Car alternator Voltage check for faults
A Simple guide for checking the cars alternator and voltage regulator for possible faults is an important task, especially more so for modern cars.Read on to find out more and how to check if this is working correctly in your vehicle
- First check you have access to the alternator it may only be accessible from under the car, so you may need to raise the car to gain access if poor lighting, be sure you a have a lead lamp or touch to hand to select the correct location only needed if theres a fault (step 8) .
- Next on your meter Connect black lead to "com' (common) socket the other end to the battery negative . Connect red lead to "Volts" On Multimeter other end to battery + positive on the car battery.
- Remember when checking volts, the meter must be Connected in parallel. select range for up to 200 volts DC depending on meter. DC stands for direct currant such as a supply from a battery that is used in cars AC is for home, industrial use as alternating current is it comes from an indirect source and alternates to keep a steady currant,
- Get someone to go in the car check there is no load applied such as main lights heater or powerful stereo system on then start the engine from inside the car and gradually depress the accelerator until the increase of speed is around 1000 rpm revs.
- While you observe voltage increase until regulator controls output, normally between 13.3 to 14.7 volts. This is provided there are no other loads switched on.
- The more modern and powerful the alternator this won’t be so noticeable as on an older classic car may take some time depending on the make and year of car and you location worldwide.
This voltage may vary such as older Japanese mechanical type of regulators Can go up to about 15 volts and then drop back to normal after some time. you can check the individual cars rating on all the cars maintenance pages here on Motor Car.
- Check this voltage, if possible, for several minutes Don't be caught out. Some faulty regulators seem to be regulating correctly at first glance, but tend to creep up very slowly, so give it some time. This is important a faulty regulator and or alternator is bad if it reads too low for battery. But also can result in damage to the cars electrical system if to high (above 16 Volts).
Now you have checked the voltage and there is a fault, low voltage may be down to the connections or if the car has a diagnostic socket get someone to check this first. on older cars check the cables for damage from heat moving parts and so on or remove the alternator and clean replace or get refurbished. High voltage needs to be repaired if not easy to find, or replace as fault with the voltage regulator is not east to fix .But also see the Motor car Remove a Car Alternator, Replace Car alternator bushes , Alternator How it works and alternator sevice & overhaul
Also see the Motor Car alternator load check.