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Old 06-15-2013, 10:44 AM   #1
budpln
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battery light

Whats up guys I don't know if anyone has some insight on this or not but my battery light has come on its a 2008 ses not sure if i just need an alternator or the battery is no good can the car tell that? it runs starts and drives fine but the light has me concerned i need an alternator!! anyone had this problem yet???


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Old 06-15-2013, 01:00 PM   #2
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you can always drive to a parts store and have them test the battery while its in the car. if the battery is ok then pull the alternator and have it tested also.

and its free!

i had a battery go bad a year or so ago and i never had a light. the car wouldnt start and after jump starting it there was no light. so my guess is it is the alternator
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Old 06-15-2013, 01:04 PM   #3
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the alternator generates a lot of voltage it is limited down to something like 16 volts of which 14.6 goes into charging the battery. there are three windings and a rectifier using diodes that turn the ac voltage it produces into mostly dc voltage. if you have a lab scope you can see that there is a slight ac sign to the voltage signal. if a winding or diode were to go bad the signal would become unstable and the car can pick this up and alert you to a problem
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Old 06-16-2013, 09:00 AM   #4
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Thanks for the info buddy!!
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Old 06-16-2013, 09:17 AM   #5
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I just put my multi meter to my battery while it was running it was only at 13.5 volts so Im guessing the alt. needs to be replaced
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Old 06-16-2013, 12:19 PM   #6
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13.5 should mean the alt is working.. But not getting a full 14+ volts. Id say battery issue.

Whats voltage with car off?

My batteries sit at 12.6 volts off and 14.5 on for reference.
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Old 06-16-2013, 01:13 PM   #7
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you have a 6 cell battery. each cell developes 2.1 volts for a total 12.6 volts
a cell can go bad if the fluid has boiled off or spilled out. most batteries are no maintenance so you can not pull the top off and inspect each cell. if you can you can visually check the fluid level. the lead cells should be sitting under the fluid with the fluid just touching the plastic top casing- not coming up the casing wells. the fluid consists of sulfuric acid and distilled water. you can add water to a low cell but use distilled as tap water has minerals which will corrode and cover the lead.

it is uncommon for one cell to go bad from sulfation (a sulfuric coating on the cell due to excessive discharge). it is rather tuff to try to undo this process but you are welcome to try by placing the battery on a charger
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Old 06-16-2013, 03:43 PM   #8
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Voltage while the car is off is about 12.6
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Old 06-16-2013, 05:48 PM   #9
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alt is bad if you see no corrosion on any of the surfaces...
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Old 06-16-2013, 11:28 PM   #10
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Moved to "General Technical Chat".
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