High Charging Voltage Seems to have killed my Battery - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 12-19-2005, 06:02 PM Thread Starter
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High Charging Voltage Seems to have killed my Battery

My battery (not sure of the vintage) stopped holding a charge the other day. After charging it up and then testing it, I found it was really toast. 2 seconds after hitting the key switch, voltage would go to almost zero and the engine would barely turn. Yep, a real dead battery.

So I bought a new battery and hooked it up. On start, the voltage climbs to the high 14s as expected. But when the RPMs increase, so does the battery voltage. It goes up to almost 16v. Now this is a brand new battery and has a full charge already so it should not be taking such a high charge for so long after starting.

So my charging system is not working properly. The alternator is definitley putting out juice because the voltage raises after start. But the regulation system is not holding the voltage back to proper levels and seems to be the culprit.

Can someone guide me here? Is the voltage regulator the only culprit based on this condition? Or is there anything else to check out before I start spending money?

Scott
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post #2 of 6 (permalink) Old 12-19-2005, 06:10 PM
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RE: High Charging Voltage Seems to have killed my Battery

You need a new alternator with a built-in regulator.

Felicita e un bicchiere di vino con un panino.
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post #3 of 6 (permalink) Old 12-20-2005, 07:35 PM Thread Starter
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RE: High Charging Voltage Seems to have killed my Battery

OK, noted. But I am somewhat familiar with electronic things and this still seems odd. When a transistorized component fails or starts to go bad, the circuit usually shows low or no output. So is it still probable that a bad or going-bad alternator/VR would put out too MUCH voltage??
S
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post #4 of 6 (permalink) Old 12-21-2005, 05:24 AM
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RE: High Charging Voltage Seems to have killed my Battery

Quote:
Captain Scott - 12/20/2005 8:35 PM

Is it still probable that a bad or going-bad alternator/VR would put out too MUCH voltage??
Yes.

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post #5 of 6 (permalink) Old 12-21-2005, 12:20 PM
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RE: High Charging Voltage Seems to have killed my Battery

Voltage rectifier turns AC voltage output of alternator into DC. Voltage output is directly proportional to engine rpm. If it is putting out 12V at 1000rpm, it should output 24V at 2000rpm. In order to keep the voltage between 13V and 14V at all times, Voltage regulator is used.

Voltage regulator either
1. Grounds the excess voltage so that the system voltage never exceeds 14-15V OR
2. Adjusts the strength of electric magnets inside the alternator so that the output is less than 15V at all rpm's.

2. is more common in cars. 1. is how most motorcycle charging system works.

Overcharging is almost always failed Voltage regulator.
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post #6 of 6 (permalink) Old 01-09-2006, 03:53 PM Thread Starter
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RE: High Charging Voltage Seems to have killed my Battery

A new battery and a new alternator fixed me up.
She now cranks hard and starts smartly.

What's next?

Whatever; I'm ready for it...

[8D]
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