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How to Check a Voltage Regulator on a Motorcycle

by Chris Gilliland

The voltage regulator in your motorcycle has the duty of preventing your battery from being overcharged, as well as ensuring that the proper voltage is being supplied to your bike's other systems. A weak or dead battery is often the first clue that your voltage regulator is faulty, preventing the battery from being recharged while the motor is running. Luckily, testing the voltage regulator is a fairly simple task.

Testing A Voltage Regulator

Step 1

Set your multimeter to 20 volts DC (Direct Current) and connect the positive (+) and negative (-) leads to the corresponding battery terminals. Your battery should be charged, giving you a reading at or just above 12 volts.

Step 2

Start your motorcycle and rev the motor to 5000rpm, maintaining the engine speed during the testing.

Step 3

Using the multimeter, test the battery terminals again. A constant reading of 13.5 to 14.5 volts should be present. This is the proper voltage that will allow the battery to recharge properly.

Replace the voltage regulator if the reading is higher or lower than the 13.5 to 14.5 volt range to prevent insufficient or excessive charging. Replacing the rectifier, which converts the alternating current (AC) from your motorcycle's stator/alternator to direct current (DC) before recharging the battery, is also recommended at this time.

Tip

  • When either the regulator or the rectifier fails, it often causes the other component to fail as well, so replace both at once to prevent any further complications within the charging system. If you still experience problems with the motorcycle's charging system, have a qualified technician inspect it. The problem could lie deeper than most DIY repairs can handle. Don't rush this job or you will create more problems for yourself. Take your time.

Warning

  • The method shown above is the simplest and most effective method to test a voltage regulator. Other methods exist, such as testing directly at the stator. However, a higher degree of technical skill is required and the job may be more complex than you anticipate. Use caution when inspecting your motorcycle's electrical and charging system. Electrical shocks, causing injury or even death, can occur. If you doubt your ability to complete the test, have the work done by a qualified technician.

Items you will need

  • Motorcycle with a fully-charged battery
  • Access to the voltage regulator
  • Multimeter
  • Model-specific service manual, if available

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