Set an end timer to charge your electric car

by Ernie Hernandez on July 6, 2014

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Why should I set an end timer?

All electric cars and many EVSEs (electric vehicle supply equipment) come with a timer that offers the ability to set a start time, end time, or both to enable you to charge your electric car within a specific time window. This article offers a sound reason to use the end timer function provided for your use.

A recent study by a company called Opower has highlighted the fact that a western US region showed higher electrical power usage by electric vehicle (EV) owners than non-EV owners, and specifically a sharp spike in power usage at midnight with usage dropping dramatically after 1:00 AM (found here). While Opower is picking on Tesla owners in the title of this blog post, they are actually targeting all EV owners. Based on their findings, there is some reason to.

Many energy companies offer time-of-use (TOU) rates for EV owners. These TOU rates may run from midnight to 5:00 AM or they may be as broad as 11:00 PM to 7:00 AM, depending upon the market and the utility company. Energy costs are significantly less during these non-peak hours as the utility companies generally have much lower demand for electricity during these times. By encouraging EV owners to charge their EVs in the middle of the night rather than in the evening when they come home, the utility ends up selling just as much power, but managing their power generation more evenly.

The challenge for the grid is that as EVs gain popularity, if everyone sets their charge timer to kick on at midnight, it can cause a huge surge in demand all at once. The way to alleviate this is to set the end time rather than the start time. Depending on the vehicle or equipment the timer may read as “Start” and “End”. Or it may read as “From” and “To”. It doesn’t really matter what the words are, but it does matter that you understand your vehicle or your equipment.

As we have learned with our range remaining indicators, there is much wiggle room in the proclamation of these numbers. The same can be said for the end time settings – these are rough estimates rather than precise determinations. Most electric cars will stop charging well before the end charge time is reached. For our purposes as EV drivers, this is fine. We still have a fully charged car so we can go where we need to go. As importantly, for the utility company, there is no large spike in demand at midnight. Rather there is a more even demand spread out throughout the the night as EV driver’s vehicles recharge with varying start and end times. The end result is that this works well for everyone involved. Do not set a start or from timer at all. The use of an end timer will provide you with the same result as using the start timer, but it works out better for the utility. Which means it will probably work out better for you when it comes time for your state’s public utilities commission to review utility rates.

{ 4 comments… read them below or add one }

SteveF April 9, 2015 at 3:04 pm

Maybe I’ve been thinking wrong about the charging timer. I assumed it was to define a block of time where it’s desirable to charge the car, and if you plug in during that span of time it will start charging. I’m starting to suspect a “start” time will only matter if the charger is attached at that time. By not setting a start time, will the car estimate how long it will take to charge and start at the end-time minus the duration needed? If there isn’t enough time to fully charge before the end time, would it just start immediately to get as much as it can?

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Ernie Hernandez April 14, 2015 at 8:41 pm

Steve – Welcome to Living LEAF. You are exactly right. The idea of the timer is so that you can plug in as soon as you park, and it will start charging when it reached the start time. Your second statement is also correct. I personally always recommend using only the end timer. The car knows how much time it needs to charge. When you plug in it will determine when to start charging based on that need. Also, by charging this way, the car sits with a full charge for the least amount of time thereby prolonging the life of the battery.

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Ben December 11, 2015 at 8:33 am

How can the Leaf determine how much time it needs to charge when it has no idea how much power the EVSE is going to supply to the car? The implementation of the “timer” on Leaf model S is very confusing and meaningless. Even Nissan is unable to explain its operation in the manuals.
I have had situations where my car stopped charging prematurely and other situations where the timer had no effect. This really is very bizarre.

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Ernie Hernandez December 11, 2015 at 10:38 am

Ben – Welcome to Living LEAF. That is a great question, and a variable that I had not considered before now. I will reach out to Nissan to see if they have an answer.

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