ive always wondered......and who is right? my friend says blowers can be activated at any time like they show in the movies.but i say that blowers run all the time from when you crank the engine until you shut it off.
A crank-driven supercharger is connected to the crank via a belt and, as 6T6NOVA mentioned, rotates as the crank rotates...but there are applications whereby a supercharger is driven by an electric motor. On the vehicle side of things, I've seen presentations by companies who are targeting electric, fuel cell and electric-hybrid vehicles with an electric motor-driven supercharger - variable speed screw-type units and centrifrugal-type units. Some of that electrically-driven supercharger technology also comes from air conditioning for high pressure applications, such as air cabins (planes), etc.
back in the early 60's there were electrical driven superchargers.... they were not very effective...
all forced induction is belt driven.. it has to be unless you install a bypass.. the air is drawn through the super charger.. if the super charger is not spining how does the air get to the engine? with out a bypass....
I guess you could install or fab up a electrical clutch like is used on a A/C compressor..
The term "Blower" is slang for a supercharger. A supercharger is mechanically driven. A turbocharger is driven by exhaust pressure.
Supercharging takes a lot of power to compress air, but it yields more power than it consumes.
I built a torque cell (strain gauging) drive hub once and measured the torque/hp required to spin a Ford Lightning supercharger under full boost. It was around 57 hp. Top Fuel superchargers use at least 300 hp.
A 'Mad Max' style electric clutch would have to be very strong and I'm not sure the benefit would outweigh the problems caused by the sudden surge in boost pressure.
Clutches aren't needed with the advent of boost bypass valves. These allow the supercharger to "freewheel" unloaded. I think the old T-bird S/C supercharged V-6's were the first with this feature. New ZR1 does the same.
It used to be fairly common to place the blower ahead of the engine and couple it to the nose of the crank as a direct drive (no belt). I've never seen one that was switched (other than electric drive units). Someone is thinking of the Interceptor from the movie Mad Max and The Road Warrior. Just movie BS.
The only type of Blower/Supercharger that COULD be turned off and the engine still run would be a centrifugal style like a Vortec, Paxton, ATI ProCharger, etc.. There are guys that actually remove the drive belt for little drives here and there just to save on the wear-n-tear.
If a Roots/screw style blower quits spinning, the engine will NOT get any air and thus will DIE!!!
As Paul mentioned earlier, there are bypass valves in the newer generation Eaton screw-style superchargers that bypass the BOOST to make them substantially more efficient under normal driving conditions but they still HAVE to spin 100% of the time or it will DIE.