"Andre" wrote in message
Next problem . How to delay turn-on long enough to charge a fairly
hefty capacitor to boost start the fan ?

I'm thinking some type of MOSFET, and a capacitor/resistor combination
to get the 5 second or so delay . Possibly also a zener diode .

e.g. it waits until the voltage is more than say 3.6V and start
charging the capacitor . When the voltage hits the MOSFET's turn on
voltage it starts, dumping the charge stored in the main reservoir
capacitor into the motor .


No need for that. The cap is in _series_ with the motor, and in _parallel_
with the resistor or diodes or LM317. On startup, the cap acts as a very low
resistance shunting the resistor to apply full voltage to the fan. When it
charges up its resistance goes high and it is effectively no longer there,
so the resistor does its job. When the fan is powered off, the resistor
discharges the cap so it's ready to go again. Great idea, so simple like the
best of them!

Dave