New alternator 15 volts 2002 Lesabre

[Rocky1]

2002 Lesabre, has new battery, all terminals are clean including the battery to Frame in both locations… My old factory alternator charged at 14.7 -14.8, installed a new Duralast alternator and it fluctuates between 14.8-15 volts, I did see 15.1 briefly on the digital display it mostly 14.9 to 15 volts . I checked at the battery with my DVOM and I’m reading 14.95 at idle with the heat on low to medium speed. Is this a normal range on these cars?

 

[Rocky1]

2002 Lesabre, has new battery, all terminals are clean including the battery to Frame in both locations… My old factory alternator charged at 14.7 -14.8, installed a new Duralast alternator and it fluctuates between 14.8-15 volts, I did see 15.1 briefly on the digital display it mostly 14.9 to 15 volts . I checked at the battery with my DVOM and I’m reading 14.95 at idle with the heat on low to medium speed. Is this a normal range on these cars?

I just checked my 2003 Lesabre and it’s about the same 14.7-14.9

 

[ohioriver]

My '04 does the same...everything is OEM.

 

[Rocky1]

My '04 does the same...everything is OEM.

I appreciate you checking, for the heck if it I swapped the new alternator into my 2003 and it was roughly 14.8-15 volts so I’m assuming it’s ok, I normally just watch the temperature and seldom go to voltage on the digital display….

 

[Rocky1]

I tried a different alternator, rechecked all the connections and at highway speeds I’m running 14.9-15 volts constantly , around town it will drop to 14.7-14.8 volts. I’d think after driving a while especially at highway speeds the voltage would decrease

 

[RD_Atlanta]

The PCM monitors the battery voltage and adjusts the alternator output via PWM signal to a transistor inside the alternator which switches the field current on & off. The default is set to 80% or 14.94 volts. I think the PCM monitoring and control function is regulating the voltage well on your Lesabre because the PWM signal is maintaining close to 14.94 volts. In reference to should the voltage decrease after a period of driving? Actually, the battery voltage would 'naturally' increase with driving time because the battery's internal resistance increases as the charge % increases. But since the PCM is doing a really good job is regulating the voltage, it backs off on the PWM output and holds a very respectful range between 14.9-15.0 volts.

I (personally) am accustom to having the ability to adjust the voltage regulation. Unfortunately (I've recently noticed) in the GM P04 PCM O.S., the PCM program does not include a tunable parameter to adjust the % commanded duty cycle. I have seen on some of the newer GM PCM programs where this parameter is available. That being said, I think the 80% (14.94 v setpoint) is fine. Especially on the 00-05 LeSabre where the battery is located under the back seat. The point being; there is some cable length between where the PCM is sampling the voltage and the battery, so, there might be a slight amount of voltage drop at the battery.

Commanded Duty Cycle.

10% 11.00 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.50 V

 

[Rocky1]

The PCM monitors the battery voltage and adjusts the alternator output via PWM signal to a transistor inside the alternator which switches the field current on & off. The default is set to 80% or 14.94 volts. I think the PCM monitoring and control function is regulating the voltage well on your Lesabre because the PWM signal is maintaining close to 14.94 volts. In reference to should the voltage decrease after a period of driving? Actually, the battery voltage would 'naturally' increase with driving time because the battery's internal resistance increases as the charge % increases. But since the PCM is doing a really good job is regulating the voltage, it backs off on the PWM output and holds a very respectful range between 14.9-15.0 volts.

I (personally) am accustom to having the ability to adjust the voltage regulation. Unfortunately (I've recently noticed) in the GM P04 PCM O.S., the PCM program does not include a tunable parameter to adjust the % commanded duty cycle. I have seen on some of the newer GM PCM programs where this parameter is available. That being said, I think the 80% (14.94 v setpoint) is fine. Especially on the 00-05 LeSabre where the battery is located under the back seat. The point being; there is some cable length between where the PCM is sampling the voltage and the battery, so, there might be a slight amount of voltage drop at the battery.

Commanded Duty Cycle.

10% 11.00 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 15.50 V

That makes perfect sense, I appreciate this information greatly. Eases my mind for sure

 

[02LTD2.0]

Mine drops to 14.4 -14.5 after a few minutes. I have a new battery. I'll check it again if I out to the store later.

 

[RD_Atlanta]

Mine drops to 14.4 -14.5 after a few minutes. I have a new battery. I'll check it again if I out to the store later.

I think it's rare for the regulator & alternator to hold as close as Rocky 1, his regulation is very impressive. I agree, it's more typical to see some swing like your describing. But none the less, holding as close as what you are describing is still very good.

 

[02LTD2.0]

Mine has acted this way with the original alternator and with a rebuilt alternator. I agree that this is normal operation.

 

[Rocky1]

Mine has acted this way with the original alternator and with a rebuilt alternator. I agree that this is normal operation.

I’ve had better luck with used oem Delphi alternators vs the reman units, I’ve tried two from Auto… and both ranged at 15.2 on the car and with them bench testing both. I got a refund, the one from my local pick n pull seems to stay around 14.9 on the highway and at idle 14.6-14.8 with most accessories on. As mentioned I only recently started watching the voltage readout when the alternator quit vs temperature. I’m switching back 🤣 unless I get an indication of a charging issue. Years ago I did add another ground from the main ground to the stud above the alternator on both my Lesabres so in case the one above the starter failed I have a backup ground. So far I’m happy with the voltage readings along with what I’ve learned here on the forum

 

[ohioriver]

I can add since I have owned the LeSabre for 4 years, the charging voltage has always been between 14.7 to 15.0.
As mentioned, since the battery is in the back seat with long cables, there will be some voltage loss going on.
I am not going to bother freaking out on this one.... If it ever goes 15 + consistantly, well then maybe I would dig more into it.
The car has too many other nits to worry about this one....

 

[02LTD2.0]

I've had 7 of these 3800 powered cars since 2003. I have never had to change an alternator until owning my current Buick. I would have bought a new alternator if I had more time but I needed one in a crunch so I got a re-manned unit from an independent parts store and so far it's been fine. The parts store deals with a lot of professional mechanics so they only deal with reputable rebuilders.

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