This article summarise what Model S owners can expect when using the Supercharger network.

What is a supercharger?

Superchargers are proprietary, privately operated, rapid chargers that are built, operated and maintained by Tesla exclusively for the use of their cars.

The network covers most of the countries Tesla sell cars in and is rapidly expanding: for the current status take a look at www.teslamotors.com/supercharger

Access to the supercharger network is by paying a one-off fee (included in the price of some variants of the Model S) which provides unlimited use of the whole network for the life of the car.

How does supercharging work (briefly!)

Whenever you charge your car AC power (from the mains) needs to be converted to DC power to be fed into the car battery.

When you charge at home or at any Type 2 charge point, the single or dual charger modules inside the car perform this function, converting AC to DC at up to 11kW or 22kW depending on your car’s configuration.

A supercharger uses twelve of these charger modules, housed in an external cabinet, to provide up to 120kW DC directly to the car battery (bypassing the internal chargers in the car entirely).

A supercharging station is built with pairs of charging stalls, with each pair of stalls sharing access to a supercharging cabinet.  This means that if both of the stalls has a car charging in it then each car may charge more slowly than if they were alone. At larger sites (with 2 – 5 pairs of charging stalls) the charging stands are usually labelled A and B and so, in order to maximise your charge rate, you should try to avoid parking in a stall whose “twin” is already occupied.

How do I use a supercharger?

Drive into the space, making sure you’re the right way around (the charging cables are short, heavy and relatively inflexible so good positioning is important). Plug in the charging cable, and wait.  It’s extremely simple.

If you have the Model S iPhone app you will get notifications from the car when it has reached 80% and when it is full, and you can always check progress on the app or from inside the car itself.

When you want to leave, unlock the car and unplug the connector by pulling it out of the charge socket while pressing and holding the release button built into it.

How quickly will I really charge?

Tesla claim that you can refill a car from 10% – 80% charge in under 40 minutes, and that you can half-fill the car (i.e. reach 50% charge) in as little as 20 minutes.

These are both achievable, but they represent the optimum outcome and there are various factors that affect speed.

Temperature

If your car battery is either very cold or very warm, charge speed will be reduced so as not to damage the battery.  A cold battery will warm up as it is charged, which will allow charging to get faster.

State of Charge

The battery can charge at a much higher rate when it is relatively empty than when it is full (to avoid damaging it).  This tapering effect is discussed in more detail below.

Charge Rate Tapering

A supercharger is an extremely high powered charging unit which is capable of delivering 120kW of DC power to the car.  The car’s battery can only handle this level of power for a short time, and when it is mostly discharged.

The full 120kW is only available until the battery is about 25% full. As the battery fills, the charging rate slows down, and therefore at very high state of charge it becomes barely more than a trickle. Above 80% charge the rate really begins to slow down. Tesla recommend charging to 80% at a supercharger before setting off for your destination or the next charge site.  If there is another charger further along your route it is almost certainly preferable to stop charging, drive on, and stop a second time, rather than continuing to charge above 80%.

Above 95% the rate of charge is slower than many home AC charge units.  And by 98% charge the rate is so low that it is almost certainly not worthwhile for you to wait for the last 2%.

Sharing (A vs B)

Each supercharger cabinet feeds two charging stalls, so if two cars are charging at the same time their charging rate may be reduced. Since the maximum rate at which cars can charge decreases as they fill (due to Charge Rate Tapering) it is often the case that a car arriving at a supercharger with a low state of charge receives a large proportion of the total available because the first car’s battery is likely to have already filled up and therefore its charge rate will already be tapering. However, if two cars of equally low charge are connected to the same supercharger unit then the system splits power between them in a way that favours the car that arrived at the supercharger first. The second car therefore gets a smaller share of the available power initially, but this increases over time as the first car’s battery fills and its maximum charge rate reduces.

What if there is a problem?

The supercharger network is extremely reliable, especially when compared with other public charging networks.  All sites are actively monitored by Tesla from a central location and faults are quickly fixed.  It is extremely rare for an entire supercharger site to be offline.

If you have a problem supercharging (unexpectedly slow rate, or charge will not start at all) then try

• unplugging/re-plugging the connector
• another charging stall
• rebooting the centre console (press and hold both steering wheel scroll wheels).

If none of those works, contact Tesla customer services who are available 24/7.