are some examples of the many variations that could be done to this project.
  • The enclosure could be made more compact if you glue it together so when the lamp eventually burns out, you just throw it away and build a new one. This part of the project would be about $5.00 if built this way.
  • Omit the switch. You can have it so you plug it in to turn it on. By doing this, the whole thing could fit into the 1" pipe cap.
  • Build it in to something you already have.
  • Make it brighter! 20, 30 and 40 watt lamps are available. Just remember, the brighter the lamp, the more battery power it will take to deliver a useable burn time. Something as bright as a car doesn't do much good if it only lasts 5 minutes.

The possibilities are endless. That said, here's the variation we built. We had a workshop where we built 26 units at a cost of $34.00 each including light, battery pack and charger.

Materials (per unit)
1ea. - 10 watt, 6 volt, Halogen Lamp with MR 13 base
1ea. - 2 pin screw terminal to connect to the back of the lamp
1ea. - Waterproof pushbutton switch (push-on, push-off)
1ea. - 2.5 mm Male coaxial power connector with cord. (Power wire)
1ea. - 2.5 mm Female coaxial power connector
1ea. - 7.5 volt dc wall charger with 2.5mm Male coaxial power connector (omit if using alkyline batteries)
1ea. - 8" piece of zip cord (AKA speaker wire, lamp cord etc.) It should be at least as heavy as the wire on your wall charger.
1ea. - 1" PVC pipe cap
1ea. - 1¼" ABS compression fitting
1ea. - PVC solvent cement
5ea. - Nickle Metal Hydride (NiMH) Recharable Batteries. Size "4/3 AA"
1ea. - 4 cell alkyline battery holder for "AA", "C" or "D" cells


Safety Glasses
Hot Glue Gun
Soldering iron or gun
Volt Meter
Screwdriver (small flat)
Drill & bits

Step 2: Make Some Holes!

Clamp the 1" PVC pipe cap into the vice and drill a hole in the center of it to accomodate the pushbutton switch. Ours was ½", yours may be different.
Next, off center, drill another hole to accomodate the wire that will pass out of the back of the pipe cap and connect to the battery.
DO NOT HOLD THE PIPE CAP IN YOUR HAND WHILE DRILLING! And please, wear safety glasses. You only have one spare eye. Do what you can to protect it.
This pipe cap will make up half of the light body.

Step 3: Begin Wiring!

Take the end of the power wire without the connector on it and split the two wires as shown. Each side should be about 4" long.
Next pass them into the small hole in the PVC pipe cap.
Finally, tie what is known as an underwriter's knot in the wire. This knot will keep the wire from being pulled out of the light body and destroying the wiring in the process.

Step 4: Warm Up the Soldering Iron!

Cut half of one of the 4" leads off and strip the two remaining ends of the power wire. Also strip both ends of the short wire you just cut off and tin the ends by heating the wire with a soldering iron and applying solder.
Wear safety glasses! This stuff is about 700 degrees and some types of solder spit tiny droplets of molten resin when heated.

Step 5: On to the Actual Wiring!

Solder the short wire you just cut onto one side of the 2 pin screw connector. Next solder the longer wire of the power wire onto the other side of the 2 pin screw connector. 
This will leave you with 2 wire ends remaining. They will connect to the switch and this part can get very confusing for some folks, so follow along closely and don't jump ahead.
  1. Lay the 2 wire ends next to each other.
  2. Slip the nut from your switch onto both wires.
  3. Slip the washer form your switch onto both wires.
  4. Pass both wires from the inside of the body out the hole in the back.
  5. At this pointif you look at the back of the body you should see the power wire coming out the small hole and teh two stripped wires coming out the large hole with the washer and nut on the inside of the body.
  6. Solder the two wires onto the two terminals of the switch.
  7. Slip the switch into the hole and tighten the nut onto it with long nose pliers.
If you did this right the switch should be securely held in place and the 2 pin terminal should be hanging out the front of the body.

Step 6: Make a Carrier for the Lamp!

As stated earlier, the compression fitting I find may not be the same as the fittings you find. You're looking for three elements.
  1. The lamp should fit into the threaded section and not fall through.
  2. The lamp should fit within the bezel ring.
  3. When you put it all together, the lamp should be securely held in place with several turns of the bezel ring onto the threads.
From there, it would be nice if the inside diameter of the fitting was also the same as the outside diameter of the 1" cap, but that is hoping for a lot. The way we addressed this issue was to use a butt joint to attach the back of the compression fitting to the front of the 1" PVC cap.

Step 7: Trim the Lamp Carrier!

This fitting has a lot of extra material on it the takes up space and is an eyesore. Cut it off with a hacksaw and sand away any cut marks.
Sanding is best done with 220 grit sand paper laid on a flat surface and riding the cut edge of the fitting across it in a figure "8" pattern.

Step 8: Assemble the Light!

Once the compression fitting is cut and sanded from the previous step, glue it on to the front of the 1" PVC cap. Simply apply a small amount of PVC solvent cement to the front edge of the 1" PVC cap and to the back inside edge of the compression fitting and hold the two together. The stuff works pretty quickly so you should be able to set it down to let it cure in 3 or 4 minutes. Let it cure for at least an hour then install the lamp and tighten down the bezel ring.
Hook it up to your power source and push the button! If you did everything right, it's going to light up!

Step 9: Build the Battery Pack!

We used 4/3 AA NiMH rechargeable batteries with solder tabs.
Begin by straightening the tabs and tinning them with solder as described in step 4.
Solder the cells together in "series". This means that you solder the negative side of one cell to the positive side of the next. When connected in this way, each 1.2 volt cell adds it's voltage to the rest. With five 1.2 volt cells in series, you get 6 volts. If you're using alkyline batteries, they are 1.5 volts each so you only need 4 cells to get 6 volts. Test this with a volt meter.
A note about the physical configuration. One of our guys put them in a straight line and wrapped the whole thing in heat shrink tubing. Then he hid it inside his seat post and ran the wire through his frame.

Time for a little math. 

We are using a 6 volt, 10 watt lamp.
Using Ohm's law, if we divide 10 Watts(W) by 6 Volts(V) we get 1.667. This figure is Amps(A) and it is the same as 1667 milliamps (mA). 
The battery packs we used are 4200 milliamp-hour (mAh). This means the battery pack will deliver 4200 mA for 1 hour or 2100 mA for 2 hours, or 1050 mA for 4 hours. See how that works? So if we divide 4200 mAh of available power by the 1667 mA the lamp consumes, we get 2.51 hours of burn time from this setup.   

Step 10: Wire Up the Battery Pack!

Plug your wall charger in and test the voltage. The Male coaxial power connector on it has two parts to it. The inside that slides over the pin of the connector on the battery pack, and the outside (or sleeve). Determine if your wall charger is center positive or center negative. This will be labeled on the charger too, but test it just to make sure.
Get a piece of zip cord and strip the ends as follows. There are two conductors. One should have a stripe or ridge on it to identify it from the other. On one end, separate the two conductors for a length of about 3" and strip ½" from each. On the other end, separate the two conductors for a length of about ¾", cut ¼" from the length of the side without a stripe on it and strip ¼" from each. Tin them all as we did back in step 4.
Solder the unequal length ends to the Female coaxial power connector. Connect the striped conductor to the center pin. Make sure not to short the pins together. Test this with an ohm meter or continuity tester.
Place the plastic insulating hood over the coaxial power connector and test for a short circuit again.
If your wall charger is center-positive, connect the striped wire to the positive side of your battery pack. If it's center-negative, connect the striped wire to the negative side fo the battery.

Step 11: Finish the Battery Pack!

We found an easy way to add structural integrity to the battery pack...HOT GLUE!
Just lay in a bead of hot glue between each battery down each side of the battery pack and it will gain a bunch of strength. If you like you can cover up the metal parts with liquid electrical tape, but it's probably not necessary.
Finally, pop the whole thing into a $3.00 camera bag and you're ready to roll!

Step 12: Mounting!

The easiest way to mount this is to use two hose clamps. One around the light and one around the handlebars, interlocked.
You can also mount it to your helmet with velcro or zip ties.
When we ride mountainbikes at night, I wear one on my helmet and one on my bars. I get over an hour from it running both on one battery pack. That just about how long we ride anyway so it's perfect! 

Step 13: Sources

Here's where we got our stuff and what we paid for it.

6 volt, 10 watt Halogen Lamp
Battery charger 
$2.50  American Science and Surplus
$0.89 Gateway Electronics
$3.31 x 5
$0.51 Home Depot
ABS Compression fitting
$1.21 Home Depot
Female power Con.
$0.42 Metro Electronics
Male power Con. w/wire
$1.98 Metro Electronics
Hot Glue
$0.20 Home Depot

We had some other costs like shipping and insurance that are not reflected here, but this is the bulk of it.
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