Subject: Automobile Engineering

Topic: Electrical System, Starting Systems & Alternator

Difficulty: High

When the generator speed is very low, due to which the output is not sufficient to balance the battery voltage, the necessity to cut out the generator from the battery arises otherwise the battery could discharge into generator.. A simple cut-out relay is as shown in fig 15.2.

The electromagnet consists of 2 coils, shunt & series. When the generator is producing sufficient voltage so that the field due to both the current and voltage coil support each other, the electromagnet pulls down the armature the contacts are closed & the generator battery circuit is complete.

When the due to beo engine speeds the generator voltage fall below battery voltage the current flows from the battery to generator , then the field due to current & voltage windings become opposed to each other & the contacts open cut & the battery is cut out from the generator .