How Do You Restore Residual Magnetism in a Generator?

Ian Mutuli
Updated on

Remanence or residual magnetism in a generator is the amount of magnetism left in a generator after getting rid of the external magnetic field from the generator. This occurrence can be seen in portable generators, motors or transformers. When the generator loses its ability to start up, there is a chance that the residual magnetism is lost, and the generator can not produce power. This phenomenon can occur often, and the big question is, how do you restore residual magnetism in a generator?

We will share why generators lose their residual magnetism and how to restart if the generator fails.

How to Restore Residual Magnetism on a Generator

If the generator can not produce electricity, there is a chance that the residual magnetism is lost, and the current flow can not be triggered. The good news is that the generator can be restarted using a few steps to build the residual magnetism. Use the following steps keenly to get the generator up and running.

You will need to get a 12-volt battery for this activity. A car battery will do just fine, especially for a small generator. Ensure you use a current limiting device when attempting to get power generation on the generator.

  1. Get rid of the exciter fields from the voltage regulator. Ensure you remove both the positive pole and negative pole from the voltage regulator. If you do not unplug the brush wires from the automatic voltage regulator, the regulator may be destroyed when you begin voltage buildup.
  2. Take the exciter field resistance reading from the positive pole to the negative pole. There should be resistance as you measure the field winding, a continuous winding. Ensure no flow goes to the ground before you begin the field excitation. If you see an infinite resistance reading, there is an open in the exciter field.
  3. Of the two generator brushes, connect the F+ to the positive pole of the battery.
  4. Hold the F- lead wire on its insulated parts to avoid an electric shock. Do not contact wires of different poles to avoid shock by dangerous voltages. Touch the wire to the negative pole of the battery for about 3 to 5 seconds and remove it. Once you have removed the wire, there should be an arc to confirm a complete circuit.
  5. If the generator fails to work, you should increase the voltage buildup. Ensure you follow all the instructions to avoid an improper operation. Ensure a circuit breaker protects the generator to avoid overheating.
  6. This process should make the generator work once a voltage has been induced in the rotor winding. (If this method fails, you can try out the electric drill method by plugging the electric drill into the generator receptacle. The magnets present in the dill's motor induces a voltage into the motor winding).

How do Generators Lose Residual Magnetism

One of the main causes for portable generators failing is the loss of residual magnetism. The generator may be running without producing power, which may leave you scratching your head. The generator produces electricity by building its magnetic field.

It is vital to know that generators do not have magnets and produce electricity by creating a magnetic field. Generators use field coils to produce a magnetic field through which moving electrical conductors pass, making the generator work. When the engine of the generator turns, the magnet moving the electric field through the stator windings allows the production of more power. Therefore, the generator needs residual magnetism in the generator exciter field to allow voltage build-up during a start-up.

The iron core within the field coils might lose magnetism from the last time the generator was used. Here are some reasons why a self-excited generator loses its residual magnetism and fails to generate power even when running.

  1. If the generator has been out of use for a while, it can lose the residual magnetism.
  2. Connecting a load with the generator shut off can lead to a loss of residual magnetism.
  3. Running the generator for too long without a load on it.
  4. New generators can lose magnetism from too much vibration during transportation.

Final Take

It is important to note that apart from losing magnetism, there are other reasons why the generator may run but not produce electricity. Those reasons may include poor connections, excitation wire blockage, tripped breaker, etc.

Ian Mutuli

About the author

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.