Tesla’s liquid-cooled Supercharger cable could enable faster charge times

Tesla Supercharger

Once again, Tesla has come up with an innovation that could be far more significant than is apparent at first glance. Speaking at the latest shareholders’ meeting, Elon Musk said that Tesla has “just introduced” a liquid-cooled cable to the Supercharger system (around 24 minutes into the video below). Liquid cooling allows the cable to be thinner and more flexible while carrying the same amount of current.

The first working model is at the Mountain View Supercharger location.

Okay, it’s easy to see that recharging your car with a thin and supple cord is more convenient than having to wrestle with a big stiff snake of a cable, but what’s the big deal?

The possibility of a big deal is implied by Musk’s next remark: “It also has the potential for increased power of the Supercharger long-term.”

The two main drawbacks of current EVs are limited range and long charging times. Even DC fast chargers can take up to half an hour to deliver a full charge. While the range issue is slowly but surely receding, some believe that there may be an unavoidable limit to how quickly a battery can be charged.

Tesla’s Superchargers are already some of the highest-power chargers out there. Most operate at 120 kW, and some can go as high as 135 kW (although some early Model S systems can’t handle this power level). Tesla being Tesla, it’s widely assumed that there are plans to push this level even higher.

However, at some point the quest for faster charging could run up against the laws of physics. There’s only so much power you can push through a conductor of a given diameter before the cable heats up and melts. Could actively cooling the cable allow substantially higher power levels, and how much faster might that let us charge our EVs? It will be interesting to find out.


Tesla Motors: Liquid Cooled Supercharger with Thermal Imagery video added 6/20/15.



Source: Tesla
Image: Jeff Cooper (CC BY 2.0)

  • brian_gilbert

    This might make flywheel energy storage practical in a car. At present the weight of a flywheel with a useful range is too high. However if a smaller flywheel could be ‘recharged’ quickly thanks to high amperage cables, while the car was moving, this problem would be solved.

    • BlackTalon53 .

      The range any practical sized flywheel in a car can give you is measured in meters, not kilometers. very efficient for accelerating after frequent stops at a red light (read, bus or taxi) or after a very tight curve (read, race car) but for nothing else.

      • brian_gilbert

        I am not talling about ordinary car flywheels. Look up Flywheel Energy Storage on the internet. As I said they are mostly used in stationary locations because of their weight. Commonly used for spreading the load on electric powered subway trains. Also used for recovering the energy usually lost in braking. They are used in some formula 1 racing cars.

        • dogphlap dogphlap

          I’ve never seen any one talk about this so maybe this is not a real problem. But: spinning a flywheel to the kind of rotational velocities required for even moderate amounts of energy storage creates a gyroscope. A gyroscope in a vehicle wants to stay were it is if the car is stationary or to keep travelling in a straight line at the same speed if the car is in motion. Use in race cars not withstanding any major use of a flywheel for energy storage is more likely to be confined to non-mobile installations for this reason (like the basement of a house, but even there the consequences of a bearing failure or flywheel disintegration would be pretty bad). If my logic is faulty please correct my understanding.

          • brian_gilbert

            Air bearings solve one problem. They have obviously solved the safety problem as they are using them in racing cars. Mounting them in gymbals to avoid precession problems is sufficient for many applications Do Internet searches for :-
            Wiki ‘Flywheel energy storage’ to locate an encyclopaedic entry for this specifically.
            William flywheel energy storage to locate a commercial supplier. I believe it was originally a subsidiary of williams racing cars but has since been sold to another group.

            Who knows you may bring a particular piece of knowledge or logic to the subject to improve its viability.

            I have hopes that it can be applied to using driverless electric taxis in a driverless zone. With a small flywheel and the ability to recharge it while moving by brushing contacts at the side of the guideway it would be very low cost.

          • vperl

            Amazing all the deep thinkers have not made one and sold their brainstorm for a billion duckets

          • brian_gilbert

            The only sure way to sell a new idea is to produce it yourself and spend a lot of money marketing it. Without Flywheel Energy Storage electric cars are a huge improvement on petrol cars but look how long it is taking the world to realise it. I went personally to a dealer. He had one electric car. It was not in the showroom but boxed in in his car park. It took them a long time to even understand I was interested and even then they made no effort to give me a trial run. I understand there is little commission in it for them and the reliability means low servicing profit and few breakdowns.

          • nordlyst

            Yeah, that’s the ONLY way. Just look at Tesla’s marketing budget!

          • QKodiak
      • brian_gilbert
    • QKodiak

      This has already been done by Volvo, and it apparently worked very well, increasing mileage by 25% and dropping 0-60 times by 1.5 sec. It is a good idea.


      • brian_gilbert

        Thanks Qkodiak. Quoting sources makes for greatly improved communication.

    • nordlyst

      You don’t recharge a flywheel on the go via electric cables, but via mechanical links. It’s very energy efficient for short storage times – stop and go traffic – but I’m not sure how cost effective. Maximum power rates during charging are huge however! The braking energy of an F1 race car is about two megawatts. And the more you can capture, the less you need to cool the discs, leading to better aerodynamics. KERS for EVs seem a plausible way to improve their efficiency even further. But compared to how batteries evolve (or otherwise change), it’s a marginal issue.

  • ned_plimpton

    Is that twitter picture supposed to be the new thin and light cable? It doesn’t look much smaller… Any idea about the change in diameter?

    Also, I’m not an E-engineer, but aren’t the efficiency losses significantly increased when the diameter of the conductor is reduced? Sure you can cool the copper so nothing melts, but I wonder how much energy is now wasted as heat…

    • JS

      Good questions!

      Given the same diameter cable, cooling the cable will decrease the electrical resistance and thus decrease heating losses. From an energy point of view it is worth doing this as long as the avoided heating losses are greater than the energy cost of running the cooling system.

      With a smaller diameter cable, as you note there is the opposite effect – increased electrical resistance. How these two opposing factors interact I do not know. I also don’t know whether there is a net decrease in losses with the new cables, or whether this is all about convenience.

      It would be good to hear from someone who understands the physics involved and can answer these questions. Ideally a Tesla engineer who knows the specifics…

  • JS

    Your second last paragraph is evidence of a lot of confusion.

    First, Tesla’s Superchargers are THE highest power chargers out there. CHAdeMO’s peak output is half the power, and in practice often considerably less.

    135 kW is the amount that one Supercharger – connected to two stalls – can put out. The most you’ll usually see in the car is 120 kW. So, if one car is plugged in, and its battery is close to empty, it will see 120 kW. This will taper down over time. If another car plugs in to the paired stall, it will get the remaining capacity, or at least 15 kW. This sharing is not likely to be a problem for long – a 60% charged Model S battery will see roughly 67 kW, leaving 67 kW for the paired stall. Nevertheless, unless the Supercharger site is more than half full, it’s worthwhile taking a minute to figure out which stall you can park in to be sure of having a Supercharger to yourself.

    Some early Model S batteries are not capable of charging at more than 90 kW. At this point there are relatively few such batteries, as a percentage of the total population.

    • Johnny Le

      135 kW shares between 2 stalls, really? That sucks.

      • vperl

        This is common knowledge to people that actually own a Tesla.

        Ones that complain, try to drive your volt 100 miles then recharge. That sucks.

        A tow truck and all afternoon.

    • QKodiak

      CHAdeMO charges at 62.5kW and CCS Combo charges at 50-70kW (depending on the station).

  • Johnny Le

    I want to see 250 kW charging. What is the chance of that happening?

  • Oollyoumn

    I may have forgotten a lot, but I don’t think there is any laws of physics that limits the power going across a given diameter of cable. There may be a current limit, but that does not limit power. For example 250kw could be carried on standard 12ga copper conductor if the voltage is 12.5kv. This raises insulation problems and how to use such high voltage at the other end, but it is possible to have higher voltage batteries or using AC with a step down transformer. Neither of these may be practical at this time, but things change. There is also the possibility of much lower resistance conductors. Gold is not practical, but there may be breakthroughs with graphene or other materials that significantly reduces the resistance allowing relatively small conductor diameters to carry far more than standard copper.

    • nordlyst

      Excellent point. I’ve wondered why 400 volts. What are the things that determine optimal voltage level? Certainly at 5000 volts thin wires can carry an awful lot of power.

      Presumably there’s some point at which arching becomes a risk, but where’s that point, and can we mitigate it?

      I actually think the cables will disappear anyway. Wireless charging is now, at high power, supposedly as efficient as a caked connection. It’s obviously more convenient, especially when combined with a car that can park itself with nobody on board. I’d love to be able to exit my car outside the entrance of the condo, and let the car go charge in the parking cellar! And sci-fi as it may seem, we are very close to being able to today.

      • nordlyst

        One obvious point: using a given chemistry, higher voltage means more of the cells in series, so fewer in parallel for a given capacity. Which means lower power, in our out. So increasing battery voltage makes it easier to transfer theenergy quickly to the battery, but more difficult to store it quickly…

  • http://www.chargedevs.com/ Charles
  • Electric Bill

    Funny how an article on liquid-cooled charging cables became a discussion of flywheels (actor Kevin Coster was a heavily-invested advocate some years ago).

    One aspect of charging stations that was not mentioned in the article was the problem of copper thieves. With liquid cooling reducing the conductor diameter, there is less incentive for crooks to try to filch a cable.

    As someone else mentioned, hopefully soon someone will make graphene charge cables feasible. Considering their ultra-low electrical resistance and the low cost of raw materials (carbon is very CHEAP!), even liquid cooling may soon be unnecessary– imagine charging from a cable that resembles a length of spaghetti!

    There is a huge area of Los Angeles that has no practical charging stations (USC and some museums have “free” charging, but you get hit with a steep parking fee). I’m in the process of scouting out a location for two or more charging stations, but it’s not easy because of the petty thievery in the area, the scarcity of all-night businesses, and the need for an off-street, well-lit site. Whatever it takes, we need much more convenient charging in L.A. if it is to become more acceptable to drive electric.

    (Ned: there is only one working Tesla liquid-cooled charging station so far… in Mountain View… you can see it in the Tesla video… the one you see in the article is one of the old-school, thick charge cables.)

    • Gbrandstetter

      Why dont you look for a gas station. Its fuel, of one kind or another, and the gas station store might benefit from customers actually shopping for 20 minutes.

      • Electric Bill

        Hi, Gbranstetter– a couple of advantages to trying to get a location in, a gas station is that they are typically open all night, and are well-lit. There some problems, though… gas station owners often perceive EVS as a threat to their livelihood and see increased EV use as rather terrifying. As EVs increase in numbers, gas sales will drop, and gas stations will close. Gas stations are a huge investment in underground storage tanks, gasoline pumps, etc.; it is quite expensive to remove all that hazardous hardware, have it disposed of in environmentally acceptable ways that comply with, the EPA, etc; EVs are a gas station owner’s worst nightmare.

        Shifting from gasoline sales to supplying electricity from chargers is by no means easy and inexpensive. I can’t really blame them; EV charging stations are not sustainable as a single source of income as gasoline is– imagine if you completely shifted an entire gas station to EV charging… you would have, say, 20 spaces for car charging, and even if they are high speed chargers like Tesla’s, the cars would be there for something like 25-30 minutes to get something like a dollar’s worth of net revenue from the sale of, say, 5 or 6 dollars worth of electricity. Once EVs achieve a secure foothold on our transportation, the infrastructure will be quite different than it is today– charging will be done primarily at home, or their places of business– wherever it is they work– or the places they do business, such as restaurants, malls, churches, schools, etc.

        Street lights are likely to become one of the biggest players in EV charging infrastructure. Fifty years ago, all street lights were energy-hungry tungsten bulbs (300 watts or so) that required thick copper cables. Less than a month ago, the street lights on my own street were replaced with LED lamps only requiring 80 watts– that means those beefy cables have a lot of unused current-carrying capacity that can be used instead for charging stations. The street lights will remain, the cables will simply have a dual use going forward– providing charge for parked vehicles.

        Problems remain; copper thieves are already a menace today, so charging stations will need to be protected somehow, perhaps including security cameras mounted above, sirens to scare off thieves, and well-protected charge cables whenever the chargers are not in use.

        So, gasoline stations are becoming obsolete, and will not be replaced by single-purpose facilities for charging EVs; they may become dual-purpose businesses such as Starbucks, or other forms of fast-food eateries… hopefully FAST food, rather than FAT food, such as what we are offered at McDonald’s.

        One more player in the development of an infrastructure for feeding our EVs will be inductive charging setups– it is far too early to tell what form those might take. Inductive charging is not as efficient as direct, metal-to-metal interfaces, but it would also be rather inefficient to have every EV to have half its weight composed of an expensive battery. If we had a ubiquitous inductive charging network that could charge us up easily, quickly and automatically every time we stopped for even a few seconds at a stop light, stop sign or while passing through a fast-food lane, and there were some form of accounting system so drivers old be billed for their hundreds of accumulated bits of charge in a day’s driving, it would eliminate the need for huge battery packs, make our cars much lighter, simpler, more nimble and less expensive. It would also help to relieve some of the need for the special materials such as lithium, manganese, aluminum and other materials otherwise needed to build those expensive battery packs.

        If you are not yet driving an EV, I do hope you’ll be able to be doing so soon… I particularly love the near-silence driving experience,, being able to eliminate smelly gas stations from my daily routine, know I am not pumping out pollutants for others to breathe– I know my money is staying here in the US rather than finding its way into the pockets of terrorists and tyrant oligarchs in foreign lands.

        • nordlyst

          I don’t think this is accurate. As far as I know, gas stations usually make their profits not from the fuel they sell, but from the hot dogs, magazines, CDs, chocolates, coffee and gazillion other incredibly needed things they divulge. If so, EVs are perfect customers since charging takes more time but less attending than filling up. More hamburgers is what it means…

          But the number of stations that could be sustained is much smaller, and the best locations utterly different. As we move to 60 kWh and more, 95% will do 99% of charging at home. We will visit a charger very infrequently compared to how often we used to visit gas stations.

          Most stations will disappear eventually, but it’ll obviously take decades. Even if every car sold starting now was an EV, half of cars would be fossils ten years from now. And most reckon 25% market share, 25% of new cars being EVs, by 2030 is optimistic on behalf of EVs.

          There’s little reason for station owners to worry that their business will suddenly collapse, in short.

  • QKodiak

    Half an hour is nothing. That’s like a coffee, a donut, and a couple funny Youtube videos. Using the bathroom would add a few minutes to that time.

    • nordlyst

      It’s nothing for many of us, who don’t regularly drive distances that require charging along the way. I’ve been able to live with a 2012 LEAF as my only vehicle for a year. But there have been times when faster charging would have made a big difference. Like when I changed the charging program and forgot, came out of work in minus seventeen Celsius to find I hadn’t charged, and I came to the nearby fast charger to find three people in queue already – the location has two DC points, one of which was inoperative that day. That was a cold, long wait. 🙂 Although also a social one as we got into one car running the cabin heat on high and chatting away the time.

      I don’t even consider going far because it takes too long with the frequent and long charging stops. An average rate of 60 kW would do for me, but not for everyone.

      And besides, there’s the economics of charging stations. The more power, the cheaper the network becomes (at least when there’s enough cars for stations to often be busy). Less land and gear to get the same capacity matters much more than more expensive components to handle high currents.

      Batteries will also accept more power even if no radical breakthroughs occur. Internal resistance is lowered every year. As for the bulky cables, wireless charging simply eliminates them. At high power it is already as efficient as cables!

  • jstack6

    Cool idea, Pun intended. But what about battery life? To be sustainable the battery should last 10-20 years at 80% capacity or better. My FORD Focus EV doesn’t even do fast charging so the battery is good for 20 years at 80% or better. So far 3 years in Phoenix heat and not even 1% loss. I’m very impressed.

    • nordlyst

      How did you establish that there’s no loss? Hopefully you don’t believe the car will start showing a full charge as less than 100%, because it won’t.