Ran across this pic:
I've been racking my brain trying to figure out what purpose that little battery on the right could serve when the car already has a battery as big as a king-size mattress from which 12v power could easily be converted. Is it for flashing a "drive battery dead" light at you after you run down the drive battery perhaps? Giving you some added survival time at a high cost if you run your battery down in an arctic storm? 
12V Accessory systems are still normal in cars and that voltage requires high amperage to run certain components. High amp DC converters are expensive. A reasonably sized converter (still pretty powerful) and a 12V battery for the big draws and pulses is easier. Lead acid batteries are still the common easily replaceable battery and less expensive than Lithium so they get the task.
The Leaf does as well. All the accessories are driven off the 12volt circuit tied into this battery - like the blower fan, lights, radio, etc. I believe it's charged from the main pack via a DC-DC inverter.
Ah so that makes some sense. I wonder how long it would take the cost of additional replacement batteries to equal the cost of a high-amp DC-DC converter though.
That's the car's Soul.
Given that in cold weather climates, a normal 12V battery usually lasts at least 5 years, and the replacement cost is around CDN$75-150 retail, it's unlikely that this will change anytime soon.
Having worked for Ford, their hybrids required a 12V signal from the ignition to the PCM to allow cranking, even though the high voltage battery was used to start the engine.
In reply to GameboyRMH:
What matters is the price to build the car... and as pointed out, if a battery lasts 5 years and the design life of a car is ten, it's good enough.
MrJoshua wrote: 12V Accessory systems are still normal in cars and that voltage requires high amperage to run certain components. High amp DC converters are expensive. A reasonably sized converter (still pretty powerful) and a 12V battery for the big draws and pulses is easier. Lead acid batteries are still the common easily replaceable battery and less expensive than Lithium so they get the task.
I wonder if the AC compressor is 12 volts or on the HV circuits with some sort of VFD. Same for the heater coil. Defrost grid(s) are certainly 12 volt, along with various motor power accessories(seats, windows, etc). ABS pump is probably 12 volt, those are fused pretty high IIRC.
In reply to BrokenYugo:
Heater coil is most certainly not on the 12v circuit. My Leaf's heater draws about 4.5 kW for an extended period of time while heating up the cabin.
I tried to buy one. The dealer told me to leave, Gingers can't have a soul.
Ever see a Li-Po fire? That bag of goo pack a nasty F-4 Phantom style napalm drop.
^That's why there are no Li-Pos in production cars...which is kind of too bad really, because they would be awesome for performance, and it's not like most cars have been driving around with a tank of apple juice anyway...
uh... that mini napalm grenade is what's in my phone?!?! next to my sax and cymbals?! what's the science behind that thing going off?
slowly removes phone from pocket
In reply to bluej:
They do go off on their own, pretty rare though, I remember a guy on my floor in college had an iPhone light his bed on fire. I have no idea what caused it, might have been something dumb on his part.
That gif makes them look a little more sensitive than they really are. Usually they just expand and pop the device apart. https://www.youtube.com/embed/7-xPHopebiE
The high voltage battery is disconnected when the car is off. All EVs do this and they all (to date) have some kind of 12V battery.
BrokenYugo wrote:MrJoshua wrote: 12V Accessory systems are still normal in cars and that voltage requires high amperage to run certain components. High amp DC converters are expensive. A reasonably sized converter (still pretty powerful) and a 12V battery for the big draws and pulses is easier. Lead acid batteries are still the common easily replaceable battery and less expensive than Lithium so they get the task.I wonder if the AC compressor is 12 volts or on the HV circuits with some sort of VFD. Same for the heater coil. Defrost grid(s) are certainly 12 volt, along with various motor power accessories(seats, windows, etc). ABS pump is probably 12 volt, those are fused pretty high IIRC.
AC compressors, if electric, are always on the high voltage bus. They would take far too much current to drive on only 12 volts, and part of the push for HV systems in the first place is to make electric A/C viable.
The fun part is some of them have the motor internal to the compressor. Means you have to use a special refrigerant oil that is non conductive. Any contamination will have the car sense a HV leak to body and open the contactors, leaving you dead in the water, at best. I have heard of Priuses burning to the ground, at worst.
(The HV systems "float" relative to chassis 12v. They do not share a ground. If any of the HV legs finds contact with ground, the computer pulls the breakers, for safety reasons. Makes me feel a lot safer working with the cars, they do their damnedest to err to the side of caution)
LiPos are bags of goo, no hard case to speak of. They don't tolerate abuse. Usually they just puff up, but puncture the bag(s), and who knows if it turns into a blow torch. Which is a shame, because they rule for power output.
If the gasoline-powered combustion engine were invented today, there's no way in Satan's playground the nanny staters would ever allow it into vehicles that ply public roadways.
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