Using this tutorial as a guide, I have put together simple DIY wind turbine capable of giving around 2.5V - 3V output across the motor when spinning the fan blades. I can also light up some LEDs when connected directly across the output.
When connected via the DC booster, the USB output is a steady 5V. As soon as it is connected to a mobile phone, it shows a charging indication on the device and it stays that way as long as turbine is running. However, the phone battery does NOT charge. The phone goes into to "charging" mode (even with the device switched off), but fails to increase in battery percentage.
I have had the identical results with 3 different android devices and micro-usb cables. All seem to indicate charging has started, but the battery percentage does not go up at all, even if left running for hours. I also tried this with three different boosters: similar to one, two and three - all perform in the same manner.
The current shown on android apps varies wildly - most of the "battery charging / ampere" apps show a positive charging current of around 200mA ~ 500mA when the turbine is running. However one app (AccuBattery) always displays a negative charging current averaging around -200mA.
Any idea on what could be wrong with this setup or what can be done to improve things?