Summary
The objective of this procedure is to show you how to check a charging system. Remember to note the voltage readings from the DVOM at all stages of the procedure.
Part 1. Preparation and safety
Objective
Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
Safety check
- Make sure the hood stay rod is secure.
- Always make sure that you wear the appropriate personal protection equipment before starting the job. It is very easy to hurt yourself even when the most exhaustive protection measures are taken.
- Always make sure that your work area/environment is as safe as you can make it. Do not use damaged, broken or worn out service department equipment.
- Always follow any manufacturer's personal safety instructions to prevent damage to the vehicle you are servicing.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- DVOM stands for Digital Volt Ohm Meter.
- DVOMs come in many forms. Always follow the manufacturer's instructions in the use of the meter, or you could seriously damage the meter or the electrical circuit.
Part 2: Step-by-step instruction
- Set up the meter for a voltage check
Prepare the Digital volt ohm meter or DVOM for testing for voltage by inserting the black probe lead into the “common” input port, and the red probe lead into the “Volt/Ohms” input port.
- Check the meter function
Turn the rotary dial until you have selected the mode for “Volts DC”. The reading on the meter should now be at Zero. Some meters will automatically sense the correct voltage range when a voltage is detected. On other meters you will have to set the voltage range before using the meter.
- Check the battery voltage
Place the Black probe onto the Negative terminal of the battery, which will be marked with a Minus sign, and place the Red probe onto the Positive terminal of the battery. This is marked with a Plus sign. Note the voltage reading from the battery.
- Check the voltage after starting
Start the engine. The voltage now shown on the display should be within the 13.7 to 14.4 Volt range when the engine is running at approximately 2000RPM.
- Check the voltage with additional load
With the engine still running, turn the headlights of the vehicle ON and note any differences in the reading. The meter may “fluctuate” a little before settling down. Provided it retains a voltage reading within the original specifications, the voltage regulation side of the charging system is operating correctly.
- Carry out load test
Place an ammeter in series by clamping it over the cable, in accordance with equipment manufacturers instructions, between the AC generator output terminal and the positive battery terminal and connect a carbon pile regulator across the battery terminals. Operate the engine at about 2500 RPM and adjust the carbon pile to obtain maximum current output. This reading should be compared against the alternator’s rated output. Normally, readings more than 10 amperes out of specifications indicate a problem.
