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Cold Start Voltage Drop
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02-16-2020, 10:12 AM | #1 |
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Cold Start Voltage Drop
I have an N52 E70 X5 but posting here since it gets more traffic.
I have had an issue for a while now, where the voltage drops significantly when I start the car. Based on the readout on my radar detector, sometimes it gets down to <11.2V. It seems to be worse if I turn on the accessories 1st, then actually start the engine. I can't say that it's gotten worse with the cold weather, but I'd like to get it fixed before it messes something up and I end up stranded somewhere. I've changed the battery in the last year, and I don't think it's the alternator since the voltage ramps up to >13.5V after a few moments of initial stumbling. It also doesn't seem to happen after the engine is already warm. Any ideas? Am I overthinking it? |
02-16-2020, 12:57 PM | #2 |
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When you replaced the battery did you get the proper size
and type. Did you reprogram the car for the new battery type and size? Try putting a full charge on the battery and see if the symptoms go away. Do you let the car sit or only drive it short distances? Not driving enough for the battery to charge. |
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02-16-2020, 02:51 PM | #3 |
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First, you don't have a problem, as 10 to 11 is the normal voltage drop when starting a car. Batteries have internal resistance, and when, say the starter draws 300 amps, a small amount of voltage is dropped across the battery itself.
Do some reading on Google before you start replacing stuff. |
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02-17-2020, 06:51 AM | #4 |
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For my E70, the voltage drop is much greater when measuring at the cigarette lighter. If you measure at the battery with a voltmeter, the voltage drop will be close to one volt higher.
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02-18-2020, 06:18 AM | #5 | ||
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Yes Over the summer I do, but now that it's winter I drive it every day to work. It has plenty of time to charge. Quote:
I have a mirrortap connected to my radar detector. I have the same style in my 440i and it doesn't register this much of a drop. But that car I've owned since new and I take care of it. I bought my E70 with 70k and I've been fixing all the little stuff, this is just one of the last things that's bothering me. |
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02-18-2020, 07:34 AM | #6 |
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You might be comparing apple to oranges.. Most likely you are running a AGM in the E70. These are deep cycle batteries and don't behave like standard batteries..
The AGM's has a much lower "safe" voltage compared to standard, you can easily take a AGM down to 7V without damaging the battery. The AGM prefers a slower charge than a standard. The full charge voltage on AGM is higher than standard also, 12.8V vs 12.6V respectively. The 440I might have a bigger battery or standard, not sure if they a still using AGM.. Anyways I have to agree that you have no issues. |
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02-18-2020, 09:19 AM | #7 | |
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02-18-2020, 05:02 PM | #8 |
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Both of my cars do the exact same thing, takes like 5-7 seconds then the alternator kicks in and start charging the battery like normal.
BTW I have a literally brand new Alternator from FCP Euro in 1 of the cars so it appears to be just normal operation. |
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02-19-2020, 06:42 AM | #9 |
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Thanks everybody.
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02-19-2020, 09:04 AM | #10 |
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Kern, what happens to battery voltage during starting has nothing to do with system voltage during normal running. Starting puts a short term very high load on you battery, and you see a short term drop in battery voltage. The alternator recharges the battery after starting. If you want to worry about something, worry about world peace.
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02-19-2020, 09:47 AM | #11 | |
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