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An electric supercharger is a specific type of supercharger that uses an electrically powered forced-air system that contains an electric motor to pressurize the intake air. By pressurizing the air available to the engine intake system, the air becomes more dense, and is matched with more fuel, producing the increased horsepower to the wheels.[better source needed]
Power supply for electric superchargers
An electric supercharger, if supplied by common stock electric accumulators, runs independent of the engine to which it provides its boost. However, electrical energy consumed is often higher than what a production-line generator (e.g. alternator) of the engine can supply. Larger alternators are therefore fitted to recharge accumulators during the engine run.
The efficiency of an electric supercharger is curbed by several energy conversion losses (alternator for charging), damp energy while charging the accumulators and the compressor providing boost. The losses are in general higher than direct kinematic linkage of intake air compressor to engine crankshaft. If the vehicle implements kinetic energy recovery, then the battery can be charged on otherwise wasted energy.
Electric assisted turbochargers
Electric assisted turbochargers are turbochargers employing a coaxial electric motor to overcome the time lag of the exhaust gas driven turbine. The electric motor supports the exhaust gas driven turbine at low-end revolutions to compress enough air into engine's intake, while it can be configured as an alternator to extract energy from the exhaust gas driven turbine at high-end revs, which would otherwise need be bypassed via wastegate and eventually replacing the current mechanically driven alternator. Special consideration need be given to the coaxial electric motor operating in proximity of a hot turbine at very high rotational speed (up to 100,000 rpm).
Several companies sell low-cost aftermarket products, claimed to be electric superchargers. These devices are typically simple ducted fans or blowers, often directly repurposed from marine and naval supplies, and are simply not capable of providing an intake manifold pressure increase, or a flow rate greater than what an engine draws. They can not measurably compress air or increase airflow, and instead draw electrical power and act as an obstruction for air flow to the engine. Usually, this leads to a slightly reduced power output, never an increased one. In order to effect a performance increase in any automotive engine, a compressor must force (compress) a significantly greater volume of air into the engine than it would otherwise draw naturally. This requires a large amount of energy. An effective electric supercharging system requires additional batteries onboard, and uses multi-horsepower electric motors and high-speed compression impellers similar to those used in exhaust-coupled turbochargers.