Exact "Proper voltage reading questions"

[Tuesdak]

Continuing the incomplete discussions that litter the search results like this one: What is the correct operating voltage of the 3rd Gen charging system?

Agreed the "under-volt" case is kinda covered, but, what about a good solid constant 14.5v measured from the lower cig lighter at 90 degrees outside during a 30 min run? The same voltage appears on both batteries. Just replaced "old" for high heat AZ batteries as they kept covering the top with acid after cleaning. I am not used to this voltage as I usually am around GM's smaller batts and that is ~13.5v.

So at what absolute voltages should I worry at? High/low? Is there a battery temperature chart to reference? Time after startup chart?

 

[Prairie Dog]

That's about what mine runs all the time. (This is a much cooler temp - probably around 60~70)
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[lpennock]

Mine runs around 14.5? When my batteries where going out I would see 15.2. ECU measures temp on driver battery to determine max charge rate.

 

[Ozymandias]

15.2 is also normal at low exterior temperature.

You can check the voltages with a decent scanner, there is a value that the ecm commands and a value that shows the actual system voltage.

If they match each other then your system is fine.

Battery pole connectors should be clean and thight already.

 

[Regcabguy]

That's about what mine runs all the time. (This is a much cooler temp - probably around 60~70)
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That's what my dash gauge has read from new.

 

[Tuesdak]

Thanks! Looks like my voltage is fine then and I was just pushing the batteries too long for age in this extreme heat.

 

[PWong]

My nominal reading is arouud 14.5-14.7 volts.
Expect to see 15 volt on a COLD morning.

 

[Ozymandias]

Thanks! Looks like my voltage is fine then and I was just pushing the batteries too long for age in this extreme heat.

Your Truck has a temperatur sensor under the passenger side Battery, so the ECM knows how high he can push the Alternator voltage for an optimally charged battery.
So it doesn't matter how hot or cold it's outside, the charging is always correct.

With 13.5 like your old GMs you can't load a battery to the Top, 13.5 means no more then 50% SOC.

 

[jelag]

I personally believe there is no set voltage... when the ECM looks at the outside air temperature and the battery temperature and than changes the voltage.... the graphs from this formula means that the voltage can be all over the place... my brake controller has a digital volt meter on it and its very seldom reads the same voltage... but look at the brighter side... most of these trucks go there life without ever adding water to the batteries... That's because this formula works... granted, the batteries never seem to be more than 85% fully charged... based on open circuit voltage tests... but the truck always starts and runs in the coldest of temperatures...

Often buzzing down the highway on a hot day the voltage is low... 13.8 - 14.1... on a cold day it be as high as 14.5 or 14.6....

Just my thoughts..

 

[nmurray]

Where is the temperature sensor for the battery? I have a 2010 3500 C&C so it is like a 2009 pickup. It has a 220 amp alternator. At the end of last winter I hade the alternator charge from 13.5 to 15.2 at a frequency of about 0.5 Hz (AKA 2 second count from 15.2 down to 13.5 and back to 15.2) Sometimes this would happen for several minutes. You can really notice it when the headlights are on. The truck voltage gauge does not change but with a multimeter you can see it on either battery so it is not like the driver's side battery has a connection problem. I replaced the batteries and cleaned all terminals last winter and it still did it. Then it went away as spring temperatures arrived. I ran all summer and into the fall with no issues and now it is starting to do it again. Talked to the dealer but they have no clue. I do have a used 220 amp alternator from a wrecked truck that I tested and it is good. I got it for $75 so it rides in the truck as insurance. I have tried to find more on this weird/complex charging system but there is very little out there. I do not know what you really get with the PCM controlling the alternator output. I like the simple self regulating alternators. No charge. Check batteries, clean connections, remove alternator have it tested/rebuilt/exchanged and reinstall. Problem solved. In addition I removed the "control" connector that goes to the alternator. It was clean and dry. Pins and sockets looked good with no corrosion. Any help would be appreciated before I pay the dealer to learn the system.

 

[lpennock]

On my 06 the Temp sensor is under the drivers side battery. When you lift up the battery there is about a 2" diameter plate and is lightly spring loaded on mine.

 

[p-Bar]

Did a little research for you guys . each cell in the battery is actually 2.1 volts so this brings the batt. voltage to 12.6-12.8 volts. The charging system has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. So it really starts charging at 13.8 volts. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate. If you are charging over 14.7 volts you are making excess gas and will cook off the battery . Hope this helps

 

[lpennock]

If you are charging over 14.7 volts you are making excess gas and will cook off the battery . Hope this helps

Not true when the battery temperature is monitored a battery can be safely charged at voltages as high as 15.2. Without temperature monitoring 13.6 is all that should be used. Do a search for temperature compensated battery charging and you will find a ton of information.

 

[p-Bar]

You are probably right on that . I was reading an old skool site . Very important on these parallel battery trucks that the temp is monitored so it can shut down if a battery becomes shorted and won't over charge the other battery.

 

[MMeier]

I always look for 13.5 - 15.3 volts, the cooler it is the more voltage you will have .

 

[PWong]

At the end of last winter I hade the alternator charge from 13.5 to 15.2 at a frequency of about 0.5 Hz (AKA 2 second count from 15.2 down to 13.5 and back to 15.2) Sometimes this would happen for several minutes. You can really notice it when the headlights are on. The truck voltage gauge does not change but with a multimeter you can see it on either battery so it is not like the driver's side battery has a connection problem. I replaced the batteries and cleaned all terminals last winter and it still did it. Then it went away as spring temperatures arrived. I ran all summer and into the fall with no issues and now it is starting to do it again.

Your charging system and grid heaters are working 100% as designed, like a champ!!!

 

[Tuesdak]

Not true when the battery temperature is monitored a battery can be safely charged at voltages as high as 15.2. Without temperature monitoring 13.6 is all that should be used. Do a search for temperature compensated battery charging and you will find a ton of information.

This explains the big difference in the systems any why the higher voltages! Thanks for that.