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Published on July 2nd, 2019 | by Dr. Maximilian Holland

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Initial Testing Suggests New 62 kWh Nissan LEAF Suffers From #Rapidgate On Longer Trips

July 2nd, 2019 by  


A recent road test by German EV rental specialist Nextmove has found that the new 62 kWh Nissan LEAF still suffers from similar DC fast charging throttling (#Rapidgate) issues at elevated temperature as the 40 kWh LEAF. On highway journeys requiring more than one DC charge (i.e., journeys over 310 miles or 500 km), onwards progress in the new 62 kWh LEAF may become frustratingly slow. Let’s take a look.

Nextmove’s video has English subtitles — just ensure captions are turned on.

Background

The 2019 62 kWh Nissan LEAF brings some positive updates to the vehicle, first launched in 2010 and still clinging onto the global top spot in cumulative EV sales. (The LEAF will be overtaken in cumulative sales by the Tesla Model 3 later this year.) The most notable updates to the LEAF are the more powerful motors and an improvement to Nissan’s ProPilot driving assistance system.

But there’s also a steep price increase, with the Tekna trim price being £35,895 in the UK (higher prices than its battery electric competition, the Hyundai Kona EV or Kia Niro EV) and €47,000 in Germany (more than the Tesla Model 3 Standard Range Plus). The 40 kWh variant is still available from £27,995 in the UK for those who don’t need the additional range and power.

One crucial aspect that has not changed however is the battery thermal management. Nissan is steadfastly sticking with zero active cooling for the battery, instead counting on heat generated during driving and charging to passively dissipate into the surrounding air. If you need a primer on why this is an unusual design decision for a modern EV, have a look at our original coverage from last year. All of the LEAF’s competitors, except the VW e-Golf (which is soon to be replaced by the ID.3), have robust active cooling systems for their batteries, which keep temperatures in a healthy range and helps preserve their longevity.

In prolonged high power scenarios (fast driving, frequent hard acceleration, or repeated DC charging), the LEAF “manages” heat by reducing the power available (both in driving and in charging).

Whilst the e-Golf has been marketed primarily as a city EV, the 2018 LEAF was often marketed at a “go anywhere” EV, with many customers expecting to be able to take occasional longer journeys of several hundred miles involving two or more DC fast charges. See the below advert from Nissan Spain for a typical example — “Go where you want… without restrictions….”

To be clear, the LEAF performs fine for typical commutes and local driving duties. It can also handle leisurely longer journeys if these are driven slowly and with passengers expecting to take frequent breaks of an hour or more.

Nissan’s strategy of “reduce power to manage heat build up” was not made clear in marketing materials nor — in many cases — by sales staff in dealerships. Many of the 2018 LEAF’s owners were dismayed to find that these power restrictions often came into effect on longer highway journeys (roughly, distances over 205 miles or so), typically making trips involving more than 1 DC “rapid” charge frustratingly slow, and severely delaying travel times. Since shortly after the dawn of the motor vehicle, these are the kinds of journeys that drivers expect to be able to make from time to time, without having to put up with unexpected delays. The issue came to be known as #Rapidgate, referring to the frequent inability of the LEAF to make 2 or more DC “rapid” charges at expected charging speeds.

Photo by Jennifer Sensiba, CleanTechnica

To its credit, in some regions, Nissan has recognised the issue and offered a software update to make the charge power restrictions a little less stringent. This effectively changes the battery management firmware to allow the battery to reach somewhat higher temperatures before restricting the DC charging power. In mild climates, the degree of intervention/throttling is thus reduced in practice, typically making charging session not quite as frustratingly slow as under the original firmware settings.

Of course, this also comes at the expense of potentially exposing the battery to more heat more frequently, which may reduce the longevity of the pack. Perhaps for this reason, Nissan has chosen not to make the update available to owners in North America, where some parts of the continent can experience temperatures above 35°C (95°F) for significant portions of the year. (You can sign a petition requesting Nissan to reconsider this stance.)

Photo by Jennifer Sensiba, CleanTechnica

EV designs with active battery cooling avoid all of these power throttling issues, and it was hoped that Nissan might implement a basic active battery cooling system in the new 62 kWh LEAF. After all, such a system is implemented in the LEAF’s commercial sibling, the E-NV200, redirecting cool air from the vehicle’s HVAC unit over the batteries. This relatively simple solution does indeed help to keep the E-NV200’s charging power reasonably high, avoiding undue delays on longer trips.

Nextmove’s Findings

The people at Nextmove, having placed a first day reservation for the 62 kWh LEAF, and getting their hands on one before many European dealerships, specifically wanted to test whether this charge power throttling issue was still present.

Image courtesy NextMove

Their test was performed in warm summer weather in Germany, with ambient temperatures between 25°C and 30°C (77°F to 86°F). Whilst these are certainly “summer” temperatures in Germany and other mild climates, in other parts of the world, these are often “normal temperatures,” experienced (or greatly exceeded) during much of the year.

Nextmove’s managing director, and head of testing, Stefan Moeller, drove two journeys on adjacent days, each of 500 km (310 miles). He recorded 2 DC charging session on the first day, and another on second day. The 3 DC charging data points (seen in blue in the graph below) suggest that — at elevated temperatures — the relationship between battery temperature and actual DC charging power is indeed very similar to the 40 kWh LEAF’s charging profile. Note the the graph shows the 40 kWh LEAF with both the original software (red dotted line) and the updated software mentioned above (green line):

The 62 kWh LEAF was launched with a headline peak DC charging power of 100 kW, and supposed session-average DC charge power of around 70 kW, when on high power chargers capable of delivering 250-300 amps or more. Such chargers are exceedingly rare however, as most CHAdeMO DC fast charger stalls top out at 50 kW (and/or 125 Amps). The maximum power of the chargers in Nextmove’s test was 125 amps, so it is possible that the 1st recorded charge (peaking at around 44 kW) was limited by the charging stall itself, rather than being thermally throttled by the LEAF. However, that power level was delivered when the pack was at 38°C — corresponding exactly with the charge curve of the 40 kWh LEAF (with the firmware update). Is this just a coincidence?

More worryingly, whether or not this best-seen-charge-speed of 44 kW was temperature-limited or charger-power-limited, the drastically lower power (28 kW and 24 kW) delivered at subsequent DC charge sessions, corresponding to higher battery pack temperatures (47°C  and 49°C, respectively) can only be explained by thermal throttling. The 24 kW (corresponding to 49°C) was seen on the 2nd DC charge session on the first day of the test.

What caused this?

If these reduced charging speeds at higher temperatures turn out to be representative, and not just an unfortunate and unusual result only seen in Nextmove’s early testing, the remaining question then becomes — were these elevated pack temperatures normal? Were these high temperatures the result of an abnormal driving style, or abnormal conditions, or do they (and the throttled charging power that accompanies them) accurately represent what 62 kWh LEAF owners might expect on longer journeys?

Unfortunately, these battery temperatures appear to have simply resulted from normal highway driving speeds, and a normal pattern of DC charging. The ambient temperatures of 25-30°C (77°F to 86°F) would be considered mild in some regions. We can see this from the details Stefan provides about his journey.

Not-a-LEAF, in Leipzig. Photo by CleanTechnica.

The first day’s 500 km (310 mile) drive began at 7pm in Leipzig (24th June), with a full state of charge and ambient temperatures around 28°C. The battery pack was also at 28°C at the journey start. After just over 2 hours of driving at around 120 km/h (75 mph) — 235 km — the pack temperature had risen to 38°C, and the remaining charge was 19%. Note that this suggests that the full range at these speeds (in these conditions) may have amounted to ~290 km (~180 miles), which is about what’s expected for the LEAF. This is within ~10% of the EPA highway rating of 325 km (202 miles), which corresponds to steady 70–75 mph cruising, in ideal conditions.

At this point, Stefan stopped for his first DC charge, and received 44 kW peak power. The charging power reportedly tapered at around 60%, and it took around 50 minutes in total to reach 80% state of charge (from the 19% start). At the end of the session, the battery temperature had risen to 48°C. Note that, had the peak power been allowed to reach Nissan’s headline “100 kW” for any duration, and averaged 70 kW, the battery temperature would likely have greatly overshot 56°C. This 56°C has long been the temperature “redline” for past LEAFs, the temperature at which driving power gets restricted, and the temperature the charging software is designed to avoid at all costs. For this reason, I don’t think the 44 kW @ 38°C was simply a function of the charger’s power limit. I think instead, this is indeed indicative of LEAF’s heat management software.

Stefan then drove for another almost two and a half hours to a second DC charger, some 12 km short of the 500 km total journey target. He drove this stage more slowly, cruising at 110 km/h (68 mph), covered ~250 km, and saw the battery get down to 5% state of charge. Notice that this corresponds to improved total range of around 333 km (207 miles) at this slower cruising speed. The pack temperature had increased to 49°C by this point.

This 2nd DC charge session saw peak speeds of only 24 kW. Stefan admits that, with the time being around 1:00am already, he did not want to wait to let that 2nd DC charge session reach a high state of charge, preferring to go to bed and let the LEAF top up on a 6.6 kW AC charger overnight.

Even with pack voltage rising over the charging session, the peak DC speed of that session would anyway not have climbed very much beyond that 24 kW if at all. That’s very significant throttling compared to the likely 50 kW output cap of the charging stall. Had the session continued at 24 kW (or perhaps marginally higher), pack temperatures would likely have climbed from 49°C up to 51–53°C. Reaching 80% state of charge would also have likely taken well over 100 minutes. No wonder Stefan decided to head to bed, and do an AC overnight charge instead.

What kinds of journeys can avoid thermal throttling?

What does this preliminary test by Nextmove suggest to us? That on a warm day, starting from a full charge and driving at 120 km/h (75 mph) speeds down to 10% remaining charge (roughly ~260 km or  ~165 miles, depending on conditions), the 62 kWh LEAF will likely be able to give owners a reasonably quick 1st DC charge session. It can likely recover from ~10% back to ~80% state of charge in somewhere between 40 minutes and just over hour, depending on the charger, the conditions, and the actual battery temperature. This will be acceptable for some owners, even though alternative EVs like the Teslas can get same charging task completed in well under 30 minutes.

After that 1st charge break, driving the next stage from 80% down towards 10% state of charge, at the same highway speeds, another 203 km or 126 miles is likely possible before needing to stop to recharge once more (or, if you’re lucky, reaching your destination). Note that about 10% more range on each stage could be gained by dropping from 75 to 70 mph (120 to 110 km/h). However, after that 2nd driving stage, the 2nd DC charge (and all subsequent DC charges) will necessarily be slow — likely at 30 kW power levels or below (perhaps well below, as seen in Stefan’s 24 kW example above), if the ambient temperatures are around or above 25°C. These kinds of charging speeds will involve waiting likely 80 to 100+ minutes to return from 10% to 80% SOC.

Photo by Jennifer Sensiba, CleanTechnica

In sum then, the 62 kWh LEAF seems to be perfectly suited to taking convenient longer trips up to around 310 miles or 500 km, which only need one mid-point DC charge. Much beyond this, if it’s a moderately warm day (or hotter), any further DC charging sessions are likely to be throttled and progress may become frustratingly slow.

The 2nd and subsequent DC charges requiring 80 to 100+ minutes to regain 80% state of charge only give you around 90 to 100 minutes of highway driving at 75 mph (120 km/h). That approximate 1.1:1 driving time to charging time ratio for covering distances beyond the 2nd DC charge is actually similar to the ratio that 40 kWh LEAF delivers when given the same task. The best solution here is to drive more slowly (around 100 km/h or below) which will allow the pack to cool off between charging sessions. For more tips on long trip driving strategies, see my earlier discussion of the 40 kWh LEAF best strategy, much of which still applies to the 62 kWh version. See also Jennifer’s very detailed account of the her experience making a 1200 mile tour in the 40 kWh LEAF.

Photo by Jennifer Sensiba, CleanTechnica

Which LEAF to Choose — 40 kWh or 62 kWh? Or neither?

If you’re not too concerned about the slight power-output difference, the main distinction between the LEAF’s two battery sizes is the initial range they cover. The new 62 kWh version at least allows you, with 2 driving stages punctuated by a single DC fast charge, an initial 320 miles (500 km) highway journey. This should normally be possible without undue waiting around. In the 40 kWh LEAF, that initial delay-free range is going to amount to around 205 miles (330 km) only. If you almost never drive longer distances than this by car (and prefer to cover such journeys by plane or train), of course the LEAF will fit the bill perfectly.

Some families own two vehicles and will use the LEAF only as a 2nd vehicle for mostly local driving, or perhaps leisurely longer drives where frequent breaks and local visits are anyway part of the plan. Either of the LEAF variants will be fine if that’s the case.

The important question is whether the information about the vehicles’ capabilities and limitations is made very clear to owners up front.

Nissan upset a lot of owners last time around by not being clear to prospective buyers that the LEAF 40 KWh had (and still has) this charge throttling limitation on longer journeys. The UK advertising standards agency even officially ruled against Nissan for being misleading about this. Whilst many EV observers had hoped that the 62 kWh LEAF would — finally — be given some decent active liquid cooling (or even active air cooling), Nissan seem to be sticking to their engineering compromise and staying with passive cooling. So long as this limitation is made very clear to prospective buyers up front, that’s fine of course.

At the moment, the Nissan UK website has some bottom-of-the-page fine print that reads, “The Nissan LEAF is designed to support the majority of journeys in daily life and is equipped with charging safeguards to protect the battery during repeated rapid charging sessions in a short period of time. The time taken for successive rapid charging can take longer if the battery temperature activates the battery safeguarding technology.”

We can only hope that people read this or have their attention drawn to it. If anyone has already been in to a Nissan dealer or showroom to enquire about the new LEAF, I’d be interested to hear any account of whether the sales staff are making the charge throttling situation clear to prospective buyers, or not.

Photo by Zach Shahan, CleanTechnica

However, as Stefan points out in the video, in the region of the €47,000 price point of the 62 kWh LEAF “Tekna” trim in Germany, there are several much more capable long-range pure EVs available, including the Hyundai Kona, the Kia Niro and Soul, and the Tesla Model 3. All have well designed liquid cooling of the battery, which will not only help charging performance, but also battery health and longevity. For anyone wanting to do longer highway journeys in their EV, all of these EVs are much better options that either of the current LEAFs. The Tesla especially is designed for long highway range and very fast charging, with a road-trip experience not significantly different from any other vehicle.

What do you think about the new 62 kWh Nissan LEAF? Is this a vehicle that will work for you? Is the 40 kWh the more sensible option? Please let me know in the comments. 
 





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About the Author

Max is an anthropologist, social theorist and international political economist, trying to ask questions and encourage critical thinking about social and environmental justice, sustainability and the human condition. He has lived and worked in Europe and Asia, and is currently based in Barcelona. Follow Max on twitter @Dr_Maximilian and at MaximilianHolland.com, or contact him via LinkedIn.



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