GM Battery Charging - Regulated Voltage Control

[WA4CUA]

I noticed the battery voltage on my new 2009 Chevy Cobalt seems to run consistently low after an hour or so being parked (~ 12.2 volts no load).

I found this article on the Internet which gives some very important details on the charging mechanism for certain GM cars. Some of us might want to force headlights on to obtain higher alternator output.

http://www.waiglobal.com/techups/Central_techs/GM_Regulated_Voltage_Control.pdf

I still don't know if my low battery terminal voltage is normal. Perhaps there has been a change in automotive battery chemistry that has lowered nominal cell voltage???

73

John Helms
WA4CUA

[N8EKT]

Leave it to GM to replace the simplest and most reliable charging method with a technical nightmare. LOL!

Any way you alice it, a 12 volt lead acid starting battery needs at least 12.65 volts in order to float.

Anything less and you are in discharge.

Isn't GM the same company that invented the "daytime running lights" that caused premature failure of alternators and headlights?

Hmmmmmmmmm

[K5LXP]

I doubt very much it's a different battery topology.

Clearly they're using an algorithm and specific feedback to determine how much charge to give the battery and when depending on circumstances that may not be immediately obvious to the operator.  You just need to base it on faith that the battery is going to get the right amount of charge in a timely manner.  So at any given moment it may seem to be getting too little or too much, but over time it should average out.  

Mark K5LXP
Albuquerque, NM

[K0BG]

You didn't phrase your question very well.

A standard, flooded lead acid, SLI battery will eventually settle to about 12.2 to 12.4 volts depending on the ambient temperature. The charging voltage applied to the battery also varies on ambient temperature, and maybe as low as 13.5 volts to as high as 14.5.

Charge and regulation strategies vary between makes, and they're too numerous to explore here. However, the GM system does incorporate the engine CPU are part of its strategy, so alternator load does play a part in the voltage you see while the engine is running. When it isn't, almost every vehicle on the road will drop to 12.2 or so given enough time.

Alan, KØBG
www.k0bg.com

[K0BG]

I'll have to comment on the DRLs.

No! GM didn't invent daytime running lights. Depending on your sources, it was either the Canadian or German parliament. DRLs have been required in Canada for about 10 years.

As for premature failure of the battery and alternator as a result, is pure fable! Call it an urban myth is you like. If you doubt the premise, then look up the actual load requirements of the various ancillary devices on a modern vehicle, and the mythology behind the fable will become glaringly evident.

Alan, KØBG
www.k0bg.com

PS: DRLs add about 3% to 5% of the total demand load. Bet you can't guess the most significant load?

[VE7DQ]

Not only that, but most DRLs use the high-beam circuit at reduced voltage, at least on the vehicles I've dealt with.  

Most of my headlight failures have been the low beam filaments.  

DRL was in Europe before it was introduced in Canada.  The Swedes did research on it and found it reduced crashes (they're rarely 'accidents'!) significantly.  Why do many people so despise a proven safety feature that increases one's visibility?... especially with all the other incompetant drivers out there.   I've noticed this attitude on some other US vehicular websites also.

End of thread hi-jack.

[KD4LLA]

My 08 Silverado p/u does the same thing after running awhile.  I do not like it, but maybe it will make the battery last longer.  I didn't need the built-in cellphone, GPS, or XM radio either...  Daytime running lights (DRL) are very annoying also.  No need for the nanny state to tell me when to turn on the lights.