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Bicycle Dynamo Battery Charger Circuit

Bicycle Dynamo Battery Charger Circuit

The post explains a simple constant current bicycle dynamo battery charger circuit which can be used for charging a Li-Ion or Ni-Cd battery from a bicycle dynamo electricity source. The idea was requested by Mr. Saif Khan.

Technical Specifications

I want to charge a battery through a dynamo fitted to a cycle. Can you please tell me how to design the circuit for it. I don't know electronics. I will be really grateful.I don't know much but i live with electronic engg guys who know about it so if given a complete schematics they can do it. Can i order these online?

I am not sure a dynamo would be able to produce 28/30V. I have read that it can be limited to 4-20 V mostly
(I am using a simple motor..which will rotate and as well charge the battery). I know i am a total noob.

Just few points:
1. The input voltage, being connected to a dynamo fitted to a normal cycle will vary a lot but mostly be less than 20V, right?

2. The Li-Ion battery that will be charged needs to power an LED lamp for about 2 hrs. It has to be charged within 1-1.5 hr of cycling. That's pretty much my project.

1) The Design

The second circuit shown in the following link can be implemented for the above application:

The dynamo input should be connected across the points referred 30V and ground, VIA a 1N4007 DIODE.

The 10K variable resistor which may be a pot or a preset should be adjusted to get the desired output voltage.

The LM317 should be mounted on a suitable heatsink.

The IC LM317 can work right from 3V to 35V inputs, so input variations won't affect the outcome.

The pictorial presentation of the proposed bicycle dynamo battery charger circuit is provided below.

It must be ensured that the pinouts of the IC are correctly connected as per the shown designations.

How to calculate current limit for this bicycle dynamo battery charger circuit

Rx is the current control resistor which must be selected as per the charging current specifications by using the following formula:

Rx = 0.6/charging current.

The next idea below explains how to simply charge Ni-Cd cells quickly using a dynamo device.

2) Charging 1.2 V Ni-Cd Cells (for Science Projects)

The second concept explains how to use a 6V dynamo for charging 3 Ni-Cd cells or Ni-Mh cells in series.

The design was requested by Mrs. Jennet through email, as given below:

"My daughter is in grade 10 and her science project is to charge a small battery using an exercise bike and a dynamo. Would you be able to assist in a schematic for this, as well as advise on what needs to be purchased in order for this to be built? Any assistance would be greatly appreciated. "

Materials Required

The materials required for this bicycle dynamo converter project are:

  • 6V Dynamo = 1no
  • 1.2V AAA Ni-Cd or Ni-Mh Cells = 3nos
  • 4.5V Battery Box to Fix the above cells in series = 1no
  • 10 Ohm, 2 watt resistor wire wound = 1no
  • 1N4007 Diodes for making Bridge Rectifier = 4nos
  • Any Cheap Small 100 mA Ammeter = 1no (optional, for indicating charging status)

The image of the battery box can be seen below:

4.5V battery box for3nos 1.2 AAA cells

Dynamo Specifications

The dynamo specifications can be studied from the following data:

6V Dynamo image
Dynamo internal parts and layout

It is basically a 6V dynamo, with a maximum current capacity of 500mA. Even at a slow bicycle speed of 5 km/hour, this type of dynamo will produce a decent output of 6V @ 100mA. This power could be used for charging an Ni-Cd or N-Mh cells or even a Li-Ion cell. Li-Ion cell might take a long time to charge at this rate, unless a buck converter is employed.

dynamo working test report with constant 6V and constant load

The cell specifications could be as indicated below:

How to Connect Dynamo with Battery

Connecting the dynamo with the battery and the rest of the mentioned parts can be implemented using the following wiring layout:

The connections look pretty simple. You will need a soldering iron and solder wire for joining the shown parameters.

Begin by making the bridge rectifier using 1N4007 diodes, as explained in this article.

Next, insert and fix the cells in the battery box.

After this, install the dynamo on the bicycle frame.

Finally, join the ends of the shown components using flexible wires with one another. Be sure to connect the ammeter with correct +/- polarity, otherwise the meter needle will deflect towards the left side instead of right side. (+) of the meter will go to the 10 ohm resistor.

Warning: Since the dynamo body acts like one of the output terminals, make sure it does not come in contact with any of the wire connections of the circuit, except the point where the lower orange wire is hooked up. In short, keep the diode side circuit secured inside a plastic box.

Testing the Charging Response

Once you have finished the procedures, start peddling the bicycle. You will start seeing some deflections on the ammeter. This will indicate that the battery is consuming power from the dynamo and is getting charged.

Now, as the bicycle is operated continuously, the battery will gradually get charged. This will be indicated by proportionately reduced deflection on the ammeter. Until, finally no deflection or reading on the meter will be seen, which will indicate that the battery is now fully charged.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

15 thoughts on “Bicycle Dynamo Battery Charger Circuit”

  1. Sir i am a mechanical engineer pl sujest me i need a dynoma for mobile charging system dynoma rotate per hour 10 kilometers there are 5 leds bulbs and mobile charging round the the clock dynoma rotating mobile charging should exceed normal level pl advice me with crcuit diagram suitable dyonoma and where is available address pl urgently pl give miss call to 9480106295 / 9449950392 sincerly

    • Hello Nagabhushan, you can try the last circuit for charging the mobile phone, the meter will not be required and the 10 ohm resistor should be replaced with a 2 ohm 2 watt resistor. For the LEDs you can use 20mA 5mm LEDs, put all of them in parallel, make sure to have a 100 ohm 1/4 watt resistor in series with each LED

  2. Hi I’m 16 and am creating a dynamo – battery charging unit for a DT project. I don’t have any expertise in electricals and was wondering if you could help me understand how to use / adapt this or another circuit to suit my need and also where to purchase all the necessary components.

    • Hi, I can surely help you. Please let me know the battery ratings that you are going to use. Or you can simply tell me about the dynamo specifications, so I can suggest which battery could be suitably used with it, and other related parameters.

  3. Hello, I have build a robot with battery switching feature. Another part which I am currently working on is to generate energy from the robot's motors using dynamo. The dynamo would charge the system's battery one at a time based on the voltage conditions. My question is, what is the appropriate considerations need to be count in while designing the battery charging part. I mean how should I modify the above circuit to a lithium polymer friendly circuit. I am using a 3 cell 11.1V 2200mAh lithium polymer battery. Looking forward for a reply.

    • Hi, the above circuit does not have an automatic over charge cut-off feature which may be highly recommended for a lipo battery.

      I'll design the required circuit soon and post it in this blog for your reference.

    • Suyog, there are many circuit options possible, you can use a 7805 IC, or a LM317 as shown above or any other similar voltage regulator with a bicycle dynamo for getting a cranked charging output for charging the cell phone.

      The above circuit example is the best that you can get.

  4. Hello, swagatam
    The above circuit is very nice. I seen a hand cranked flashlight circuit, there is no electronics in it, not even a diode, the dynamo is wired through a series of LED and a double contact switch. the LED working both as a variable rectifier and light source. its the simplest design… can you explain/post the circuit?

    • Hello Max,


      The Hand cranked device that you are referring to might be having output limited to LED voltage that's why no other parts are involved, a bicycle dynamo voltage could range from zero to 20V making it essential for some sort of regulation to avoid LED damage.

      I'll try to investigate the details.

  5. I am sorry Karaveer, i have discontinued the offer because it could get too confusing to handle and publish so many responses.
    But no issues, if you have any elaborate topic to learn or discuss with me, you can send it to homemadecircuits@gmail.com, I'll respond and publish it as effectively.

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