Tesla: Five Minute Recharging On The Way, Without Battery Swap

By · July 16, 2013

Tesla SuperCharger

How fast, in theory, could a Model S driver fully charge and return to the highway? (Photo: Brad Berman)

California-based Tesla Motors is streets ahead of the competition when it comes to both the range of its electric cars and the speed at which they recharge. But Tesla isn’t content to simply maintain that lead: it wants to refill a battery pack in just five minutes, without battery swap technology.

Speaking with the MIT Technology Review, Tesla’s Chief Technical Officer JB Straubel said that in the future, Tesla cars will be able to refuel at its supercharger stations as quickly as five minutes. “It’s not going to happen in a year from now,” Straubel said in a recent interview. “It’s going to be hard. But I think we can get down to five to 10 minutes.”

Currently, the company's 120-kilowatt DC supercharger stations provide Model S owners—at no additional cost—up to 200 miles of range in about 30 minutes. Tesla also recently announced plans to offer battery swap capability at select Tesla superchargers for drivers who can’t—or don’t want to—wait for their car to recharge. The swaps, which would come with a fee, would provide a fully-charged pack in about 90 seconds (not including any time spent in queues).

Tesla isn’t the first company to explore the option of super-fast DC recharging. Last month, PluginCars.com reported on the Silex Hypercharger—a 1.5 megawatt ultra-fast recharging solution for the as-yet-to-be-built Silex Chreos. The grid-connected Hypercharger is hyperbole at this stage, but Tesla’s interest in super-fast charging provides more legitimacy to the concept. For example, to recharge an 85 kilowatt-hour Tesla Model S battery pack from empty to 80 percent full in five ten minutes would likely require a 720 kilowatt supercharger. That's half the power of the theoretical Silex Hypercharger.

Moreover, Tesla’s plans to introduce grid-tied energy storage (via stationary batteries) at its supercharger stations means it’s possible to provide high power to recharge an electric car quickly without dramatic impacts on local grids.  When not charging a car, these battery packs would be gradually replenished to prepare for the next customer, either through on-site solar panels or by a more modest flow of electricity from the grid.

Awareness of Hurdles

Summoning 720 kilowatts of power to supercharge a Tesla is theoretically possible, but there are significant technical hurdles, such as managing heat. The faster you charge a battery pack, the hotter it gets. While the Model S features an active liquid-coolant thermal management system capable of maintaining optimum temperature in the pack, the amount of heat generated by charging at 720 kilowatts is much higher.

Straubel is aware of the challenges. “To do that kind of charging, everything has to be designed and working in perfect synchrony,” Straubel explained.

Comments

· · 39 weeks ago

Ok, sorry, but this article is the biggest pack of nonsense I've heard yet on plug in cars.

1). The numbers don't make sense.

720 kw * 5 minutes is 60 kwh.
80% of 85 is 68 kwh, usually.

Where is the magic 8 kwh going to come from? Ok, lets assume it had a 9.4 % charge when parked and wasn't totally dead to start with..

"...The faster you charge a battery pack, the hotter it gets......"

Where does all this heat come from, if we are not taking losses into account.

2). Since we have to take into account losses, lets say 720 kw for 10 minutes.

Maybe Tesla will float another stock offering and then have enough cash to build these 10 minute "Hyperchargers".

Meanwhile, the charging cable is going to be 1500 volts at 480 amps. Seeing as Tesla's own EVSE futuristic looking 80 amp thing supposedly overheats and the owners have been told to not use more than 60 amps, I'm not sure I'd let Tesla design this one. Plus they better have a crane to lift it for anyone who didn't eat their Wheaties this morning.

· · 39 weeks ago

Not to mention amount of power swing on the grid. That is lot of power draw "on/off" for a supercharger station. It better has its own battery backup stations.

Also, even at 5% loss @ 720KWh, that is 36KW heater.

Last time I looked, a 36KW heater is pretty powerful, about 25 hair dryers or portable space heaters blasting at the same time...

· · 39 weeks ago

Thanks guys, and sorry for the errors.

I guess I should have used the words 'approximate' and 'usable' in reference to this one. I'm pretty sure that 80% useable SOC will be nearer 60 kWh on a battery that big, but you're right: my math is out. And I'm sorry.

Heat will come from the increasing internal resistance of the pack. The higher the current, the more the pack will resist the flow of electricity into the battery pack, so the more heat will be lost.

You're right too: there are some physical hurdles to overcome too, including the size of the connections used. As for the heating? I was thinking about this last night. Maybe Tesla will have to change the pack design to include more cooling as a mid-cycle update? I'm not an engineer, sadly.

I'll make that math corrections now...

· · 39 weeks ago

It's all right, Nikki. At least one person didn't take the 5 minutes to be literal to the second. I got it that Tesla is talking in generalities.

Don't shoot the messenger, guys.

· · 39 weeks ago

Nikki:
Congratulations on just straightforwardly saying that you slipped on the math.
It happens - to all of us on occasion.

· · 39 weeks ago

@Bill,

For a rough order-of-magnitude calculation, I can see how one would arrive at 720kW. It's quite simple. 5 minutes is 6x faster than 30 minutes. 720kW is 6x faster than 120kW.

"Currently, the company's 120-kilowatt DC supercharger stations provide Model S owners—at no additional cost—up to 200 miles of range in about 30 minutes"

Otherwise, your points are all valid. This is a major engineering challenge. One that, in my opinion, is completely unnecessary. Stopping for 30 minutes every 200 miles isn't really a bad thing. If people are more rested, our roads may even become safer. Plus, unlike filling a gas tank, you don't have to stand next to an EV while it's recharging. Go use the restroom and grab a snack.

· · 39 weeks ago

There is something I don’t get about the charging voltage of 1500 V.
If the 18650 cells have 3.7 V and there are 8000 of them in a pack, when they are in a serial arrangement that gives a 29600 V value not 1500 V. A standard car plug is not operating at a low 1500 V neither so why stick to such a low value. At 29600 V you need 20 times less amperage, so the cable is much smaller. Perhaps not the full 29600 V but 6000 V would certainly be a better base to start with. The charging process could also be made with secured under the car connectors so that no hand manipulation is necessary.

· · 39 weeks ago

With an under the car connecting it would also be possible to make a simultaneous double hydraulic connections for cooling. Sending a 3 gallon per minute flow though cooling liquid would be able to draw the 5% heating gently. Leaving the cooling back to the car system once the charging is over.

· · 39 weeks ago

@Priusmaniac

Why stick to a "low" 1500 volts? Because it is the highest voltage that reasonable cost (under $1000) connectors exist.. Once you get over 2000 volts you have alot of problems with corona and keeping water away from the connections, etc... 1500 is hard enough.. The only reason 'commodity' lowcost solutions exist is because of use by the oil-pumping and mining industries. So unless Tesla wants to reinvent the world, I would imagine they would have 1500 volts as an upper limit. They have problems with those red and silver 80 amp EVSE things. A red roadster owner friend of mine recently got his model S and was told to not use the thing at 80 amps. but derate it to 60 because the thing has a problem of overheating at 80. Also, he says he has burned out 2 - 40 amp uninversal mobile connectors on the Roadster (I don't have this problem, I unlike 99.9% of other Roadster owners, use a j1772 adapter only). So Tesla apparently needs to get someone else to design this stuff for them since they seem to be having more than the usual trouble.

@Brian Schwerdt

HI!
The reason you can't just multiply everything by 6 is that at those charging rates the battery internal resistance will create losses 36 times greater, not 6. That's why I'm supposing 10 minutes is doable, but not 5. And again, in view of Tesla designed equipments having multiple heating problems, they should get someone else to review their designs. I'll do it if they want.

· · 39 weeks ago

Just to set the record straight and to make Nikki feel a bit better, I was criticizing the information, not Nikki. Nikki you apparently thought this was against you, but in your defense u were only reporting on J. B. Straubel.

These comments of his boarder on ridiculous as mentioned. Every word I type is disected with a fine-tooth-comb, and I'm not paid a bit. Straubel gets $millions so I'm sorry, self appointed "Source Authorities" I hold to a somewhat higher standard.

· · 39 weeks ago

Guys, you can't compare it to conventional charging technology, fast charging concepts have been demonstrated by ABB recently and they are talking about seconds and not minutes. Check out the link to find out more. http://www.abb.com/cawp/seitp202/F32C9DED54DC0B20C1257B7A0054972B.aspx

· · 39 weeks ago

@TKS

Interesting press release, but the highest power levels I saw anywhere in those documents were 400kw. If you notice my postings, I'm not criticizing even 720 kw as not working. By the context, I'm saying even 720 kw will work, I'm just saying it won't work in 5 minutes, but 10 minutes is doable.

Electricity behaves in a certain way all the time. Until they can change the way that electricity behaves, stuff which is a non-problem at lower speeds will continue to show up with high-speed charging. Now as far as busses are concerned 4 minute charging will work, because the batteries were relatively small. And we're talking proportion here. 400 kw is not so overly huge an amount where you're talking about a bus.

The thing I would question with ABB is that there is are huge cabinets worth of equipment at every single bus stop... If they would just put a decent sized battery on the bus to begin with (and as BYD is doing with 324 kwh batteries on their busses), then no infrastructure is needed at the bus stop at all. As it is, the ABB link looks to me just as a "GEE WHIZ look what we can do!!". Or, a Solution looking for an imagined problem.

If all you want to do is push a push a bus down the street for a work shift, then BYD seems to solve this problem. LA seems to think so since they've ordered 5 of their busses.

· · 39 weeks ago

bill said: "this article is the biggest pack of nonsense I've heard yet on plug in cars"

Whoa-wee-whoa. Hyperbole much there Billy boy?

· · 39 weeks ago

@Edhead

You mean you've heard greater nonsense than this? Its certainly the silliest thing I've heard come out of Straubel's mouth to date...

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