Odd Voltage and Battery Readings (Yet Again)

[EddieC]

On our 2008 Tahoe, in the past few days the voltage reading on the dash gauge has been consistently low, near 12 volts. What has been previously seemed normal is a consistent variation above and below 14v but generally around 14v.
After driving about 10 miles yesterday with the gauge near 12 volts I used a hand held Solar tester Cranking voltage (not running) the battery voltage was 12.4 and 12.6 with failing CCA if 348 and 319 on a 10 month old 760 CCA rated battery with a NG message.

I was prepared to return the battery but after sitting overnight the battery CCA is back up in the 700s.
I will add that the truck started up fine this morning and the weather is going into Fall with morning temps in the mid 40's.

I ran what limited tests the Solar tester could do on the charging system yesterday when the CCA was low and test results were deemed ok (except one item) by the instrument. I didn't do any specific routine to test other than cycle through the options and let it do it's thing on the ALT option.
Cranking voltage was 11.52v, voltage 14.9v, SOH 43% which I think refers to the battery, Ripple 14.9v (meaning of which I don't know). Also SOC 100% which I also assume refers to the battery.
The item reported as BAD was 9.87 m ohms which was reported with the SOC..

I have been hearing a whistling sound lately that seems to vary with engine speed but have not pinpointed it yet.

Any advice where to focus regarding the readings?

 

[j91z28d1]

you've probably already read but the truck ecm has a whole program in it trying to prolonge battery life. lot of times that's what you see causing the voltage change. if I remember right turning the headlights on always triggers it to command full voltage. so maybe try that next time you see it low on the gauge.


the sound is probably your alternator. they can make noise when loaded heavily even when good. but shouldn't when there's no load. a cheap 30$ DC amp clamp on the alt to battery wire would have you can idea if it's loaded hard enough to be making noise or just going out.

 

[Fless]

There shouldn't be much ripple in a well-functioning DC auto system. 14.9 V seems like something is wrong, or stated incorrectly.

Alternator AC ripple: What it is and how to test for it

Understanding alternator AC ripple: Learn why excessive ripple voltage can cause electrical issues and how to diagnose and fix the problem.

ricksfreeautorepairadvice.com

 

[EddieC]

This morning I threw the charger on the disconnected battery for a couple hours.
When it reported full charge the CCA was then 899 and a 15 minute ride brought it to 960. Those were up from 348/319 the day before.
The ripple after the charge was .09 and .17. I see an error in my original post in the the ripple was originally .21v, not 14.9.
An odd thing is that there is no fluctuation from 15 volts on the gauge today.

Could the regulator have caused the low CCA and gauge voltage reading yesterday? Or something else?
The only thig done differently was to turn on the fog lamps which haven't been used in a very long time.

 

[EddieC]

you've probably already read but the truck ecm has a whole program in it trying to prolonge battery life. lot of times that's what you see causing the voltage change. if I remember right turning the headlights on always triggers it to command full voltage. so maybe try that next time you see it low on the gauge.


the sound is probably your alternator. they can make noise when loaded heavily even when good. but shouldn't when there's no load. a cheap 30$ DC amp clamp on the alt to battery wire would have you can idea if it's loaded hard enough to be making noise or just going out.

No matter what I turn on or off hasn't caused the voltage gauge to ever react for me.

 

[EddieC]

Duh. A bit of oxidation on the cable lugs appears to have been affecting the test gauge readings.
Probably not affecting the whine but certainly affected the readings.
Keep it simple stupid, right?

 

[mikez71]

No matter what I turn on or off hasn't caused the voltage gauge to ever react for me.

Same here, I'm not sure if it was because I changed ECM alt settings or not..
But the headlight trick doesn't seem to bump my charging voltage.