I made myself a usb charger for charging my phone with a 6V 3W dynamo.
It works well: bridge rectifier -> 470UF 100V -> buck converter 5V all protected with a zenerdiode.
Charging a powerbank is not a problem, but charging my phone doesn't work because my phone won't charge because a low voltage (some phone shuts down). I can charge my phone if I ride 20km/h and unplug my phone and reconnect it again. Then the charger is charging my phone. So the there is enough voltage.
So I want to make a mosfet delay switch to let me start riding until approx 20km/h (let's say 15s to get there?) and the switch should turn on. When I ride 20 km/h the DC voltage is around 14 V.
I know I have to use a resistor to slowly fill a capacitor until the threshold voltage is reached. But what are the specs (100UF and 220kOhm)? And should I use a MOSFET of BJT (because of the low current)?
And do I need the place a 2nd capicitor beside my 470UF for the mosfet?
Hopefully you can start me up
Thanks in advance!