Tung Lin Dynamo + Super Bright LED

Prelude
In my quest to minimize battery use I recently embarked on building a self powered headlight for my bike. The purpose of this post is to help others with similar aspirations. I found numerous instruction sets across the web but none of them addressed all of my needs in a clear and well documented way. So here is my attempt at adding something useful to the web. I hope it helps.

The bottom line is that I wanted a self powered super bright light that would make me aware of rocks and potholes when riding home from school in the dark. I quickly learned that I did not have enough time or energy to build my own dynamo or light source from custom LEDs so my project consisted of finding suggestions of design and hardware from across the web - ultimately blending them all into my final product. Major sources: 1, 2, 3 

Reasoning behind the parts
The Tung Lin dynamo is easily the cheapest and most powerful one I could find. It claims to pump out 12 volts AC from its headlight port which is the right amount for the pre-made 12v MR16 LED lamps out there. Further, it has a second taillight port that pumps out ~4v AC for future expansion. In testing the voltage with a multimeter I found that the headlight port will pump out upwards of 24 volts at higher speeds.

When testing it with my friend David cranking on the bicycle (on a stand) as hard as he could the dynamo but out 70 volts. But for real world conditions I figured it’d be best to mount a multimeter on my bicycle along with a GPS to tell my speed. Unfortunately at 20mph I hit a bump and my multimeter and GPS went flying into the street so I was only able to track the amperage; here is the amperage I was able to map out with the tung lin dynamo:

7mph   = 1.0 Amps
10mph = 1.15 Amps 
12mph = 1.23 Amps
15mph = 1.28 Amps
19mph = 1.34 Amps

I chose the MR16 LED lamp for two reasons. First, because it already has the circuitry embedded to deal with variations in voltage that dynamo produces, as explained above. Second, because they can easily handle the AC voltage the dynamo produces. And LED was chosen because the brightness simply kills halogen and incandescent and requires far less power.

The rest of the parts were found as Kristen and I wandered Home Depot and Ace Hardware looking for the right pieces to reasonably mount the light. If you buy the parts listed below you might save yourself a lot of time. 

Mandatory Part List

  1. Dynamo - 12v Tung Lin Dynamo - Amazon
  2. Super Bright LED - 4w, 4 LED, 440 Lumen, MR16 - Amazon. 
  3. 18 Gauge Electrical Wire - Radio Shack
  4. Conduit Hanger size #1 - Home Depot
  5. 3/4” #20 Bolt + Locking nut - make sure it fits in ↑ (#4)
  6. Flexible PVC Coupling 1.5 inch → 1.25 inch. - Home Depot
  7. Electrical Tape / Solder + Soldering Iron

Additional Optional Part List

  1. MR16 Socket - Amazon
  2. Drain Bushings to fit on dynamo head - Ace Hardware

Tools

  1. Drill + Drill bits
  2. Wire cutter/trimmer
  3. Flat head screw driver
  4. Washer for the 3/4” inch bolt

 The Steps

  1. Drill Holes in the 1.25” Portion of the Rubber PVC coupling

    There are two holes to drill: one to attach the conduit hanger, the other so that the wires attached to the LED lamp can leave the PVC coupling. 

    First, put the conduit hanger against the 1.25” side of the PVC coupling to see where the best position is for the hole. Then choose a drill bit smaller than the diameter of your 3/4” bolt. This will allow you to have a very tight seal after pushing your bolt through.

    Second, drill a hole for the wires that need to leave the coupling. Choose the place for this hole farther back than the lamp will extend from the 1.5”. Also consider where you’ll be mounting the light. You’ll see where I drilled mine in the photos.

  2. Attach the Conduit Hanger

    Slip the washer onto the 3/4” bolt and then push the 3/4” bolt through the PVC coupling so that the head is inside of the coupling and the threads are sticking out into space. Then slip your conduit hanger to the bolt and solidify it’s place with the locking nut. 

  3. Attach Wires to LED Lamp

    If you have the MR16 socket: Simply attach the socket to the lamp.
    If you don’t: Solder or use some other method to attach the two separate 18 gauge wires to the electrical posts of the lamp.

  4. Add the LED Lamp to the PVC Coupling

    Loosen the metal straps on your PVC coupling. Then insert your lamp into the 1.5” side of the PVC coupling - electrical wires first. Push the lamp in so that three or four millimeters of the coupling extends over the lamp. Next move the wire strap on the 1.5” end so that it is flush with end of the rubber - then tighten it to the level that you are confident the lamp won’t pop out the front of coupling when you’re riding over bumps at 20 mph. Don’t tighten it so much that you crack the glass on your lamp. 

    Now thread the wires through the second hole so that they are hanging outside of the coupling. Your light fixture should be looking snazzy at this point.

  5. Mount your Lamp Fixture

    Pop the conduit hanger portion on to your handle bars or wherever else decide your lamp should be. Make sure that it’s secure. I added some electrical tape prior to installation so that the conduit wouldn’t scratch up my handle bars. That move certainly wasn’t necessary though.

  6. Install the Dynamo

    Anywhere you want. I chose to mount if on my pannier rack so that it got drive from my rear wheel. But I don’t see any reason you couldn’t do the front. 

    Make sure that the dynamo head is pretty close to your tire. Mine is 4-5 mm off the tire when it is not released. Tighten the attachment quite a bit as the internal spring in the releasing mechanism is likely to rotate the attachment a bit if not tightened. 

    Throw a drain bushing or two onto the plastic head of the dynamo. This will preserve the plastic head and can cheaply and easily be swapped out as they wear down.

  7. Connect the Wires From the Headlight to the Dynamo

    Two 18 gauge wires should be sticking out of the lamp fixture. Attach one to the port labeled “H” on your dynamo. Attach the second wire anywhere but the “T” port. That means any part of the arm, or any the silver bottle part itself. Attach using electrical tape or solder. 

    Make sure you tuck away your wires with tape or some other means so that you don’t tear your lighting fixture off when ripping up a mean hill on the way to work.

  8. Go for a ride!