What does an alternator do? A cars alternator is a device that transforms the mechanical power of crankshaft rotation into electric current. The energy it produces is used to charge the battery and power various electrical devices while the engine is running. In some cars, this unit is also used to start the engine. Enter your reg to find your parts: www.partbusters.com #partbusters #autoparts #enginefilter #mechanic #londongarages #carshowroom #carparts #unitedkingdom #london #mechanicmemes #ca