How to test varistor & diode generators

Written by thomas bourdin
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How to test varistor & diode generators
It is important to test diode and varistor generators to determine generator functionality. (Jupiterimages/ Images)

Diodes and varistors are similar electronic components which only allow a current to flow in a single direction. Diodes and varistors are important components of generators, as they convert AC signals to DC signals, which can then be used by the generator. Testing generators with these components is important for determining the specifications of the generator, especially on vehicles. Testing diode and varistor generators is a straightforward process with enough knowledge of electronics and automobiles.

Skill level:

Things you need

  • Digital multimeter

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  1. 1

    Connect the digital multimeter to both battery terminals and start the engine.

  2. 2

    Turn on all electronic components in the vehicle, including high beams, high blower, air conditioning, windshield wipers and radio, with the engine running at around 1,500 revolutions per minute. This creates a current load on the generator, which will be displayed on the digital multimeter. A voltage higher than 13.5 volts indicates a strong generator, while a voltage below this amount indicates a weak charging generator.

  3. 3

    Turn off all electronic components and increase the engine rpm to 2,000. A voltage above 15.1 volts indicates overcharging, which could be caused by a defective voltage regulator or a poor connection between the battery and the generator.

Tips and warnings

  • If the generator voltage is below 13.5 volts, look for a loose or worn generator belt, and check the connection voltage drops for corrosion, which may explain the weak charging generator.
  • Different makes of vehicles may have different optimal generator voltages. These values can be learnt by testing various generators.
  • Take all necessary precautions when working with electronic equipment, as vehicle motors can produce high voltages and currents.

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