Testing Alternator while in the car.
 

How do you test the alternator while the car is running? I am not sure where to put the multimeter leads? My car had to be towed home today, and I suspect the alternator and or battery. I'd like to try to test the alternator before removing it.

Re: Testing Alternator while in the car.
 

Just put them on the battery posts. I forget what the output spec is, but you should be seeing 13V or more.

Re: Testing Alternator while in the car.
 

SIMPLE TEST

Connect the POS and NEG leads of the multimeter to the POS and NEG battery terminals. Set the meter to DC voltage.

On a fully-charged battery, you should read about 12.7V with the car off.

Start the car and the voltage should go up at least 1V above that. this indicates the alternator is charging.

Now load the system by turning on the lights and blower motor. The readings should initially dip and rebound. This indicates the alternator is handling the load.

If the readings drop and not rebound, or slowly continue to drop, your alternator is having a problem with charging.


The best way is to have it properly load-tested off of the car.


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Re: Testing Alternator while in the car.
 

The battery is completely dead, it won't start with out a jump. Will it make a difference in testing if the battery is dead to begin with?

Re: Testing Alternator while in the car.
 

It's best to have a fully charged battery with a battery charger.

Many people believe it's not good for the alternator to completely charge a dead battery.

Re: Testing Alternator while in the car.
 

Thanks everyone. The alternator turned out to be okay, just too much corrosion on the negative battery terminal I think.:o:o I'm seeing 14v when the engine is idling.

Re: Testing Alternator while in the car.
 

Right on as always! ...except... sometimes our alternator can be erratic and work great "only" part of the time. A load test could possible check out fine, at the moment, and that would make it harder to diagnose the problem when it occurs again. (If this sounds like mutiny, it isn't) You are a life saver for us!:)

For the SVX folks that are pretty aware about all the "why's", we have a variety of ways to determine exactly what the problem is even if we can't catch it "in the act"

Keith:cool: