It's not thermally managed. You need it to provide current at very low temperatures and rather high ones - things Lithium isn't good at.
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It's not thermally managed. You need it to provide current at very low temperatures and rather high ones - things Lithium isn't good at.
An ICE battery generally is never discharged much. Ot keeps things working overnight, then one start event in the morning before being recharged by the alternator. Car electronics are specified to have very low power draw when the car is off, this prevents having a dead battery when you get back to airport after week long vacation.
S/X have higher standby current draw (always connected networking, key fob detection, use of full Linux HW). To maximize efficency, the car only charges the battery when it's fairly low and then likely does not top it off (charge rate drops at high end). Deep cycling in general wears out batteries more quickly and this cycling is going on whenever the car isn't running, wearing the battery out.
Most lithium batteries have the constraint that they can't be charged when the temperature is below freezing. So it would need its own thermal management system with addition power loss to heating.
Chickenlittle
Banned
In the case of mine it was a battery that was defective. First year model S had a supplier that sub contracted another supplier that provided subpar 12 volts. Since then I have had 4 Tesla’s over 5 years without another 12 volt battery issue
FlatSix911
Porsche 918 Hybrid
A good read ... Syonyk's Project Blog: Tesla Model S 12V Battery Analysis
Cars have to operate reliably over a huge range of temperatures, and lead acid is really good for providing basic power to a car. Also, every single car part out there in parts bins is designed to work on a 12V lead acid battery operating range. The Model S uses the 12V system to run pretty much everything. The computers run off the 12V system, the interior electronics (locks, windows, seats, etc) run off 12V, and the main contactor for the big battery underneath requires a functioning 12V system. If the 12V battery is dead, so is the car. There are jump start terminals (which, by the way, you shouldn't use to jump another car), but the Model S is entirely reliant on this 12V lead acid battery to function.
If you replaced this 12V battery with a lithium battery, you'd have to add heaters and the like to it - you simply cannot safely charge a lithium battery below about the freezing point of water. Of course, if you never let your car below about 40F, a LiFePO4 drop in replacement would probably work fine, assuming the computers didn't notice and complain.
RayK
Active Member
One could say that you haven't had a car long enough to encounter a problem with the 12V battery.
Correct. ICE cars usually have their battery last 5-8 years (regular or AGM).
Tesla has few design flaws that ruin 12V battery.
1) Tesla draws too much power while parked. Modern ICE cars have a 70-80mA limitations (quoting 7-series BMW, it will bring up an error message if more is drawn while vehicle in sleep). Tesla has excessive draw (many times more). That draw is nonsense and has no excuse. Some BMW's and Nissan Leaf are also constantly online. My phone is constantly on cellular and can handle that on 10Wh battery for days. 12V battery Tesla has 500Wh available (half can be used safely).
2) Tesla has incorrect charging algorithm for 12V battery. By the way, same story was with 2011-2012 Leaf's. They killed 12V battery as often as once per year. Algorithm was fixed later on and now premature failures are rare.
3) Tesla doesn't use precise stand-alone BMS module on negative battery pole (BMW does use since 2004). Module that keeps track of 12V battery charge state and CHANGES charging current accordingly. It also measures battery temperature and adjusts charging voltage accordingly. Nissan Leaf for example has only one value for temperature compensation - Above +3*C and charging voltage is 13.0V. Below that it's 14,5V. Plus every time vehicle activated voltage is at 14.5V until charging current drops to preset level of few amps. Which is slightly too simple but at least it works. BMW changes charging voltage from 13V up to 15.5V according to many parameters.
If any of those 3 would be solved, there would much less problems. In this term, I'm extremely disappointed. Bad job Tesla.
AFAIK, most li-ion batteries can be charged below freezing (water freezing). Nissan Leaf's LiMn2O4 with LiNiO2 chemistry can be charged down to at least -20*C. Though charging speed is reduced significantly. Tesla's chemistry is the most inappropriate for that. But 12V system can only use LiFePo Li-ion type. Which is not afraid of cold temperatures like LiMnO. So yea. It should be easily doable, but it is pointless in the long run. Should better solve 3 previously mentioned problems otherwise it will F up LiFePo as well.
Not true. Can't charge fast (relatively speaking).
Fun fact - Before intelligent lternators and AGM became available, 12V battery heating blankets were available. They did actually heat the battery so charging happened faster. It's history now.
The only thing that I am going to address about the post above is that I have two 2011 Nissan Leafs and the 12 volt lead acid batteries have no problems. I also have a lithium battery in my Tesla and it is much better than the lead acid that was in it.
FWIW, some generations of Audi A8 did have a spare battery. It is rare, though.
Only if one could deduce that they were owned serially with all ownership periods significantly less than the initial failure time.
navguy12
Active Member
All good stuff. The cherry on top would be roof mounted solar panels powering some/most/all of it.
Signed: a net producer of electricity......until I get my Model 3 of course......
Interesting, that would at a minimum require an extra level of charging protection (temp vs current) for a Li type over PbA to prevent Li plating. In the bad idea/ inefficient world, seems like they could also use a different chemistry with some alternator diodes to reduce output voltage (with any appreciable current).
1) I think Tesla current draw was a design decision due to use of full PC style HW vs low power sleep mode microcontrollers. Makes the devepment cycle a lot simplier/ faster if you can rely on the huge battery pack under the floor instead ifof creating a reliable low power instant boot version on Linux.
3) For a long time cars were fixed voltage alternator (and you had to top up the water), then sealed batteries reduced water loss, finally OEM started adjusted voltage to temp. With battery temp monitoring and voltage control heath is maintained. Culomb counting is useful for system health, but a little overkill for PbA (great on though). I think it was a reasonable reduction of complexity.
Edit: battery blankets, like block heaters, are still useful. Check out the options for automatic backup generators.
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navguy12
Active Member
Couldn't agree more.
They need to work that issue until it is correctly solved IF Tesla wants to sell millions of these cars to "Joe average".
navguy12
Active Member
Evoforce, could you provide some details such as make and model number, length of time it has been in service, lowest temperature it has been regularly exposed to, things like that please? Cheers.
None of those cars keep the cabin from going hot while parked. None of them run a battery TMS to keep the pack happy while parked (and Leafs experience massive degradation in hot climates as a result.) And none of them have anywhere close to the level of functionality by phone app (though I'm not sure why that would tie to more power drain when you aren't checking the app - it means a lot more data to pass when you do check, of course.)
The draw may be excessive, but there certainly are some excuses.
Long time ago I had A6 and it had second smaller battery in the trunk. That battery was solely to the Webasto fuel heater, so whenever it was running it couldn't drain the main battery. So in a sense it wasn't spare battery, although it had 2 batteries.
As someone with what seems to be a similar issue, I’m concerned that this happened while my car was on 2018.4.6
When cabin overheat protection is active, it draws power from HV pack (contactors engages). So 12V draw has nothing to do with that new feature that came lately.
Battery TMS is not cooling the pack when vehicle has been left alone. This includes Tesla. BMS is checking for battery temperature and might switch on heating if temperature is below specified limit (like -15*C). But there is no cooling. Cooling requires AC compressor. Which requires contactors.
App functionality has nothing to do with parasitic draw. Like you said. I do agree that when "wake" command has been sent to the vehicle, it will draw more power. Honking horn and flashing lights - hardly happens. Tesla has problems when vehicle is asleep.
So no. There are no excuses. Vehicle MUST, I emphasize, MUST consume less than 100mA when asleep.
BMW 7-series and Merc S-class have much much more tech than Model S fully loaded. And these vehicles consume 30-50mA.
They have keyless access, summon, preheat, alarm, app functionality etc.
It has the right to wake up for few seconds to do some tasks. For example if wake command is received from server (app).
Problem is that modules consume a lot of power all the time. @mongo might be right, Tesla might have chosen random components that consume a lot (relatively speaking).
Musk should read that. This is old school stuff for BMW.
http://freemaxx.de/e90forum/03_Power Management.pdf
Tesla has voltage adjustment. Should be easy to adjust according to chemistry specs. LiFePo is very safe, compared to other types.
Well, Leaf has that sensor. It's just a cheaper model with no internal memory (IBS sensors on BMW's have their own logging function so nothing else must be energized for logging to happen). Tesla also measures current somehow.
If I could give a hand, I would:
a) de-energize all modules except 1) alarm 2) telematics (Bluetooth/NFC/cellular). These two modules should fit into 30-40mA. Let's make it 50mA. Have a direct bus-line for wake command between HV battery BMS and 12V battery IBS.
b) Keep lead acid battery as it is today. Keep SOC between 60-80% when parked (smart sensor required, Intelligent Battery Sensor | HELLA ) That is 20%. Out of 45Ah. 9000mAh. Good for 9000/45=200h=8 days.
Wake up every 7 days no matter what to trickle charge 12V battery. Otherwise wait for 60% SOC. Stop wakeup if HV battery <30%.
If HV battery above 80%, wake up daily. If 12V battery above 80%, allow shallow sleep (keep MCU on standby). This happens same day after charging/driving.
If 12V battery <60%, deenergize telematics module. Have direct link between alarm module and door handles. (my BMW wakes up if door handle is pulled). Send report to Tesla server and app owner.
PS:
I don't know how but latest BMW's have nominal sleep draw 7-21mA
. Can be found in that PDFSimilar threads
