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Voltage drop

Old 11-28-2009, 11:02 AM
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Hello,

What is normal voltage drop for the battery over night (approx 12 hours)?
Mine went from 12.3 volts and dropped to about 11.9. to me this does not sound as too much, or? Anyone know?`

Reason why I am testing is to find out if the IBS is faulty. Have disconnected it for this night and will see tomorrow morning what the voltage drop is without IBS.

But from 12.3 to 11.9 is that a lot, or?

Best regards,
jan
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Old 11-28-2009, 05:47 PM
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That's not alot, but I think you should be starting at around 14v.
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Old 11-28-2009, 07:19 PM
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I don't think it is an overt reason for concern yet, but I would keep an eye on it. The battery may have a bad cell. If the battery is getting old or does not get completely charged, it may be on its way out. If it continues to degrade....
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Old 11-29-2009, 12:34 AM
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Originally Posted by Guzzler550' post='1064298' date='Nov 29 2009, 05:19 AM
I don't think it is an overt reason for concern yet, but I would keep an eye on it. The battery may have a bad cell. If the battery is getting old or does not get completely charged, it may be on its way out. If it continues to degrade....
Many thanks for your replies.

Yestereday during all day I drove something like a total of 90-100 km. When I measured the voltage at night before disconnetctig the IBS I got 12.3 volts again. I was expecting some higher voltage after all that driving. And as Pennetta mentiones I should be starting around 14?

So this might indicate a bad battery? Good to know. It is 5 years old now so...
As I measured the voltage this morning after having the IBS disconnected the voltage drop was exactly the same. So I think I might rule out the IBS beeing faulty.
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Old 11-30-2009, 12:18 AM
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Jan,

From the 'secret' menu, before starting the car, my voltage flickers between 12.5v and 12.6v, after starting the engine its rises quickly and flickers between 14.7v and 14.8v and after a long run flickers between 14.4v and 14.8v. As its a 12v battery I would expect 12.5v to be 'normal' and the higher voltage while running to be as a result of the alternator doing it's job.

regards
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Old 11-30-2009, 10:21 AM
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Originally Posted by pennetta' post='1064279' date='Nov 28 2009, 06:47 PM
That's not alot, but I think you should be starting at around 14v.
No. You should be _running_ at 14v [when the engine is turning the alternator]. Normally the battery should be 12.

11.5 volts is the ABSOLUTE minimum voltage the battery should ever reach. If it goes below the 11.5 volt SOC then damage occurs to the lead plates.
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Old 11-30-2009, 10:30 AM
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Originally Posted by or_550i' post='1065065' date='Nov 30 2009, 02:21 PM
No. You should be _running_ at 14v [when the engine is turning the alternator]. Normally the battery should be 12.

11.5 volts is the ABSOLUTE minimum voltage the battery should ever reach. If it goes below the 11.5 volt SOC then damage occurs to the lead plates.
When I said "starting" I didn't actually mean "cranking", I meant with the engine running. My radar detector has a voltage mode and its actually all over the map. When I had my SMG, on shifts the voltage would drop 1/2 volt and then come back, this happened during cold weather.
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Old 11-30-2009, 10:37 AM
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Originally Posted by pennetta' post='1065076' date='Nov 30 2009, 11:30 AM
When I said "starting" I didn't actually mean "cranking", I meant with the engine running. My radar detector has a voltage mode and its actually all over the map. When I had my SMG, on shifts the voltage would drop 1/2 volt and then come back, this happened during cold weather.
Ok. Good!

You can resolve temporary drops using 1uF caps. I if you don't want to pony up for a large unit, you can build an array of small 1uF caps. Works great for audio systems... ;)
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