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#1
12-18-2003, 05:30 PM
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Battery Voltage
Does any one know what is an acceptable voltage range (min and max) that I should be reading from my apperently fully charged car battery after its been sitting for a few hours. [Engine off, and no accessories running].
Thanks Phil 
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#2
12-18-2003, 05:45 PM
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Sitting after a while it should be around 12.5 to 12.8 Volts I believe
Charging is 13.8 to 14.5 plus or minus Dieseldiehard
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#3
12-18-2003, 08:24 PM
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I get 12.6 with nothing on. 13.9 charging, and under load at idle I get 13.00. Is that 13.00 enough at idle? Volts go up as rpm's go up but I'm just making sure.
Last edited by Steve 300D; 12-18-2003 at 08:57 PM.
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#4
12-18-2003, 08:55 PM
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Steve,
That's about the same readings I get on my 85 300D. I did put in a different voltage regulator, not bosh, and at idle, nothing on, I get 14.2 volts. Read somewhere that european altenators were set a little lower than the US ones. Edit: I ment 14.2 revved up with nothing on, 13.2 at idle. Last edited by russb; 12-18-2003 at 09:10 PM.
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#5
12-19-2003, 12:58 AM
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12.67 rested or higher is fully charged. When applying a charge the system should hit 14 plus but never over 14.8. This is boiling time.
As long as the system is putting more juice in than taking out it is okay but a good thing to remember is that with that low of voltage your amperage at idle is also very low. Add a blower motor, wipers and headlights and the system is very likely discharging at idle. Add to that the fact that you just ran a full cycle on the glow plugs and short stop and go traffic in town could feasibly run your battery down too low to start the car... I had a '73 Dodge and it had the worst charging system in the world. The voltmeter woudl drop to like 11 volts at idle. You can test your charger by watching the voltage it is putting to the battery until it peaks. That is full charge as long as it is above 14 volts. Let the battery set for about 4 hours or apply a 20 amp discharge for 20 seconds to take off surface charge then check the battery. that is yoru battery t full charge. they all vary slightly. Gives you a pretty good basline at the current temp. Lastly, voltage varies with temperature. Colder equals lower voltage. Sorry to be so verbose. I own an RV and knowing your batteries in the winter are everything!
__________________
'99 S420 - Mommies '72 280SE 4.5 - looking to breathe life into it '84 300SD Grey - Sold '85 300SD Silver - Sold '78 Ski Nautique
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#6
12-19-2003, 01:51 AM
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My battery tested over 1400cca. It has been 12.9V at idle and 13.12v at 3000rpm. I have never had any problems at all with it, even at 19*f outside. I just ordered a non-bosch voltage regulator and I'll have the output tested again.
Is 12.9/13.1v too low? All I use for electric is the glowplugs, starter, radio, and main+acc electric radiator fans.
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#7
12-19-2003, 09:51 AM
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In theory if your charging system is a higher voltage (in other words after you start the car the voltage goes up) you are fine.
The numbers above are specific to deep cycle batteries. Frankly the numbers you show seem a little low to me but I have not checked my 300 for voltage output. If I get a chance I'll put the tester on it.
__________________
'99 S420 - Mommies '72 280SE 4.5 - looking to breathe life into it '84 300SD Grey - Sold '85 300SD Silver - Sold '78 Ski Nautique
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