A portable electric motor driven reciprocating air compressor unit has a compression cylinder having a piston that reciprocates in the cylinder. The piston is driven by an electric motor that is attached to an electrical circuit having a predeterminable current capacity. A manually controllable valve mechanism is mounted to an inlet to allow for the channeling of air into the compression cylinder. The manually controllable valve mechanism allows for control of the amount of air that the piston draws and compresses for each reciprocation. The amount of electric current used by the electric motor to drive the piston depends on the amount of air drawn and compressed. A user can therefore control the amount of electric current that the compressor unit uses by using the valve mechanism to control the amount of air that is drawn into the compression cylinder and compressed during each reciprocation of the piston.