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?

[UPDATE: 10/1/17 – Updated to include information about charge rates and times with L1 and L2 EVSE]

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.

Using the end timer on a LEAF

Let’s say your super off-peak electricity rates are from 11:00 PM to 7:00 AM. This provides an eight hour window to charge your car. If you use the 120 Volt trickle-charge cable that came with your LEAF, it will charge at a rate of about five miles of range for every hour plugged in. The math shows that you will gain about forty miles of range in this eight hour period. If you drove over forty miles, the car cannot be fully charged in an eight hour window. It will stop charging at 7:00 AM, but you will not have a full charge. If you have your end-time set and the car charges beyond the end-time, take it into your dealer for inspection. If you need a full charge, don’t set the end timer.

If you have driven more than forty miles and want a full charge in the morning, you will need to plug in prior to 11:00 PM. Your car will start charging before your super off-peak rates kick in, but you will have a full charge when you wake up. Your are now faced with the dilemma of saving time or saving money. Analyze whether you really need that 100 percent charge every day. If you are not arriving home with an empty battery each day, perhaps you can recharge forty miles each night and go to a 100 percent charge on the weekend. Or you could buy a 240 Volt EVSE.

Even the slowest 240 Volt EVSE (portable or wall-mounted) will charge in less than half the time of the 120 Volt unit. Many residential garages already have a 240 Volt dryer outlet installed. If not being used for the dryer, this could supply your LEAF assuming an appropriate breaker is installed. Since the LEAF S has no start timer, when you plug in the EVSE, the EVSE and the car communicate via the charge plug. The car then determines the capabilities of the EVSE and will start charging accordingly. You do not need to wait until 11:00 PM to plug in your car.

Check the amperage rating on any 240 Volt EVSE that you buy. The higher the amperage rating, the faster the charge. Low cost 240 Volt EVSE units typically operate at only 16 amps and take almost twice as long as units that operate at 30 amps. Most dryer breakers are 30 amp breakers, so they will support this EVSE use.

{ 8 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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Marshall September 24, 2017 at 5:38 pm

We just leased a 2017 Leaf S and were told there is no ability to program a start or end time for charging. Were you able to get a response from Nissan regarding Ben’s question?

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Ernie Hernandez September 25, 2017 at 8:34 am

Marshall – Welcome to Living LEAF. Unfortunately, not all Nissan sales consultants are as familiar with the LEAF as they should be. If you look on pages CH-23 thru CH-25 of your owner’s manual you will see directions for setting an end time for your LEAF charge timer. Regarding Ben’s question, when you plug the EVSE into the LEAF a communication takes place between the car and the EVSE to determine the charge rate. It then calculates an approximate time for achieving a full charge from the current battery state. If there is not enough time for a full charge, it will start charging immediately. This is outlined in the note on page CH-23. All the best with your new LEAF!

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Sara Lee September 30, 2017 at 10:34 am

We have a 2017 Nissan Leaf S and have been dealing with the charging problem. We could like to take advantage of the super off-peak electricity rate. The ideal time to charge the Leaf is 11pm to 7am. We use L1 charger, make sure charging timer on, and set the end time to 07:00. We plug in to charge at 11:00pm at night. However, the next morning, it keeps charging and doesn’t stop at 7am. Maybe 2 out of 10 times it would stop, and most time it doesn’t. We call the Nissan Support and even go to Dealer. I still couldn’t get an answer. Probably will get a wall power outlet timer to control the charging time. That is more reliable. Any suggestion???

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Ernie Hernandez October 1, 2017 at 9:14 am

Hi Sara – Welcome to Living LEAF. Congratulations on the purchase of your LEAF. You left out one important piece of information – what is the status of your battery when you plug it in. Just like an empty gas tank takes longer to fill than one that’s only half empty, the LEAF charge time varies based upon how far you’ve driven and how much state of charge is left. You did state that you use an L1 charge station, which is useful. This may help you understand your charge situation. With an L1 EVSE, your LEAF only gains about five miles in range for every hour that it’s plugged in. With your eight hour charge window that will put about forty miles of range back into the battery. On days that you drive over forty miles your eight hour charge time just isn’t enough. It seems it continues to charge past the end time set. This is not normal and you should have the service department look at it. It should still stop charging at your end time. Make sure someone didn’t turn off the timer though. A 240 Volt L2 EVSE will be able to fully charge your battery from any state within an eight hour period. Think of it this way – the 240 Volts are pushing the electricity through the lines faster than the 120 Volt L1 EVSE so it takes less time. If you do a Google search for 240 volt evse you will see many results. I recommend at least a 20 amp unit. 30 amps is better. The higher the amperage rating, the faster the charge. You can find some low cost L2 EVSEs on the market, but they are typically only 16 amp units. The cost to charge is no different whether your are drinking 120 Volt juice or 240 Volt juice, so you might as well charge faster.

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