Surely this fan is designed for variable speed, otherwise whywoudl it say its supply voltage can be 20 to 58V?
The current monitor is needed because certain currents correspond to certain speeds, and we must monitor the current, the micro reads the current and varies the duty cycle which speeds up/slows down the fan to the required speed.
Do you think its a single phase BLDC fan, or a 2 or 3 phase BLDC fan?
Also, we have a 100u electrolytic across the fan right now but would like to make it non electrolytic and just 10uF, do you think that would be OK?
Regarding start up, surely this is a potential problem due to the BLDC not locking up to the drive signals?....whether they be from an encoder or resolver, or from back-EMF sensing....back emf sensing is more likely for space/cost reasons.
Where on the datasheet does it say its a fixed speed fan?