Yes, you can do this. You will need a charging device that regulates the alternating current of your dynamo to constant direct current. The manufacturer SON recommends the universal charger "USB-Werk" from Busch & Müller for USB devices that operate with low power consumption. Modern smartphones in browsing mode with the screen permanently lit need 2 to 4 watts of power.

Few charging devices are efficient enough to work with these devices. The most efficient devices, regardless of speed, are the "Forumslader V5" and the "NC-17 AppCon GT1".

In any case, care should be taken when charging during a bike ride: USB cables plugged into the smartphone during the ride can damage the charging socket due to shaking. Even otherwise splash-proof mobile devices can be damaged by rainwater if the rubber seal of the USB port is removed and the cable is plugged in instead. Under no circumstances should you let your smartphone or GPS distract you while driving!

Most charging adapters do not charge at all or only with a fraction of the rated power when the lights are switched at the same time. If a USB device is to be charged, it is recommended that the lights are switched off. With the universal charger "Forumslader V5", an Edelux DC 6 to 75V headlamp can be connected to its 12V output and the lighting and USB devices can still be operated - provided the charge level of the buffer battery is high enough.

Most simple charging devices supply no more than 400 to 500mA at their USB-output. Modern devices (such as the USB-Werk) can sometimes deliver more than 800mA (corresponding to 4 watts). However, for such high output powers, a cycling speed (in a 28" wheel) of well over 20 km/h is required, even with efficiently working charging adapters.

Smartphones from Samsung© or Apple© require constantly high charging power. This will be difficult to achieve without a buffer battery. On your leisure GPS, like Garmin©, device warning messages may appear as soon as you stop at traffic lights due to lacking power supply. A buffer battery will help.

Connect charging devices to a hub dynamo in parallel with the headlight, not at the rear light output of a headlight. SON manufacturer recommend to crimp 4.8 mm piggy-back connectors to the feedcable of a charging device. The headlight cable connects to the tongues on the piggy backs. If you connect and disconnect the charging device frequently, the Coaxial Junction Box will be a good choice. (see SON Accessories).