I am wondering how Aptera will manage the 12V subsystem.
The lead-acid is heavy and is not reliable.
During the pandemic, I had to jump-start my Citroen C-zero (aka I-Miev) when I wanted to use it again.
On my Ioniq, no problem as the car is monitoring the lead-acid battery voltage and will recharge it from the traction battery if needed, and will tell you that when you start the car the next time.
If the Aptera use a lead-acid battery, I hope that it will do like the Ioniq.
A better option would be a 12V LFP battery or even better a DC/DC converter and remove the accessory battery to save weight and increase reliability.
Of course the DC/DC will use a little bit of energy, and anyway there will be one to charge the 12V battery from the traction battery. For efficiency while the car sleeps, a second low power DC/DC converter would be nice, and a special place we can open from the outside. There, a key could be use to switch off the DC/DC converter to put the car in storage mode if needed. When in storage mode, we could then also plug some jump-start cable if needed (like if the car traction battery is at 0%, and then won't allow a charge as the car could not communicate anymore with the charger).
Exactly*: The sweet spot that's been working great for me so far is the way smaller gel motorcycle battery shown hand-held in blue above. It only needs to power the door locks, then run the alarm system (until I unlock it), then activate the traction battery's contactors. That connects the DC-DC converter which starts & runs everything else in the 12V system.
* It doesn't seem to catch surge loads. I downsized mine by 95% from 60Ah to only 3Ah & there were no issues at all. There's likely plenty of surge capacity in the 24kWh traction battery. Also, the DC-DC converter has to be able to handle blasting everything, or else the 12V will go dead if you do that. You could probably downsize the converter to handle everything except very momentary loads like windows & locks, & even a tiny 12V like mine should handle such short loads.
Isn't the 12V battery in a BEV mostly there to get things started and catch surge loads? Starting up 100-200W worth of onboard controllers and such is easy to do through a DC-DC inverter off the traction battery, but if you're blasting tunes and running the fan and high beams and roll down both windows all at the same time... that DC-DC inverter has to be way more robust than if there's a battery backing it up. Can be a way smaller gel cell since there's no starter to crank, but the sweet spot for weight/$$$/performance feels like a motorcycle battery.
@zajethesage Yes, thanks. More air for the inverter below the charger too.
However they're both liquid-cooled, with no problems I've heard of. So I prefer to think of it as less heating of the 12V battery, which can die in as little as 22 months due to the heat from the adjacent charger & inverter.
I try to always charge the car in cooler times/places & leave the hood open when doing so. I also added some stryofoam insulation, & my original 12V battery was still going strong even after I'd owned the car for 5 years:
@OceanDragon I seem to have failed quite spectacularly at making my point clear about the choices I listed for my own BEV:
1) $130 for 40Lb name-brand replacement 12V battery with OEM 60Ah & 630CCA
2) $130 for 1.3Lb name-brand Li-ion 12V with 3.3Ah & 130CCA
3) $25 for 3Lb name-brand lead-acid 12V with 3Ah & 50CCA
#2 & #3 are NOT an option "with any car battery", since they will not even function in a gas car. Yes, one can downsize a BIT, but nowhere near this much. This amount of downsizing means there's no extra cost to go with Li-ion, but it also means that even without Li-ion there's nearly as much weight saved even for LESS cost.
Hey Kite, I think that philosophy can be taken with any car battery. Does one put in a name brand battery of same cold cranking amp capacity? Or does one put in a smaller, Asian manufactured battery of less cold cranking capacity or warranty term? That is a pretty flexible option with car owners, much like tires and windshield wiper blades. The manufacturers batteries in both my Lexus and Mercedes CL coupe were both 84 month warranty period batteries, but I had options to find batteries at a quarter of the price. You get what you pay for.
@OceanDragon For a BEV, it doesn't need to cost more money to save weight:
- My BEV works fine with a $25 lead-acid 12V that only weighs 3 pounds (OEM is 40Lbs).
- It would also work fine on a 1.3Lb Li-ion 12V that costs $130, the same cost as an OEM replacement ($110-$145 depending on brand)
LiFePo4 battery sounds like a good option for now. If it can charge via solar panel. Then should last a very long time. Maybe once it reaching min voltage it switches to traction pack.
Good question Raj. A smaller battery is required on an EV to allow entry functions into the vehicle as well as to switch on the traction battery system. Certainly a SLA can eventually be replaced with a lighter Li Iron Phosphate battery like on other motorcycles. But like many things it will cost more money. The traction battery as well as the DC-DC converter should not be left on while the car is not being used for safety and security reasons. I am hoping the company will progress with their current design plans and get a functioning production model out by 2022. We can always find things to make the EV heavier, more expensive, or delay the production date.
I hope at some point Aptera can figure out a way to get rid of the silly 12V battery & just step down the voltage to 12 volts for the cars accessories from the traction battery. Confused on why no ev company has done this yet.
Don't get me wrong, I am TOTALLY on-board with cutting weight & cost. I cut my own BEV's starter battery weight by 89% & cut cost by 52%, with just 1930s gel lead-acid tech:
I just couldn't justify spending $100 more to save only 3 more pounds with 1990s Li-ion tech from Antigravity.
In order to avoid draining the drive battery, my BEV doesn't ever charge the 12V when parked unplugged. But it charges it from the moment I turn the key on, until I turn it off, AND from the moment I plug the car in, until charging stops (when done or unplugged).
All that charging is good for lead-acid chemistry but bad for Li-ion, which is another reason I chose lead-acid. Very low starting current & very low depth of discharge are also more gentle than a gas car, so...:
The reason starter batteries die fast in my BEV is heat from the onboard charger, which was poorly-placed right beside it (left, in pic below). The charger gets pretty warm when driving, since it shares coolant with the motor & inverter, AND it gets even warmer with L1 charging, which takes over TEN TIMES as long as driving (if I average 50mph). L2 is "only" TWICE as long as driving, but with an even hotter charger. So the poor 12V battery is getting overheated to a lower temperature than a gas car, but for MUCH longer. All that heat is also far from ideal for a Li-ion starter battery.
Many other users have had theirs die in as little as 22 months, but mine lasted over 5 years because I added insulation, & always try to charge at cooler times/places & leave the hood open when practical.
Aptera's own solar cells could likely be tasked with trickle-charging the 12V starter battery, but that's only an issue when parked unplugged, & it won't help at night or in a garage or underground parking, or shade or snow...
Tesla finally moved to a lithium 12V battery in the Plaid, that's the right interim solution. In the long term the low voltage system should be 48V not 12V but that requires changes in all of the subsystems, a company like Aptera which is buying all of those components from outsiders can't move to 48V until the industry does but they can use a Lithium 12V battery rather than a lead acid one. The lead acid 12V batteries have been a common problem, the ID.3 and the MachE both have had dead battery issues in new cars. In Tesla's early battery death, two or three years, is common, supposedly there was a software fix for this but only time will tell. It's counter intuitive, when I read about the Model 3 battery issues, hasn't happened to me yet, my reaction was how come the battery in my Chrysler, that had to crank over a big V8 engine, lasted 8 years before it needed replacement but the battery in an EV, which cranks nothing, only lasts two. However the way the 12V battery works in an EV is different than in an ICEV and lead acid batteries aren't well suited to it. 12V lithium batteries are off the shelf and can be dropped in place of a 12V lead acid. The down side of lithium batteries is that they are more expensive and Aptera is focused on keeping the costs down. The appeal of the Aptera for me is the range, price is secondary up to a point, I'd certainly be willing to pay for a $200 lithium battery option if it meant that I'd have a low voltage battery that lasted the life of the car rather than one that needed replacement on a regular basis.
In the world of EV's, every gram counts. You can still have a 12v system that is lightweight and robust without using a heavy dinosaur lead acid battery. The fact that this will have it's own trickle charger on the exterior, I would opt for a LiFePo option. You don't need 600 CCA, you just need a design that will run the electrical functions.
Every BEV I know of uses a pretty reliable 12V battery in order to completely isolate the HV drive battery from any non-internal discharge while parked unplugged. The 12V is used to reconnect the HV by powering up its contactor relay (electromagnetically-activated switch).
My own ancient 2013 BEV came with a $150 40Lb 60Ah 12V. In order to save the HV battery from discharge, it charges "only" when the car is charging or the key is on.
When it was near its end of life, I replaced it with a 1/10-size $35 4.4Lb 6Ah 12V & it has been fine for over 6 months & counting, so long I drive it at least once a week OR plug it in OR turn it on.
The very lightest option is a $130 1.3Lb Li-ion.
In other words, eliminating the 12V entirely would only save a minimum of 1.3Lb & a maximum of 4.4Lb.
I wasn’t aware there were any EVs that didn’t charge their 12 volt subsystems battery from the traction battery at need. Anyway, it is only likely to be a matter of a handful of pounds traded for all of the convenience of the standardized 12 volt subsystems.
And if the traction battery power becomes unavailable, you can still power up the control systems with the 12 volt to tell you what is wrong.
Get the car and then buy a drop-in replacement (undoubtably more expensive) Li battery, if you feel the need.
A potential idea for the next iteration of Aptera. I want Aptera to stay with current, proven design for the first production vehicles. The discussed approach adds complexity when simplicity of design and manufacturing is needed. No time for extra engineering trade offs at this point in the schedule. Aptera is already the MOST efficient. We have had lead acid batteries for decades and have learned to deal with their vagaries. I am 77 and never had a catastrophic failure/issue with a led acid batter. Just be watchful, pay attention to battery maintenance guidelines.