How Fast Can You Really Charge Your Plug-in Car? The Answer is More Complicated Than You Think

· · 7 years ago

We are quickly approaching the launch dates of the Nissan LEAF and Chevrolet Volt—the first two globally-distributed and mass-market plug-in cars the world has ever seen. Beyond those two groundbreaking vehicles, every major automaker has now committed to delivering some sort of plug-in vehicle within the next five years. As the public's attention shifts to the battery-powered drivetrain and its perceived shortcomings, the question of how long it will take to charge the battery has rightly taken center stage.

To this point, much of the conversation regarding plug-in car charging times has revolved around what kind of charging station you use. In the US, as many of us know, there are essentially three types of charging:

  1. A standard 3-prong household outlet, also known as "Level 1 charging"
  2. A specialized home charging station, also known as "Level 2 charging"
  3. A commercial quick charging station, known alternately as both "DC fast charging" and "Level 3 charging."

Listening to radio and TV shows, and reading through internet threads devoted to the topic of "How long will it take me to charge my electric car," it is apparent that there is a very big information gap out there when it come to charging times and what you might reasonably expect for your Nissan LEAF or Chevy Volt or Coda Sedan or whatever other electric car come down the pipe.

A battery is just a storage device for energy. Any given battery's potential energy storage is rated in terms of kilowatt-hours (kWh). For instance, the Nissan LEAF effectively has a 22 kWh battery, and the Chevy Volt effectively has an 8 kWh battery. In the US, your standard household outlet (Level 1 charging) can deliver about 1.6 kW (after accounting for losses and other items). To figure out how long it will take you to fully charge a given battery, simply divide the battery's size by the outlet's output. For instance, a 16 kWh battery will take 10 hours to fully charge from a standard outlet (16 kWh/1.6 kW).

So, if you install a Level 2 home charging station in your garage, how much shorter will the recharge times be? In the US, Level 2 stations are rated up to 14.4 kW (240 Volt / 60 Amp) outputs, but most of them will probably be installed on standard dryer circuits (240Volt / 30 Amp) and be able to output about 6.5 kW (after accounting for losses and other items). Of course, you can go higher if you buy a station that is rated higher and you pay for the upgraded wiring and circuitry to get you to 60 Amps, but for the sake of discussion, let's assume an output of 6.5 kW for a Level 2 station.

Using the same logic as for your standard household outlet above, you'd think a Level 2 station could charge that 16 kWh battery in about 2.5 hours, but this is where things get a little tricky. As it turns out, the station is just the energy supplier in the charging world—the actual device that regulates charging speed is on-board the car. And, as it also turns out, this on-board charger is the absolute critical piece to understanding how fast you can charge your brand spanking new electric car.

If you wanted to take maximum advantage of your typical Level 2 station, you'd want an on-board charger that could handle at least 6.5 kW. In fact, looking back at previous electric cars that were released back in the California mandate days, the original Toyota RAV4 EV was equipped with a 6.6 kW charger. Today, things are quite a bit different though. The first gen LEAF is shipping with a 3.3 kW charger, same as the first gen Volt. The Coda Sedan, however, is shipping with a 6.6 kW charger.

So even if your Level 2 station is rated at 6.5 or 6.6 kW, if you have a LEAF or Volt, you'll never be able to push more than 3.3 kW to the battery at any given time—resulting in charging speeds that are half that of what you might expect based on the charging station's stats. However, if you have a Coda, you'll be able to take full advantage of it. Even more confusing, the on-board charger doesn't affect how fast you can charge your plug-in at a DC fast charging station. In that case, the DC station is just dumping energy very quickly into the battery and kind of bypasses the on-board charger. You could get a Nissan LEAF battery from 0-80% full in about 25 minutes at a DC fast charging station. The Volt and Coda don't have DC fast charging capability.

In their defense, Nissan has said that the inclusion of the 3.3 kW charger was a choice they wouldn't make again in retrospect, and they plan on upgrading to a 6.6 kW charger for the next generation LEAF. At that point they also plan on making the 6.6 kW charger available for installation in the first gen LEAF, likely for some additional cost. My guess is that the Japanese Nissan LEAF engineers, working in a secretive Japanese world when first designing the LEAF, based their assumptions on Japanese outlets. A standard Japanese outlet is rated at 200 V and 15 Amps, or about 3 kW. In Japan there won't be any Level 1, Level 2, or Level 3 charging—just standard household outlets and DC fast charging while on the road—so there's no need for a charger rated higher than 3.3 kW. Whoops...

Yet, in the end, all of this talk of charging speeds and times from empty to full really doesn't make much sense because we're rarely going to be filling our plug-in cars from empty to full. More likely you'll drive the thing 40 miles in a day and then come home at night and plug it in. When you wake up in the AM it will be fully charged no matter how long it took. But if you only have to drive 40 miles a day, even a charge on a 3-prong outlet is a reasonable 6 hours, so focusing the charging speed becomes less important.


· Kei Jidosha (not verified) · 7 years ago

You are correct that in the overnight charging commuter scenario that most will use, 3.3 or 6.6 kW charging are both sufficient. However, a 3.3kWh charger makes public opportunity charging almost useless. Add to that that the LEAF will not have Quick Charge capability unless you BUY it. A must if you ever want to venture outside of your 40 mile radius driving bubble. Nissan's decisions to go with a 3.3kW charger, and leave off L3 charging, are not helpful to EV adoption.

· · 7 years ago

Nick, I disagree that the charging speed isn't that important. Sure for most days the slower 3.3kW overnight charging will be fine, but there lots of instances where it isn't. My MINI can charge at 6.6kW (32 amps) or at 12kW (50 amps) and I'm really glad it can. There are plenty of times I get home late at night and need to leave early the next day. Maybe I went to a friends house or a dinner that was far from our home and I get home at 2am and need to leave for work at 7 with a full charge. Also charging at work I have become accustomed to driving as much as I need to during the day and only needing an hour of charging to produce the 35 miles of range I need to get home. I would need to charge the LEAF about 2 1/2 hours for the same amount of charge. Maybe I'm spoiled now that I've been charging at 12kW, but I'm not buying an EV with a 3.3kW charger. I think it was really shortsighted of Nissan not to have at least 6.6 kW charging built in.

· · 7 years ago

Tom and Kei,

To clarify, I didn't mean to suggest that charging speed wasn't important at all. I'm just as down on the fact that the first gen LEAF only has a 3.3 kW charger as the next guy. I would love to see all electric cars support the max 14.4 kW charging speed that Level 2 can deliver. My last paragraph was simply there to help us bring a dose of reality to the conversation. What I said was that (to paraphrase), if you only drive 40 miles in a day charging speed isn't important. For sure, there are clearly situations where it is important and I'll be the first one to say that. In fact, I would go so far as to say that Nissan should just come right out and suggest that when a 6.6 kW charger is available as an upgrade, all first gen LEAF owners should get one for free, if only as a reward for being part of the early adopter vanguard.

· · 7 years ago

Kei: I'm about to write an article on this very topic, but just so that everyone in this thread is clear on the topic, Mark Perry, Nissan's Communications guru for North America, has told me that some of the LEAFs that are being sold to people in the initial launch markets (the same ones that are part of the EV Project run by ECOtality: California, Washington, Oregon, Arizona and Tennessee) will have the DC fast charger installed for free. That is due to federal money that is being allocated for that to happen b/c those launch markets are getting a bunch of DC fast chargers over the next year. Other markets may not have DC fast chargers for quite some time so Nissan has made the calculation that most people in those market would opt to not have the device and save on upfront costs. I'll leave it to others to determine if that was the best business decision.

· · 7 years ago

Kei: the post describing how some people will get the DC fast charging port for free is now up. There are some good details in the there.

· Kei Jidosha (not verified) · 7 years ago

Since I live between the LA and San Diego ECOtality project areas, I should be able to travel all of California using their public infrastructure. But my county is not eligible, so QC is an extra cost option for me, and only on the more expensive SL model. And the thousands of Level 2 charge sites being installed are not time efficient with a 3.3kW charger.

I’m afraid that ECOtality will end up “proving” that Public/Quick Charge infrastructure is unnecessary because people don’t use it. Missing the real reason which is because they can’t, without a faster charger or QC connector.

· · 7 years ago

Kei, there's quite a bit of truth to your statements, but I also think that regardless of the availability of DC fast charging capability and 6.6 kW chargers on any given EV, the public infrastructure may be used so little that it may not justify the expense of operating it. Once we have 5 years of data under our belt, that's when the conversation on public charging infrastructure will really get interesting. And in that 5 year time, we'll also see Nissan's capacity skyrocket to greater than 150,000 EVs/year (with a 6.6 kW charger) so we should have some really meaningful numbers. If it turns out that most chargers sit idle 80% of the time, then I'm not sure where we go from there.

· · 7 years ago

So, I'm thinking, if I get an EV with a 6.6 kW on-board charger, and rarely if ever drive more than 50 miles per day, there's really no need for me to install a Level II charging station in my house. I can just plug into a regular 120V, level 1 outlet at night, and even if I've driven 90 miles (an extreme rarity), with the 6.6 kW capacity, I'll be at full range capacity after about 8 hours?

Is this correct?

If so, I'm definitely not going to invest a couple grand in a Level 2 charging station for our Colorado home. However, if I'm not doing my math right, please let me know -- maybe we do need that Level II home charging station after all.

· Anonymous (not verified) · 7 years ago

ONE CRITICAL point: All batteries have an optimum charge rate and it usually varies as the charge goes along; AND directly effects the longevity of the battery. In all cases, as a battery is charged, some of the charge energy is lost, turning into heat - i.e. the battery gets HOT, even in your cell phone. As the battery heats up, the charge process becomes more difficult. The answer is NOT to throw more power into it - remember all the explosion warnings about charging batteries with the wrong amp/volt charger? So the charge system is regulated [read: wait time]. Additionally, beside the 'heat up' loss, all charging systems have a loss in their conversion too - i.e. the charger gets HOT! Throwing MORE electric into it causes the entire "lossy process" to increase very quickly and once the battery cools, you see the actual charge amount, most likely accounting for the DC "slam" charge only yielding in at 80% of a full charge.
BUT in other words, your wasting electricity - so what good is that???

SO THERE WILL ALWAYS BE a wait time and count on it being a good bit more than the 'numbers' calculate...

· · 7 years ago

Anonymous (It would be nice if you came up with a more unique handle),
You're right and Nick missed the temperature factor. Charging is slower if ambient temperatures are high or the vehicle is designed with insufficient cooling to reject the heat from a faster charging process.

· Anonymous (not verified) · 7 years ago

It should also be noted that charging at faster rates decreases the long term life of the battery, so being diligent about using the level 1 charger could turn out to be a good thing if you can manage it...

· · 7 years ago

Anonymous -

Faster does not always equal less life. It (mostly) depends on how the heat is handled. And as others have mentioned - slower is sometimes worse for the batteries than faster. There is no absolute here.

Nick: I just read this article on another site (reprinted with permission). I didn't notice it was you who wrote it at first, and I was all in a lather to come back here with a link. I was very impressed to *finally* read something on the subject that had the facts correct. So very rare to see. Thanks for this great piece.

· Anonymous (not verified) · 7 years ago

no comment

· Sheldon (not verified) · 7 years ago

Nick... great article.
Just a quick correction though on battery capacity... The leaf will actually have a 24kWh battery.

· freeridelectric (not verified) · 7 years ago

Sheldon, Nick was making referance to what is usable of the pack. 24 kwh is the total of the pack in the Leaf, since it will hold some energy in reserve it only uses 22 kwh. The Volt will only use 16 kwh pack but will utilize only 50% so 8 kwh.

· Sheldon (not verified) · 7 years ago

good point... had not thought about that aspect.

· · 7 years ago

Freerideelectric - thanks for the back up! That's exactly right. Nissan has told me that the LEAF will be allowed to use up to 95% of its battery's capacity.

· Carl H (not verified) · 7 years ago

Using only HALF of a battery is ridiculous, but leave it up to Chevy to screw the pooch on something like this. With a cost of roughly 41k for the volt, there's simply no way it's worth it. I don't know what type of cooling systems these cars have, but all electric cars should have a good cooling system for the batteries so they can be cooled, not just when running, but when charging as well. Keeping the temperatures reasonable is a key factor not only to get the maximum charge, but for battery longevity as well.

I'm waiting for the Tesla Model S - a REAL CAR, with a decent range. Even the "small" 160 mile battery will be far more than enough for me. My commute is only 25 miles round trip, so I could theoretically only charge once/week. The larger 300 mile battery will really bring electric cars into a "real world", it's just a question of how much additional this will cost.

The electric/gas hybrids are for the birds. Why would I want to buy a car that has all the problems of both technolgies? I want to leave ICE on the side of the road along with all of it's antiquated items like gas tank, gas lines, fuel pumps, exhaust pipes, heat shields, spark plugs, camshafts, drive shafts, clutch or torque converter, ignition, catalytic converters, etc.

If you absolutely NEED to take a longer trip, I see no reason why small trailers couldn't be created that housed a small diesel engine that produced sufficient electricity to power the car. Of course, once battery technology advanced by a factor of 10x or so and battery packs that last 3000 miles exist, then who needs a charging station.

· · 7 years ago

> I see no reason why small trailers couldn't be created that housed a small diesel engine that produced sufficient electricity to power the car.

And it has already been proven effective for the Rav4EV. Toyota actually commissioned these, but after three were made, the EV program was cancelled.

- Darell

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