alex0264
Member Since: 16 Apr 2012
Location: Taunton
Posts: 136
  
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| Voltage variation - not consistent |
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I've noticed a few times that whilst driving the car, the voltage drops right down to 12.1 volts, but at times it is jumping up to 13.5, then 14.8, then back to 12, then back up again. I know the alternator is going to kick in every so often, but I find this very bizarre behaviour, and would expect a bit more consistency than this. If I rev the engine over 2000RPM I can get it to increase by .4 volts, but then it drops down again.
Today I had started and stopped the car several times in quick succession, and after this I was driving on the motorway and again it was staying between 12.1-12.5 and then every so often it would go up and down quickly. It drops to around 10.9 when starting, which I'm assuming is normal given the lump it has to turn over?
Battery is genuine LR - 850CCA, can't remember if they're 90 or 95Ah, and was replaced a Christmas - BMS was reset just after fitting. Please can someone confirm if this behaviour is normal, or is it possible that the alternator and/or something in the charging system is 'iffy'?
Cheers ------------------------------------------------------------------------------------
2016 - D4 HSE Luxury Scotia Grey - Pending...
2014 - D4 HSE Indus Silver - A total mystery
2011 - D4 HSE Stornoway Grey - Legendary car
2006 - D3 HSE Buckingham Blue - Moneypit v1
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 31st Mar 2024 4:54 pm |
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itsaguything
Member Since: 20 Dec 2023
Location: Manotick, On
Posts: 260
  
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Not bizarre at all. The modern AGM battery and generator system at work. Reduces the chance of overcharging, improves on efficiency, improves on battery lifespan on these new electrically aggressive machines. It it very well described in the workshop manual. 2015 LR4 HSE Lux Aintree Green
2013 LR2 HSE Radiance Red
2007 XKR Jaguar Racing Green
2005 XJR Jaguar Racing Green
2002 S-Type R British Racing Green
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| 31st Mar 2024 5:24 pm |
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alex0264
Member Since: 16 Apr 2012
Location: Taunton
Posts: 136
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Thank you, good to know it's nothing unusual. Yes, I certainly wouldn't want to be either the battery or the alternator. How they keep up with the demand I do not know. ------------------------------------------------------------------------------------
2016 - D4 HSE Luxury Scotia Grey - Pending...
2014 - D4 HSE Indus Silver - A total mystery
2011 - D4 HSE Stornoway Grey - Legendary car
2006 - D3 HSE Buckingham Blue - Moneypit v1
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| 31st Mar 2024 5:45 pm |
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itsaguything
Member Since: 20 Dec 2023
Location: Manotick, On
Posts: 260
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I concur…. I wonder if this is a step forwards or backwards…. my opinions change frequently. 2015 LR4 HSE Lux Aintree Green
2013 LR2 HSE Radiance Red
2007 XKR Jaguar Racing Green
2005 XJR Jaguar Racing Green
2002 S-Type R British Racing Green
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| 1st Apr 2024 1:23 am |
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Gareth
Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26775
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It’s the battery management system (BMS). My new Defender is the same. Generally the volts are high when the vehicle is coasting and drop a bit when accelerating.
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| 1st Apr 2024 12:21 pm |
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M3DPO
Member Since: 22 Sep 2010
Location: Notts.
Posts: 8230
 
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All D3/4 are designed do it, charge high when coasting low when pulling. It can when others can't,
It will when others won't,
It goes where others don't.
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| 2nd Apr 2024 2:31 pm |
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alex0264
Member Since: 16 Apr 2012
Location: Taunton
Posts: 136
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Thank you all - all very useful replies and a great insight into how the alternator / battery setup works on a D4 and others. I guess in reality if the battery wasn't charging I would know about it!
Cheers ------------------------------------------------------------------------------------
2016 - D4 HSE Luxury Scotia Grey - Pending...
2014 - D4 HSE Indus Silver - A total mystery
2011 - D4 HSE Stornoway Grey - Legendary car
2006 - D3 HSE Buckingham Blue - Moneypit v1
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| 4th Apr 2024 8:45 pm |
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