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Discussion Starter · #1 ·
Please can anyone say exactly when the 12V battery is 'supposed to be charged'?

I have just had an issue with low battery volts at the moment of failing to start the petrol engine while driving in hybrid mode, and locking out the petrol motor until the next system re-start (after a system sleep as much as 1 hour after turn off and lockup.

My 12V battery only showed about 12.4V, and at that time was not charged by the petrol engine running.

Much later it all seemed logical and plugged into the mains charger resulted in a level of charge at 12V, subsequently (after 1 hour plus) running the engine in 'Charge battery' or 'Cross country mode' produced charging as might be expected.

I am suspicious there is a bug that disabled charging for a time ... anybody seen a similar problem? There are so mny loads on the 12V a good 12A when unlocked, opened and turned 'on' in hybrid mode, this falls away after many minutes....

David Osborne
 

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A charged lead acid battery should read 12.8 volts, by the time it is at 12v it will only have about 40% charge and any further discharge will damage the battery, other battery types will be different, as your is the hybrid version, i am not familiar with the battery technology used, but if its not holding charge, then either the charging system has an issue or the battery does.
 

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Discussion Starter · #3 ·
QUOTE (grendel1960 @ Sep 10 2020, 05:04 PM) <{POST_SNAPBACK}>A charged lead acid battery should read 12.8 volts, by the time it is at 12v it will only have about 40% charge and any further discharge will damage the battery, other battery types will be different, as your is the hybrid version, i am not familiar with the battery technology used, but if its not holding charge, then either the charging system has an issue or the battery does.

Agreed...
As far as I can tell the PHEV has a crankshaft motor/generator on the petrol engine which operates on the 300V ish hybrid battery. This battery is charged when you plug the car into the AC power or operate a manual control that makes the petrol engine run. The electric traction is quite separate from the IC engine and works the back axle, while the IC engine works only front.

The large (95Ah) 12V battery probably does everything that the non hybrid version does .. computers, box, heaters, lights etc but does not directly start the engine. There are draws of 10 to 20A without lights and heaters. I am guessing that the electric powered Aircon for cabin (and hybrid battery?) runs off the 300V battery due to the necessary high power level.

There is an inverter responsible for controlling the 12V charge levels from the 300V battery. It can operate when plugged into the AC power, and when turned on in any engine mode.
Mine (almost new) decided not to charge at a vital time leading to a 'temporary transmission error' apparently (according to garage) caused by a drop in 12V voltage detected as I tried to accelerate from battery only to combined mode. This error was latched until the computers went to sleep so as to reboot (takes 45-60 minutes off and locked). It had the effect of preventing petrol engine start. It seems at this point the inverter had 'forgotten' that it needed to charge the 12V.

So I am now monitoring charge status by voltage to discover if this issue manifests again. This morning the battery just got to 14.01 after trying the various modes and then switching 'off' which has various multi minute timeouts, and in this case continued charging allowing this typical end of charge level before I exited.

On a previous day after an 8 mile battery trip I was surprised to find 12.36V, with the load in the region of 5 to 10A which suggests a rather low charge state, and none of the usual methods would induce any charging. After a couple of hours it was plugged into the AC mains charger and this time started charge, initially at at least 10A over the loads, this seemed 'correct' and I supposed the car had slept, been rebooted and corrected the dubious flag that had prevented charging when most needed.

I have asked my dealer to investigate the possibility of a software bug, meantime I will monitor regularly.

David Osborne
 

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not a great result, but it sounds like you at least know what is happening, id does sound like a software glitch though, rather than a hardware failure, its the software not switching the hardware on correctly., good luck with this and hope you resolve this sooner than later.
 

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Discussion Starter · #5 ·
QUOTE (grendel1960 @ Sep 11 2020, 11:49 AM) <{POST_SNAPBACK}>not a great result, but it sounds like you at least know what is happening, id does sound like a software glitch though, rather than a hardware failure, its the software not switching the hardware on correctly., good luck with this and hope you resolve this sooner than later.
Yea! Finally studied the issue and have a 'resolution'...
I observed that when driving the 12V battery charging is continuous (maintains about 13.7V) as it is when the car is shut down, however when the hybrid battery drops to about 55% this 12V charging ceases, apparently to optimise range. Happily it is restored after shut down, so you normally start off with a full 12V battery (over 14V).
It seems a curious algorithm, but acceptable.
This is now working consistently following a software update. I think before it did not restart 12V charge on shutdown reliably.
Now I am very hopeful that it will no longer 'forget' the 12V unit.
Volvo was very obtuse refusing to explain the planned algorithm at all, pointing me at my dealer expert, who turned out to be expert but not to have access to that sort of detail.
Now to try to enjoy a good drive!
David.
 
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