What specifically don't you understand? The tech of supercapacitors? What the 12V battery does? Or something else?
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Model S range and interior update imminent?
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What specifically don't you understand? The tech of supercapacitors? What the 12V battery does? Or something else?
Olle
Active Member
I though I understood that the 12V battery powers the car when the HV pack is off or depleted, so that you can unlock the car, communicate with it, open doors after an accident, open windows if the car gets submerged and other nifty things. I don't understand why we have lead acid instead of li-ion for the 12V system. What I really don't understand though is why a capacitor would perform these tasks better than a battery.
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As far as I can see, it wouldn't. For a small battery like this, lead acid is cheap and hard to damage. You're not really worried about energy density.
I do think it's a bit of an anachronism to have this battery in there at all. I'm sure, in the next few years, Tesla will dispense with the silly 12V electrical system altogether and draw accessory power from the main vehicle battery.
I think the main reason is that you can't charge a li-ion battery when it is below freezing, so you would have to have a battery heater for the 12v battery. It just isn't practical.
The 12V battery is not just an emergency backup, it powers all the electronics in the car. I'm having to replace mine now so I've been searching. There is a company called Ohmmu that makes a LiFePo Li-ion replacement for the lead acid 12V they claim lasts 4X longer. It costs 4X more, but if it means having to get in there 1/4 as often it's worth it. Tesla service charges a fair bit to replace the 12V battery and you have to tear apart the frunk to get at all the bolts holding in the battery (one is buried by the HEPA filter in the S).
One advantage of supercapacitors is they have vastly more cycles in a lifetime than batteries, and you can rapidly charge and discharge them with no risk of damage. They also don't heat up like batteries do when you rapidly discharge them. Supercapacitors are just capacitors that can hold much more charge than a normal capacitor.
They are vastly simpler than batteries, they are two electrical plates and a dielectric. The capacity of the capacitor is based on the area of the plates and the qualities of the dielectric. Many cylindrical capacitors are rolled to give them huge surface area to the plate. Think of two sheets of foil wrapped on the same tube. Supercapacitors have come about due to some major advancements in dielectrics that allow for much higher capacity capacitors.
Capacitors are common in just about all electronic devices. The higher capacity standard capacitors are electrolytics which have a liquid electrolyte. If you see little cans around a circuit board, those are electrolytic capacitors. There were some counterfeit Chinese electrolytics that made their way into computers and TV about 15 years ago and they caused these devices to die prematurely (I restored an NEC monitor I had with replacement capacitors), but if the capacitors are made right, they will last the life of the product.
Small capacitors are used in many circuit boards to filter out noise picked up from other electronics. The higher the frequency a signal on a wire is, the easier it is for that signal to jump off the wire and get picked up by other wires. Small capacitors placed around the board help filter out these induced signals. Those are so small you wouldn't notice them unless you know what you're looking for. Other times you want to hold a charge for some purpose in electronics. If you've had an electronic device that kept its settings when you changed the batteries, it probably had a capacitor backup to hold power to the circuitry while you changed the batteries. There are other signal conditioning and uses for their use.
In a car, a supercapacitor replacement for the 12V battery would probably last the life of the car. It could be buried just about anywhere and you could forget about it. Supercapacitors have much lower charge holding capability (per volume) than batteries so for the battery pack that runs the car, they are impractical until they get to at least 10X the current charge density, probably more. Getting supercapacitors with charge densities up around battery cells would be a game changer for the car industry. Supercapacitors are far simpler than li-ion battery chemistry and are both cheaper and far quicker to make. They are also capable of being charged and discharged far faster than batteries which makes supercharging as fast of faster than going to a gas station and it means performance cars would be limited by how much current the motors and wiring can take rather than what the battery can put out.
While there have been some big improvements in dielectrics that have really boosted the capacity, they are still way below li-ion battery densities. Even if a supercapacitor with the same energy holding ability as the 12V battery in a Tesla took up more space, Tesla could tuck it in just about anywhere they wanted because nobody would ever have to access it.
Tiger
Active Member
No need for battery upgrade to 2170 Tesla Model 3 2170 Energy Density Compared To Bolt, Model S P100D - Tesla Motors Club
This is interesting. I always wondered what the real numbers were. One thing to note, though, this only talks about the cell level, not the battery level. The 2170 is 5mm taller than the 18650, and so you're going to get 5/65 = 7.6% more energy in the same area vehicle floor, even if the energy density is exactly the same. And we also don't know how much space is lost to cooling/heating/structure/whatnot in the two batteries. Just speculating, with fewer, larger, cells, the 2170 pack probably permits tighter packing.
I'm really struggling to wait for more range in the Model S. May have to go ICE unfortunately, in addition to my X. Hope something happens in the next couple months.
avesraggiana
Member
I'm not at that point yet, but man, it would be so great not to have to stop to supercharge at any time during my weekly 280 mile roundtrip commute.
Note: I could theoretically manage it in an S100D but I'd have to drive at suicidally low freeway speeds. Here in Southern California, nothing less than 80 mph on the 5 between San Diego and LA will do.
Absolutely agree. I frequently drive up and down CA, roughly 300 miles one way which means no way I’m hitting that without any stops in the S with real world driving.
People love to talk about the convenience of super chargers and the need to stop for a break - unfortunately doesn’t work for extremely busy people. When you can complete the same trip without any stops, that matters.
People love to talk about the convenience of super chargers and the need to stop for a break - unfortunately doesn’t work for extremely busy people. When you can complete the same trip without any stops, that matters.
FlatSix911
Porsche 918 Hybrid
I believe the volumetric difference has already been accounted for in the analysis based on Wh/kg and Wh/liter... the 18650 wins.
Oldschool496
Member
I was considering moving to a 100, I can see now through these two posts that its not necessary. Since you have to stop anyway whats the point. Leaving not fully charged though from start and stopping for 10-20 minutes 100 + miles down the road. All depends on geography of where things are located also.
Of course I am not dealing yet with having to wait for Supercharger and I assume you guys might be waiting or never know you have to wait. That would be frustrating.
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Tiger
Active Member
I don't mind stopping on my own terms, but I'd hate to stop for more than 15 minutes mandated by refilling. If every place where I want to stop had a supercharger, it would not be an issue. However, currently you have to stop both for your chores and again for refilling.
mknox
Well-Known Member
On road trips, my wife complains about having to eat when the car is hungry...
AZ Desert Driver
Rare combination
OK - please educate me. I thought a Capacitor would accept a high rate of "supercharger" - making the time for filling brief. Then the capacitor would bleed off into the battery - filling it at an optimized (warm, not hot or cold, slow instead of shock) rate.
What I'm seeing is talk about replacing the entire battery with capacitors entirely. Not using the good parts of both systems, but replacing one with the other.
What I'm seeing is talk about replacing the entire battery with capacitors entirely. Not using the good parts of both systems, but replacing one with the other.
Capacitors take up more volume than batteries per kWh and are more expensive. So the application you describe to refill one from the other as well as battery replacement may never be practical. But replacement of 12v subsystem batteries seems reasonable. If it turns out there are advantages to making batteries for average power instead of peak power, then having both may make sense, both for performance and regen.
Supercapacitors don't have the energy density to serve as the primary battery in the car, but they can be used as range extenders and to help save wear and tear on the battery. In supercharging, they would be only of limited use. They might be able to push the taper off to a little higher rate of charge by storing energy quickly, then charging up the battery at a rate that is good for the batteries.
As supercapacitor in an EV will likely only be a few KWH at best. It can be used to absorb regen braking more efficiently than batteries can do, and can be used as a booster when accelerating to save big discharges on the batteries. It would make EVs more efficient, especially in stop and go traffic or on surface streets.
Another possible plan for superconductors is to replace the lead acid battery in Tesla with one. This would be an occasional maintenance item in the existing cars that could be done away with. the supercapacitors would likely last the life of the car. The 12V battery today is around 33 WH, so a relatively small supercapacitor could be used. It would be larger than the current battery, but the shape could be something that fits in a void in the existing equipment on the car. Because it would rarely be replaced, it can be buried as deep and needed.
AZ Desert Driver
Rare combination
Your opening paragraph is exactly the point I was trying to make. You just phrased it much better. "In supercharging, they would be only of limited use. They might be able to push the taper off to a little higher rate of charge by storing energy quickly, then charging up the battery at a rate that is good for the batteries. " Store energy quickly; charge the battery later. Dont replace battery, just round off some of the rough edges.
The idea of a permanent replacement of the 12v unit seems like a good thing - but not the only thing. Buffering the battery for regen, for sprints, for supercharging assistant - seems like additional good things.
I keep reading that the time spent supercharging is too long and something just gotta be done about it. Personally, I find a 20 minute charging stop is a welcome break. But whittling this down to a shorter charging stop seems desirable- and fits my understanding of what a capacitor can do. The size/density issue is a flaw I cant get my head around. Cant they be molded into just about any shape and used to fill voids to save time?
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