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spiderlane
Member Since: 17 May 2017
Location: London
Posts: 97
 
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| Alternator/Battery Charging Voltage - Advice Please |
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Hi All,
My car (2010 D4) recently threw up a "Charging System Fault" whilst driving. Checking the voltage it was showing about 11.7 whilst driving along. Suspecting an alternator fault I had the car recovered home.
The fault code was shown as "P065A-00(2F) Generator system performance" on the IID which made sense. If I cleared it, it would return immediately.
So I replaced the alternator this week with a Denso DAN1105. The car started up immediately after this and the error message was gone and I measured 14.8V across the battery, so that was all good.
The next day I ran the car for 30/40 minutes or so to top up and bleed the coolant and the voltage was hovering around 14.7-14.8 the whole time.
Fast forward to yesterday and I replaced the undertrays/wheel and took it out for a drive around the block. To my surprise the voltage was showing about 12.1 - 12.2V. I did notice it jump up to over 13V a couple of times when braking.
I am aware of the BMS which does the "intelligent charging" and that it charges during braking as a sort of re-gen system but I'm surprised that the voltage is so low overall.
Everything is working correctly (heated seats/windscreens/reverse camera etc) and the IID shows no faults whatsoever. The battery had been on a CTEK conditioner for a few days (charging through the towing electrics so the BMS should be aware of the battery SoC). The battery appears very healthy - its a Varta H3 from 2019. I didn't reset the BMS.
So my question is, is the alternator working correctly? As it stands I have no problems and the car is performing exactly as expected and TBH I've never monitored the voltage during normal operation previously, but I'm very surprised to see the voltage around 12.1V all the time.
I am due to take it on a long journey over Christmas so I want to be confident there isn't a problem lurking there waiting to catch me out. (Especially given the fact that the RAC took over 24 hours to get me home and another 24 hours to get the car back)
I'd appreciate any advice.
Cheers
Mark
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 12th Dec 2021 11:55 am |
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spiderlane
Member Since: 17 May 2017
Location: London
Posts: 97
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Just a little update in case anyone stumbles across this in the future.
So I ran the car for an hour with every single electrical load on I could think of (full beam, all 4 heated seats, blowers on full, heated screens etc) and it worked flawlessly with the voltage still around 12.1/12.2V. After I turned the car off the battery voltage settled at a nice 12.6V.
Moved the car briefly around the drive a couple of times and voltage was showing over 14V both times.
So I guess it's all working as designed and it's just the BMS managing the alternator output according to its algorithms and the prevalent data.
Cheers
Mark
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| 15th Dec 2021 5:42 pm |
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eightfoot
Member Since: 12 Apr 2015
Location: sunny essex
Posts: 762
  
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regenerative charging system  thats how it works when all is good  please excuse any grammer/punctuation mistakes,i'm thick,thankyou
current vehicles 2005 d3 2013 d4
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| 15th Dec 2021 7:03 pm |
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Sidewaysste
Member Since: 10 Oct 2021
Location: Pinxton Nottinghamshire
Posts: 23
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Your D4 doesn't have regenerative charging, but as you correctly surmised, it does have smart charging. Unlike an old "dumb" charging system, a battery voltage of around 13v doesn't necessarily indicate a fault on a smart charge equipped vehicle.
Yes it's working as designed. Carry on and enjoy your xmas.
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| 17th Dec 2021 10:33 am |
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DaveJLBI
Member Since: 07 Mar 2014
Location: Clare
Posts: 662
 
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Sorry to dig up an old thread, perhaps someone might be able to give some advice.
A few times recently (in the hot weather) my infotainment system has shut down while driving and then rebooting. Has happened a few times.
I have also noticed that my cig lighter voltage reader (I know not accurate) has dropped from its normal reading of 14.5 / 14.7 to 13.5 / 13.7 when all things are settled and I am driving.
Could these two issues be a sign of a poorly alternator?
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| 7th Jun 2023 10:47 pm |
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Madrilleno
Member Since: 13 Oct 2014
Location: Nottingham
Posts: 1743
 
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It’s possible that one ‘phase’ of the alternator has failed. You need to check the state of charge on the battery itself, and whether the voltage output by the alternator is ‘noisy’. A voltmeter will only tell you the average voltage, an oscilloscope will tell you if it’s noisy. There was a discussion on here about it, I think Robbie wrote some of it, but I can’t find it. There are two rules for success,
1. Never tell everything you know.
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| 8th Jun 2023 6:11 am |
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