Silverado charging issue

[dlbleak]

my truck is eating batteries up. The alternator tests fine and sho s it's putting out 12 volts. I'm sitting outside the gun show with it running and the bolt gauge is flucuating between 12 and 14. It's not bouncing back and forth but just moving. I don't think ant to drop the cash on an alternator if it might b something else.

 

[918evo]

The alternator should be putting out around 13.5 volts, but more important is the amp output. Is it fine to drive around and then dead in the morning or how do you end up needing a new battery? Oriellys and autozone can test the alternator, but remember the person behind the tester is usually not a mechanic and not qualified to use it. It is usually a good idea to get it tested at a couple of different places and have them tell you the alternator's amp output.

 

[swampratt]

Take a multi meter and with the truck turned of check battery voltage. say it is 12.7 volts.
Now start the vehicle.. look at the multi meter it should be more than your initial 12.7 volts.
Now rev it up to about 2500rpm. It should again be more than 12.7 if it drops below that voltage you are running on battery voltage and the alternator is not keeping up.

Now turn on the headlights the AC to high and the hazzards.
This will put a load on the alternator.. the voltage should still be above battery initial voltage.

Like 918evo stated 13.8 is more like what you should see but I will say my alternators read higher 14.3 to 14.7 on my GM old school alternators.

 

[KOPBET]

As important, it should NOT put out anything measurable as AC.

 

[travisstorma]

What year?


GM has been using a charging technique for several years that control the voltage based on many factors including calculated electrical loading and ambient temperature. A reading of 12.x volts could be perfectly normal when running.



Here is some info. I’ve tried finding a TSB they put out a few years ago to address customer concerns over fluctuating voltage. It basically said it was normal to be 12-14v.

http://www.agcoauto.com/content/news/p2_articleid/350

Sent from my iPad using Tapatalk

 

[dlbleak]

It's an 06. Ad I rolled into okc, the dash said check charging system. I'll check some things with the voltmeter tomorrow.
I came out of the show and turned the key, just clicked and I'm thinking 'oh crap'. I was parked next to my brother and had jumper cables just in case. Tried it again and it started.
It's done this before and I've changed the battery and it will be fine for months.

 

[MacFromOK]

Check the electrolyte level every week or so. If it's overcharging, it may be boiling the water out of the mixture.

If you can, check the old one.

 

[dlbleak]

Truck started fine this morning to go to work. I just walked out to check it and it started fine BUT the clock had reset to 12:00. So at some point between the house and work it had lost ground. I suck at electrics and it's a truly intermittent problem that could be hell to track down

 

[swampratt]

If ya want to you can bring it by here I will take a look at it.

 

[dlbleak]

Thanks SR. Found this test on the net.
With your meter set on AC and low(less than a volt). Start the engine and test between battery posts.
If any reading more than zero is there, it could be a possible bad diode in the alternator.
Not enough of a draw to indicate a bad alternator.
Mine was quickly going from .19 to .82

EDIT: that wasn't the problem!