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For clarity, I understand why they still have a 12v system, moving away from that to 400v lights, radio etc. would be stupid. Why retain the battery though, and not just have a transformer off the main battery?
A quick Google gives the reason they if the big battery goes flat, the critical electronics still function. There must be more that though, even if the main battery didn't have enough juice to power the traction motors, there would still be plenty residual to drive critical 12v stuff for hours.
You can't use a transformer as they only work on AC but your point is still valid because you could some sort of DC-DC converter. My best guess would be for redundancy, so that the car could itself cut the quite dangerous 400v power to all parts of the car in case of an accident or even just when not running while leaving the 12V still available to start itself up again. Don't actually know though
I think the traction battery is isolated when the car is not powered.
If the traction battery was flat the discharge of the electronics could over time deplete it to the point of damage.
I bet the charge management software runs on the 12v side. Useful in the case of both batteries being dead that you could swap the 12V one and then charge the traction battery.
For safety reasons, apparently.
We asked Hyundai's EV engineers why the 12-volt battery persists, and Ryan Miller, manager of electrified powertrain development, responded. "All the ECUs in the vehicle are powered from the low voltage, as well as the power relays that separate power from the high-voltage battery pack and the rest of the high-voltage network in the car," he said. "That separation allows us to safely disconnect the high voltage from the low voltage when the vehicle is not being driven or in the event of a crash." You don't want first responders to contend with door locks powered by Doc Brown's Mr. Fusion.
https://www.caranddriver.com/features/a38537243/electric-cars-12-volt-batteries/
So you don’t have to power up the high voltage systems just to run some of the low voltage stuff. In reality, an EV is never really “off”, there’s always something running on the 12v side of things, even if at very low current demand - alarms, remote locking, contact via the app etc.
Because your transformer would be taking current permanently even when the car is switched off just so it could be switched on again which would slowly flatten the main battery. The 12V battery provides a voltage to the on/off switch with no or negligible current flowing when the car is switched off.
It's not really anything to do with flattening the HV battery. Sure that would be a downside but it's sort of irrelevant compared to the safety aspect of having no way to isolate the HV side by ECU control (if they were reliant on HV as their power source via DCDC). Basically, what the Hyundai engineers said. If you really want to nerd out, look up iso26262 and assigning automotive safety integrity levels and how that drives the need for redundancy etc. It's just an added bonus that the car can sit unused for a month draining the 12V battery but as long as it can close the HV contactors it can then access a fully charged HV battery.
Are the 12v batteries still lead acid?
Most 12v batteries still old tech. Lithium ones are very expensive (usually fitted to track cars for weight saving).
They do mostly have a lead acid 12v battery. Here's a tip, don't let anyone jump start their car from it. A friend had to have the control electronics and traction battery replaced on an iPace after it was damaged by somebody doing this without asking...
Two main reasons:
1. Most existing electronics designed to work in cars (computers, windscreen wiper motors, electric windows, headlights etc etc) is designed to work on 12V. So you have a separate 12V system supported by a battery, which makes manufacturing easier and also allows you to maintain critical systems (hazard lights, antilock brakes, parking brake) for a short time if there's a fault in the traction battery.
2. The high voltage battery is isolated from the inverter and motors by a big contactor. In order to close this and connect the battery to the inverter and motors you need another power source, which in this case is the 12V battery. Disconnect the 12V battery and this contactor will open, isolating the high voltage battery from the car.
So when your electric van has a tantrum and parks itself (I believe there was a fault in the software that meant an erroneous sensor for the air con would disable the van) you can disconnect and reconnect the 12v battery briefly which allows the handbrake to be released and roll the van out of the middle of a car park, and then leave it disconnected for 20 minutes so the computer can sort itself out!
It's now had a software update so hopefully there will be no need to turn it off and back on again in the future!
Most 12v batteries still old tech. Lithium ones are very expensive (usually fitted to track cars for weight saving).
Peanuts compared to the cost of the 100 kWh Li-ion traction battery...
Thanks thols2 and rsl1, that makes sense.
And multi21, I'll warn my dad as he has an e-golf and a set of jump leads.
I like hearing the 'clunk' of the big battery being connected when I turn the LEAF on!
DrP
I'm sure this is a silly question but:<br />I assume the 12v battery is also recharged when the HV battery is recharged - if so, what happens if you leave the car for a month and the 12v battery slowly drains but allows the vehicle to be moved, is there a scenario where the HV battery is OK but the 12v battery dies?
Yes, used to happen to the pool car where I used to work. Went long periods of time not being used. The 400V system 2as left on a granny charger but they never gave any thought to the 12Vvsystem. On the rare occasion someone wanted to use it, it was going nowhere.
I couldn't move my fully charged LEaf because of a flat battery the other day. Needed to put the 12v on charge for an hour or so to power up the on/off switch to turn the car on. No different to a flat battery on a ICE car but it prevented my even rolling the car anywhere so had to run and extension lead out onto the road.
I wonder how the keyless entry would have coped if I had bothered to lock the little piece of shit?
if so, what happens if you leave the car for a month and the 12v battery slowly drains but allows the vehicle to be moved, is there a scenario where the HV battery is OK but the 12v battery dies?
That is exactly the scenario. Discharging the HV battery fully would wreck it, just as it does for the 12V battery - but that is only £80 to replace at Halfords rather than £4k.
It makes more sense for them to be AGM batteries, but for some reason (cost, I assume) Nissan decided to spec normal lead acid which can't deal with deep discharge.
There is some chat in the Facebook group of PHEV Kugas being crap with 12V batteries.
They are quietly replacing them with AGM batteries for a few people but I haven't been able to moan enough yet, but do carry a battery booster pack to get us out of trouble.
if so, what happens if you leave the car for a month and the 12v battery slowly drains but allows the vehicle to be moved, is there a scenario where the HV battery is OK but the 12v battery dies?
My ID3 has a setting called “Optimised Battery Use” which apparently keeps the 12v battery charged from the HV battery even when it’s not in use.
My ID3 has a setting called “Optimised Battery Use” which apparently keeps the 12v battery charged from the HV battery even when it’s not in use.
Oh yeah my Hyundai also had that.
if so, what happens if you leave the car for a month and the 12v battery slowly dies?
this is exactly what i saw James may whining about with his tesla. It wasn’t a month though. Was a fair while. 12v battery powers the locks and other low voltage stuff and always under low drain but when it dies there’s no way to get into the car. Needs the 12v battery charging. But the 12v battery is apparently only charged when the car is running so no way to charge it easily
end result was take loads of panels apart to get a cable in to charge the battery. And about 2 or 3 hours work i think. Absolutely stupid design!
the cybertruck doesn't have a 12V battery, they've moved everything to 48v (possibly the first to do it). Its still not the high-voltage main battery though
end result was take loads of panels apart to get a cable in to charge the battery. And about 2 or 3 hours work i think. Absolutely stupid design!
Looks no more complicated than I remember trying to get to the battery in some Audi SUV?
https://www.tesla.com/ownersmanual/model3/en_us/GUID-3567D5F4-A5F4-4323-8BE0-023D5438FFC6.html
The Model S had 12V cable access behind the tow hook if I remember correctly.
Looks no more complicated than I remember trying to get to the battery in some Audi SUV?
IIR its compunded by the fact you cant actually open anything to get at the panels. Namely the bonnet. Without taking the wheel arch apart
no 12v charging access as std
But the 12v battery is apparently only charged when the car is running so no way to charge it easily
That's no different from an ICE car though, the problem lies with poor maintainability, not the use of a 12v battery.
That’s no different from an ICE car though, the problem lies with poor maintainability, not the use of a 12v battery.
Yeah but there's no good reason not to charge it as the drive battery is charged. It makes no real sense as long as there is suitable segregation.
The 12v battery in my 2015 Zoe is a pain in the neck. I've owned the car 5 years and replaced it twice already.
It's a known issue apparently.
I love it when the dealers say "Its a known issue" as if that's the end of the matter.
"My battery dies every 18 months" "Yes sir, that's a known issue".
It is the new version of the 1970/80s Lancia dealers
"My car has rust on every panel after 18 months" "yes sir, they all do that"
I’ve got a certificate for passing a course on how to deal with EV’s regarding flat batteries and starting them.
That was three or four years ago now, and TBH while I’m perfectly happy jump-starting an ICE vehicle, I’ll have to think a bit before doing it to an EV - IIRC, it involves NOT TOUCHING THE ORANGE WIRES.
There are certain makes which, if the 12v battery goes flat, it will brick the car, probably throwing up an extensive error list on a diagnostic test which all have to be cleared, but sometimes that doesn’t work either. One in particular was a huge problem, and despite a few hours with a laptop and trying everything he could think of, our whizzy tech guy couldn’t get the thing to start, or get it out of drive. After a month or more cluttering up our arrivals area, Mercedes sent a flatbed truck and dragged it on with the wheels locked.
One reason I avoided buying a car with an electronic handbrake.
Most 12v batteries still old tech. Lithium ones are very expensive (usually fitted to track cars for weight saving).
Teslas have been fitted with Li-ion 12V batteries for some time now.
Well, late 2021 was when it started, at least that was for the M3. Im not sure if the later X and S have moved over.
Something wasn't quite right with our Kia Soul EV 12v battery - we had to have two replacement batteries in 3 years.
It seemed to run flat very easily.
£200 each time and you have to argue the toss as the warranty might not cover it. Luckily our lease agreement did anyway.