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:
https://www.homemade-circuits.com/how-to-build-simplest-variable-power.html

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:

Dynamo Specifications

The dynamo specifications can be studied from the following data:

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.

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.