wild variations in voltage

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Watching the voltmeter on my newest truck, an 18 Chevy Express 3500 with the 6.0. It goes from just over 12 volts all the way up to nearly 15, truly a wide range.

I read online that it is a newer GM idea, but I had never before noticed it in our other GM trucks.


Note that vans have always been the stepchildren of trucks and get the "innovations" later than many others. We never had DBW throttles when the pickups did.


Thoughts and comments welcomed...
 
It sounds like a smart charging system and they can be really weird in what you see as the OE's are using different control methods and strategies...

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Charging rates as high as 15 volts are observable on some vehicles, depending on current demand and battery SOC, along with values as low as 12.9 volts.

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



Edit: Yup looks like it is... Regulated Voltage Control (RVC)

Quote
Regulated Voltage Control (RVC) is GMs' platform for computer controlled charging systems. This system is designed to raise and lower the alternator's voltage set point based on vehicle electrical needs. This maximizes charging system efficiency by reducing voltage output when higher voltages are not required. The system uses the Powertrain Control Module (PCM) along with a Body Control Module (BCM) to monitor battery state of charge, vehicle electrical loads, under hood temperatures and vehicle conditions. The BCM then calculates the optimum voltage set point and communicates the desired set point to the PCM. The PCM then commands and monitors the voltage regulation.

General Motors vehicles equipped with RVC utilize a battery current sensor to measure current flow into and out of the vehicle's battery. This current sensor sends a variable duty cycle signal to the BCM to aid in calculating the voltage set point. When there is a failure with the current sensor, a Diagnostic Trouble Code (DTC) will be set and the battery warning light will illuminate.

https://www.remyautomotive.com/dam/...ice%20Bulletin%20-%20November%202017.pdf
 
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Originally Posted by SteveSRT8
Watching the voltmeter on my newest truck, an 18 Chevy Express 3500 with the 6.0. It goes from just over 12 volts all the way up to nearly 15, truly a wide range.

I read online that it is a newer GM idea, but I had never before noticed it in our other GM trucks.


Note that vans have always been the stepchildren of trucks and get the "innovations" later than many others. We never had DBW throttles when the pickups did.


Thoughts and comments welcomed...


Before I lost sleep over it I would make sure the voltmeter is accurate.
 
This is completely normal. Soon the MFG will damp the voltmeter needles like they do with oil pressure and water temp to prevent complaints. Most gages are pretty much worthless on modern cars. If you have a computer readout that displays temp and and they are usually accurate and quite different than the dash display.

Enjoy your longer battery life.

Rod
 
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Do they have battery temperature monitoring? All the Jeeps I've had recently had temperature monitors and will push 15 volts on a cold morning after a start. But if it's warm out or the battery is getting warm, they''ll drop down to 13.5 or so
 
One way you can tell for sure is to look at the negative battery cable. If there is a ring around it with a sensor wire coming off, you have a "smart" system.

My 2015 Impala has this and battery voltage is all over the place as well. I'll occasionally be cruising down the road at just over 12 volts, then up to 15, then back to 12. It tends to "act like an old school" system in cold weather and when you have a bunch of electrical stuff on, I see it doing lower voltage stuff in the summer time more often. I have the stop/start system as well, which makes it even more interesting. It seems to work well so far, and if I wasn't watching I'd have no idea it was toying with the voltage so much. Dash lights, blower speed, headlights all seem blissfully unaffected by it.
 
Guessing the PCM is trying to save a small amount of fuel by only loading the alternator occasionally-does voltage seem to jump up when decelerating to a light or downhill? I seem to recall some imports doing that (BMW or VW?).
 
Sounds pretty normal. now if you start seeing under 11.8v and over 16v perhaps an issue.
The smart charging systems today are incredibly complicated sometimes and they love to undercharge battery.

The antique version of smart charging on the 2010 accent.. Loves to keep it at 12.2v-12.3v (in 60f temps)
Thought I had a battery or alternator issue... nope operating as moronically designed.
I could put the charger on it every night.. and it would hold 12.6 12.7, until driven cold days it was even lower
which seems terrible when you need max power to start at 0f and lower.. luckily the car for all its other hyundai issues.. starts very well in cold.

How about we just dont save 10cents worth of gas and keep my battery fully charged.. oh and I dont care if it accelerates .1s faster to 60mph either.
 
On my F150, what you are seeing is normal, and is part of the battery management system. Voltage runs anywhere between 12 and 15, depending on a ton of stuff.

While GM has done better than ford at giving you real gauges, when they start moving around like this, it makes people wonder if something is wrong. The end result will be either a wildly dampened gauge (more like an indicator light) or removal of the gauge entirely (F150's don;t have one for example (standard 4 are oil pressure, fuel level, coolant temp, and transmission temp).
 
What would be a problem would be someone putting in an AGM battery into one of these situations because AGM doesn't like voltages above 14.7.
I wonder how many AGM's are dying an early death because of that in these situations.
 
Funny - the system in my F150 has an AGM battery, and in the cold we've been having routinely runs at 15.0 volts. But that's only when its cold - in the summer it usually peaks out around 14.6. The charge voltage is dependent on battery temp.
 
Originally Posted by MNgopher
Funny - the system in my F150 has an AGM battery, and in the cold we've been having routinely runs at 15.0 volts. But that's only when its cold - in the summer it usually peaks out around 14.6. The charge voltage is dependent on battery temp.

I wonder though if it decreases the useable life because of it over time, even if it's just using 15v when it's cold.

I know in the manual for my Oddesey AGM battery I had put in the Journey, it said under no circumstances should charging voltages exceed 14.7 as the vents on the battery would open at 15v.
 
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Originally Posted by StevieC
What would be a problem would be someone putting in an AGM battery into one of these situations because AGM doesn't like voltages above 14.7.
I wonder how many AGM's are dying an early death because of that in these situations.

I've heard 14.8, close enough. I've given up warning people about this aspect of AGM batteries. I get told I'm wrong, then I'm ignored.

Then the same people complain about declining AGM battery quality, when they die early, and now they're trying a different brand. OK....
 
Originally Posted by HangFire
Originally Posted by StevieC
What would be a problem would be someone putting in an AGM battery into one of these situations because AGM doesn't like voltages above 14.7.
I wonder how many AGM's are dying an early death because of that in these situations.

I've heard 14.8, close enough. I've given up warning people about this aspect of AGM batteries. I get told I'm wrong, then I'm ignored.

Then the same people complain about declining AGM battery quality, when they die early, and now they're trying a different brand. OK....


Here is a snap-shot for the charging procedure for Odyssey AGM batteries... They go on later to talk about the vents opening at 15 volts so 14.7 listed below is the safe limit between this and 15v with a buffer of .3v
(Most chargers I have seen that can charge AGM will stop at 14.7v as their maximum for AGM mode)


Battery volts.png
 
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It depends what multi-meter you are using as well. Cheap meters usually have a .2v difference from proper RMS multi-meters.
 
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Donald: these are real gauges, actually quite accurate and only slightly dampened.

Ragtoplvr: same as above, no fancy readouts on this truck except tire pressures. remember, vans are not "high tech" yet.

Miller88: yes, one of the features is battery temp monitoring. I picked this truck up in Connecticut when it was 30 degrees or so and it ran pretty much at 15 most of the ride back to Fl.


MichiganMadMan: yes, everything seems completely unaffected.

Bullwinkle: This is a 6.0 gas powered van that weighs just shy of 9000 pounds so fuel savings are indeed minimal!!!


CT8: Haw! that's probably it.


Wyrtwister: no need to test, these are "real gauges. We buy these vans regularly and I have always found them to be amazingly different than my pickups.
 
Originally Posted by SteveSRT8
Donald: these are real gauges, actually quite accurate and only slightly dampened.

Ragtoplvr: same as above, no fancy readouts on this truck except tire pressures. remember, vans are not "high tech" yet.

Miller88: yes, one of the features is battery temp monitoring. I picked this truck up in Connecticut when it was 30 degrees or so and it ran pretty much at 15 most of the ride back to Fl.


MichiganMadMan: yes, everything seems completely unaffected.

Bullwinkle: This is a 6.0 gas powered van that weighs just shy of 9000 pounds so fuel savings are indeed minimal!!!


CT8: Haw! that's probably it.


Wyrtwister: no need to test, these are "real gauges. We buy these vans regularly and I have always found them to be amazingly different than my pickups.


Believe me, I know what your carpet cleaning equipment weighs! At least you're smart enough to buy a van that can handle the weight you put in it, unlike my company's Transits! I've trying to get them to go back to GMC/Chevy, but they seem to enjoy down vans & (useless) Ford dealership visits.
 
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