How to manage a battery

Door mux op vrijdag 8 november 2019 12:47 - Reacties (23)
Categorie: Nissan Leaf mods & videos, Views: 6.348

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In this article, we will take a very in-depth look at lithium ion batteries used in cars and how they are managed. This includes balancing, thermal management and capacity estimation. Using this information, we can deduce what Nissan did wrong with their overheating Leaf battery packs

What is a battery?

To be clear, we will be talking about lithium-in batteries in an automotive context - BEV batteries. In the automotive sphere, the term 'battery' is generally used to point at the box that sits under your car - which contains much more than just a big electrochemical cell. A battery typically contains:
  • Electrochemical cells ('cells')...
  • ...grouped together in modules containing 2 or more cells
  • Compression frames around the modules or groups of modules
  • Some thermal management (cooling/heating) system
  • Multiple temperature sensors
  • Voltage sensing on each cell
  • Shunt resistors (used for balancing) on each cell
  • A current sensor for the entire pack
  • A big honking fuse
  • Large contactors (the name for really big relays)
  • A precharge resistor and relay
  • A big steel or aluminum housing
All of these components have an important function and basically none can be left out for a well-functioning automotive battery.

Cell grouping and compression frames
Lithium ion cells, like all other electrochemical cells, store energy in chemical bonds. More precisely; they produce a current (and voltage) when converting one chemical into another, and for lithium-ion chemistries, this reaction can be reversed by reversing the current. But however well this chemistry is optimized, you are still dealing with two different chemicals in the charged and discharged state, and different chemicals tend to have different physical properties. One of these properties is density, or how closely-packed the molecules are, and for the most common types of lithium-ion batteries, the active ingredients in the battery tend to take up more space when the battery is full compared to when it is empty. In other words; the battery expands a little bit when charged.

This has big consequences for longevity. When a battery is charged and it expands, it may not expand the same way everywhere. If we take a pouch-type lithium-ion cell like those used in the Nissan Leaf, the pouch tends to bulge outwards on the large faces when charged. In the middle of the pouch, this means the active material is least dense, while on the edges it is closer together. This causes a lower resistance path to form on the edges of the cell, increasing the rate of discharge there as compared to the middle of the cell and heating up the sides a little more. Moreover, the mechanical movement of the middle of the cell will 'mash' the insides of the cell, causing mechanical damage over time. This is why cells tend to have a big metal cage around them, called a compression frame. This frame makes sure the cells stay flat throughout. They also generally make for easy to assemble packages with relatively few electrical and mechanical connecions. The MUXSAN extender batteries use modules with 12 cells in a compression frame, Nissan uses a few different groupings; cells are grouped 2 at a time and then grouped with 6-16 groupings in a compression frame.

And why do we use many cells and not just one? Well, this all has to do with the types of voltages you need to efficiently deliver the power needed to drive a car. Cars have standardized to about 400V, and with li-ion cells being about 4V per cell, you need roughly 100 cells in series to get to that voltage. Moreover, if you would make one giant cell and even if you could run a car off 4 volts - that cell would have terrible thermal characteristics, likely boiling in the middle even with the sides touching a refrigerated surface. It helps to chop up the battery in many tiny bits to increase the surface area and improve thermals.

Thermal management
There are a lot of misconceptions about thermal management, so let's try to reduce them a bit. Batteries are chemical devices, so they have to obey Arrhenius' law of reaction speed. Roughly speaking, for every 10C increase in temperature, chemical reactions occur twice as fast. In batteries, this means batteries will be better able to accept and provide current at higher temperatures - by quite a lot. Here is a table of the internal resistance of Nissan's 40kWh battery as it changes with SOC and temperature:

Looking at the temperature dependence, the internal resistance doesn't quite reduce by a factor of 2 for every 10 degrees, but for some intervals it isn't that far off. Of course, reaction speed isn't the only thing that determines internal resistance. There is also the resistance of the copper and aluminum conductor plates that form the terminals of the battery and some other more complex physical processes that don't scale exactly according to Arrhenius. Internal resistance isn't one 'thing', it is a representation of all lossy processes inside the cell.

But, well, low internal resistance is a good thing, right? Low internal resistance means lower losses, so a battery should be kept at high temperature? 60 degrees, nice and full, that's clearly good according to this graph?

Well, not so fast. IR isn't everything. If only we would have a world where everything is decided by a single number. Higher temperatures means batteries will be more cooperative, but they also degrade faster thermally. A battery is a big bunch of chemical reactions. We prefer the particular reaction that charges or discharges the battery, but many more are possible, just discouraged. At higher temperature, those possibly damaging side-reactions will also go faster and degrade the battery more quickly. This is why there is a bit of an optimum. Around 25C, the battery is both warm enough to be spared of the low reactivity of cold weather and simultaneously cold enough to avoid calendar degradation.

But thermal management isn't just about removing or adding heat to get the temperature to around 25C. As you may know, Tesla heats up their batteries before fast charging - that reduces the internal resistance. But during driving, it keeps the battery colder. Clearly, there isn't one particular 'best' temperature at all times. What really counts, is that the battery is at a consistent temperature! After all, when one part of the battery is at a higher temperature than another - or worse: when one part of a *cell* is at a different temperature from another part - you will get parts of the pack that charge at a different rate from the rest. Or even that degrade differently. This is a big problem in the 40kWh and 62kWh Nissan Leaf, where the top of the pack typically is 5-10C hotter than the bottom. This will cause the pack to degrade and charge unevenly, ruining performance and longevity.

So really, we shouldn't think of thermal management as heating or cooling the battery - we should primarily see it as keeping the entire package at the same temperature throughout. Exactly what temperature is not as important.
quote: practical example: 40kWh Leaf battery losses
The internal resistance causes losses in the cell, and these can be large. Say we have a pack at about 50% charge and 25 degrees C and we accelerate at full power. This is about 400A draw or 200A per cell at an internal resistance of 1.14 mohm per cell or 96x1.14=109.44 mohm. The total losses then are P = I^2R = 2 x 200 * 200 * 0.10944 = 8754W. This is an extreme example, but about 6.7% of the power is wasted in the battery, heating it up.

Well, actually, 6.7% isn't that bad. But this is just the beginning; we're actually doing what batteries like: being discharged at around 25C. How about charging, and how about charging a degraded battery? Here is the degradation characteristic of the 40kWh Leaf battery:

You can see that the initial bit of degradation - from 100% to 90% - is not bad at all. The internal resistance only goes up by 9%, which is practically negligible. The real damage occurs when batteries pass about 88% SOH; internal resistance goes up really quick, almost doubling for every 10% additional degradation. A battery at 80% SOH has an internal resistance of around twice that of the original battery. In the industry, a 100% increase in IR is typically the point at which a battery is considered end-of-life. Nissan considers the batteries EOL at 60%, when the IR has risen to 6.3X as much as new.

When discharging the battery, internal resistance is dominated by different effects than when charging the battery. This usually means that the effective internal resistance (or maybe more accurately: the internal losses) when charging are much higher than when discharging. Nissan doesn't give a charging IR table, but they do give a polarization characteristic with this tidbit in it:

This means the battery has similar losses when discharging at 150A or charging at 62.5A - 2.4x less. This in turn means the internal resistance when charging is approx. 2.4 squared or 5.76x higher, over long time periods.

So let's put all of this together and figure out why the 40kWh Leaf rapidgates (overheats when quick charging). Let's try to charge at 25C again, but with a battery at 90% SOC. This gives us an internal resistance of 109.44 x 1.09 x 5.76=687 mohm. At maximum charging speed - 125A from CHAdeMO or 62.5A per single cell - that translates into 2 x 0.687 x 62.5^2 = 5367W. All of this goes into heating the battery. Say you charge your Leaf battery from empty to full. On average, the fast charger provides 44kW, but in reality the battery only absorbs 44000-5367=38.6kW, so it takes almost exactly a full hour to charge the 38kWh of usable capacity in the battery. In that time, you will have also pumped 5300Wh or 19MJ of heat into the battery!

This heat has to go somewhere, and this is where thermal management comes in. The Leaf has almost no ability to get rid of this heat. At 0.8J/gK of heat capacity and a total weight of about 300kg, the battery will heat up by 1 degree for each 375kJ. 19MJ then means a temperature rise of 50 degrees C! Yes, it is probably nearly impossible to fast charge a Leaf 40kWh battery from empty to full at full speed without it catching fire.

Cell balancing
As we saw in the previous chapter and example, even when charging each cell in a battery with exactly the same current, the cells may not really fill up evenly due to temperature differences. Maybe the manufacturing tolerances cause some cells to have a very slightly larger capacity than others. This means the pack will charge and discharge unevenly. But not just that; the strongest cells will suffer less during (dis)charging, so they remain good for longer than the weaker cells. The strong stay stronger, the weak become weaker. This is a runaway process that will ruin a battery pack in the long term.

So it's really important to balance the cells in a pack. This is done very simply; cells at a higher voltage are discharged very slightly and slowly. This will restore them to roughly the same voltage as the other cells, evening out the pack. This is what balancing (or shunt) resistors do in a pack, and it's a vital part of battery management.

Contactors and fuses
For safely handling batteries, especially in a dirty and chaotic environment like a factory or workshop, it is important that the batteries are completely disconnected from the rest of the car whenever the car is off. This is why there are always big, heavy-duty contactor relays inside batteries. These are special relays designed to safely disengage even when large currents are flowing. If you're familiar with welding - that's just a large electrical current flowing through the air. Air can conduct electricity, as can practically anything else if you try hard enough. Believe me, cars and EV traction batteries try REALLY hard.

Automotive contactors have special anti-welding (yes, they can weld stuck) and arc extinguishing features that make them a safe choice for disengaging the pack voltage from the outside. But now we run into another problem; you can't 'just' engage a battery.

In devices like electric motor controllers, there are very large capacitors that will quickly charge up when exposed to the battery voltage. Extremely quickly. Think kilo-amperes, many thousands of amps, if you don't do anything about it. This current can cause damage to wiring and relays, cause massive electromagnetic interference and will generally ruin your day. This is why all automotive batteries also feature a special extra relay and resistor called the precharge relay/resistor. This resistor limits the flow of current when starting up the car, avoiding damage to the electrical system.

Battery voltage, SOC and SOH

You can't have electric energy without both voltage and current. When no current is flowing through a battery, the battery sits at it's so-called open circuit voltage (OCV). This OCV is lowest when the battery is depleted and highest when the battery is fully charged. Most lithium-ion chemistries are empty at 2.5-2.7V and full at 4.2V. In between, it varies but not necessarily linearly. Older types of batteries (e.g. LMO and LCO) have an almost constant voltage from a state of charge between 20-80%, only dipping significantly below that voltage when really empty and only storing a minor amount of energy when charged to higher voltages.

So batteries don't have a fixed voltage. But a lot of batteries have a 'nominal' voltage, often 3.6-3.8V. This is often a voltage chosen to reflect the average voltage over the entire charge range, often a voltage that works well when multiplying the coulombic charge of the battery (Ah rating of the battery) with nominal voltage to get the total energy (Wh rating) for that battery.

Talking about Ah and Wh; these are quite different things. Ampere-hours or Ah(r) tell you for how long you can discharge the battery at a constant current before it depletes. A 25Ah battery can be discharged at 1A for 25 hours. But its voltage, and thus the discharge power, will change significantly during such a discharge.

A more useful rating is the Wh rating of a battery, which tells you for how long you can draw a fixed amount of power from a battery. A 100Wh battery allows you to draw 10 watts for 10 hours, for instance. When nearly full, this translates into, say, 2.4A at 4.2V. When nearly empty, this means 3A at 3.3V. In electric vehicles, we are usually more concerned with power than with current.

As a battery is charged or discharged, the voltage changes. First of all, this is because of internal resistance; a current flowing through any resistance will cause a voltage drop, and this is no different in batteries. But batteries do weird things as you charge or discharge them. They tend to be really good at supplying or taking current for a very short amount of time - a few seconds - but then suddenly their internal resistance rises substantially. In the long term, they can accept or supply progressively less current, even ignoring the fact that the battery will become emptier or fuller. So it is quite hard to estimate exactly how full or empty a battery is based on its voltage. That can change with circumstances.

Additionally, as we saw in the example a while ago, when charging a battery, it may charge slightly better or worse depending on - mostly - temperature. So it is not quite necessarily easier to determine the state of charge of a battery based on how many Ah it has absorbed or spent.

So how do we determine state-of-charge (SOC)? Well, it's a big educated guess. It is, for all intents and purposes, a matter of software tuning and experience. Various battery management systems will do this differently. But they're not magic and they do make errors. For instance, if you mostly drive your car between say 40-80% SOC and never really completely fill it, nor completely empty it, at a certain point the BMS will have to guess how much capacity is left in that bottom 40% or top 20%. It may be a few percentage points off, which has in the past led drivers of electric vehicles by the side of the road even though they had a few percent left according to the car.

The same goes for state-of-health (SOH). This is how much capacity is left compared to the original capacity of the battery, i.e. how degraded the battery has become. Cars like the Nissan Leaf report this with many significant digits, but in reality the error bars on this capacity are quite large and it is largely a guessing game. You can even see this guessing game in action; on typical drives the BMS will just automatically deduct 0.01% of capacity for each charge cycle, and then once every 20-30 cycles it will recalibrate and do a 'proper' measurement, suddenly chopping off 0.3-0.5% of the capacity.

Oh, and your battery's capacity? It's usually measured at really low discharge rates; 0.2C is a common rate. 0.2C means the battery is discharged at 0.2x its capacity rating per hour, aka it takes 5 hours to fully discharge the battery. For the Leaf 40kWh battery, that would mean discharging it at approx. 8kW. In practice, you are almost always either not drawing any significant current or drawing/charging at much more, so this capacity isn't even reflective of real-world capacity.

Degradation mechanisms

Of course, the big question that every EV owner has is: how do I make sure my battery lasts as long as possible? This goes into the way batteries get damaged over time. The two most important factors are temperature and voltage.

Batteries don't like to be hot for a long time. It's actually fine - comparatively - if you live in a temperate or cold climate and occasionally through subsequent fast charges or long trips heat up your battery a lot. These short periods of high temperature aren't that bad. It's being at high temperatures for very long periods of time - e.g. sitting still doing nothing in a desert climate like Phoenix, AZ. This is all down to Arrhenius again; those pesky side reactions that damage the battery from the inside that do their work that much faster at high temperatures.

But that damage doesn't happen quite as fast all the time. You need the second factor: high voltage. Batteries really don't like to be completely full, because voltages over say 4.0V/cell promote damaging chemical reactions in the battery. This is why so many EVs have the option to charge your battery to 80%; this typically leaves the battery at 3.8-4.0V/cell and avoids the 'danger zone' of high voltages. Again, this doesn't mean you should never charge your battery to full. If you know you're about to go on a long trip, by all means plug in the night before and charge to full. But if you want the absolute best longevity out of your battery, use that surplus energy and leave it at 80% or less when the car is sitting still for long periods of time.

Batteries also don't like to be really empty, but for a different reason. Actually, they're quite fine being empty - really empty, just a few percent remaining, at around 3.0V/cell. The problem is that the BMS in the battery still uses a tiny bit of energy - and in some cases the entire car periodically wakes up to do some stuff and uses energy from the battery. This will slowly drain the battery to a dangerously low level. Draining it too much, below about 2.5V/cell, will also cause irrecoverable capacity loss, although not nearly as bad as overcharging it.

Another reason why low SOC isn't a great idea is because older, degraded batteries tend to be very unbalanced at low SOC. Often, one cell may sit at 3.0V while another is 2.7V, so even though on average there is some energy left in the battery - even a small amount of discharge will cause that weak cell to become dangerously low and lose even more capacity. Moreover, the BMS tends to try to balance out the battery whenever it has time to do so. During a drive or charge, it can't compete with the current flows caused by using the car, but when sitting still for tens or hundreds of hours it'll happily balance the pack at whatever point it's at. But remember; at low SOC, the battery is VERY unbalanced, so balancing it at that point will... cause the battery to be very unbalanced when subsequently charged to full! This is the difference between what's called 'top-balancing' and 'bottom-balancing'; balancing the cell voltages when full and empty respectively. To maximize usable capacity and minimize internal resistance, all EVs use top balancing. Leaving a battery very empty for a long period of time will mess that up and causes apparent capacity loss.

  • Charge to 80%
  • Only charge to full when you need the surplus capacity
  • Do not leave the car at <25% for long periods of time
  • Do not leave the car in hot environments for long periods of time
All this being said; use the car for its intended purpose - don't overdo the babying. A well-designed electric car will do much more for battery longevity than these tips.

So, what does Nissan do wrong?

Now we can go through the history of Nissan's Leaf batteries and find out why they are so bad. In the EV space, Nissan's batteries rank among the very worst batteries, in multiple respects. Their early batteries had poor energy density, longevity and charging performance, and the new ones have only partially fixed the energy density issue - making the rest arguably worse. Why?

A lot of this has to do with history, and actually some really good foresight on the part of Nissan. Around the time they started developing the Leaf - circa 2006 - lithium ion batteries for automotive applications barely existed. A123 and Kokam supplied the bulk of high-spec batteries, but even those wouldn't be enough to satiate their ambitions on the EV market. So they chose to build their own battery factory and called it AESC. AESC in turn chose basically the only chemistry available at the time that had good enough performance for an EV - LMO (lithium manganese oxide). And they standardized on a battery shape that would basically fit in any car; a skateboard-type pack with a hump under the front and rear seats to accomodate more volume of cells. From an engineering perspective, all of these choices were great.

For the time it was developed, the first 24kWh battery pack was fine. It didn't have any kind of thermal management, but considering the modest power demand this was actually fine (for an LMO pack). Battery management was quite advanced for the time, using real-time capacity and performance estimation using table lookup. If I think back at what battery management looked like even in literature around that time - when I was just beginning to delve into the topic for my study - they were doing very well indeed.

But around 2010-2011, two new technologies started to become commercially available in large quantities: NCA and NMC li-ion batteries. NCA in particular combined much, much lower internal resistance with similar energy densities to LCO at the time, as well as a more favorable discharge curve for fast charging. Upcoming competitors in the EV space Panasonic and Yuasa immediately began using these chemistries and produced much better products as a result. Nissan? All I can think is that they were tied to AESC and their technology, tweaking their 24kWh battery offering slightly to cope better with high temperatures, but not really going with the times.

Around 2014 they launched the e-nv200 with the exact same battery modules, but with a fan inside the casing to help with evening out internal temperatures and even actively cooling (albeit poorly) during fast charges. The larger battery casing allowed for more air space inside, improving characteristics even though the battery was otherwise absolutely identical - even the firmware. This paid dividends; even quite intensively used e-nv200s with 60kmi/100Mm on the odometer tend to have 85%+ SOH, something almost unheard of in Leafs.

But Nissan couldn't afford the change in battery shape underneath the Leaf, even though they did increase capacities. It took until 2015 when they launched the 30kWh Leaf with NCA cells - well, mostly NCA. The chemistry change alone accounted for the capacity increase, as well as the much improved fast charging. However, this battery did get a little warmer than the 24kWh. It could have definitely benefited from a fan like the e-nv200.

Time moves on, Nissan needed to compete with the e-golf and other EVs in the late 2010s. They brought out the 40kWh Leaf. Same battery casing, higher capacity, so how did they do it? Well, batteries are constructed out of the active material - the stuff that actually stores the energy, electrodes that conduct the electricity out of the cell and packaging - the stuff that keeps all the gubbins in. They thinned out the electrodes and increased the density and volume of active material to get to the higher capacity. This... massively increased energy density and reduced thermal conductivity of the cells.

This is what eventually led to rapidgate. Mind you, other cars WITH thermal management rapidgated - the e-golf for instance! Nissan must have known this and thought it was OK; after all this issue had already existed for 2 years before the new Leaf came out. The higher inherent internal resistance as well as the increased motor power made it a hot house beyond any other car. And compared to the 30 and 24kWh, the battery shell only got fuller and fuller.

Now we're in 2019. Nissan made the 62kWh Leaf. Almost the same case - they made it very slightly taller so it hangs a little lower under the car. Do you think they increased electrode thickness? Do you think they added a fan inside, or even a heat exchanger? Oh, they increased the fast charging speed to 100kW. Can you guess how that ends?

Nissan engineered themselves into a corner with the Leaf. They started out with great engineering choices - at the time. But then they - either through choice or necessity because of their exclusive involvement with AESC - held onto those choices far beyond the point where they made any sense. High internal resistance, disparate temperatures within the pack and resulting rapid aging, relatively outdated battery chemistry choices and missing thermal management aren't a result of Nissan not knowing what they're doing wrong. It's a result of choices made probably 13 years ago coming back to haunt them.

But, with all this knowledge in hand, we can fix it. MUXSAN will try to fix what Nissan couldn't. Make the Leaf great again!

Volgende: Elektrische auto's verdienen trekhaken! 05-'19 Elektrische auto's verdienen trekhaken!


Door Tweakers user mvdam, vrijdag 8 november 2019 14:36

Ik kan niet anders zeggen dan dat ik het een goed verhaal vindt :).

Nu nog zo'n fijn accu-tje :>

Door Tweakers user naftebakje, vrijdag 8 november 2019 15:40

Bedankt voor de heldere uitleg _/-\o_
Nu vraag ik me wel af: ga je hun accupack redesignen? Wat cellen eruit, vloeistofkoeling (of toch vooral temperatuur-egalisatie) er in, en dan de overgebleven cellen in de kofferbak stoppen?

Door Tweakers user mux, vrijdag 8 november 2019 16:43

Het project 'fix de Leaf' is een veeltrapsraket. De extenderaccu's die we al maken zijn echt een veel grotere oplossing gebleken dan ik in eerste instantie had gehoopt, en dit doet echt een hele hoop voor bijna alle problemen. We gebruiken packs met een belachelijk lage interne weerstand en koppelen ze thermisch aardig goed aan elkaar, waardoor de extenderpakketten zelfs zonder actieve koeling de bulk van de stress in de auto opnemen zonder er zelf stuk aan te gaan. Het nadeel is natuurlijk het extra gewicht.

De volgende stap zal toch echt iets moeten zijn met temperatuuregalisatie in de originele accu's. Waterkoeling is onmogelijk - althans, prove me wrong! Ik denk dat het niet haalbaar is. Het verwijderen van een aantal cellen en die ergens anders plaatsen is een veiligheidsnachtmerrie. Ik denk dat er maar twee opties zijn: ofwel een hele zoot fans in de accu plaatsen om een flinke hoeveelheid interne luchtstroming te genereren, ofwel de accubehuizing permanent veranderen om zo meer ruimte te creëeren voor luchstroming. De e-nv200 accu is een goed voorbeeld daarin.

Op de langere termijn zullen we ook zelf volledige vervangende accu's moeten gaan maken die from the ground up ontworpen zijn voor actief warmtemanagement. Dat is echt nog heel ver weg, maar de mogelijkheden zijn superinteressant.

Door Tweakers user Mickey77, zaterdag 9 november 2019 11:15

Eens met mvdam, een goed verhaal. Ook leuk dat je heel duidelijk vertelt wat Nissan fout doet zonder dat je ze keihard in de hoek zet. Technisch en tactisch slim. Als je hier geen 100 complimenten voor krijgt dan is het verhaal mogelijk iets te technisch voor de gemiddelde tweaker van 2019 :X

Door Tweakers user matroosoft, zaterdag 9 november 2019 14:08

Erg interessante blog om te lezen als eigenaar van een 2011 Leaf.

Ik moet in de winter tot 100% laden voor woon-werkverkeer om ook de auto nog een beetje warm te hebben. Begrijp ik het goed dat het in de winter minder erg is om tot 100% te laden, vanwege de lagere temperatuur? Sowieso zorg ik er met de oplaadtimer voor dat hij pas kort voor vertrek volledig geladen is.

In de zomer staat de auto op het werk vol in de zon, maar dan is de batterij al zon 40% leeg, dus dat zou dan ook niet al teveel kwaad kunnen?

Edit: Ik hoor de laatste tijd steeds vaker dat snelladen helemaal niet zo slecht was als we dachten, goed om te horen dat je dat ook kunt bevestigen.

[Reactie gewijzigd op zaterdag 9 november 2019 14:11]

Door Tweakers user Pwuts, zaterdag 9 november 2019 17:39

Hele interessante post, ik ben benieuwd naar de toekomstige ontwikkelingen van Muxsan. :)

Door Tweakers user mux, zondag 10 november 2019 10:40

matroosoft schreef op zaterdag 9 november 2019 @ 14:08:
Erg interessante blog om te lezen als eigenaar van een 2011 Leaf.

Ik moet in de winter tot 100% laden voor woon-werkverkeer om ook de auto nog een beetje warm te hebben. Begrijp ik het goed dat het in de winter minder erg is om tot 100% te laden, vanwege de lagere temperatuur? Sowieso zorg ik er met de oplaadtimer voor dat hij pas kort voor vertrek volledig geladen is.

In de zomer staat de auto op het werk vol in de zon, maar dan is de batterij al zon 40% leeg, dus dat zou dan ook niet al teveel kwaad kunnen?

Edit: Ik hoor de laatste tijd steeds vaker dat snelladen helemaal niet zo slecht was als we dachten, goed om te horen dat je dat ook kunt bevestigen.
Hier gaan we een woud van nuances in die ik... niet echt expliciet heb genoemd in de post. Ook bij hele lage temperaturen zijn hoge spanningen niet 'goed'. Het is niet zo dat het ene goed het andere kwaad compenseert. Bij lage temperaturen is het beter als de accu juist op een iets lagere spanning zit. Echter..

In deze context is lage temperaturen -10 of lager, niet rond vriezen of zelfs boven het vriespunt. Dus eigenlijk is er niet zoveel aan de hand. Qua volladen kun je de auto hetzelfde behandelen bij 0 graden als bij 20.

De auto in volle zon zetten in Nederland is niet superboeiend. De accu wordt dan misschien 30 graden - dat vindt-ie juist fijn. Het grootste probleem ga je zien als je dit in de Algarve of Italië doet of - zoals in het blog genoemd - Phoenix of Las Vegas. 40C+ maandenlang. Dan vermoord je de accu in 3 jaar.

En inderdaad, snelladen is lang niet zo erg zolang je het maar met een warme batterij doet.

Door Tweakers user Dacuuu, zondag 10 november 2019 11:04

Mooie lap tekst, bedankt voor deze nuttige informatie! Ik heb zelf geen e-auto, maar wel een e-fiets, en lees regelmatig stukken over accu cellen etc.

Door Tweakers user matroosoft, maandag 11 november 2019 06:53

mux schreef op zondag 10 november 2019 @ 10:40:


Hier gaan we een woud van nuances in die ik... niet echt expliciet heb genoemd in de post. Ook bij hele lage temperaturen zijn hoge spanningen niet 'goed'. Het is niet zo dat het ene goed het andere kwaad compenseert. Bij lage temperaturen is het beter als de accu juist op een iets lagere spanning zit. Echter..

In deze context is lage temperaturen -10 of lager, niet rond vriezen of zelfs boven het vriespunt. Dus eigenlijk is er niet zoveel aan de hand. Qua volladen kun je de auto hetzelfde behandelen bij 0 graden als bij 20.

De auto in volle zon zetten in Nederland is niet superboeiend. De accu wordt dan misschien 30 graden - dat vindt-ie juist fijn. Het grootste probleem ga je zien als je dit in de Algarve of Italië doet of - zoals in het blog genoemd - Phoenix of Las Vegas. 40C+ maandenlang. Dan vermoord je de accu in 3 jaar.

En inderdaad, snelladen is lang niet zo erg zolang je het maar met een warme batterij doet.
Thanks, duidelijk. Deze blog gaat bij de bookmarks d:)b

Door Tweakers user lvdgraaff, maandag 11 november 2019 11:52

Dank voor het delen. Met veel plezier gelezen en erg veel van geleerd.

Door Tweakers user RMvanDijk, dinsdag 12 november 2019 13:08

Duidelijk verhaal, denk wel dat ik het nog een of twee keer moet lezen om alles te bevatten.

Ik kwam er laatst achter dat ik regelmatig langsfiets, had de naam toen gezien op de gevel maar niet de link gelegd.

Door Tweakers user mux, dinsdag 12 november 2019 13:24

loop vooral een keer binnen :)

Door Tweakers user onok, donderdag 14 november 2019 12:23

Mooie post, heldere uitleg!
Ik ben nu ook eigenlijk wel benieuwd hoe de andere merken het doen in verhouding tot Nissan. Ik heb bijvoorbeeld vaak gehoord dat Tesla zijn thermal management al veel beter op order heeft, maar wat dat precies betekend weet ik niet. Misschien leuke stof voor de part 2 van dit stuk? :)

Door Tweakers user HyperBart, zaterdag 23 november 2019 13:53

Stel dat je dan vandaag een elektrische wagen zou willen bezitten, niet leasen. Maar voor de langere termijn (8 tot 10 jaar). Wat is dan qua battery management een goede of zeer goede wagen?

Ik vermoede een Tesla, maar ik kan me moeilijk voorstellen dat er geen andere wagens en merken zijn. Een Hyundai Kona?

Door Tweakers user mux, zaterdag 23 november 2019 14:44

Geen Leaf, geen i3, geen PHEV, dan heb je de rotte eieren wel zon beetje gehad. Tesla is op zich heel goed, maar het geld nooit waard als het je alleen om het verschil in batterijkwaliteit gaat - zoveel verschil maakt dat nou ook weer niet. En waar ze in thermal management ver vooruit lopen, zijn ze op andere betrouwbaarheidsvlakken redelijk gemiddeld. Daarmee wil ik niet zeggen dat ik een Tesla afraad, meer dat ik ze niet boven anderen zou plaatsen obv de batterij. Kies een auto die het beste bij je behoeften past.

Door Tweakers user matroosoft, dinsdag 26 november 2019 22:23

mux schreef op zaterdag 23 november 2019 @ 14:44:
Geen Leaf, geen i3, geen PHEV, dan heb je de rotte eieren wel zon beetje gehad.
Dat je de i3 afraadt kijk ik wel een beetje van op, die heeft toch vloeistofkoeling?

Door Tweakers user mux, woensdag 27 november 2019 07:00

De oude i3, pardon. Nee, de 22kWh heeft geen vloeistofkoeling. En daarbij komt dat hij 110kW ontlaadsnelheid heeft, wat op dat pakket teveel stress geeft

Door Tweakers user matroosoft, woensdag 27 november 2019 22:34

Hee dat is nieuw voor mij, ik dacht dat ze allemaal vloeistofgekoeld waren. Goed om te weten!

Door Tweakers user assje, zondag 1 december 2019 08:37

  • Charge to 80%
  • Only charge to full when you need the surplus capacity
  • Do not leave the car at <25% for long periods of time
  • Do not leave the car in hot environments for long periods of time
Als je dan tot 100% laadt is het dan nog wel zinvol te zorgen dat hij zo kort mogelijk op 100% geladen staat? Of, is dit alleen een argument bij hoge temperaturen?

Door Tweakers user mux, zondag 1 december 2019 08:40

Jazeker! Hoewel het bij hoge temperaturen een groter effect heeft, is er altijd veel stress op de batterij als je boven ~4V/cel gaat, dus hoe korter je daarboven zit, des te beter. Ook bij lage temperaturen.

Een (piepklein, in de meeste gevallen) nadeel is dat de interne weerstand iets lager is bij hogere spanning, maar zoals je kunt zien in de tabel is dat maar een paar procent verschil.

Door Tweakers user RulazZ, maandag 2 maart 2020 11:47

mux schreef op zaterdag 23 november 2019 @ 14:44:
Geen Leaf, geen i3, geen PHEV, dan heb je de rotte eieren wel zon beetje gehad.
Raad je alle PHEVs af, of bedoel je hier specifiek de Outlander? Ik heb zelf sinds enkele maanden een VW Passat GTE 2e hands en die heeft voor zover ik weet wel een actieve vloeistofgekoelde accu (NMC of NCA dacht ik). 2 ton op de teller en de accu is nog steeds zo goed als dat ik zou verwachten bij nieuwe aanschaf, al zou het goed kunnen dat de eerste bestuurder die hem in de lease had natuurlijk niet zo'n goede stekkerdiscipline had.

P.S. Mocht je hiervoor ook ooit nog eens een extender optie voor aanbieden dan houd ik me van harte aanbevolen, een elektrische range van 100 km lijkt me best leuk omdat ik dan alleen op vakantie nog hoef bij te stoken ;)

[Reactie gewijzigd op maandag 2 maart 2020 11:50]

Door Tweakers user mux, maandag 2 maart 2020 11:51

PHEVs in het algemeen hebben vééél zwaardere belasting op hun accu's. Je ziet eigenlijk geen enkele oude PHEV met nog goede SOH. Outlanders zijn wel het ergste (die zijn al sub-80% SOH rond de 60.000km), maar zelfs de beter gemanagede PHEVs hebben ondanks goed ontworpen, high performance accu's nog steeds weinig over na zeg 150 000km.

Chemie maakt bijna niet uit, als je cellen met 5C gaat laden en ontladen zit je gewoon op de rand van wat li-ion kan zonder sneller stuk te gaan. Ze rekenen er echt op dat je de benzinemotor 90%+ van de tijd gebruikt, en dat de tractie-accu dus eigenlijk maar voor enkele tienduizenden kilometers over de hele levensduur wordt gebruikt, misschien niet eens 20 000km.

Passat/Golf GTE zijn wel echt de meest duurzame en best ontworpen accupakketten (ondanks een gigantische recall), maar ook die zou ik niet meer in goede staat verwachten na 2 ton. Ik denk dat die accu weinig opgeladen is geweest.

Door Tweakers user RulazZ, maandag 2 maart 2020 12:35

Thanks voor de reactie. Met de kleinere accu's heb je naast de hogere C-rate natuurlijk ook te maken met veel meer laadcycli over eenzelfde aantal kilometers. Ik hoop in elk geval dat we er nog wel richting een tonnetje goed gebruik van kunnen maken (15-20kkm per jaar, op het moment halen we zo'n 80% elektrisch) en dat er tegen die tijd een goede BEV in dezelfde categorie te vinden valt. Helaas zijn er nog steeds geen station BEVs (afgezien van een paar custom made Tesla's), dus voordat die tweedehands betaalbaar zijn, zijn we ook snel 8-10 jaar verder.

Onze tweede auto ga ik in elk geval wel door een BEV vervangen binnen een paar jaar, daar ben ik destemeer van overtuigd geraakt door onze gateway EV. En 150-200 km is dan een prima range.

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