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It can be worrying to see your alternator smoking. Below we will look at all the causes of why this happens and also when it’s dangerous and not.

Briefly that before we get into details, the most likely causes of a smoking alternator are 

  • Bad alternator bearings or diodes
  • A battery that’s been connected incorrectly
  • Loose or corroded cables
  • Bad alternator grounding
  • The wrong car battery voltage
  • The alternator is wet

Possible Causes Of Alternator Smoking

Bad Alternator Bearings or Diodes

The alternator bearings and diodes are two parts that are located inside the alternator. Alternator bearings spin thousands of times per minute when the car is running.

Their job is to allow the rotor inside the alternator to spin smoothly. Like all bearings, They resemble metal balls lubricated inside the chase. 

As they age, the lubrication dries out, and the bearings can come in contact with each other and the outer casing. You would normally hear squeaking or squealing noise associated with these bearings drying out, but I’m not always.

In extreme situations, they can start to smoke because of the friction caused between them rubbing together and against the chase.

Alternator Diodes

Alternator rectifier diodes convert alternating AC into direct current DC.  

When they go bad, they can stop this conversion and send alternating current out of the alternator to electrical components. 

Bad Alternator Diode and Car Battery: A Draining Relationship

Because the diode allows AC to escape the alternator and is not designed for this, it can overheat and smoke. 

Bad alternator diodes are normally accompanied by a wind or whistling noise, especially when the accelerator is pressed down.

Both alternator bearings and diodes can be replaced. However, if the alternator is old, it is often best to replace it as other parts may be prone to failing after the alternator has been on the car for 80 to 100000 miles or seven years or more.

Incorrect Battery Installation

Has the alternator started smoking since you replaced the battery?

This is a bit of a long shot, but if you have wired up your battery incorrectly and have the negative cable to the positive terminal and vice versa, your alternator will not only smoke but also ruin your battery and other electrical systems that run off the battery.  

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It is quite a rookie error for a car shop to do this, and it should be apparent very early before the alternator starts smoking that something is wrong.

Not only will the alternator smoke, but you’re likely to see the battery smoke too.

You might be fortunate because most cars have a fusible link, and modern cars are tested for reverse charging to see if the electrical systems in a car can withstand a short period of negative charging.  

If you’ve got to the stage where the alternator and battery smoke, you may have damaged these circuits, such as headlights and starter, beyond repair.

Battery Cables That Are Corroded or Loose 

Battery cables are a cause of the alternator smoking. When they become corroded or loose, it prevents the normal flow of electricity to the battery. If it doesn’t reach the battery, it can cause the alternator to get extremely hot.  

Battery cables are cheap and always worth spending a little money on if they look worn. The increased resistance in worn cables can cause them to get extremely hot but rarely can cause the alternator to smoke too. 

Grounding Alternator Smoking 

An alternator that is not grounded properly can still produce the correct voltage, but the electrical circuit isn’t complete. In some alternator designs where the voltage regulator is outside, this can cause the alternator to get extremely hot and ruin the diodes. 

That being said, because the voltage is only 12 volts, any problem with the grounding of the alternator would generally blow a fuse, preventing the alternator from getting too hot and smoking.

Alternator Vents Blocked

In winter, the vents on the alternator case can become blocked with debris – dirt, leaves, etc.- as most alternators are air-cooled, and any blockage can cause overheating. Generally, the alternator would blow a fuse before any smoke was seen but not always.   Packed plant debris in the vents could, in theory, get very hot and start smoking. 

Alternators have a cooling fan within them; if they cannot suck in the air through the vents, they become useless and can’t do their job properly.

Alternator Wet and Smoking

If your alternator appears to be smoking after going through a lot of water, it’s maybe that the heat of the alternator is causing steam rather than smoke. 

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Alternators are not waterproof, but they are water resistant. They can’t be submerged for long periods, but they can stand a good soaking either through being washed or driven through water.

What you are probably seeing is the heat of the alternator drying the water and causing steam, not smoke.

Alternator Smoking When Battery Hooked Up

All cars are even negative or positively grounded. If the battery ground has been connected to the wrong terminal, this can cause issues with the alternator. Another thing to consider is the red-colored cable isn’t always the positive. 

It’s difficult to go into detail without knowing your car’s specific make and model. A quick search on forums should help you discover your car’s setup. 

Alternator Smoking When Car Is Off

If you’ve noticed that your alternator is smoking after you’ve stopped driving and parked up, it is likely that a bearing has become very hot and hasn’t cooled down yet.

Your alternator was probably smoking while driving, but you wouldn’t have noticed it, as any smoke will dissipate into the atmosphere. 

Have a quick check of the alternator/ serpentine belt for signs of wear. Being made of rubber, they are prone to smoke when they get hot, and if the alternator is seized and prevented from spinning around from the crankshaft in the engine, it could cause excess heat and the smoke you are seeing. 

New Alternator Smoking

It is not normal for a new alternator to smoke. There may be a small amount of protective oil or lubricant on certain parts of the alternator to keep it from rusting at the car shop, but that is it.

As the alternator is new, the smoking is probably due to it being fitted incorrectly. Check the grounding and that the cables are around the right way and tight.

You can rule out all the other courses listed above with a new alternator, as the parts will not have worn out, and dirt or grime won’t have built up around the vents.

In Conclusion

In a failing alternator, the bearing may smoke due to too much friction. You’ll have to replace it. If the alternator’s fuse blows, that can also cause smoke. A bad fuse is good news because the alternator is probably still serviceable.

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