7 Common Symptoms of a Short in the Alternator (+Fixes)

A short in a car’s electrical system not only drains the car battery power but can cause a fire too. A car alternator can short out and not be able to keep the car battery topped up as needed.

So, how you can tell if indeed there is a short in the alternator? Is a short preventable and what causes it?

There’re probably several questions you need answers to prevent and decide on the best course of action in case of a short in the alternator.

This post lists signs that can point to a shorting alternator, explains why an alternator may short out, if it can be repaired and whether it is worth it.

Symptoms of a Shorting Alternator

#1. The car battery fails to charge

If the car alternator has an internal short, it will not be able to charge consistently or charge at all.

#2. The battery can drain overnight

It can also drain the battery charge. The car battery may be drained overnight for instance.

#3. The alternator feels warm to the touch (make sure the car engine is switched off and has cooled!)

With the car switched off and the engine has cooled, monitor the alternator’s temperature. If the alternator is draining the car battery power, the car alternator will be warm when you touch it.

Testing an Alternator for a Short

Unfortunately, these symptoms in themselves can be attributed to other faults and may not confirm a short in the alternator. Tests need to be done to confirm if it is indeed a short in the alternator.

Option 1: Get the Alternator tested at a reputable auto parts store. Arrange to have the alternator (and car battery) tested at an auto parts store.

Option 2: Own testing or use a good quality portable tester

Using a good quality multimeter set to measure ohms, switch off the engine and connect one test lead to the B+ stud of the alternator and the other to the engine ground.

The meter will read zero ohms if the alternator output is shorting to the ground.

What Shorts in an Alternator?

A short in the alternator may be caused by the output terminal or wire connecting to the ground along its length, the stator windings, or one or more diodes may be shorting.

What Causes a Short in an Alternator?

A car alternator may develop a short if any of the following happens:

#1. The alternator output is grounded when the alternator is charging the battery. This results in results in an excessive current draw that can cause diode or alteration winding failure. There are several reports of this happening if care is not taken when fitting a wire to the alternator’s output terminal.

#2. Interchanging the alternator ground and positive terminals during the alternator installation can also cause the alternator to short out.

#3. Disconnecting the car battery when the engine is running. The voltage spikes can damage the diodes and cause them to short too.

#4. The alternator can fail and short out if the car is used to jumpstart another with a damaged or faulty battery.

#5. Wear and tear of the alternator or low build quality can also lead to the alternator failing and shorting out prematurely.

Should you Repair a Shorted Alternator?

If it is a shorting diode, if you have the skills, you may easily replace the shorted diodes or have the alternator windings rewound depending on the type of alternator at a fraction of the cost of a new alternator.

That said, buying a new alternator has several benefits. A new alternator comes with a warranty – some have lifetime warranties! With a reputable brand, you can be confident of many years of service.

Can You Prevent an Alternator from Shorting Out?

While it is probably impossible to prevent an alternator from shorting out, avoid:

  • accidentally grounding the alternator output,
  • disconnecting the car battery terminals when the car engine is still running,
  • or attempting to charge a damaged and shorted battery has the potential of minimizing the chances of failure.

Related Posts

Can an Alternator Short the Car Battery?

Yes, it is possible for a faulty alternator to short out and drain the car battery. This can explain why for instance the alternator may feel warm to the touch even when the car engine is not running and has cooled.

Can an Alternator Short to Ground?

Yes, it is possible for an alternator output to be grounded. This is can happen if the wires connecting to the positive stud make contact with the grounded casing of the alternator housing.

Closing Thoughts

Alternators can have shorted diodes or windings. These shorts lead to a lower power output from the alternator which causes battery charging problems. Shorts can also lead to unexplained draining of the battery

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