How to Check the Charging System in Vehicles

by Contributing Writer

The charging system in your Vehicles consists of an alternator and a voltage regulator that combine to produce a specified level of electrical current. The voltage regulator receives current from the alternator, and automatically adjusts the level of output to accommodate demands of the battery, the ignition coil, and any lights you might turn on. With a fully charged battery, problems are confined to either the alternator or voltage regulator. A voltage meter is used to check the output and capability of your Vehicles charging system.

Under The Hood:

 How to Check the Charging System in a GMC Sierra Truck

Charging System Component Check

Open the hood and locate the battery in the front driver's side of the engine compartment. Check the battery terminals and cable clamps. Make sure they are tight, clean and free of any white, flaky corrosion, which can be removed with a wire brush or emery paper.

Check all the external wiring on the alternator and make sure the connections are tight and clean.

Check the alternator mounting bolts. They should be tight and secure.

Check the condition of the drive-belt. Cracks on the "V" portion of the belt are normal, but if the belt looks very worn or is missing ribs, replace it. The belt is tensioned by a spring-loaded tension assembly. If the indexing arrow is lined up with the indexing mark on the tension assembly, replace the belt.

Start the engine and check the alternator for abnormal noise.

Alternator Check

With the engine off, attach the probes of a voltmeter to the positive and negative terminals on the battery. The red probe goes to the red (positive) terminal and the black probe to the black (negative) terminal.

Take a reading from the voltmeter. If the battery is fully charged it should register between 12.4 and 12.6 volts.

Start the engine and perform the test again in the same way. This time the reading should be higher. Up to 14.7 volts is normal. Higher or lower readings could indicate a malfunction on the alternator.

Take the vehicle to a dealer service department. They will attach a scanner to the on-board computer which will generate a problem code to diagnose the problem more specifically.

Items you will need

  • Wire brush or emery paper

  • Voltmeter

 How to Check the Charging System on a 1994 Honda FourTrax 300

Voltage Regulator

Park the four-trax and allow the engine to cool completely. Voltage readings are more accurate when the bike's components are cool. Remove the rider's seat to access the battery.

Open your service manual to electrical system section. Refer to the diagrams and locate the alternator and voltage regulator on your ATV. Depending on your body kit, it might be necessary to remove sections to access these parts. Remove the necessary fairings or covers using your metric tools.

Connect the red voltage meter wire clip to the positive battery terminal. Connect the black wire clip to the negative battery terminal. Set the voltage meter on the next scale, up from 12 volts. This might be 20 or 24 volts, depending on your meter.

Start the ATV engine and look at the reading on the meter. It should read between 13 to 14 volts with a fully charged battery. Watch the meter and twist the throttle grip until the engine speed is at 1,600 rpm. A rise in voltage indicates a faulty voltage regulator. Proceed with the check when the voltage remains constant between 13 to 14 volts.

Allow the engine to return to idle speed. Turn the headlight on and observe the voltage reading on your meter. A drop in voltage indicates a faulty alternator or a problem with the circuit wiring. Disconnect the meter clips from the battery and turn the engine off.

Alternator and Wiring

Allow the engine to return to idle speed. Turn the headlight on and observe the voltage reading on your meter. A noticeable drop in voltage indicates a faulty alternator or a problem with the circuit wiring. Disconnect the meter clips from the battery and turn the engine off.

Look at the wiring diagram in your service manual and locate the wire connectors for the alternator. Pull each connector apart one at a time and inspect them for dirt, dust or corrosion. Clean a dirty or corroded connector using electrical contact spray. Reconnect each wire connector as you go.

Connect the voltage meter clips to the battery as before. Start the engine and repeat the check of the charging system. A constant voltage reading of 13 to 14 volts during the test indicates the problem was a dirty wire connector.

Items you will need

  • Service manual

  • Metric tools

  • Voltage meter

  • Electrical contact spray

 How to Check the Charging System of a Polaris Sportsman

Check the battery cable connections and the main circuit breaker that is located adjacent to the battery. If the main circuit breaker is good, proceed to the next step.

Test the battery specific gravity using a hydrometer with numbered graduation from 1.100 to 1.300, rather than one with just color-coded bands. Specific gravity is the density of the electrolyte as compared to pure water.

Connect a 0 to 20 DC voltmeter to the battery terminals. Connect an inductive tachometer to the spark plug. Start the engine and increase engine speed to 4,000 rpm. Read the voltage indicated on the voltage meter. it should read between 13 and 14.6 volts.

Check the charging system wiring harness and connectors for dirty or loose-fitting terminals; clean and repair them as required. If the wiring harness and connectors are acceptable and no problem has been found after performing the previous tests, you can consider the regulator/rectifier to be defective by a process of elimination.

Items you will need

  • Hydrometer

  • DC voltmeter

  • Inductive tachometer

 How to Check the Charging System on a WR 250 Yamaha

Battery and Fuse Inspection

Lift the sides of the seat up slightly to access the pair of bolts that secure the seat to the frame. Remove the bolts with an Allen wrench and pull the seat off the motorcycle. The fuse box will be visible between the seat rails.

Push the fuse box cover's tab inward and lift the cover to open the fuse box. Inspect the fuses visually, looking specifically at the metal bridge within the fuse. Replace any fuses that have a damaged or "blown" bridge.

Test the battery's voltage with a multimeter. Set the multimeter to DC (direct current) voltage scale using the setting dial on the multimeter's face. Place the multimeter's red positive probe on the battery's positive terminal and the black negative probe on the negative terminal. Take note of the battery voltage indicated on the multimeter's display.

Charge the battery with an automatic battery charger if the battery's voltage is less than 12.1 volts DC. Test the battery's voltage again after charging is complete. Replace the battery if the voltage is still less than 12.1 volts DC.

Charging Output Voltage Testing

Start the motor and open the throttle halfway, using the twist grip on the right handlebar. This action increases the engine speed. Maintain this engine speed for the duration of this test of the charging system's output voltage.

Place the multimeter's red positive probe on the battery's positive terminal and the black negative probe on the negative terminal to test the voltage that is being transmitted to the battery by the motorcycle's magneto, charging coil and voltage regulator. Note the charging voltage indicated on the multimeter's display. Ideally, the battery should indicate a minimum charging output voltage of 14.1 volts DC.

Stop the motor. If the charging output voltage is less than 14 volts DC, test the magneto, charging coil and voltage regulator to determine which component is faulty.

Magneto, Charging Coil and Voltage Regulator Inspection

Locate the magneto's wire harness on the left engine cover and follow it to the charging coil's connector. Pull the connector halves apart.

Turn the multimeter's dial to the Rx100 resistance scale.

Connect the multimeter's red positive probe to the white wire within the magneto's half of the connector. Connect the multimeter's black negative probe to the magneto connector's black wire. Take note of the magneto's resistance measurement.

Repeat the test on the wires in the charging coil's half of the connector, matching the red positive probe to the white wire and the black negative probe to the black wire. Ideally, the magneto and charging coil should have a resistance of 0.288 ~ 0.432 Ω (ohms) indicated on the multimeter's display.

Replace the magneto or charging coil if either components resistance is above or below the 0.288 to 0.432 Ω (ohms) specification range. Replace the voltage regulator, if the magneto and charging coil are both within the specified resistance range.

Items you will need

  • Allen wrench

  • Fuses

  • Multimeter

  • Automatic battery charger

  • YTX5L-BS battery

  • AC Magneto

  • Charging coil

  • Voltage regulator