Instructables
Picture of Hand crank USB charger / LED headlamp
Charge your mp3 player and light your way anywhere anytime!

This DIY gadget makes a highly satisfying project and is extremely useful for long road trips, mp3 players with tired batteries, plain neatness, and impressing your friends.


The idea is very simple: use a crank charge headlamp and re-route some of the power from the light to a USB port for charging USB devices. We rely on the battery to soak up the voltage peaks so that while you're cranking, it should be around 5v.

P.S. if you like this, please vote so in the back to school contest.


 
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Step 1: Materials

Materials and tools you will need:

-Hand crank headlamp: http://www.leevalley.com/en/garden/page.aspx?cat=2,40731,58277&p=58277
-Female USB port single or double  (you can get them out of old computers)
-Knife
-Wire
-Soldering iron & solder
-Multi tester
-Small screwdriver

----------Disclaimer  disclaimer------------
This project is "do at your own risk". In other words, I'm not responsible if you fry or damage something in the process. Yada yada yada now let's get on with it.

Step 2: Construction / destruction

Picture of Construction / destruction
All right, time for the screwdrivers. Clear off your desk and put on some good music.

Unscrew the dynamo cover, remove it and take a good close inspection.

Cut out a square in the side of the dynamo case the size of your USB port. You can heat up your knife blade which might make it more tidy and or easier. Press the USB port into the socket you made for it and put a little glue in if necessary to keep it in place.

Step 3: Wiring

Solder two short wires onto the USB power pins, the two outermost pins (other than the mounting legs).  Looking at the open side of the USB port with the pins down, the far left pin is POSITIVE and the far right pin is NEGATIVE.

Now solder the other end of your USB port power wires to the headlamp power cord jack.  Put the USB positive to the red one on the jack and the USB negative to the black. Be SURE to get the polarity correct.

salz7773 years ago
Hi fellas,

I wonder, is there any way to store it up and charge whenever the switch is on? (assume we attach switch to control the power flow)
Thanks :)
I am working on this instructable and I wired it right from + on the circuit board to the positive on the usb port and the negative from board to the - if the usb and i am only getting 3.9 volts and it wont show my phone as charging but it does say mp3 charger. is this power enogh to charge a phone or do i need a beeffer crank and also the batter is warm to the touch but its not shorted its over 2.6 m ohms between the terminals and it reads as 3.9 volts.

thanks for the instructable
Earthling! (author)  jehovahgodofgaps3 years ago
Hi there,
I have had a similar problem with trying to charge phones. As far as I can tell, they are quite picky about what they will charge off. I don't think they will even work off of a generic wall plug USB charger. I'm not sure why though.

Maybe they need some kind of a rudimentary data exchange before they will start charging. I'm glad someone is making use of the instructable!
earthling

I just got it to work i charged the cranks chargers internal battery over the dc in port via usb and it now reads 4.13 volts and when i hook it up to my phone it shows the lighting bolt on the battery meter that says its charging. since i commented i also had a bad contact in the first usb port i soldered in. while desoldering the first usb port i must have pulled it to hard and the contacts pulled out the back but i replaced it with a better usb outlet
Earthling! (author)  jehovahgodofgaps3 years ago
Nicely done! I am very glad it all worked out.
LuciferRex4 years ago
Quick question: How efficient is this at charging your mp3 player?
Earthling! (author)  LuciferRex4 years ago
Hi,
Thanks for the question. After exercising a bit of rusty math and a multimeter I have determined the dynamo will put out at least 2.48 watts with a external load of 7.2 ohms. I think that's as much as most normal mp3 players would take in while charging but I can test mine once the battery is discharged.
Earthling! (author)  Earthling!4 years ago
I tested how much my player used to charge it's empty battery while plugged into a USB wall charger and it was somewhere between 100 and 110 mA. According to that, It should take the same amount of time to charge as it would if it was plugged into a computer or normal charger.