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13.5V alternator when driving and idling #5450980 06/11/20 02:57 AM
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apollo18 Offline OP
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Hey guys so I recently fully charged my battery in my hummer h2 since it sat for 1-2 weeks and the battery was fully dead. I put it in the truck today and then I remembered that my radar detector does a voltage reading so I turned that on and I noticed that my voltage would only be between 13.5 -
13.6v while driving with no Ac/fan and the stereo shut off. I even shut the lights off and same thing, when I got home I let it idle and it was between 13.5-13.6v

is this normal because my battery was just recently fully charged? Or is something wrong? The alternator is about 5 years old and it’s a China one so it could a about to go but just wanna make sure what values I should be seeing. I’m also going to be getting a HID kit very soon so I don’t want anything to go wrong with that especially

Re: 13.5V alternator when driving and idling [Re: apollo18] #5450989 06/11/20 03:41 AM
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ctechbob Online Content
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I would get a better reading off of the battery posts with a real meter. Since you said the battery was completely dead, it could be damaged, or the alternator could have something wrong with it, but I wouldn't trust a voltage display on a radar detector.

Last edited by ctechbob; 06/11/20 03:42 AM.

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Re: 13.5V alternator when driving and idling [Re: apollo18] #5451059 06/11/20 07:25 AM
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5AcresAndAFool Offline
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That is not out of the realm of a normal output from the alternator. I see your in canada, what was the ambient temperature during your readings? So many factors play into the output of the alternator which is likely controlled by the pcm in this vehicle, one of which is ambient temperature and under hood temperatures in many cases.

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451081 06/11/20 07:50 AM
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GSCJR Offline
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Sounds normal to me apollo18.

Last edited by GSCJR; 06/11/20 07:52 AM.

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Re: 13.5V alternator when driving and idling [Re: apollo18] #5451083 06/11/20 07:51 AM
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Donald Offline
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Decent meter at the battery post. Or check power with engine off and then start the engine and it should climb at least 1V if no significant load.


2015 Ford F-250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: 13.5V alternator when driving and idling [Re: 5AcresAndAFool] #5451093 06/11/20 08:07 AM
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apollo18 Offline OP
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Originally Posted by 5AcresAndAFool
That is not out of the realm of a normal output from the alternator. I see your in canada, what was the ambient temperature during your readings? So many factors play into the output of the alternator which is likely controlled by the pcm in this vehicle, one of which is ambient temperature and under hood temperatures in many cases.



Temp was around 10 Celsius and I don’t think the vehicle was at operating temp but probably near

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451118 06/11/20 08:32 AM
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5AcresAndAFool Offline
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Originally Posted by apollo18
Originally Posted by 5AcresAndAFool
That is not out of the realm of a normal output from the alternator. I see your in canada, what was the ambient temperature during your readings? So many factors play into the output of the alternator which is likely controlled by the pcm in this vehicle, one of which is ambient temperature and under hood temperatures in many cases.



Temp was around 10 Celsius and I don’t think the vehicle was at operating temp but probably near


13.5 volts sounds right under those conditions.

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451162 06/11/20 09:06 AM
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ragtoplvr Offline
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13.5 is not enough to keep a modern battery charged. Most GM will run at least 14.5 and may go up to 15 volts when it is cold. Some GM vehicles have a sensor mounted at the battery and once the computer determines the battery is charged it will reduce the voltage to 13. something range. It also has a desulfation mode where you can see over 15 volts for some time. This system is called RVC or SARVC. There may be later versions. These are supposed to provide longer battery life AND lower fuel consumption.

You need to research the internet and see if you have one of these systems. You need a real voltmeter, attached to the alternator output terminal or battery if you can get to it. Simple alternators are rapidly disappearing.

Rod

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451247 06/11/20 10:21 AM
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UncleDave Offline
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Lots of alternators put out about 13.5 my sprinter alternator hangs right at that. They usually burst higher after a start then come right down.

A standard alternator without something like a Balmar kit on it will NEVER fully charge any battery regardless of distance driven.
Put it on a smart charger after a road trip and watch it take a charge.

A basic flooded lead acid battery is fully charged at 12.7 volts, starts to degrade itself around 12, and is basically dead at 11.5.

UD


Uncle Dave
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Re: 13.5V alternator when driving and idling [Re: apollo18] #5451257 06/11/20 10:47 AM
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SubLGT Offline
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It might be OK.
GM has a complicated charging scheme.

https://www.motor.com/magazine-summary/are-you-smarter-than-a-smart-charging-system/

https://www.motor.com/magazine-summary/trouble-shooter-july2015/

https://www.motor.com/magazine-summary/trouble-shooter-september2015/

Quote
There are two types of RVC systems in use—integrated RVC and stand-alone RVC (SARVC). Integrated systems use a battery current sensor to inform a body control module (BCM) how much the battery is being charged or discharged.

SARVC systems (found mostly on trucks) do not use the BCM for operation. They have a generator battery control module mounted to the negative battery cable, to interpret battery current and voltage and battery temperature inputs. The battery current sensor is internal to the module. This module also directly controls the generator L terminal duty cycle instead of the ECM/PCM.

The purpose of the RVC system is to maintain the battery state-of-charge at 80% or above and support vehicle loads. To accomplish this, it has several different modes of operation. Six common modes of operation are Charge Mode, Fuel Economy Mode, Voltage Reduction Mode, Start Up Mode, Windshield De-Ice Mode and Battery Sulfation Mode.

The PCM/ECM (generator battery control module on full-size trucks) controls the generator through the generator L terminal control circuit. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 5V PWM (pulse width modulated) signal of 128Hz with a duty cycle of 0% to 100%. Normal duty cycle is between 5% and 95%. The ranges between 0% to 5% and 95% to 100% are for diagnostic purposes.

The control module enters Charge Mode whenever one of the following conditions is met:

Under WOT conditions and when the fuel rate (sent by the ECM/PCM) is greater than 21 g/S and the throttle position is greater than 90%.
The headlamps are on, low or high beam.
The wipers are on for more than 8 seconds.
The electric cooling fans are on high speed.
The rear defogger is on.
The battery SOC is less than 80%.
When one of these conditions is met, the control module ramps up the voltage slowly to a level between 13.4 to 15.5V (depending upon the mode of operation the system is presently in) at a rate of 8mV to 50mV per second.

The control module enters Fuel Economy Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 15A and greater than –8A.
The battery SOC is greater than 80%.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 13.0V. The control module will exit this mode once the criteria are met for Charge Mode.

The control module will enter Voltage Reduction Mode when the following conditions are met:

The calculated ambient air temperature is above 32°F.
The calculated battery current is less than 2A and greater than –7A.
The generator field duty cycle is less than 99%.
This mode’s targeted generator output voltage is 12.9V. The control module will exit this mode once the criteria are met for Charge Mode.

After the engine has started, the control module sets a targeted generator output voltage of 14.5V for 30 seconds (Start Up Mode).

The control module enters Battery Sulfation Mode when the battery voltage is less than 13.2V for 45 minutes. Once in this mode, the generator battery control module will set a targeted output voltage between 13.9 and 15.5V for five minutes. The control module will then determine which mode to enter depending on voltage requirements.

In RVC Mode, the control module bases the charging voltage on battery SOC, which is estimated during a key-off event every eight hours, after three voltage measurements every 24 hours thereafter, and then monitored constantly while the ignition is on. These voltage measurements are then compared to estimated battery temperature, as battery temperature vs. battery voltage directly corresponds to battery SOC. While the engine is running, the system uses both the battery voltage and estimated battery temperature to determine the battery current in and out of the battery. The control module then regulates the charging voltage to keep the battery above an 80% SOC.

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451309 06/11/20 11:56 AM
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Silverado12 Offline
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Battery resting overnight in the morning should be 12.5 volts. Charging should be around 14ish volts. Have someone crank the engine and if it goes below 10 volts the battery is bad. This is how I have done it over the years. YMMV.


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Re: 13.5V alternator when driving and idling [Re: apollo18] #5451317 06/11/20 12:16 PM
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JMJNet Offline
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Load (not voltage) test the battery? or if it is more than 1, needs to do it one at a time.

Load testing is the only reliable way to check if the battery is still good and can hold charges.

After you know the battery is good, then you can determine if the alternator is good by loading up the electric, turning all electrical/electronic components in the car/truck.


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Re: 13.5V alternator when driving and idling [Re: Silverado12] #5451328 06/11/20 12:35 PM
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UncleDave Offline
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Heres a pretty standard table outlining voltage, vs state of charge, vs specificities gravity per cell.

Batteries all vary a bit and higher end one will post their exact parameter so a charge profile can be specifically created.

[Linked Image]


Uncle Dave
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Re: 13.5V alternator when driving and idling [Re: UncleDave] #5451747 06/12/20 04:16 AM
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apollo18 Offline OP
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Thanks! I actually checked the battery posts with multimeter with the vehicle running and was hitting 14.2-14.3V I believe which I assume is good enough. It’s odd because even my gauge in my truck has the need at about 13.5-13.7 ish but I guess the battery posts are most accurate

I assume I’m good then?

Re: 13.5V alternator when driving and idling [Re: apollo18] #5451947 06/12/20 10:04 AM
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UncleDave Offline
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Originally Posted by apollo18
Thanks! I actually checked the battery posts with multimeter with the vehicle running and was hitting 14.2-14.3V I believe which I assume is good enough. It’s odd because even my gauge in my truck has the need at about 13.5-13.7 ish but I guess the battery posts are most accurate

I assume I’m good then?


You're good.

UD


Uncle Dave
Cat 3126/2 MB3500/Titan/RX400H/17 Ridgeline
700HP V10/ 725HP BBC/ Raptor 700/ KFX450/ YZ250/Onan 8K/ Cat3011C
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