How to Charge a USB Device by Riding Your Bike
Design a circuit that can take the ~6 volts from the motor, store it, and then convert it to the 5 volts that are needed for the USB device., Select a motor., Attach the motor close to the rear brake mounts directly on the bike frame using a piece...
Step-by-Step Guide
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Step 1: Design a circuit that can take the ~6 volts from the motor
The circuit designed in this example complements the function of the MintyBoost USB charger, originally developed by Limor Fried, of Adafruit Industries.
The MintyBoost uses AA batteries to charge portable electronic devices.
This independently constructed circuit replaces the AA batteries and supplies power to the MintyBoost.
This circuit reduces the ~6 volts from the motor to
2.5 volts.
This allows the motor to charge the BOOSTCAP (140 F), which in turn supplies power to the MintyBoost circuitry.
The ultracapacitor stores energy to continuously charge the USB device even while the bike is not in motion. , In this example, the Maxon motor was chosen due to its smaller diameter.
It also provides 6 volts whereas previous motors often give upwards of 20 volts, and that could make over-heating a huge issue.
The cost of the Maxon 90 was US$275; for those wishing to build this project, a cheaper motor will suffice. , # Connect the motor and circuit.
Speaker wire is a stranded wire, but it's durable because of its large diameter.
Attach it to the frame with zip-ties. , This will be the most difficult challenge of the process.
Here are the details for the circuit in this tutorial:
Electricity from the motor first travels through a voltage regulator which will allow up to a continuous five amp current; a larger current than other regulators would pass.
From there the voltage is stepped down to
2.5 volts which is the maximum the BOOSTCAP can store and safely handle.
Once the BOOSTCAP attains
1.2 volts, it has enough power to allow the MintyBoost to provide a 5 volt source for the device being charged.
On the input wires, a 5A diode was attached so that there's no "assisted-start effect," where the motor would start to spin by using the stored electricity.
The 2200uF capacitor was used to even out the power flow to the voltage regulator.
The voltage regulator used, an LM338, is adjustable depending on how you set it, as seen in the circuit diagram.
The comparison of two resistors, 120ohm and 135 ohm, connected to the regulator determines the output voltage.
It is used to reduce the voltage from ~6 volts to
2.5 volts.
The
2.5 volts are used to charge the ultracapacitor, a 140 farad,
2.5 volt BOOSTCAP made by Maxwell Technologies.
The BOOSTCAP was chosen because its high capacitance will allow us to hold a charge even if the bike is stopped at a red light.
The next part of this circuit is the Adafruit MintyBoost.
It is used to take the
2.5 volts from the ultracapacitor and step it up to a stable 5 volts, the USB standard.
It uses a MAX756, 5 volt boost converter coupled with a 22uH inductor.
Once we get
1.2 volts across the ultracapacitor, the MintyBoost will begin to output the 5 volts. , In order to protect the circuit from external elements, an enclosure is necessary.
A "pill" of PVC tubing and end caps is used in this example, with a diameter of 6 centimeter (2.4 in) and a length of 18 centimeter (7.1 in).
While these dimensions are large when compared to the circuit, this made construction more convenient.
A production model would be much smaller.
The PVC was selected based on durability, nearly perfect weather-proofing, aerodynamic shape, and low cost.
Experiments were also performed on containers crafted from raw carbon fiber soaked in epoxy.
This structure proved to be both strong and light weight.
However, the construction process was extremely time consuming and difficult to master. -
Step 2: store it
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Step 3: and then convert it to the 5 volts that are needed for the USB device.
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Step 4: Select a motor.
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Step 5: Attach the motor close to the rear brake mounts directly on the bike frame using a piece of a meter stick between the motor and frame to act as a spacer
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Step 6: then tighten 2 hose-clamps around it.
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Step 7: Build the circuit.
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Step 8: Build an enclosure.
Detailed Guide
The circuit designed in this example complements the function of the MintyBoost USB charger, originally developed by Limor Fried, of Adafruit Industries.
The MintyBoost uses AA batteries to charge portable electronic devices.
This independently constructed circuit replaces the AA batteries and supplies power to the MintyBoost.
This circuit reduces the ~6 volts from the motor to
2.5 volts.
This allows the motor to charge the BOOSTCAP (140 F), which in turn supplies power to the MintyBoost circuitry.
The ultracapacitor stores energy to continuously charge the USB device even while the bike is not in motion. , In this example, the Maxon motor was chosen due to its smaller diameter.
It also provides 6 volts whereas previous motors often give upwards of 20 volts, and that could make over-heating a huge issue.
The cost of the Maxon 90 was US$275; for those wishing to build this project, a cheaper motor will suffice. , # Connect the motor and circuit.
Speaker wire is a stranded wire, but it's durable because of its large diameter.
Attach it to the frame with zip-ties. , This will be the most difficult challenge of the process.
Here are the details for the circuit in this tutorial:
Electricity from the motor first travels through a voltage regulator which will allow up to a continuous five amp current; a larger current than other regulators would pass.
From there the voltage is stepped down to
2.5 volts which is the maximum the BOOSTCAP can store and safely handle.
Once the BOOSTCAP attains
1.2 volts, it has enough power to allow the MintyBoost to provide a 5 volt source for the device being charged.
On the input wires, a 5A diode was attached so that there's no "assisted-start effect," where the motor would start to spin by using the stored electricity.
The 2200uF capacitor was used to even out the power flow to the voltage regulator.
The voltage regulator used, an LM338, is adjustable depending on how you set it, as seen in the circuit diagram.
The comparison of two resistors, 120ohm and 135 ohm, connected to the regulator determines the output voltage.
It is used to reduce the voltage from ~6 volts to
2.5 volts.
The
2.5 volts are used to charge the ultracapacitor, a 140 farad,
2.5 volt BOOSTCAP made by Maxwell Technologies.
The BOOSTCAP was chosen because its high capacitance will allow us to hold a charge even if the bike is stopped at a red light.
The next part of this circuit is the Adafruit MintyBoost.
It is used to take the
2.5 volts from the ultracapacitor and step it up to a stable 5 volts, the USB standard.
It uses a MAX756, 5 volt boost converter coupled with a 22uH inductor.
Once we get
1.2 volts across the ultracapacitor, the MintyBoost will begin to output the 5 volts. , In order to protect the circuit from external elements, an enclosure is necessary.
A "pill" of PVC tubing and end caps is used in this example, with a diameter of 6 centimeter (2.4 in) and a length of 18 centimeter (7.1 in).
While these dimensions are large when compared to the circuit, this made construction more convenient.
A production model would be much smaller.
The PVC was selected based on durability, nearly perfect weather-proofing, aerodynamic shape, and low cost.
Experiments were also performed on containers crafted from raw carbon fiber soaked in epoxy.
This structure proved to be both strong and light weight.
However, the construction process was extremely time consuming and difficult to master.
About the Author
Kimberly Hughes
Brings years of experience writing about practical skills and related subjects.
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