Porsche is known for track cars. Tesla made electric vehicles quick, but they had no thermal durability. It’s well documented that the Model S can only handle a lap or two around a road course at pace before the battery overheats. The Model 3 is better as it has an improved battery cooling system, but it still derates power due to excessive battery temperatures. Porsche knew if it brought an EV to market, not only did it have to be quick, but it had to be able to withstand extended high-power usage. Being able to drive hard for a long time also translates into being able to charge faster because both require sustained high power and keeping the battery from overheating. As it turns out, it requires a full system level approach.
First, we’ll examine the basic EV architecture. Obviously, there’s the battery pack which is mounted in the floor. It’s the heaviest single component of the car, so it keeps the center of gravity nice and low. Every EV has a Battery Management System which is the brains of the battery pack. From the looks of Porsche’s design, the BMS box also contains the electrical contactors (on/off switches) and fuses. The battery is connected by high voltage cables to the motor inverters and High Voltage Distribution Box. In the case of the Taycan, it has front and rear AC motors. The battery pack puts out DC current, so the inverters that are attached to the motors converts the DC battery pack current to AC current for the motors. EVs typically have a High Voltage Distribution Box which is like the central hub for all the electrical power. Power goes in/out of the HVDB from the battery pack, charge ports, and every electrical device on the vehicle. It looks like the DC on-board charger is part of the HVDB. All of the high-power electronics like the inverters and HVDB are typically liquid cooled. In some of the super high-power charger concepts out there, the charger handles are liquid cooled.
The Taycan has two cooling systems from the looks of it. One is glycol coolant based and the other is refrigerant based. The coolant loop uses the radiator in the left front corner of the car and it’s used to cool the motors. The A/C refrigerant system has the condenser mounted in the right front corner of the car. The refrigerant goes from the compressor to the condenser and then to what I think is a combo expansion/distribution valve. The expansion valve part of it does what expansion valves do in A/C systems which is turn the high-pressure warm refrigerant into low-pressure cold refrigerant. That cold refrigerant is then sent to either the evaporator in the cabin to provide cold air to passengers or to the battery pack. The batteries sit on top of these long cooling plates which have the cold refrigerant flowing through them. In a perfect world, all the battery cells would be kept the exact same temperature. However, in the real world, that’s hard to implement. In the case of Porsche’s design, the battery cells on the left side of the car will stay cooler than the cells on the right side which implies the hotter right-side cells won’t last as long. However, there might be some tricks in the BMS system with regards to cell balancing and whatnot to mitigate the issue. This battery cooling system with refrigerant and cooling plates is the same concept as used in the BMW i3. There looks to be a high voltage heater which can be used to warm up the battery pack in cold weather.
This is the exploded view of the high voltage battery pack. The battery pack enclosure structure is extremely stiff with all those cross beams. It has to be stiff because Porsche is using it as a stressed member like how engines are often used as stressed members in open wheel race cars and motorcycles. Plus, the cross beams are used to transfer loads in the case of a crash. So now I’m going to get into why I think the cooling system is only mediocre. First, there’s nothing innovative about the cooling system as it’s basically a copy of the BMW i3 design which has been out for quite a while. The goal with battery cooling is to cool the batteries (duh). The Nissan Leaf saw massive battery life degradation because they don’t have a cooling system. So, all those Leafs in Arizona had their batteries lose capacity quickly because it’s so hot there. Li-ion battery cells like to live around 30C temperature. Once they hit that 45C-50C temperature area, they may start to lose capacity.
Looking at the heat conduction path from the battery cell to the battery cooling plates, there are many interfaces which means many resistances; each interface is a resistance to thermal heat conduction. Along with that, there’s a lot of thermal mass/capacity to manage too. It looks like the heat conduction path is: cooling plates > battery enclosure > battery module > battery cell. Between the cooling plates, battery enclosure, and battery modules are likely a heat conduction paste or thermal gap pad creating more interfaces. A paste or gap pad is required because all of those surfaces are not perfectly flat, so you need the paste/gap pad to take up the imperfections to increase the contact surface area. Porsche is using LG pouch cells inside the modules, so there’s a question in my head about the heat conduction path between the battery module shell and the cells inside. Anyway, we’re likely not going to find out for a while until the car goes on sale and a company rips one apart. From the looks of it, the cooling plates control the temperature of the battery enclosure which acts as a massive thermal sink for the battery modules. If this is the case, it should help prevent the battery cells from increasing in temperature too rapidly.
We have to look at Tesla’s cooling schemes because they are the benchmark. With EVs, how long and hard you can drive also translates into how fast you can charge. It’s the same situation in both, how long the battery pack can handle high kW of power without overheating. When driving hard, it’s kW leaving the pack. With charging, it’s kW entering the pack.
17 comments
I think aluminium ammonia heat pipes are going to be a big part of high density battery cooling (if they aren’t already). They are light, safe, and proven. They can be easily shaped and fitted, plus, the materials are cheap and recyclable.
Pouch/prismatic cells are also much easier to heat and cool than cylinder cells although I wonder how Porsche deals with gas swell in the pouches.
I came up with something along those lines already….
https://patents.google.com/patent/US10153524B2/en?oq=US10153524B2
I didn’t know you worked at Faraday Future! What other places have you worked at and keeping from us!?
I knew others must have thought of heat pipes, they have been used to cool all kinds of electronics and aluminium ammonia pipes have been used for decades to cool spacecrafts and military avionics.
I was thinking about moving heat to a water radiator right next to the cells then cool the water with a standard radiator, yours skips water completely which is great for weight sounds like a nightmare to manufacture/service unless you are transferring heat from pipe to pipe in shorter sections or using individual radiators.
Heat pipe manifolds, that’s probably the more novel idea hahaha.
Just think of it as an A/C system. Condenser (front radiator), evaporator (heat source/battery pack), and refrigerant running between the two. All established technologies for decades. Honestly, take this i3/Taycan cooling plate which is already designed for refrigerant. Just plumb it to a standard front automotive A/C condenser and you’re done for a 100% passive cooling system. Now to sub cool below ambient and to handle high power loads, you’d need to add the chiller. Say the pack is cooler than ambient and you don’t want to heat it up, just put some solenoids in the lines to cut the flow of refrigerant. If you want to heat up the pack, could run the compressor like a heat pump in residential applications. Anyway… I’m out of automotive now for the day job. Using heat pipes in my current job!
Porsche uses a chiller for the Taycan.
It already uses one for all the last e-hybrid models !
The schematic used here is just a simple representation of the battery cooling.
It’s allready much better than that in the e-hybrid models.
For the Taycan and range/charging option, Porsche has a range simulator online and shows the charging options too.
A Ionity charger will charge a Taycan in 30min for 8€ in Europe.
The range is not the greatest or most impressive, but most Porsche owners won’t really need more. And with the network of ionity chargers, and “destination charging” stations (luxury places and Porsche centers that have an agreement with Porsche and Turbo-chargers available for charging Taycans at 350Kw for free), range won’t be a problem.
One option will be critical for Taycan owner : Getting the Connect service which will unlock a lot of functions very useful for long trips (Charging planners the pre-conditions the battery for fast charging prior to arrival at the charging station etc…).
As a Porsche Tech / Hybrid Tech / Smart Mobility Expert I’m more worried about the 4 screens failing inside than the reliability or longevity of the powertrain !
Ben, thanks for the info! It’ll be interesting to see what’s in there for real once that information becomes available. No joke about all those screens!
I found a picture from my last hybrid training of an opened 388v Panamera E-hybrid batterie.
https://i53.servimg.com/u/f53/13/27/76/86/img_7631.jpg
You can see that the cooling system is already very intricate !
All the black strip are the wiring for the individual cells, with temp sensors etc.
Thanks for the link of pic. Looks like two layers of prismatic cells with 3 layers of cooling plates. I feel bad for the engineers that had to do the coolant plumbing!
so this thing gets a double wishbone suspension but the Cayman and 911 have to make do with the McCrap strut…
Excellent article. Well written and great presentation of information. I think the Taycan seems like a logical step up from the now 8yr old Model S, but at what cost? I still haven’t heard a peep about Taycan MaRP which usually means it’s ludicrously expensive. I’d be shocked if it wasn’t 50% more expensive than the closest equivalent model S.
It’ll be between $150k-$200k depending on the model. Keep in mind that’s how much the Panamera goes for. If I had the money, I’d go Taycan all day over the Tesla. I really dislike the Tesla interiors. But, I don’t even have Tesla Model 3 money….. so mute subject, ha!
Super interesting article, however I think your explanation of Ohmic heating being reduced with higher pack voltage is misleading. For a fixed cell, series/parallel configuration doesn’t affect loss in a battery pack, only cell count and total output/input power (at least when it comes to ohmic losses within the cells themselves). You somewhat hint at this “okay that really isn’t the whole picture”, but as far as I can tell that isn’t the picture at all. I^2 numbers are meaningless without the R. If Porsche took the same pouch cells and arranged them in a 400V pack architecture, their loss would be the same at a given output or charging power. I think the main source of increased performance (which you allude to) is decrease ESR of the pouch cells. They most likely traded absolute capacity for performance (thicker anode/cathode, etc.). Regardless, a super interesting and informative read as usual!
Hey Derek! You’re right… I came to the same conclusion about the ESR. I was writing a bit stream of consciousness, and I was like, I’m missing something… Would be nice to break down a pack and take real measurements. Hope you’re doing well up there!
I hope that Porsche doesn’t forget the Arctuc silver thermal paste! Or is that for the next-gen Taycan (sorry, that name still gives me the shivers.)
https://www.newegg.com/arctic-silver-as5-3-5g/p/N82E16835100007
Will ‘enthusiasts’ be hacking the cooling system and pumping LN2 through it? Don’t say it can’t be done.
https://www.stirlingcryogenics.eu/en/products/custom-closed-loop-cooling-systems/closed-loop-liquid-nitrogen-cooling-systems
A good ole water sprayer on the condenser would help!
Kindly notify me on the latest EV battery technology design and longest range capability