Why is my alternator dying?

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Evergreentrees
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Joined: Sat May 08, 2021 9:42 am
Car: 2009 Infiniti G37 S 6spd M/T

Why is my alternator dying?

Postby Evergreentrees » Sat May 08, 2021 5:50 pm

On 70% of cold starts, the battery icon will be illuminated on the dash. With the warning light still on, the voltage reads about 11.9v with the engine running. After revving to about 3k rpm, the voltage regulator suddenly decides to start working and produces the acceptable voltage range in accordance to the fsm (13.3-14.6v). The battery warning light switches off and never comes back on after revving once at start up. If the engine is warm, and restarted the light does not come back on. Only at cold starts I will have to tap the accelerator to "kickstart" the alternator.

I probably need a new voltage regulator, but why does tapping the gas solve this issue? Anyone have a suspicion whats going on internally either around the brushes or internal voltage regulator in the alternator?


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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Why is my alternator dying?

Postby VStar650CL » Sat May 08, 2021 6:31 pm

Make sure it isn't that the belt is slipping cold. Dunno what your vehicle is, but if it has an overrunning clutch on the pulley then that may be causing your issue. If the clutch doesn't catch immediately then the alternator output will be very low until it does. It could also just be failing silicon in the regulator. Lastly, if it has a "smart" charging system under PWM control, they're well known to get stupid on many N/I models. There's a way to disable it on most vehicles and put the alternator on fixed regulation.

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Rogue One
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Re: Why is my alternator dying?

Postby Rogue One » Sun May 09, 2021 4:49 am

:welcome:

In order for us to help you, you're going to need to provide a little more info. Your post (and your profile) is missing some crucial information. We can surmise that you own an Infiniti, however it would be helpful to know the model and year. Oh, and for this topic the mileage on your vehicle would be helpful as well.

Evergreentrees
Posts: 7
Joined: Sat May 08, 2021 9:42 am
Car: 2009 Infiniti G37 S 6spd M/T

Re: Why is my alternator dying?

Postby Evergreentrees » Fri May 14, 2021 9:32 pm

I think I figured out the problem, long story short due to bad physical connection, (loose terminal) and corrosion. The battery hasn't been able to charge as efficiently, losing some cell life. My battery is at about 12.35v (there is no drain) and this puts a lot of strain on the alternator at idle to recharge it. Sometimes it refuses to do so at idle speeds as the alternator isnt at peak efficiency to do so.

Im pretty sure I need a new battery to take the stress off my alternator to at least preserve it before it needs a rebuild.

This is all on a 2009 Infiniti G37

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Why is my alternator dying?

Postby VStar650CL » Fri May 14, 2021 9:49 pm

Evergreentrees wrote:
Fri May 14, 2021 9:32 pm
My battery is at about 12.35v (there is no drain) and this puts a lot of strain on the alternator at idle to recharge it. Sometimes it refuses to do so at idle speeds as the alternator isnt at peak efficiency to do so.

This is all on a 2009 Infiniti G37
Normal "float" voltage on a battery depends how long it's been sitting, but 12.4V is pretty normal unless the car was just shut down with a full charge. Your car has the often-dumb "smart charging system" with the alternator under IPDM/BCM control, and it's about 90% probable that's your issue. Significant numbers of them just don't work right as cars age. Cut and cap the white wire at the alternator or the yellow at pin 76 of the IPDM (it's the same wire with a color change at a wire-to-wire connector). That will put the alternator on 14.2V internal regulation and prevent the system from under-charging, especially on short trips..

Evergreentrees
Posts: 7
Joined: Sat May 08, 2021 9:42 am
Car: 2009 Infiniti G37 S 6spd M/T

Re: Why is my alternator dying?

Postby Evergreentrees » Fri May 14, 2021 11:24 pm

I have noticed the lowest the alternator puts out (after long drives) is 13.3v at idle. At cold starts its usually at 14.2+ (cant remember exactly how much)

Im probably going to run some tests on the voltage regulator pins to see if its potentially failing as well (there is an oil leak onto the alternator)

The belt was starting to squeal (and probably slip) ran the oem belt for 117k miles which is pretty decent life. Ive replaced it and thought this improved the battery lamp indicator at start up as the first start up after installation I only had to tap the gas to 1.5k rpm vs 3k like usual, but this at the next start up I was back to taping to 3k to get the battery light to turn off

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Why is my alternator dying?

Postby VStar650CL » Sat May 15, 2021 5:00 am

The only way to test the regulator is by unpinning the white wire, the alternator should go to between 14.0~14.5V and remain in that range even with high beams and blower on. There's no effective way to test with the "smart charging" still enabled, since the BCM/IPDM determine the output under those circumstances and not the regulator.


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