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Bicycle Dynamo Battery Charger

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 n00b :/

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.

And can we charge Ni-MH battery with it if i don't find Li-ion battery anywhere

Thank you once again. Apology for my n00bness i am just a chemistry grad.

Sir i have bought all u asked for lm317..please guide me further thank u


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

Need Help? Please leave a comment, I'll get back soon with a reply!


  1. 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, I'll respond and publish it as effectively.

  2. 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?

  3. 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.

  4. Sir i want to make a hand cranked mobile charger for 2000mAh battery. How design circuit and dynamo.

  5. 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.

  6. 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.

  7. 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.

  8. helo sir,
    i want to know what about Rx. what is the use of it.

  9. helo shiva, it's for restricting the charging current to the desired safe limit as fixed by the calculated value of the Rx

  10. 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.

  11. 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.

  12. I'm sorry but I have no idea about battery size or the dynamo's specifications. I have bought the parts for the above circuit (- dynamo and battery) and put it together on a breadboard. If you could give me a link to anywhere I could by a suitable dynamo and battery I would be much obliged,

    Thank you.

  13. No problems,the circuit above circuit includes a current control so your battery will be safe anyway. For the dynamo you could buy a standard bicycle dynamo rated at 12V 6 watt. The battery could be a 12v 5Ah.

    Just make sure to add a bridge rectifier between the dynamo wires and the circuit input, so that the AC from the dynamo is correctly rectified.

  14. For Rx you could use a 1 ohm 1/2 watt resistor

  15. Do you know where I could get the dynamo and the battery?

  16. you can get it from amazon or eBay


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