With the capability to add 170 miles of range in just 30 minutes to Tesla Motors’ flagship Tesla Model S luxury sedan. Tesla’s proprietary Supercharger rapid charging stations are the most powerful electric car charging stations in the world.
Unlike other designs of rapid charging stations, which tend to house the heavy power electronics needed to turn high-voltage three-phase AC electricity into the direct current power needed to charge an electric car battery pack, Tesla’s Supercharger design houses its power electronics away from the actual charging stalls. This results in a smaller, more ascetically pleasing charging station that is connected to Tesla’s modular Supercharger units by a long, heavy cable which passes to the charging stall and then on to Tesla’s hidden Supercharge electronic units, often hidden to one side behind a wooden fence.
As any electronics engineer will tell you, the cable is the bulky thickness it is in order to allow 120 kilowatts of high-current electricity to pass along it without causing the cable to heat up and start a fire, with the cross-sectional area of the cable, the length of the cable, and the material it is made from dictating how much electricity can safely pass down it without major system losses.
But as Tesla CEO Elon Musk divulged during last week’s Tesla Motors Annual Shareholder meeting, Tesla engineers have found a way to make Tesla Supercharger cables lighter, more efficient, and easier to use: liquid cooling.
What’s more, thanks to YouTube Tesla Model S vlogger Christopher Allessi II — aka KmanAuto (via GreenCarReports) we’ve got a video of one of Tesla’s first liquid cooled superchargers in action, detailing how cool the cable remains in operation.
So how does Tesla’s new lighter, thinner liquid cable work? To explain, we’ll need to delve into a little physics.
While all metals are capable of conducting electricity to some degree or other, every metal has some degree of electrical resistance, meaning that the conductor has some opposition to the passage of electric current through it. For electric wiring, high-conductivity metals such as copper and aluminium are preferred, allowing an electric current to pass along as unimpeded as possible.
That opposition to current flow — or a wire’s resistance — is dependent on what it’s made of, it’s length, cross-sectional area, temperature and the current being pushed through it.
Increasing a cable’s length, and the current flowing through it, and more of the electrons passing through it will collide with the atoms inside the cable, reducing its efficiency and turning some of the electrical energy into heat energy — which warms up the cable. Thanks to the wonders of particle physics, when atoms warm up, they gain more energy, meaning they move around more in the metal and increase the probability of so-called ‘collisional process’ within the wire. Which in turn raises the resistance of the cable further, reducing its efficiency even more and of course, leads to more energy being converted to heat.
(For those who are curious, that’s essentially what happens when you blow a fuse in an electrical circuit, but the wire inside the fuse is designed to quickly burn, breaking the electrical connection, if the current drain is too high.)
Here comes the clever part. To reduce the resistance of a cable for a given current, you can either increase the cable’s cross-sectional area, or reduce its temperature. A super-cooled cable is capable of carrying a much higher current than the same cable in a warm climate, so by cooling the cable along which the electricity passes, Tesla engineers have been able to improve the design of the Supercharger stall cables, replacing the bulky, stiff, unwieldy cables of early superchargers with a more flexible, smaller, liquid-cooled cable.
Just like liquid cooling of the power electronics inside each Tesla Model S, the liquid cooling system allows the supercharger stations to be more efficient, more compact, and capable of operating at full power across a far larger temperature range.
As the video above shows, water-cooled supercharger stalls are slightly different in their design to Tesla’s first-generation Supercharger stalls. First of all, there’s a small vent at the bottom of each stall where the cooling radiators sit. Next, the cable is thiner and lighter, with the actual charge plug replacing the mechanical switch of the original Supercharge connector with a capacitive tough-sensitive one, presumably to increase the area inside the connector for liquid cooling.
Taking an infra-red thermometer to the cabling, Christopher shows that the liquid-cooled cabling is also far cooler on its exterior than previous supercharger cabling, which results in it being more pleasant to handle, especially on a hot summer day.
It’s worth noting too that the cooling system used on this next-generation of Tesla Superchargers also opens up the possibility that Tesla may one day be able to increase the current and therefore the speed of supercharging its cars, especially if the cooling system can lower the temperature significantly enough to allow a higher charge current without sacrificing the smaller, more manageable cabling.
We can’t wait to see what innovation comes next.
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