How Would I Know If the Alternator Is Going Bad?

**richierevs** · 11-20-2019, 06:26 PM

The title explains it... I've got a 2006 Charger SRT8 with 133K on the clock... I started to have a subtle but erratic sound/feeling, almost like a misfire but not codes or pending codes... Looking for clues...

Other info: the crank sensor was changed about 2 months ago. I noticed that the voltage in the display has spiked to 14.5 (usually not that high)...

**ChuckWagon** · 11-20-2019, 10:07 PM

When mine went a couple three years ago, it was making quite a whine and my voltages were fluctuating around 12.1 - 13.5. Previously, voltages were 14 - 14.2 without headlights on.

I removed my serpentine belt and started the car and whine was gone. Had the alternator tested and it was bad. Replaced and no more noise.

**Hemissary** · 11-20-2019, 10:26 PM

As ChuckWagon points out, alternator failure root cause is overwhelmingly bearing failure, not current output.

Current generation on these alternators is pretty well fool-proof. They are blindingly simple and robust design with no active internal electronics. Current output simply increases with rpm. The current output (duty cycle) is controlled by the PCM, based on ambient temp (as it relates to BATT charge capacity) and real-time loads.

Edit: as to observed voltage output; again, this is a function of the PCM control circuitry. 14.5V output is normal, especially as temperatures drop to zero or below and battery charge acceptance decreases (ability to accept current dwindles because cell internal resistance increases as temperature drops)...

**us1champ** · 07-25-2020, 11:00 PM

Hey Simon. Way old post but follow up. I have a 2yr old battery 1 yr old alternator on mine. It sits stored on a tender. Most of the time it runs 13.9 - 14.2 driving. I noticed now it is hovering at 13.6. Think anything is going on? It is hot out but not sure how much that plays into anything.

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**Hemissary** · 07-25-2020, 11:07 PM

Originally Posted by us1champ

Hey Simon. Way old post but follow up. I have a 2yr old battery 1 yr old alternator on mine. It sits stored on a tender. Most of the time it runs 13.9 - 14.2 driving. I noticed now it is hovering at 13.6. Think anything is going on? It is hot out but not sure how much that plays into anything.

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Hi Chris, Hope all's well down your way :^)

Sounds normal; 13.6V means the battery is more charged / fully charged. Be very warm / hot means the battery's internal resistance is actually lower. In simple terms; lower internal resistance means the battery has a higher charge-acceptance.

**us1champ** · 07-26-2020, 12:13 AM

Thanks Simon

I will keep an eye on it. Hope all is well with you also.

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**KStryker** · 02-13-2021, 08:38 PM

Originally Posted by Hemissary

As ChuckWagon points out, alternator failure root cause is overwhelmingly bearing failure, not current output.

Current generation on these alternators is pretty well fool-proof. They are blindingly simple and robust design with no active internal electronics. Current output simply increases with rpm. The current output (duty cycle) is controlled by the PCM, based on ambient temp (as it relates to BATT charge capacity) and real-time loads.

Edit: as to observed voltage output; again, this is a function of the PCM control circuitry. 14.5V output is normal, especially as temperatures drop to zero or below and battery charge acceptance decreases (ability to accept current dwindles because cell internal resistance increases as temperature drops)...

Sorry to bring back up an old thread but I’m hearing a whine in the engine and removed the belt and when spinning the alternator it’s a bit harder to spin. Is it supposed to spin freely like the pulleys and stop after a second or so?

**Hemissary** · 02-13-2021, 09:01 PM

Originally Posted by KStryker

Sorry to bring back up an old thread but I’m hearing a whine in the engine and removed the belt and when spinning the alternator it’s a bit harder to spin. Is it supposed to spin freely like the pulleys and stop after a second or so?

Absolutely nothing(!) wrong with thread revivals, the threads are where good information resides for those (like you :^) who actually search to learn / share!

There will be (electro-mechanical) rotational resistance while in-situ. no electrical connection, it should spin fairly freely. More often than not the squeal emanates from the idler pulley.

Taking the belt off does not really help find the squeal. Put it back together, find an empty paper towel tube or something similar, start the vehicle, put the tube to your ear and get the other end in close to each individual rotating component until you isolate which is producing the noise.

**KStryker** · 02-13-2021, 09:20 PM

Originally Posted by Hemissary

Absolutely nothing(!) wrong with thread revivals...this is where good information resides - for all to learn / share!

There will be rotational resistance while in-situ. no electrical connection, it should spin fairly freely. More often than not the squeal emanates from the idler pulley.

Taking the belt off does not really help find the squeal. Put it back together, find an empty paper towel tube or something similar, start the vehicle, put the tube to your ear and get in close to each individual rotating component until you isolate which is producing the noise.

Thanks Simon

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