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Discussion Starter · #1 · (Edited)
Hi all,

Following the recent issues with the psycho fans and my 12V battery dying, it did get me wondering about the 12V battery and whether this might be the Polestar's achilles heel. My car had had the most recent software update and yet the car was still not able to manage it's charge even with a charged battery.

I'll put my hands up right now and admit I don't know how the 12V and HV systems are related or even if they are connected.

I've read all the other threads relating to the 12V issue and I suppose my questions could be summarised as follows:

1) Is the 12V battery topped up when the vehicle is charged? I'm guessing it must have some sort of split charge relay system. Does it?
2) It must charge when the vehicle is being driven. How? via regen or some other means?
3) How far would you have to drive for it to top it up? I'm concerned that with all the latest lockdowns my mileage might not be sufficient to keep it charged.

I might be being overly cautious and there is nothing to worry about, but my recent experience of losing 12V altogether meant the car was undriveable even when the vehicle battery was 85% charged.

Do I need to worry?
 

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The two systems are completely separated in the car; the HV system is completely turned off and disconnected when not in use, with the 12V system controlling all the electronics such as locks, displays, key fob management, seat heaters, aircon, everything. The HV system is only used for two things - driving the motors and feeding into the 12V system to help run things while topping up the battery at the same time. This topping up occurs steadily whenever the HV system is turned on, in other words whenever you're sitting in the car, but also from time to time in the background when the car's turned off. Basically the 12V system monitors its own voltage and when it detects it's drifted a bit low, due to background drains such as waiting for a key fob press or toe-poke under the boot, it enables the HV system for a few minutes and tops the 12V system up.

There are three reasons the 12V battery can go flat in an EV - the top-up checks not happening often enough or for long enough (the Kona/e-Niro/Soul had this problem until an update 6 months ago); or something causing such high drain on the 12V battery that even with taking a feed from the HV supply it's still not enough to prevent it running down; or thirdly if the system decides it's not safe to turn on the HV system and then it sits there and just runs flat. If you have option 3 and also a high drain such as fans, it will flatten the 12V battery within 10-20 minutes.

So basically when everything's fine and dandy, there's no need to worry as it will look after itself. It's only really when you have a fault in the system that prevents it from enabling the HV connection (or something breaks in the top-up circuitry) that the battery might run flat. It's normally the result of a major failure elsewhere, but of course when it does start getting low, it causes all the other electronics to go mad as they keep resetting due to detecting the voltage being a bit low which is why you hear tales of door mirrors repeatedly opening and closing and infotainment systems continually restarting.

Hope this helps!
 

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Hi all,

Following the recent issues with the psycho fans and my 12V battery dying, it did get me wondering about the 12V battery and whether this might be the Polestar's achilles heel. My car had had the most recent software update and yet the car was still not able to manage it's charge even with a charged battery.

I'll put my hands up right now and admit I don't know how the 12V and HV systems are related or even if they are connected.

I've read all the other threads relating to the 12V issue and I suppsoe my questions could be summarised as follows:

1) Is the 12V battery topped up when the vehicle is charged? I'm guessing it must have some sort of split charge relay system. Does it?
2) It must charge when the vehicle is being driven. How? via regen or some other means?
3) How far would you have to drive for it to top it up? I'm concerned that with all the latest lockdowns my mileage might not be sufficient to keep it charged.

I might be being overly cautious and there is nothing to worry about, but my recent experience of losing 12V altogether meant the car was undriveable even when the vehicle battery was 85% charged.

Do I need to worry?
Hi
Most of the problems with 12v batteries have been caused by cranky software running fans or other stuff much longer than needed. I did have a Propulsion system error after leaving the car on the drive for 7 days however after a few miles of driving it disappeared. It has never reappeared again.
Typically in EV's the 12v battery is charged via a DC to DC module. This steps down the power from the main battery and acts almost like an alternator. It will monitor the state of charge in the 12v and top up from the main battery as needed. I have a concern that EV manufacturers are using cheaper 12v batteries as they dont need the major torque load to start an engine. I have no proof whatsoever, its just a suspicion. Polestar are not the only EV maker to have major 12v battery problems. Even the mighty Tesla got it wrong in the past.
 

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Discussion Starter · #4 ·
Thanks both. That's really helpful.

If it manages the 12V battery itself I won't give it another thought.
 

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One follow up question: suppose my 12V battery is running low for some reason. Can I just put the car on life support system (read: my 11kW home charger) and hope it charges both the HV and 12V batteries? I would really like to avoid calling to tow the car due to bad accessibility to my parking spot.
 

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Discussion Starter · #6 ·
One follow up question: suppose my 12V battery is running low for some reason. Can I just put the car on life support system (read: my 11kW home charger) and hope it charges both the HV and 12V batteries? I would really like to avoid calling to tow the car due to bad accessibility to my parking spot.
I think what they're saying is that if your bum is on the seat (and the HV system is active) it'll manage the 12V battery and top it up if needed. Similarly if you are plugged in this will do the same thing.

By the time your car is delivered the HVCH issue should have been done and you shouldn't suffer the same ill effects that some of us did...

Fingers crossed anyway. 🤞
 

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If all the above is true (I have every confidence)why does the display flash up after 30 mins saying continue or turn off? This makes me anxious that continuing to listen or fiddle with the display will lead to a 12 v failure. Also can I then continue to use the HVAC without worry if stuck in a snow drift?
 

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Polestar 2, Midnight (blue), charcoal interior, non-PP
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It really shouldn't be a problem - at the Tenet showing at the Fully Charged drive-in cinema, the Polestars had their HVAC on for the full 2.5 hour film with no problem, as well as running the radio for the cinema sound.
 

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I’ll go along with that and Tesla Bjorn did camp out.. but why the on screen message to cause uncertainty. Any thoughts?

supplementary: is this a Volvo legacy for when people are using the UI and the engine is off?

and again: dashcam threads are going on about parking mode being limited by fall in 12v . The above suggests again this is not a concern and so park mode can be left running indefinitely. Discuss.
 

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Most likely a legacy thing. The Kona Electric and Zoe both whinge about the electrics being on after about 15 minutes saying "Electrics running without engine. Start engine to prevent 12V running down." or similar, even though neither has an engine!

The dashcam threads are because people aren't aware that the system looks after itself. In an ICE car where there's no automatic top-up, the parking mode dashcams have to have a threshold below which they turn off to prevent running the battery completely flat. Somewhere on here there's a picture showing the automatic top-up in action - I'll see if I can find it...
 

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Found the thread:

The pictures at the bottom show the 12V top-up in action in various scenarios.
 

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Found the thread:

The pictures at the bottom show the 12V top-up in action in various scenarios.
Thank you to Pistoncracked for the images on the above thread and good to know our super moderator asked the same question a couple of months ago! Hopefullly 12v will disappear from the forum lexicography and I can get over my anxiety.
 

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Let's hope so - compared to the early days where every other post was about 12V problems or (what we now know to be) inverter and HVCH problems, it's gone reassuringly quiet on that front other than the occasional botched/lazy recall job...
 

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The HV system is only used for two things - driving the motors and feeding into the 12V system to help run things while topping up the battery at the same time.
Not quite. The AC compressor and the coolant heater are directly powered from the HV.
 

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Ok, interesting! Do you have a schematic diagram somewhere? I'd be interested to see it.
 

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Yeah, it's all a bit frustrating. I've got ready access to all this stuff for BMW, but Volvo make it impossible for a private individual to register for their VIDA system. They ask for a VAT number (no problem) and a photo of the workshop (problem).

This is the best I found:-



Everything on that page is HV - you can see it's all directly or indirectly connected to the BECM.
  • (3) HVHA is the water heater
  • (2) ACCA is an inverter which drives the air conditioning compressor (1)
  • (16) OBC is the on board AC charger
  • (19) IFHA and DCDC are the front motor inverter and 12V battery charger and appear to be combined in one physical module
  • (20) EFAD is the front motor
  • (18) ERAD is the rear motor
  • (17) IEM is the rear motor inverter
  • (7) EVI is the charge socket
  • (12) BECM is the 'battery electronics control module' and has the main DC contactors / cell balancing etc.
 

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Thanks, that's very useful! (y)
 
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