I recently got a good deal on a bicycle dynamo hub (6V, 2.4W), and ultimately want to set up a system for USB charging for long distance bike trips.
My circuitry knowledge is limited to 1 course in university 15 years ago, and frustratingly fiddling with a bread board during one of our labs, so please bear with me. As I understand it, the hub will produce a variable AC voltage based on speed, and able to supply current based on torque. To that end, what torque/current will the front wheel experience, since it's more or less just "along for the ride"?
Since a phone requires a pretty steady 5V DC signal, we want to rectify the messy variable one that comes from the hub using the magic of circuits. My first thought was a diode bridge with a voltage regulator, but my reading says these are notoriously inefficient, which is a big consideration since all the energy is coming from me. I read what I need is called a 'switch mode power supply' which apparently uses inductors which kind of acts like both a voltage rectifier/regulator, and a transformer to conserve energy.
There is this: https://www.amazon.ca/Supernova-ThePlug-III-Dynamo-Charger/dp/B00FA5HEVI
I've found which does the job, but unfortunately costs almost as much as my bike, and I want to do this on the cheap.
I saw another website which suggested using a hand crank radio dynamo with a friction drive, and that got me thinking, can I just solder the wires from the hub dynamo to where the power input from the crank is and call it a day? I have no idea if this is a switched mode power supply though, but given that it came from a hand crank, thought that maybe it is since efficiency would also be important there for human power? Or maybe since human hands probably have a pretty narrow power curve they could design around it? I really don't know much about circuits beyond being able to identify resistors and capacitors and ohms laws. Here a pic of the circuit if it helps:
My circuitry knowledge is limited to 1 course in university 15 years ago, and frustratingly fiddling with a bread board during one of our labs, so please bear with me. As I understand it, the hub will produce a variable AC voltage based on speed, and able to supply current based on torque. To that end, what torque/current will the front wheel experience, since it's more or less just "along for the ride"?
Since a phone requires a pretty steady 5V DC signal, we want to rectify the messy variable one that comes from the hub using the magic of circuits. My first thought was a diode bridge with a voltage regulator, but my reading says these are notoriously inefficient, which is a big consideration since all the energy is coming from me. I read what I need is called a 'switch mode power supply' which apparently uses inductors which kind of acts like both a voltage rectifier/regulator, and a transformer to conserve energy.
There is this: https://www.amazon.ca/Supernova-ThePlug-III-Dynamo-Charger/dp/B00FA5HEVI
I've found which does the job, but unfortunately costs almost as much as my bike, and I want to do this on the cheap.
I saw another website which suggested using a hand crank radio dynamo with a friction drive, and that got me thinking, can I just solder the wires from the hub dynamo to where the power input from the crank is and call it a day? I have no idea if this is a switched mode power supply though, but given that it came from a hand crank, thought that maybe it is since efficiency would also be important there for human power? Or maybe since human hands probably have a pretty narrow power curve they could design around it? I really don't know much about circuits beyond being able to identify resistors and capacitors and ohms laws. Here a pic of the circuit if it helps: