What is Cutout Relay? Construction and Operation of Cutout Relay in Automobile.


The cutout relay (or circuit breaker) is simply a magnetic switch that closes the circuit between the generator and the battery when the generator is producing current. Also, it opens the circuit so that the battery cannot discharge back through the generator when the generator stops or slows down. The D.C. generator is connected to the battery through a cutout relay and an ammeter.

Cutout Relay
Cutout Relay


The cutout relay consists of two windings shunt winding and series winding. It assembled around a core and a flat steel armature mounted on a hinge above the core. The series winding consists of a few turns of heavy wire. And the shunt winding consists of a few turns of fine wire. The armature is connected to the battery through an ammeter by contact points.

Cutout Relay
Cutout Relays

Operation Of Cutout Relay

When the generator is not operating, spring on the armature holds the contact points. Apart, this keeps the circuit between the generator and the battery open. The core winding creates a magnetic field that attracts the armature during the generator is on. When the contact points are closed and the generator is connected to the battery. Current flows from the generator to the battery and passes through the series winding.

But when the generator stops, the current begins to flow from battery to generator. This reverse direction of current flow in the series winding causes the magnetic field to reverse. Thus, the magnetic fields of the winding no longer aid and is so weakened that it cannot hold the armature down. The spring tension pulls the armature up, separating the contact point. This opens the circuit between the generator and the battery.

Watch the Practical video below of explaining the Function of cutout relay.

Cutout Relay
Cutout Relays

Also, read these posts:

  1. What is Lead Acid Battery? Explanation of different parts of Lead Acid Battery.
  2. How does Car Battery work? How to choose the right Car Battery?


Creative Blogger And Automobile Engineer.

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