I have the following setup:
- Shimano DH-3N72 hub dynamo
- cycle2charge.de USB charger
- LED headlight and taillight, both capacitor-backed
The headlight and USB charger are both directly attached to the dynamo. The taillight is attached to the headlight so that the switch on the headlight switches both off.
With the lights on, the USB charger hardly gets any power. My phone will show that it's charging only after some time (presumably once the capacitors of the lights are fully charged) and only if I'm going fast. If I switch off the light, it takes a much lower speed for the phone to start charging.
I do understand that the lights reduce the amount of energy available to the charger (also the manual of the charger says so), but I am surprised that the effect is this significant even with LED lights. Is that really due to the power consumption of the LEDs themselves, or is this effect due to inefficient circuitry or some kind of voltage regulator? (My hub dynamo came with a regulator device, which I didn't install. It is meant to be hooked up in parallel with the lights and is apparently some kind of ballast. In a setup with two incandescent lamps, if one of them fails, it is supposed to prevent the other from burning out.)