Alternator Failures? - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 04-15-2016, 07:43 AM Thread Starter
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Alternator Failures?

My 2010 E350 4Matic battery runs down after two weeks. I am now on the second alternator and battery has run down again. Car only has 40,000 miles. Put a volt meter on the the alternator and it is charging at the rate of 13.2 volts. My 2016 C300 puts out 14.3 volts and my 2006 BMW puts out 14.3 volts. When the new alternators were installed they would put out 14.3 for a while and then it would drop back after about a week. Shouldn't the car be putting out 14.3 all of the time? I took the car to O'Reillys and they checked the alternator and their equipment indicated an internal regulator failure. I have taken the car to Mercedes and they can't find anything wrong and they said that my car does not have to put out 14.3 volts all of the time. I DISAGREE! Why do my other cars (including my 1970 SS396 Chevelle put out 14.3 volts all of the time?
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post #2 of 3 (permalink) Old 04-15-2016, 08:04 AM
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13.5V is battery maintaining voltage.
On deeply discharged battery the charging voltage will go to 14V, but 14.5V some manufactures use for fast charging is shortening the battery life.
When you measure 13.2V on alternator what was battery voltage showing?
I would do a test with turning all lights, blower and rear defogger and observe how voltage change.

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post #3 of 3 (permalink) Old 04-15-2016, 08:59 AM
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13.8V is standard industry output of an alternator, likewise the charge voltage of an AC/DC charger on normal charge.
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