Porsche foresees 800-volt DC charging

Porsche 800-volt DC charging 1

If there’s one thing everyone can agree on about EVs, it’s that ranges need to become longer. That means battery capacities need to grow, and therefore charging levels will have to increase as well, if charging times are to stay the same (or, preferably, become shorter).

One company that’s been working on higher charging levels is Porsche, which has set its sights on 800-volt DC charging technology. The VW Group subsidiary developed an 800-volt charging system (double the voltage of the current CCS standard) for its Mission E concept, which was shown in Frankfurt last September.

In a verbose recent article in Porsche Engineering Magazine, Volker Reber explains the benefits of higher charging levels, pointing out that current EVs require frequent recharging, and that, even with overnight charging, the range that is gained remains relatively small.

When it comes to long-distance driving, a rapid-charging infrastructure needs to offer a convenient ratio of driving time to break periods. “It should be possible to get a sufficient charge for roughly 400 kilometers within the usual break time of 15 to 20 minutes.”

Porsche 800-volt DC charging 2 660Charging time limited by mainly technical factors

Unfortunately, technical factors currently stand in the way. Today’s DC fast chargers typically run at 400 volts, with 50 kilowatts of power. Even if charging levels could be increased, the capacity of the charging pins in the charging plug maxes out at roughly 100 kW, which still translates to about 40 minutes to add 400 km of range.

Further increases in charging power require some sort of cooling, and various companies are working on such systems.

Porsche 800-volt DC charging 3 660Achievable average speed in relation to the charging power

However, to get to the desired charging time, Mr. Reber finds that a shift to a higher voltage will be inevitable. Doubling the voltage to 800 volts could theoretically reduce charging time to about 15 minutes with the same electrical load on the charging pins, just enough time for a bathroom break and a quick snack.

Faster charging would be good news not only for drivers, but also for station owners. The costs of installing charging stations are high. In terms of the price per kW, a higher-power charging infrastructure would be significantly more cost-effective (a recent blog from the Dutch charging station operator Fastned reached a similar conclusion).

Porsche 800-volt DC charging 4 660


Source: Porsche

  • http://nextgenfastchargenetworks.blogspot.com/ Brandon

    What I’m wondering is if (and how it would work) an 800 volt 300 kW DCFC would be able to charge the many 400 volt cars on the road when these fast chargers start to become common place maybe mid 2020s. I doubt anyone reading this may know and be able to explain, but it’s worth a shot 🙂

    • Alexandre Moleiro

      It’s easy to make a 800VDC charger to work at 400VDC. The current CCS and ChaDeMo standards imply the chargers to be able to charge between 150 and 500VDC, so it’s not a big challenge to make a 150 to 800VDC charger.

      In fact, the 800V is not random, you can almost simply stack two 400V chargers to get 800V. So a 800V charger will be able to charge one car at 800V or two cars at 400V simultaneously.

      • http://nextgenfastchargenetworks.blogspot.com/ Brandon

        That’s cool. It seems like it wouldn’t be too hard then.

  • W0QR

    800 volts is much more prone to arcing and dielectric breakdown. 800 volts will produce an arc 3 times further than 400 volts. Doable with the right materials but not trivial and probably a whole lot more expensive.

    • nordlyst

      True – but irrelevant. Even at 400V arching is a potential problem, so it has been solved. And it’s very simple. Don’t allow any power lines to go live until you have a secure connection.

      You can even implement it mechanically for passive safety (although we do accept depending on software for our lives in many other contexts), using longer pins for the power lines and a shorter pin to push a switch that connects them. This guarantees that the power pins are connected before there is any voltage applied to the corresponding sleeves (that the pins fit into).

      As you probably know, electric current travels the path of least resistance. So there is no possibility of any arching when you’ve provided a path with one-millionth of the resistance.

  • Jim Fox

    Whatever happened to the ‘battery swap-out’ technology? OK, it means building at least two battery sets for each vehicle but all this dangerous high-voltage recharge can be dropped and the changeover time might be a few minutes at most; faster than an ICE refuel!

    • Lance Pickup

      You probably wouldn’t need 2 sets for each vehicle. This would assume that everyone wanted to simultaneously swap batteries, when in reality most people would be simply charging at home and only a small percentage would actually need to swap.

      But I think the past problem is that there just aren’t enough EVs on the road to make a viable business case. Search on Better Place Battery Swap for more details.

      I think the current problem with battery swapping is that batteries are improving so fast that keeping up with the multiple capacities in various model years would be challenging.

      And the future problem with battery swapping is that as capacity continues to go up, the instances where battery swapping would actually be beneficial are disappearing. With a 350 mile range EV you could drive for 5-6 hours straight without stopping, and I think people need a break at least that often. Even when I am driving a gas vehicle, a 12.5 hour raw driving trip takes me 15 hours (2.5 hours spent stopped). A 250 mile EV could in theory make that trip in 14 hours (3 30 minute stops), so I am already stopping for longer than an EV would require to recharge.

      • nordlyst

        I agree. Battery swapping probably has no future.

        Cell swapping, however, as envisioned by TankTwo in their ingenious string batteries, is VERY interesting. I don’t know if they are viable – there may well be some caveat unknown to me – but the idea is certainly intriguing! Basically a string battery is a collection of single-cell battery packs that together make up a logical pack. So each cell has it’s own “BMS” and electronics and terminals. They are made into little “eggs” with multiple terminals and there’s a protocol for figuring out how to configure which terminal is what automatically, so you can simply pour a bunch of them into a tank and they’ll dynamically work out how to connect to make a single logical pack.

        Microcontrollers only costs a few cents a piece, and with about 200 cells the microelectronics doesn’t add much cost to a pack. And the huge amount of flexibility it offers – there’s no reason you couldn’t mix different chemistries for example – seems to provide a future-proof upgrade path. Throw out the worst cells and replace them with the latest and greatest, and this way you incrementally increase the capacity over time.

        You could also choose to own just a certain capacity, say 40 kWh, and rent extra capacity when you go on long trips. A car could have a “tank capacity” for 500 cells but come with only 150 cells, for example.

        And battery swapping could be performed by vacuuming out your cells and refilling the tank with freshly charged ones.

        The latter options – rental and swapping – would presumably require fairly large infrastructure investments. But the upgrade path could be enabled if at least one garage in each major city was equipped to do it, which seems to me a moderate investment.

        There are other benefits as well, but I’d better redirect you to the excellent article on this very site about them:


    • nordlyst

      I think Better Place is the only entity that has ever taken battery swapping seriously. If the ingenious string batteries (that you can read about on this site) catch on, cell swapping may become a topic again. Otherwise, I think it’s dead in the water.

      But wait. What about that Tesla demo of battery swapping? What few people appreciate is that regulators (CARB) have come up with the idea of rewarding a different number of “ZEV credits” according to a bunch of rules. By making it *possible* to swap the Model S battery Tesla got more credits for every car they made. And they sell those credits on to other car makers that reckon it would cost them more to comply to the regs by making ZEVs. Tesla obviously couldn’t be coy about merely gaming the rules, so they instead went to the other end and made the most out of the marketing opportunity. For years I myself thought the swapping stations were just around the corner…

      Having driven a 2012 LEAF for the past 18 months I have to say that I think the charging time issue is fast becoming irrelevant. Yes, it is an issue on my car and that generation. Not a huge issue, for me, but not ideal. But we don’t have to wait longer than 2017 for the near elimination of it. With the Bolt, Leaf and Zoe all being able to go far enough that few people will need to use fast chargers more than a couple of times a year, it doesn’t seem very rational to regard reducing something like one or two hours per year of charging time to half an hour. I realize that *some* people drive very far much more often, but the cars of 2017 and the start of 150 kW chargers are just the beginning. By 2020 it will be much easier still.

      Unless the stats on driving are totally wrong everywhere in the world, this doesn’t just apply to me, but to more than 95% of drivers.

      An interesting thought experiment is to ask yourself the following: If you could buy a battery pack paying only $100 per kWh and with size and weight magically independent of capacity, what capacity would you opt for? I think I’d go for about 70 kWh. That would let me drive for so long that I should take a break regardless of any need to charge!

      If you want to go on a camping holiday and tow along your caravan, however, you’d want a lot more. Since in the real world capacity is linked to size and weight I think it makes sense to put batteries in the caravan floor itself, but I have never heard any serious discussion about standards (and that would of course be required). Such a solution would not only mean you didn’t have to drag around all of the superflous batteries when NOT towing. Having a ton of energy on board would eliminate the need for gas-driven systems and allow you to remotely turn on the heat (for instance en route to where you keep it in winter) and the fridge could run for years even off grid.

      But I think carvans are sort of the last piece of the EV revolution. Sometime around 2030 it may be commonplace!

  • brian_gilbert

    For safe driving you should have a break every two hours. A battery exchange could thus do the job.

    • Jim Fox

      Ha! Same idea, simultaneously- but swap out has been shown to be very fast, Brian.

      • brian_gilbert

        The way the batteries are fiitted now is not very compatible because it was not meant to be. Also I think they are worried about people swapping their battery in poor condition for a good one. However I am in favour of going completely driverles. In that case the vehicles would be owned by hire companies with the user paying per trip like a taxi. Thus the batteries would be installed in a compatible way and the hirer would own both batteries so would not risk losing out on the exchange.

  • Jim Fox
  • Joe

    The referenced article author from Porsche is trying to convince people why the 400v DCFC CCS standard is inadequate. Without saying it directly, he’s stating the same argument points Tesla does when dismissing the CCS standard as inadequate.