I want to add a second fan to cool down the controller board.
I know the standard single fan has a resistor in serial to put 15V down to 12V which
is needed by the fan electronic. I think it would be better to use a small DC/DC
converter to drive more than one fan. I guess the output (see schematics) is able
to drive enough current.
But the big question is: Is the output pulsed to control the fan speed?
When checked this by oszi I saw only 100% duty cycle, but maybe there are other
situation where the fan speed is decreased by controller firmware.