How to Fix a Dynamo

A Guide on How to Fix a Dynamo

The dynamo is a powerful yet simple type of generator, which interestingly, was fitted to older vehicle models. Nowadays, most modern vehicles are fitted with an alternator. You may think that the battery provides power for your car, but that’s not always the case. While the battery provides electricity to start the car, it is the dynamo that generates energy that feeds the electrical system.

In this post, we will be discussing everything there is to learn how to fix a dynamo. We would also be talking about how it works, as well as how to remove and inspect it. We hope that after you have read this post in its entirety, you will be able to perform this relatively easy task on your own. Read on if you want to know more.

How Does a Dynamo Work?

Before we proceed with the discussions, we first should talk about how a dynamo works. A dynamo is an electricity generator, particularly producing direct current. Typically, the stator is the permanent magnet while the rotor, often called the armature, is wound and is connected to a commutator. This also has a set of electrical connectors, known as brushes, that are made of carbon.

Electromagnets, often called field coils, are stationary in a dynamo. Typically, the current is generated in the armature, which is generally considered an extra set of coils that are attached to the shaft and turns inside the field coils.

In principle, how an alternator works is the same as that of a dynamo. However, the current proceeds into a commutator, which is a metal ring divided into segments linked to the brushes fitted in spring-loaded guides. With this, these two fragments touch the pair of carbon brushes and eventually feed current to these brushes.

As your engine’s armature turns, the direct current also changes its direction. However, by that time, other pairs of segments are already under the carbon brushes, in which the new pair is now wired up in a different direction. This process gives way for the current to come out towards the same direction.

What Causes Dynamo Failure?

What Causes Dynamo Failure


Probably the most frequent cause why a dynamo fails is wear found on the commutator and carbon brushes. Typically, the carbon brushes are the first ones to wear. However, as they grow tinier, the spring pressure that holds them together with the commutator also weakens, eventually leading to uninterrupted sparking, referred to as arcing, amongst the commutator and the carbon brushes.

This sparking is likely the cause of quick wear of the commutator, which tends to pit the surfaces of its segments. In worse cases, the solder that is found in between the windings and commutator segments melts, which then causes the decrease in output. Loss and decrease of output from the dynamo will certainly drain the battery simply because the current is not being replaced.

The ignition light, which glows faintly, normally gives the warning that there is a decrease in the generator output. You may want to check the fan belt, if the ignition light turns on and it stays on. However, if you notice that the problem originates from the carbon brushes, you need to disassemble the dynamo to perform further inspection and if necessary, repairs.

Performing inspection should be a lot easier if your vehicle’s dynamo is already fastened securely, which ensure that the whole unit will not be impaired. To inspect if there is wear on the brushes, you need to remove the endplate, in which they have been mounted. In older models, on the other hand, you need to remove the metal band found on its casing.

The dynamo is typically linked together by lengthy bolts through the length of its casing. The heads extend from the endplate and they come with screwdriver slots. You need to unscrew these heads to remove the endplate and give it a soft tap using a soft-faced hammer to be able to remove it. You may also grasp it gently using a screwdriver that is thin-bladed.

How to Reassemble the Dynamo

Here’s what you should follow in reassembling the dynamo:

  • Before you reassemble the dynamo, always make sure that the casing’s inside, as well as the field coils, are clean. You may use a brush to effectively remove dirt and dust found on the armature.
  • In addition, ensure that the endplate, front plate, and ventilation holes have been cleaned.
  • You may also need to replace the field terminal, which often features an insulating sheath where it passes through.
  • You also need to inspect if there are any wears on the endplate bush, as well as at the armature shaft. In case you are not yet familiar, the bearings and bushes of the dynamo are similar to those found on the starter motor. If necessary, you may use a high melting point grease for lubrication.
  • To add, you would want to check the armature and look for indication of rubbing, especially on field poles.
  • You also need to inspect the bearing found on the dynamo’s front plate. Do this step by spinning the plate as you hold the armature.
  • Then, you need to check the windings in terms of continuity. You can use a circuit tester, which lights up if the windings are still intact.

How to Remove a Dynamo

Removing a dynamo could be a very intricate process and we are here to help you do this job right the first time. Here’s what you should follow:

How to Remove a Dynamo


  • Before you remove the dynamo from your vehicle’s engine, you first should remove the battery. This is a very effective preventive measure against coincidental short circuits.
  • You may need to slacken both the pivot bolt, as well as the adjuster-strap bolt.
  • After, press the dynamo towards a side and then slip the belt from the pulley.
  • You need to disconnect both the field and output cables. You should be aware that these cables come in different sizes. However, if they’re not, you may need to label them beforehand by using small pieces of tape to avoid confusion.
  • Then, disconnect radio suppression tools and apply support to the dynamo while you are removing both the adjuster-strap bolts and bolts completely.
  • After doing these steps, you may safely remove the dynamo out of your vehicle.


If you found that your dynamo has wear on both the carbon brushes and commutator, it would be in your best interest to have it fixed, whether by a professional or on your own. Lucky for you, we have provided you with everything you need to know on how to fix a dynamo, as well as the step-by-step instructions on how to remove and reassemble it back into the engine.