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  Step up and get your own "dynamo hum"...(FZ).  All jokes aside, its a simple dynamo light mounted to a Planet Bike light bracket.  On about 6 cranks I get 20 to 25 minutes of light.
  There is a 3.6 volt NiMH rechargeable battery that comes in the light.  SO, by free I refer to your out of pocket cost on batteries.

Step 1: Material

1. dynamo light....Harbor Freight, 2 for $8.
2. quick release light strap...most have a screw to change the mounting base, this is a Planet Bike
3. super glue
4. fingernail polish remover........or acetone

crapsoup3 years ago
i like it. This is going on my bike very soon
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onrust (author)  crapsoup3 years ago
back @ you man!
Celt5 years ago
No no no, you see, its a dynamo-charged rechargeable battery, so you do not need to replace them.  Just crank the dynamo to recharge the internal batteries.  This is pretty cool, now imagine if you attached a cable from the dynamo to your wheel!  (hands free charging)!!
Ganoderma Celt5 years ago
Yeah, then you just have a normal light like found on about every bike. 
Celt Ganoderma5 years ago
but the battery lasts soooo much longer.
randomray5 years ago
Good instructable . Good not to have to worry about your batteries dieing on your ride . I do recommend having a cheap red blinky light for the rear it be seen much better then a reflector . In the same vein lights or reflectors on pedals make you much easier to see also .
602poop5 years ago
NICE, anything not to purchase batteries!
XOIIO5 years ago
Yeah, um these do have batteries, they just recharge.
onrust (author)  XOIIO5 years ago
Are you positive?  I was told it was a capacitor.
Of course I may be wrong, and that's cool.
XOIIO onrust5 years ago
Yes, I've taken apart 10 or so of that kind of light. Each of them had lithium ion button cells.
onrust (author)  XOIIO5 years ago
Yes, you are correct. 
Since it was featured,  I'm not going to edit it.

XOIIO onrust5 years ago
It doesn't bother me if you edit it or not, I just like solving little misunderstandings and helping people understand how things work. 
onrust (author)  XOIIO5 years ago
  I thank you because I learned more about it......I went ahead and edited it anyways because it was wrong.  I'm also new here and thought I could not edit once it had been featured.
  Stay on point, please.  I WILL do more stupid stuff in "public"!
TheZuke!5 years ago
I was hoping it would charge via the pedals or wheels...
rimar20005 years ago
Anyway, with or without battery, is an excellent instructable. And if there are  batteries, but they are loaded by hand, are welcome.
hold it
so this is a "Battery free bike light"
with a Battery in it ??????
onrust (author)  thelastonekills5 years ago
I'm no tech, but I do believe that the dynamo charges a capacitor.
In the picture you can see it in blue shrink  wrap. 
XOIIO onrust5 years ago
Why would they shrink wrap a capacitor? I bet that you can see a line sticking up from one end to the other, which is a wire underneath. I can almost guarantee that if you rip/cut that open there will be button cell batteries.
i agree, i know he probably means no batteries needed to be inserted, and i understand that that doesnt fit in the title, but its also kind of deceiving...

but its a nice idea, nice instructable, and it works pretty good i think ;)