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D2 - Interior Electrics Airbags, Sensors, climate modules, instrument clusters, switches etc |
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Thread Tools | Display Modes |
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#1
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Battery voltage mystery
Today I decided to check my battery voltage (or alternator voltage) with engine running.
I have a new multi-meter which I assume is accurate. It agrees with my old cheaper Maplins multi-meter. According to the new multi-meter my battery voltage at terminals is a healthy 14.1V But checking via VCDS shows battery voltage to be 13.86V a bit low. Which voltage should I trust? What is VCDS actually measuring, voltage at battery terminals or at some other location? |
#2
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I'd trust your multimeter. VCDS doesn't measure voltage on battery poles.
P.S. You can also check voltage without VCDS. Press and hold the recirculation button. Then press the manual flow control up arrow on left hand side of the vehicle. HVAC will go into 'engineering mode'. Select channel 36 with + and - buttons. HVAC will display voltage. To exit this mode press Auto.
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I'd rather drive on left Last edited by notorious; 2nd November 2013 at 06:13 PM. |
#3
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Thanks Sergey, very cool hidden function I will have to try that.
I'm going to trust my multi meter, in this case it looks like all systems go for the lithium-iron battery. It arrived last week, shockingly light and small for a 59Ah battery. I just need to confirm sleep mode current consumption. Or maybe I should keep it safe in the house until spring, and let the lead acid battery suffer the winter temperatures |
#4
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On VCDS each module will show power supply voltage that it gets. So ECU can show one voltage, HVAC slightly different, ABS different ect.
It's all down to losses in wires, connections, fuses.
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Currently 8less 2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D 8 history: 2006 A8 Sport 4.2TDI quattro SOLD, 1997 S8, reached end of life with gearbox failure |
#5
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Goran
Tell us more about the new battery? Dave
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2002 S8 silver with black half leather 2000 d2 S8 in Racing green pearl, RS4 manual gearbox, 2003 A4 avant TDi 1997 Volvo V40 2.0T 1992 Mazda eunos v spec 1976 Reliant Kitten 1965 Porsche 911 |
#6
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Thanks, so the VCDS is not voltage at battery terminals.
Here is more info about the lithium battery. Its put together by a company called Voltphreaks, and used in motorsport. Also a few people on the M5board have been using them for a few years. Nominal voltage is 13.3V, fully charge it should be 14.4V, it is made up of 4 cells in series, 3.6V max each. Weight is 4.9kg for the 59Ah version. Supposedly it will reduce the charging load on the alternator because it holds higher voltage than a Lead Acid battery (12.2V 50% discharged), so in theory it will release a miniscule amount of horsepower. The other main advantage appart from weight is that it has a low-voltage cut off, preserving enough charge to start the car when you come back to it even if you left the headlights on, etc. Also it has a built in on-off button. Apparently it should last 5-10 years, although to be honest my original Audi Lead Acid 95Ah battery in my previous S8 lasted 7 years before it no longer held a charge. I managed to get the 59Ah model they just discontinued at a discount, "only" £880 shipped. I guess you have to be really serious about performance to spend this kind of money. Probably not worth it and not noticable, but now I started this weight loss madness I feel I have to see it through to the end http://www.voltphreaks.com/technology.php |
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