Electronic – Converting and Stabilizing output voltage of a dynamo hub

chargerdc/dc converterstabilityvoltagevoltage-regulator

Preface – I don't know much about electronics 😛

I have ordered a Shimano dynamo hub for my bicycle. I have done a little homework and here are my findings about it:

  1. The output of the above mentioned dynamo is a 6 volt AC.

  2. The output voltage of the dynamo is not stable, it varies based on the speed of the dynamo.

  3. There are chances that the lights will blow up 😉 Reason is because of non stabilized voltage output.

Based on the above I have few questions.

  1. Is there a simple circuit which converts AC to DC output? I have read about some bridge rectifiers, but wanted to be absolutely sure about it. Also what size is the circuit, how easily it is available and how reliable it is?

  2. Most important thing which I wanted to know, how do I built a circuit so that the 6 volt fluctuating AC output from dynamo to convert to a 5 volt (USB chargeable) stabilized DC output? Are there any already available? What is the cost of such circuit or how easily can I build from scratch?

  3. I have read somewhere that plugging in a device to a non-stabilized input source (in this case the 5 volt output from dynamo to my iPhone) would blow off the device. So, if I could not achieve in building (or purchasing) the above mentioned point 2's circuit, can I use the 5 volt output to charge intermediate batteries like a spare Lithium Ion solar charger for iPhone and a AAA rechargeable batteries through a USB charger and use these to charge up my gadgets?

Best Answer

Don't use a bridge rectifier. It's inefficient, because you need two diode drops in series, and it doesn't allow you to use the frame as ground for a DC lamp (like, a modern LED bike light). Instead, consider a voltage doubler


simulate this circuit – Schematic created using CircuitLab

The 'regulator' can be a current regulator, or just a Zener followed by a limit resistor. Several LEDs in series can make use of the 'extra' voltage supplied. Accuracy, like efficiency, is less than important in this application.

I've used a 6V sealed lead-acid battery as the 'regulator'; overcharging seems not to be a problem, and a low-dropout regulator IC can ensure that the output to the lamps is a stable 6V.

Charging from a '5V' source is possible, but depending on such things is less than satisfying; the generator has all the power you need.