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E-Niro 4
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Discussion Starter · #1 ·
Is calibration really a ‘thing’ or another one of those EV battery myths that seem to become law? After watching Andy Till/Mr EV’s video earlier, do we really need to do this like in the days of NiCd batteries? Some people say as long as the cells are balanced when charged to 100% and you know what voltage your lowest cell is, the BMS will know what the pack can roughly output? The GOM will just work off what the BMS says surely but will depend on previous usage? BMS are pretty sophisticated these days and this just sounds like another one of those things that has appeared again. Happy to be told otherwise as I’m no battery expert but in simple terms once a buckets full it’s full. Running it lower and back up again won’t change the volume or it’s output right? And the BMS will take into account degradation in the pack surely as that will show up on cell voltages and capacity one assumes? I know there are many battery boffins and electrical engineers on here so what’s the truth, do we really need to calibrate or just let the BMS do it’s job?

let the discussion begin! :)
 

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Calibration is probably less important than cell/module balancing.

If the BMS battery calibration is out (e.g. the car thinks that the capacity is different to the actual capacity) then you will still get the same amount of energy out of the battery as if was calibrated correctly but the GOM might give odd results.

If cells/modules are not balanced then you will genuinely get less energy from the pack because the BMS has to behave as if all cells have the same voltage as the one with the lowest voltage one when discharging and have the same voltage as the highest one when charging. This is to avoid taking any one cell above or below it's safe voltage range.
 

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Discussion Starter · #4 ·
Well this is where I get confused, surely balancing and recalibration are the same thing as once the cells are effectively balanced it ‘recalibrates’ everything else because once the BMS knows where it’s at, that info will be reported to the other areas of the vehicle. Simply running down the battery and then charging it up again doesn’t affect this? Simply charging to 100% every now and then is sufficient To do both?
 

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you know what voltage your lowest cell is, the BMS will know what the pack can roughly output
Voltage isn't a great indicator of state of charge for lithium batteries. A lot of them tend to hold voltage fairly flat for a while, then drop like a stone towards the end. Charge counters are better for tracking state of charge.
If the BMS battery calibration is out (e.g. the car thinks that the capacity is different to the actual capacity) then you will still get the same amount of energy out of the battery as if was calibrated correctly but the GOM might give odd results.
Not necessarily. If the BMS things that a battery charge level is much lower than it actually is, it might cut out early to protect the battery from a deep discharge.
 

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Calibration is probably less important than cell/module balancing.

If the BMS battery calibration is out (e.g. the car thinks that the capacity is different to the actual capacity) then you will still get the same amount of energy out of the battery as if was calibrated correctly but the GOM might give odd results.
Nope doesn't work like that. The BMS won't allow you to use capacity that it doesn't believe exists.

If it thinks the battery has 60Ah capacity but its really 70Ah it will calculate your range remaining based on the 60Ah figure and will report low charge, go into turtle mode and shut down completely based on the 60Ah figure.

Conversely if it thinks the battery has 60Ah capacity but its really only 50Ah it will estimate more range than the battery is really capable of, but when you get down towards the bottom the voltage will be lower than it expected for that SoC and it will go into turtle mode earlier than the driver was expecting due to low voltage or will make a sudden downwards adjustment of the reported SoC.

If you discharge the battery low enough enough times the BMS will "learn" that the capacity is more or less than it previously thought, and make an adjustment to its estimated Ah capacity. How quickly that happens and how much of an adjustment it will make is highly dependent on the programming of the BMS, because batteries only ever degrade, they don't improve over time.

So the programming in the BMS has a strong tendency to believe decreases in capacity but to be suspicious of increases in capacity as that should not happen unless cells are replaced. As a result some BMS's are very reluctant to ever revise the figure upwards unless a diagnostic tool calibration is initiated. So if you did a cell swap and didn't force a calibration you wouldn't actually be able to make use of the increased capacity.
If cells/modules are not balanced then you will genuinely get less energy from the pack because the BMS has to behave as if all cells have the same voltage as the one with the lowest voltage one when discharging and have the same voltage as the highest one when charging. This is to avoid taking any one cell above or below it's safe voltage range.
This is accurate however a large imbalance (at full charge) is unlikely to develop over a short time, so it could take months or years for a large imbalance to accumulate. An imbalance of 50mV between cells at full charge is equal to about 5% of the total capacity of the battery. (Since about 5% of the total Ah capacity of a typical Lithium Ion cell is available between 4.05 and 4.1 volts)
 

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Well this is where I get confused, surely balancing and recalibration are the same thing as once the cells are effectively balanced it ‘recalibrates’ everything else because once the BMS knows where it’s at, that info will be reported to the other areas of the vehicle. Simply running down the battery and then charging it up again doesn’t affect this? Simply charging to 100% every now and then is sufficient To do both?
Balancing and "calibration" are not the same thing. Balancing is simply ensuring that all cells reach 100% charge at the same time when the battery pack as a whole is charged. If the maximum cell voltage is 4.1 volts (which is typical) you want all the cells to be at 4.1 volts at full charge. You don't want some at 4.1 volts and some at 4.0 volts etc.

This applies to any series string of cells (including lead acid, NiMH etc) however many other cell types are able to self balance when charging as they can tolerate some over charging of the high cells with the excess just turning into heat, so they naturally balance out small imbalances. The cells that get to full charge first just generate a bit of heat to dissipate the excess energy but don't overcharge as such.

Lithium Ion batteries can't tolerate being over charged even a small amount so if there is an imbalance you either have to lose useable capacity (some cells don't reach full charge) or risk overcharging some cells - which is likely to result in a fire or at the very least higher degradation. Hence why Lithium Ion batteries made up of multiple cells nearly always have balancing systems.

"Calibration" could refer to either usable capacity or state of charge. Usable capacity can't be directly measured on a Lithium Ion battery at any given moment in time, and State of Charge can only be directly inferred from voltage when the cells are nearly full or nearly empty and not under load or being charged, so the BMS has to try to track both the total usable capacity of the battery and the current state of charge over time, and the two are interlinked.

The starting point is using voltage estimation to recognise full charge. If you charge all the cells up to 4.1 volts and keep charging at that voltage until the current falls to less than 1/10th of the initial charge rate that is considered to be fully charged. You then discharge the battery at a known rate until it reaches a set minimum voltage - say 3.3 volts per cell.

The product of current x time during the discharge is a measure of Ah capacity between 4.1 and 3.3 volts. Now we know the battery is discharged and how many Ah it delivered to get there so we know the usable capacity. In future the BMS uses this Ah figure to better estimate state of charge because in the 20-80% SoC range you can't really tell from measuring voltage. This technique is called coloumb counting and would be akin to tracking the amount of water in an opaque bucket by measuring the flow in and out of the bucket via a hose.

If you never go outside about 20-80% then the reported SoC can drift away from the true value as measurement errors accumulate over time as coulomb counting is a form of dead reckoning.

Voltage can only be used to estimate the state of charge near the bottom or the top but if you charge to 100% any accumulated errors in colomb counting can be removed. You may see a small sudden jump in reported SoC when this happens. So yes a single charge to 100% will correct this form of error.

But there can also be errors in reported usable capacity aka state of health. The only way to truly measure it is to discharge from 100% down to about 20% or less, and measure the current x time product, but this isn't actually that good for the battery (as it's a deep discharge) and is not something that happens often especially in a large battery EV.

Another problem is that the raw usable capacity of a battery drops significantly in cold weather so this has to be taken into account when calculating a SoH - most EV's I believe take the approach of "normalising" the value to summer figures.

In other words if it measures the usable capacity in very cold conditions it applies a compensation factor to estimate what it would be if it was measured in summer. Without doing this reported SoH would drop in winter and go up again in summer, but you really want SoH to be a universal figure of "health" of the battery outside of seasonal variations. (Some EV's do a better job of this than others!)

So what does the BMS do about tracking SoH ? In between opportunities to actually measure it, (which don't come often) it tries to estimate it based on the age of the battery, how many times the battery has been cycled, how deeply, average cell temperatures (higher temperatures degrade faster with age) etc. It will have a degradation model where it can predict the anticipated degradation and it simply uses that predicted figure. Obviously this model is highly specific to the type of cells used in the car.

Think of this like your power company using estimated readings in between actual readings - they don't know what the exact figure is but they need a figure to go by and can't just assume you've used no power. When you see a SoH figure gradually falling what you're usually seeing is this degradation model ticking down the assumed capacity with age and mileage.

Every now and then it will get a chance to actually measure the SoH - when it does you might see a bigger jump and it could potentially be an upwards jump if the previous estimated degradation was pessimistic.

So forcing a "calibration" of the SoH and triggering an actual reading to be taken usually involves a near complete discharge from 100%, which is actually bad for the battery. (And on some BMS's it takes multiple such discharges before the SoH will be updated) In other words testing the full capacity of a Lithium Ion battery is a slightly destructive test.

If you have an EV with plenty of range to stay within 30-80% SoC then I would probably do that the majority of the time and save the 100% charge for no more than once a month or just before a long trip. And do a discharge down to 20% maybe only a couple of times a year to give it a chance to measure SoH. SoH falls slowly and small errors don't matter so it doesn't need to be measured every week.
 

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If you have an EV with plenty of range to stay within 30-80% SoC then I would probably do that the majority of the time and save the 100% charge for no more than once a month or just before a long trip. And do a discharge down to 20% maybe only a couple of times a year to give it a chance to measure SoH.
I've seen this many times, but how many people actually do this in practice? In my ZE40 limiting myself to 30-80% would drop my range from 175 miles to under 90... What on earth would be the point of buying a car with 41 kWh and only ever using 20 of them? Do people with 22 kWh Zoes try to never use more than 50 miles? Personally I charge my ZE40 to 100% every night, because my commute is 24 miles and the 4 hours of cheap energy I get on Octopus Go are enough to top off the battery every night. I wake up every day with ~175 miles of range and I just let my BMS take care of the battery.... Before moving to Octopus Go I'd only charge once a week, meaning I'd start Monday morning with 100% and usually have less than 10% on Friday. I choose to use the full range of my battery, because if I only use the middle ~20 kWh, why am I carrying the weight of 41 around?
 

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I've seen this many times, but how many people actually do this in practice? In my ZE40 limiting myself to 30-80% would drop my range from 175 miles to under 90... What on earth would be the point of buying a car with 41 kWh and only ever using 20 of them? Do people with 22 kWh Zoes try to never use more than 50 miles? Personally I charge my ZE40 to 100% every night, because my commute is 24 miles and the 4 hours of cheap energy I get on Octopus Go are enough to top off the battery every night. I wake up every day with ~175 miles of range and I just let my BMS take care of the battery.... Before moving to Octopus Go I'd only charge once a week, meaning I'd start Monday morning with 100% and usually have less than 10% on Friday. I choose to use the full range of my battery, because if I only use the middle ~20 kWh, why am I carrying the weight of 41 around?
Also to add to that, isn't there some "hidden" capacity above the quoted figure, so 100% isn't actually 100%? At least this has been said for the ZE50.
 

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What on earth would be the point of buying a car with 41 kWh and only ever using 20 of them?
The monthly recommendation is in the manual for the eNiro (and Kona I think), which have batteries that are large enough that many people probably won't feel the need to keep them topped off all the time. Few people routinely travel 150-200 miles a day, so 80% is plenty to keep at hand.
 

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I've seen this many times, but how many people actually do this in practice? In my ZE40 limiting myself to 30-80% would drop my range from 175 miles to under 90... What on earth would be the point of buying a car with 41 kWh and only ever using 20 of them? Do people with 22 kWh Zoes try to never use more than 50 miles?
I didn't say never go outside 30-80%. If you're going to make a journey that needs more range by all means charge it up to 100% the night before. It's just good practice in general to stay below 80% when you can and avoid deep discharges on days when you don't need to deeply discharge it.

If my Leaf 30 had an option to charge to 80% I would gladly use it for my daily commute. Even in the middle of winter I'm doing my 38 mile commute (heater at a nice toasty 22C) and still arriving home with about 58% left. If I started at 80% I'd get home with around 38% left so this would work out perfectly for me. When I'm planning to do a longer trip I'd fully charge it.
Personally I charge my ZE40 to 100% every night, because my commute is 24 miles and the 4 hours of cheap energy I get on Octopus Go are enough to top off the battery every night. I wake up every day with ~175 miles of range and I just let my BMS take care of the battery....
Don't take this the wrong way, but charging a 175 mile range car to 100% every night for a 24 mile a day commute is just silly. In the long term this will cause more battery degradation than if you charged to no more than 80% most of the time. Whether the additional degradation would be significant in your time of ownership is an open question and depends on a lot of factors. There is nothing the BMS can do to "take care of" the battery if you charge it to 100% every day. Sitting around at 100% charge a lot of the time causes increased degradation - there is no magic wand to wave this away.

At least by using a charge timer to delay charging you reduce the harm - I charge my Leaf to 100% on week mornings (as it doesn't really give me any way to avoid this if I want to use preheating) but it doesn't start charging until about 3am so the time spent at 100% is minimised, but I'd still much rather charge to 80%.
Before moving to Octopus Go I'd only charge once a week, meaning I'd start Monday morning with 100% and usually have less than 10% on Friday. I choose to use the full range of my battery, because if I only use the middle ~20 kWh, why am I carrying the weight of 41 around?
If you choose to use the full range of your battery on a daily basis you also choose to have your battery degrade at a faster rate. Because, physics. Increased time spent >80% charge causes accelerated age related degradation and deep discharges (below about 30%) cause reduced cycle life.

Nobody says you can't use the full range of your battery when you need it, but if you're not doing a high daily mileage then there are certain things you can do to reduce battery degradation without causing inconvenience.

The ideal commuting scenario for minimal battery degradation is to charge to 80% every work day - this avoids going near 100% at all (apart from doing an occasional long distance / balance charge say once a month) and still gives you 80% of your maximum range on tap at the start of the day.

Charging every day minimises depth of discharge related cycle life degradation - it's much better for the battery to discharge from 80% to 60% then charge back to 80% every day than to discharge from 80% to 20% over several days then charge back to 80%.

Of course this approach is only convenient if the car offers an option to automatically limit charging to 80% - many like my Leaf don't have this option and I'm not sure if a Zoe does.

One final comment - if you're on a cheap nightly tariff you're obviously watching your charging costs - most EV's have greatly reduced (some none at all) regeneration near 100% charge. The Leaf is particularly bad for this as it basically has zero regen when fully charged and will roll away down the slightest incline unless you ride the friction brake.

The driving you do with little or no regen in a built up area will be up to 25% less efficient vs driving with full regen available (even more so if you live at a high altitude and drive down to get to where you're going) so starting at 80% gives you full regen from the beginning which means better efficiency at the plug and also a better driving experience on some cars. (I really don't like driving the Leaf at 100% as I don't like that rolling away riding the brake pedal characteristic)

At the end of the day its your battery so you can treat it how you see fit, I'm just trying to offer suggestions that will help it's long term longevity. There's a popular misconception that the BMS somehow just "takes care" of all this for you. It doesn't. Spending a lot of time near full charge and frequent deep discharges most definitely eat into the life of the battery. It's well understood physics and chemistry.
 

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Also to add to that, isn't there some "hidden" capacity above the quoted figure, so 100% isn't actually 100%? At least this has been said for the ZE50.
The "hidden" capacity is very small. You're talking about less than 5% at the top typically. So when most EV's report 100% charge on the dash the true charge level is usually around 95%. While that's better than 100% it's still nowhere near as good as dropping to 80%.
 

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Don't take this the wrong way, but charging a 175 mile range car to 100% every night for a 24 mile a day commute is just silly.
I tell you what's silly, getting up at 03:30 to stop the charge.

Who's keeping these cars to the point they actually notice any degradation (if it actually happens) anyway?
 

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I tell you what's silly, getting up at 03:30 to stop the charge.

Who's keeping these cars to the point they actually notice any degradation (if it actually happens) anyway?
Some people exercise some mechanical sympathy, and enjoy doing it. It the car makes it easy to do, then it seems like a good thing to look after it.

I keep our Leaf 40 within 20 - 80% because it makes it easy to do so, and it seems like a "good thing". When I had a Peugeot Ion i charged it to 100% each night because i needed the range, and because it had no charge timers etc to make doing anything easy.
 

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I tell you what's silly, getting up at 03:30 to stop the charge.
Or buy a car with an adjustable charge limit ? A feature that is becoming more common now. I'm suggesting it as something to do on cars which have a charge limit setting. My Leaf doesn't have such a setting so I reluctantly charge to 100%, but delay it as long as possible.
Who's keeping these cars to the point they actually notice any degradation (if it actually happens) anyway?
Ah I see, to heck with trying to maintain the battery health of EV's to a good age - just keep it for 3 years and flick it on down the line to the plebs and let them worry about it. :) The typical PCP disposable car mentality.

Fine for the first "owner" of the car, not so fine for the environment when loads of EV's struggle to reach even 10 years old without high levels of battery degradation or cell failures that write off the car as uneconomic to fix.

Again, I'm not suggesting people go out of their way to inconvenience themselves, however if they have the option - such as a charge limit option in the car and a commute that is much smaller than their range you can improve the longevity of the battery with basically zero effort. So why wouldn't you ?

For those of us without a charge limit option, the harm of charging to 100% can be reduced by using the charge timer to delay charging as late as possible before the car is next driven - thus minimising time spent at 100%. This causes me absolutely zero inconvenience because I plug in when I get home and the car delays as long as possible but makes sure it is always charged by 7am the following morning.
 

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Some people exercise some mechanical sympathy, and enjoy doing it. It the car makes it easy to do, then it seems like a good thing to look after it.

I keep our Leaf 40 within 20 - 80% because it makes it easy to do so, and it seems like a "good thing". When I had a Peugeot Ion i charged it to 100% each night because i needed the range, and because it had no charge timers etc to make doing anything easy.
Get a dog? :)
 

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Ah I see, to heck with trying to maintain the battery health of EV's to a good age - just keep it for 3 years and flick it on down the line to the plebs and let them worry about it. :) The typical PCP disposable car mentality.
The 'plebs' will never notice as they don't measure battery capacity.

Anyway, what if you nanny it for years, and then some oik crashes into it as you were on your way to trade it in?

Life's too short not to invest in sleep.
 

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Discussion Starter · #19 ·
Well thanks for the input guys, it clears a few things up in my head. I always have the Niro set to 80% unless I do a long journey which have been few and far between since we've had the car. as for getting low, I think it got to 17% once after a trip to Scotlan but I think has barely got below 50% since then!
 

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Once again, nobody is suggesting getting up in the middle of the night to unplug the car at 80%, so your comment is pointless.
No, I think scare-mongering is though.

It all sounds like those people who would never fill their tank up to the top, or let it run too low in an ICE. Because, you know, reasons.
 
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