Voltage Regulated [5v] Bicycle Dynamo Light & USB Charger




Introduction: Voltage Regulated [5v] Bicycle Dynamo Light & USB Charger

Even though, there are plenty of "Dynamo Bike Light" instructions on this site, I thought I would share mines.   The great news, there are NO resistors in my circuit.    It has a fixed 5 volt output, so you can ride as fast as you want without worrying about burning out the LEDs.  Also, since this has a 5v output, you can hook up virtually any high-powered (CREE/Luxeon) LED flashlights (typically rated 4.5v - 8v).  I use this circuit to power a CREE RC-G4 Flashlight , which i bought  from DealExtreme for $17. (It's very bright, but I will most likely upgrade to SSC P7  900-Lumen LED Flash Light, not bad deal for $38.67).

I will also hook up a USB connector plug to charge my BlackBerry Phone and Ipod.  Most USB devices are rated 5v , so with this circuit like this, you will never need to deal with a solar charger to charge your phone, GPS, ipod, recharable batteries, or to power any standard USB device.  

Please refer to Step 1, Step  2, Step 3 & Step 4 for further details..

FYI: This is a work in progress, and I will update my instructions as my project progresses.  Please bear with me given my hectic schedule and feel free to contact me if you have questions regarding where to get the parts or accessories.   And don't forget to leave feedback and suggestions.   

Thank you for visiting & Have a Happy and Safe riding!


Step 1: Building the AC to DC Driver & Voltage Regulator Circuit..

Before you begin, it would greatly help if you review the following links:

      1. Useful Dynamo/LED Circuits:http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm
      2. Voltage Regulator Circuit: http://www.youtube.com/watch?v=GSzVs7_aW-Y

 Few Helpful links for novices:
      1.  Alternating Current (AC)
      2.  Direct Current (DC)
      3.  Full Bridge AC to DC rectification
      4.  Voltage Regulator
      6.  AC generator (Brushless Dynamo)
      7.  DC Motor (Commutated DC motor can also be used to as a DC generator)
      8.  Light Emitting Diodes
      9.  Soldering instructional video

And now...the Nut's & Bolts (Components Required) :

The circuit modules I used have been out there for a while, but what I did is combine both the Full Bridge Circuit & USB Voltage Regulator circuit to make something useful out of it using a bicycle AC generator.

1. [Full Bridge Circuit Diodes]
D2: 1N4007
D3: 1N4007
D4: 1N4007

2. Voltage RegulatorComponents
[Capacitors: Left to Right]
C1: 10uF
C2: 10uF
C3:   N/A

3. Voltage Regulator [7805 Transistor]
Q1:  7805

4. High Charge Capacitor
Note: I don't have it in shown the circuit diagram.  I will have to try out some high capacitance capacitors to supply voltage to the LEDs when my bike comes at complete halt.   It may take few trials to find a powerful capacitor  that fits the Altoids box, and also holds ample amount charge to keep the LEDs lit for few minutes.  I will update the instructions once i find the best match.  Meanwhile, If you have any recommendations, please feel free to suggest. 

5.  Dynamo Generator:
For this project,  I assumed you already have a dynamo generator for your bike, but no worries if you don't.   I can help get you started.

Bottle Dynamo: If you want to play and get started with one without spending a fortune,  the X Factor 3-Inch Bicycle Generator Light Set  from Amazon would be a great place to start.  They sell for $13.11 at Amazon.  A great & cheap little unit.  This is the one shown in my project.

Hub Dynamo: if you are a more serious rider, you should probably switch to a Hub Dynamo.   You can gather much more information on Hub Dynamo's and lighting on Peter White's website:   http://www.peterwhitecycles.com/shimano3n70.asp

I also highly recommend Anthony from Longleaf Bicycles. A very helpful fellow and awesome wheel builder. You can find great deals here: http://www.longleafbicycles.com

In my opinion, switching to dynamos may seem expensive to start off with, but in the long run, these units pay off and puts back money in your pocket. And, if you are like me, who enjoys cool evening rides during hot summer months, that can save you a lot of dough.

I personally prefer and use both the Bottle and Hub dynamos.  The Advantage of a Bottle dynamo is that you can engage or disengage it as needed, but with Hub Dynamos, you are stuck with it.  It doesn't matter whether or not you need the electricity or not!  This dynamo generators do add some resistance to the wheels, but not noticeable when riding.

Step 2: Mod & Prep the Flash Light

A picture says a thousand words, hopefully, its self explanatory.

Components:    Every electronic componets I have used for this circuit were all bought form RadioShack, except for the following items:

1.  High Power CREE Flash light  (you can get it from dealextreme).
       >    SSC P7 3-Mode 900-Lumen LED Flash Light: $38.67  [Recommended]

     If you are on low budget, the Romisen Cree RC-G4 Flashlight isn't a bad choice either. 
       >    Romisen Cree RC-G4 Flashlight : $17.48

 2.  Bicyle Top Tube Pouch (to contain the circuit box)
You can find these pouces from Amazon or Ebay.
       >  Axiom Power Bag 2 Top Tube Bag

 3. Glue Gun (to seal the flash light)

 4. Flashlight Handlebard Mount (Purchased from Amazon).

5. Circuit Box (I have used Altoids box in this example,but will upgrade to something better in the near future).

Step 3: Modding Stock Taillights to Be Dynamo Powered

Check out the video: Click on the images above for details

I plan on using this as an Supplementary Taillight during touring or heavy traffic. I already use a very nice Busch & Muller's dynamo taillight, and i dont want to replace it with this cheap light. I did it to see whether it could be done or not, and it actually turned out very nice.  You can power it both using a battery pack or a dynamo. 

Actually, I got this idea from this cool instructable: https://www.instructables.com/id/LiteBack---Backpack-or-Camelback-Mounted-LED-Bike-/

While the taillight which i put together worked fine with a dynamo during initial testing, but I have not stress tested it.  At worse,  it may burn out and I may need resistors to run it safely with 5V.  The problem is I am not really sure specifications of the LEDs, so it would be difficult to calculate the resistance.   I will do a stress test tomorrow and  see what happens.  If it doesn't burn out, I know it will work fine without resistors.   

This taillight in this project turned out rather cool.  Click on the images. You will get the idea and details on how it was done.  Let me know if you have any questions.   You may find cheap taillight to experiment from Dealextreme:  http://s.dealextreme.com/search/bicycle+tail+light

Step 4: Configure USB Type-A Connector Plug

I have a good news and bad news.  The good news, this circuit will charge any USB standard phones and devices, but the bad news is it wont work with Apple Ipods.  But fear not,  Apple users can gladly lookup or reverse engineer theMinityBoost Kit.

As for now, I am happy because my BlackBerry phone was my biggest concern.  I use the GPS, Email, Facebook, internet, phone & camera  all in one device, and the battery can wear out in matter of hours. But now, I dont have to worry about the batteries running out of juice during a tour.  I can always recharge it whenever i want.  That's really awesome in my book, and the best part, no bulky solar panels to deal with.  I hope you benefit from it too.

DISCLAIMER:  Please use this circuit at your own risk.  I will not be held responsible if your phone or USB device gets damaged.  

Other than that, life is good.  Time permitting, I will try to modify the circuit for Apple Ipod Touch or Phone.  However, there are already plenty of Instructables to do so: 

If all fails, you can always use this device to charge an external USB battery charger pack.

Few links to help out Apple users:

Good luck.

Step 5: Future Enhancements

I would like to add the following enhancements in the future.

 1.  A better circuit box to protect the circuit.
 2.  Add a switch
 3.  Add a female USB Type A plug
 4.  Add a super capacitor, or some sort of backup/rechargeable batteries to power the LEDs during slow hill climbs or a traffic stop.
 5.  Modify circuit to be able to charge Ipod Touch
 6.  Last but not least, upgrade to hub dynamo.

I already have a few of these items gathered, but need to accumulate and build the rest.    I will update as i progress.

1 Person Made This Project!


  • Meatless Challenge

    Meatless Challenge
  • Build a Tool Contest

    Build a Tool Contest
  • Remote Control Contest

    Remote Control Contest



2 years ago

This one is going to cost bit more.

I use buck converter it will be more efficient. I used LM2596. Since it has more sensitive components you can #1 clear voltage spikes from the input with AC diode clipper (two diodes antiseries between ac wires from dynamo close to rectifier. Diodes can be something like 15 V power zeners if available but if your buck can not handle that much go with 10 V or something). #2 add a ceramic capacitor (104) filter between ground and positive after the rectifier. #3 use something like 1000 microF electrolytic capacitor before the buck converter similarly . #4 adjust the buck output voltage to 5.0 V. #5 filter the output with 5v1 power zener diode clipper just in case (USB can go up to 5.2 V) and maybe add a ceramic capacitor and an electrolytic capacitor.

This should improve the efficiency.

Even more foil hat. Add a power transistor between the rectifier and buck converter. Use something like 5 W low value resistor as transistor's load. Control the gate and shutdown threshold voltage with zeners and currents with resistors.


5 years ago

Has anyone actually tested the range of amps that this circuit produces at some range of bicycle speed estimates (obviously wheel size and dynamo efficiencies vary) with 6v 3amp dynamo?


5 years ago

"there are NO resistors in my circuit."

except that, you see... that LM7805 chip is, essentially, a big 'ol self-adjusting resistor. When the output drops below 5V it adjusts its resistance down, when output goes above 5V, it increases its resistance, which is how it functions as a regulator. A 7805 is dead simple to wire up, but they aren't used where efficiency matters... if you hook one up to a 10V supply you are gonna automatically be wasting 50% of your energy as heat (which is why it comes in the package with the big heat sink tab.)

Good next step would be to search for "buck converter" which is a more efficient form of voltage regulation.


Reply 5 years ago

I think "600mA" is a filty lie and you shouldn't trust it. I think it'll do closer to 100mA on average, or less.


6 years ago

Hi, I made it without the rectifier part and I want to use it to charge my smart phone with my spare 12v motorcycle battery. But it doesn't charge any smart phone or tablet. My power indicator is working and I tested the output with a voltmeter and it gives me something in between 5.1-5.3 volts (its an analog voltmeter). Please give me some advice. thanks.


Reply 5 years ago

Do i read you correctly, you're attaching a 12V battery (DC) instead of dynamo (AC)? Then yes, you don't need the rectifier portion. You also don't necessarily need the capacitor C1, because the battery has a low enough ESR, but if you already have it, you can leave it in.

In order to charge smartphones and tablets via USB, the port that you connect them to must identify as a USB host or as a charger.
To implement simple charger identification according to USB 2.0 SDP (limit: 500mA or 100mA, device dependent), connect D+ to GND via 15 kOhm resistor and D- to GND via 15 kOhm resistor.
To implement simple charger identification according to Battery Charging Specification, connect D+ to D- straight or through 200 Ohm resistor (depending on version), current limit: 1.5A.
To trick Apple devices into charging at 500mA, place 2.0V on both D+ and D- via suitable resistor voltage divider networks. Aim for total resistance between GND and +5V no less than a few thousand Ohm.
To trick Apple devices into charging at 1A, place 2.8V on D- and 2V on D+.
To trick Apple devices into charging at 2A, place 2V on D- and 2.8V on D+. Note that you shouldn't do that if you use 7805 as your current controller, because it can only supply 1.5A. The voltage will drop, and the Apple device will detect a charging fault, and will then refuse until it's connected to another charger.

Most Android and Windows devices will be OK with an Apple charger as well.

To confuse yourself even more, please refer to MAXIM Application Note 5801.


6 years ago on Introduction

cool, i have a question, what if i get one of those "usb wall chargers", its says: input ac 100-240v, output dc 5.0v == 500mA

Doesnt it do the same thing? convert AC to DC to charge the phone or whatever, im thinking, all i need to do is set the wire from the dynamo to the wall charger and connect an usb cable to whatever device. Would it work?

Or maybe, i could buy one of those small crank dynamo with usb and connect the wire to the crank thing, could this work?


Reply 6 years ago

Of course that doesn't work. Your wall charger requires 100-240 volts AC on the input side, but a typical bicycle dynamo provides only 6V AC.


6 years ago on Introduction

yup, it works, i just tested with an "usb wall charger" i connected the usb wall charger to the dynamo and then my phone into the charger, perfect.


7 years ago

i have got some problems in making the voltage regulator.. how can i fix any problems in circuitry?


7 years ago on Introduction

Hi Sonnet...beautiful idea...
Have you completed it already ?


8 years ago on Introduction

Is it possible to add a battery in-between?

I would like to have the dynamo charge the battery and the battery to power the lights and for example other equipment.

Nexus dynamos add resistance only when you are using the light or drain power as far as I know but maybe you have short circuit somewhere


9 years ago on Introduction

I am working on a similar idea , the only difference is I have very low speed of cycling, around 15 rpm. So please suggest an appropriate dynamo and what changes do i need to make in the circuit to get a constant output of 5V at low speeds. please help!!


10 years ago on Introduction

Good stuff Maynard!

I'm "eagle-ing" it as we speak...

Some questions though:

Just where in the circuit (schematic) does the "big-ass-capacitor" fit?
Have you looked into Supercapacitors yet?
I've had an interest in them, but haven't found much in this niche...



10 years ago on Introduction

Another question/idea; wouldn't it be possible to put a little stack of rechargeable batteries (4x1.5V) between the rectifier bridge and the regulator in order to store some energy and feeding the regulator when not cycling ?? Therefore having some power feeding the lights when not moving.


10 years ago on Introduction

Wouldn't it be possible to use the whole bridge rectifier made of power LED as a taillight ?? Pilom suggest using one of the LED from the bridge as a taillight but why not the four of them ??

Cheeeeers !!


10 years ago on Introduction

thanks for the instructions, I have one question though. why not drill two holes in the side of the flashlight body for the wires to exit and integrate the rear on/off/mode switch of the flashlight into the wiring?

Also check out the new crop of "on/off" hub dynos. In the off position the magnets are disengaged and there is no drag, much like a bottle dyno. I have provided links to three of them below.






10 years ago on Introduction

good job i wouldnt put this on my lowrider but i wanted something for my mountain bike.