What is an alternator diode?

The alternator’s rectifier assembly

The alternator is part of your vehicle’s charging system. Its purpose is to charge your vehicles battery to provide the necessary power to operate the starter motor, ignition and all of the electronic accessories in your car. It does this by providing your car battery with a constant charge and allowing it to stay full.

Your car’s alternator (used to be called a generator) will typically have up to six diodes. These are located on the alternators rectifier assembly. Electricity flows through the diodes, which convert the alternator’s AC output to DC (which is what the battery runs on). If the diodes do not function correctly, the alternator will not work. This will stop the battery from charging, resulting in your car possibly needing jump-starting.


What causes alternator diode problems?

Heat – As electricity passes through the alternator diodes, heat is produced. At low levels, this heat is not harmful. However, high levels of heat can cause the diode to burn out.

The more electricity that passes through the diode, the more heat it will produce. Using the radio, headlights, air-conditioning and other accessories can cause more heat to pass through the diode, putting it at risk of burning out over time.

Dry diode solder joints – in use the soldering around the alternator diodes expands and contracts with the heating and cooling of the vehicle engine and alternator. Overtime this can cause a dry soldering joint for the alternator diodes, preventing them from working / charging your car battery correctly.

Reversing the car battery terminals – if someone fits a new or recently charged battery to your vehicle and accidentally reverses your cars battery terminals, it may mean that some of your alternator diodes may take full battery current which can quickly destroy them.

The other slightly less common problem is when people jump start a completely flat vehicle battery and accidentally reverse the jumper leads. This can also cause hundreds of amps to flow through the alternator diodes in the forward biased direction, which will quickly destroy them.



Symptoms of a burnt out diode:

When the alternator stops working, the battery will stop being able to charge. This may cause the following things to happen:

  • The battery will become depleted, resulting in the car not being able to start.
  • The engine will begin to run rough, lack power and eventually stall and not start again.
  • The battery warning light will turn on, warning you that there is a problem with your alternator charging system
  • The headlights will become dim due to reduced battery voltage.


Alternator Replacement Services in Hamilton

If one or more of your car’s alternator diodes fail, then your vehicle may become unuseable. When this happens, it’s usually more cost and time effective to simply replace the entire alternator, rather than individual diodes.

At Grimmer Motors, we can perform an alternator replacement on your vehicle. The new alternator will reliably keep the battery charged.

At Grimmer Motors, our mechanics are experienced in all sorts of alternator and battery repairs. This allows us to quickly identify and repair battery/charging system issues.

For fast, quality alternator repair in Hamilton, contact Grimmer Motors today!


Book Now