I am familiar with turbo chargers and belt driven superchargers, but recently read a little about electric-driven superchargers.  They can run off batteries or an alterator.  Anyone else know anything about them, or have experience with them?

We tried a powerful short-burst electric "turbo-charger" of sorts, on buses in Los Angeles. The intented purpose was to eliminate the puff associated with older Diesel engines. It worked, but for stop and go driving it ended up requiring more electrical power than even a modified charging system could provide.

The use of electric superchargers has only started to become interesting and viable with the advent of the 42v electrical system - I doubt there is anything particularly useful running on 12v, especially some of these things you see on e-bay!

The use of an electrical supercharger is attractive in a number of ways, not least the fact that boost ceases to be a function of engine speed. Without the need to worry about wasted energy through the compression of air that is simply going to be sent through a bypass valve(check valve).

Boost is a function of airflow supplied over airflow used.

Airflow used is fairly well directly related to engine speed. A crank driven positive displacement supercharger also supplies air fairly well relative to engine speed. An engine with a crank driven properly sized roots blower will have an almost flat boost curve relative to engine speed over the normal operating speed.

I would expect an electric driven supercharger will only give constant boost if it is well regulated with pressure switches and controllers to control the electric motor well enough to overcome reaction times, relative friction and inertia and if the electric motor can provide enough power to keep up with engine requirements.

As mentioned earlier by Greg, this can be a very large electric motor, needing a very powerful electrical system to support it.

Crank driven simply requires a belt and two pulleys.

I guess, the question, or the quest will be, is the total package for the smaller engine and electric supercharger, smaller or larger than the larger engine with NA, turbo or belt driven or compounded belt driven positive displacement and turbo.

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