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Monday, February 20, 2017

Supercharger Hidden Grace Period

Tesla Motors recently announced their new idling fee. The fee is designed to encourage people to move along after they have charged up. Of course, electric cars don't "idle" in the same way that gas cars do.
Idling in a gas car is sitting in one place while the engine on, emitting fumes from the tailpipe. Idling in Tesla's program is sitting at a Supercharger station after your vehicle has finished charging. This blocks the charging spot, meaning that others cannot use it. As an EV driver, if you need to charge, and access to the charging equipment is blocked by a car that is not using it (EV or not), it is infuriating.

To alleviate this problem, Tesla has instituted their idling fee.

Briefly, if a car completes its charge, and the charging stations at this location are more than 50% occupied, a fee of 40 cents per minute begins to accrue. If the car is unplugged and moved within 5 minutes of completing the charge, then all fees are waived. If, however, it's idle for more than 5 minutes in an active location then the fees keep accumulating: $0.40 per minute, $24 an hour, $576 per day. This is expensive parking. The fee is meant to encourage people to move along quickly once their charging is complete.


In an earlier post, before the program details were announced, we speculated that there would be a 30 minute grace period. As you can see above, there is only a 5 minute grace period. But perhaps there are some minutes hiding here that we can uncover?

The Hidden Grace Period

That 5 minute grace period is not all of the "grace" that a Tesla driver is granted. Supercharging includes an implicit grace period. As we discussed in our recent Supercharger powered trek article, Tesla's navigation system will tell you when you have enough charge to make it to your next location. Most Supercharger locations are within 150 miles of each other. This means if you have 200 plus miles of range in your Tesla, you won't need a full charge to get to the next Supercharger (if that's where you're going). There may be times when you truly need a 100% charge, but these are rare with a long range EV.

The charging rate of Lithium batteries slows down above an 80% charge. The last 20% can take 20 to 30 minutes. This means that the time from the Charge-needed level to Fully-charged is usually not needed and it is the slowest charging rate of the battery. This time is the implicit grace period.

Kōkua: Hawaiian word for giving to benefit others

Let's look at an example:
You're driving a Tesla with 250 miles of range. You pull into a Supercharger near empty. It's 150 miles to your destination. You plug in and walk to the nearby restaurant. You take a seat in the restaurant and order a meal. Twenty-five minutes later you receive a notice on your phone, you have 170 miles of range and you can reach your destination.

The charging does not stop just because the vehicle has enough to reach the next destination. Instead, the charge only stops when the batteries have hit the user-settable full level. In this case, on a road trip, you've put this setting at or near the maximum. The notice on your phone further says 25 minutes to a full charge. At this point, if you are a conscientious person, you would go and move your car to free the spot for others. Or maybe you can see the supercharger site and see that there are free stalls available, so you finish your meal and let the vehicle charge up for another few minutes. You make it back to your car and you are on the road before the 5-minute idle countdown even starts.

In this example, the 25 minutes from 170 miles to a fully charged is the implicit grace period. Along with the explicit 5 minute grace period, this gives you a 30 minute grace period in this example.

Driving electric is not just picking another fuel source, it is joining a community. Please practice Kōkua charging, or as we've referred to it, Lagom charging.

Happy electric motoring!