arnis
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Another reason not to charge to 100%

Wed Jan 02, 2019 7:33 pm

In addition to everything else that is known, like:
No regen
Slightly faster battery degradation

There is one more thing that is often overlooked.
Overall efficiency.
I have 2014 Leaf with 134Mm or 83k miles, lost 9% of capacity during these years.
I have always charged to 80% (except before longer trips). Very often went down to very low warning and dashes.
(PS: please do not try to be a battery health expert and tell me not to go that low, reread my capacity loss if you don't get it).

I've measured it few years ago and once again recently and got pretty much identical results.
Charging from 0% (dead battery, 0,3kWh) to 95-96% happens at full speed of 16A (standard onboard charger).
And charging from 95% up to 100% takes a lot of time.
Actually, I measured.
My somewhat degraded battery that can still fit 20.5kWh of capacity (instead of new 22kWh) needs just 6.0 hours to get
19.3kWh of energy. And another one or two hours (depending on balancing and temperature) to get that last 0.4-0,8kWh.
Charging acceptance drops like rock. But electronics are still running. And charging efficiency during that last hour is way
down... to around 60%, or even 50%.
And charging those 95%, or 19,3kWh, consumed 20.8kWh from meter. Therefore efficiency from 0% to 96% is 93%.
Total charging efficiency from 0% to 100% is no more than 89%. And even less if battery is cold (less than 4 bars).
These 4-5% of extra loss all add up in all those years.
For me it would mean 6Mwh*0,05=300kWh, therefore around 30€ each year. Just a parasitic loss of energy :|

This same story applies to those who charge any slower than 16A at 230V (aka 3,3-3,6kW).
Do not charge slower than 3kW. Especially on 110V in US. At least that one is no secret.
This efficiency loss also applies to EU "trickle charger". Which runs at 2,3kW. It's still trickle, like my signature says :lol:
Also there is almost no efficiency gains with 32A charging AFAIK.

So anybody who charges up to 80% (or even continues charge right before departure) at 3kW rate has 7% loss (maybe 6% in case
wiring from main meter to EVSE is short). Anyone who charges to 100% daily can not get less than 10% of loss.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

Leaf15
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Re: Another reason not to charge to 100%

Sun Jan 20, 2019 1:38 pm

Here is another reason to charge to 100% - when you charge to 100% the charging rate is gradually decreased and then there is 3 distinct pops in charging current right before the end (some chargers like JuiceBox Pro allows very detailed charging current graphing). One of the reason it takes more time - your battery computer performs "active" cell balancing to level cell voltages, by shunting high voltage cells and keep charging low voltage cells. The battery protection levels are determined by the lowest cell voltage, not by the average. When there is weak cell(s) - folks start with 100% battery, then drive 20-30 miles and all of a sudden battery level drops like a rock. It happens because of BMS has to protect any cell with voltage drop below the lowest level threshold, otherwise the cell will become irreversibly damaged. So not leveling those lower voltage cells will cause under utilization of the battery capacity as a whole and make those lower voltage cells to work harder, so they will degrade even faster, dragging whole battery down with them. Also, there is "passive" (while discharging) cell balancing taking place all the time, but it is not as effective as "active" (while charging) one.

I think one of (many other) the reasons manufacturers are not recommending to use Quick Charge as the only means to charge your car - QC usually does not fully charge the battery (up to 80%) and cell balancing simply would never take place. I guess, one could remedy balancing issue by topping off (remaining 20%) battery after QC with L2/L1 charger (at home).

BTW, you reside in very mild climate, so it helps a lot.
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arnis
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Re: Another reason not to charge to 100%

Mon Jan 21, 2019 2:40 pm

Sorry but that is just FUD :| . There is nothing wrong with charging below maximum limit.
BMS works all the time. Full charge/discharge is needed after few HUNDREDS partial cycles.
Balancing happens at any charging discharging and even just idling in some cases.

Today, it is 0*F outside. I hardly charge to 100%. Very hard on balancing, and it is perfect.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

Leaf15
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Re: Another reason not to charge to 100%

Mon Jan 21, 2019 4:59 pm

arnis wrote:Sorry but that is just FUD :| .
With this way of thinking, suggesting not to charge to 100% should be considered as FUD :| as well. I doubt Nissan wants owners to ruin battery sooner by charging to 100%. Myth about EPA and 80% is baseless as many cars offers option to charge below 100% (EPA does not object anyone, but Nissan?) as it is beneficial in a few situation: for example: driving down hill after charge; Or not driving car for extended time at high temperature. Besides "EV 100% charged battery" really means more like up to 92% of the battery full capacity. So car charged to 100% are not "fully" charged. I think Nissan should put it back and to let folks to choose between 80-100% of charge level.

BTW, by mild climate I was referring to the summer temperatures ~ 71F max. Should be nice there in the summers, May to September to be exact. 60-70F are awesome temperatures for humans, so I could not blame EVs for liking it too. We could only dream about it in PA as we have only few days (7-14 days total) a year in this temperature range and then keep talking about those awesome few days for the rest of the year, lol. Basicly have only 2 seasons: summer and winter and shit load of rains and crappy weather in between.

I do not have QC option on mine, so I do not know about QC policies, but in QC case charging to 80% (30-40 mins) makes perfect sense because of this type of chargers usually used while en-route, so waiting another 1.5 hours to get 20% is waste of time and prevents others from accessing the QC charger.

It is nice that you did the thorough analysis of the last phases of charging, so folks could see the better picture what is going on during this last 20%, especially last 10% is when there is dramatic drop in charging rates so when you are in the hurry - stop charging and just go.

In some situations, like charging at work for free - it simply has no material effect.
Last edited by Leaf15 on Mon Jan 21, 2019 8:03 pm, edited 1 time in total.
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LeftieBiker
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Re: Another reason not to charge to 100%

Mon Jan 21, 2019 6:29 pm

Myth about EPA and 80% is baseless as many cars offers option to charge below 100% (EPA does not object anyone, but Nissan?)
You have that a little backwards. The EPA did lower the 2013 Leaf's rated range, by introducing an average between the 80% and 100% charge settings. This is fact, not myth. That Nissan chose to never again offer the 80% off in the US, despite the EPA later giving other cars a pass (for reasons like GM renaming the option "Hilltop Mode" instead of "Long Life Mode") is a reflection on Nissan's choices, not the reality of the situation. Nissan has chosen marketing and price point over battery longevity, and that is not a myth.
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Leaf15
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Re: Another reason not to charge to 100%

Mon Jan 21, 2019 7:44 pm

LeftieBiker wrote:Nissan has chosen marketing and price point over battery longevity, and that is not a myth.
All other EV offers this option under variety of names, but majority as "charge limit", while none manufacturers advertise lower range or forced by EPA to change efficiency. So the Myth is about: Nissan could not use this option, because of "something that does not exist anywhere else in observable universe". Currently, there is nothing (but old grudge) preventing Nissan from offering this option to its EV customers. I could use this feature, but not for battery life sake, I do not like the fact the regen is almost not existent when battery is full for a mile or so, because of I start trip going down hill using brake pads instead of regen. I could just charge to 95-97% to have my regen available immediately after charging.

I think it is silly to call this straight forward setting with crazy names like "battery life saver", "Long Life Mode", it just implies the fact battery degrades - not good for marketing. Why not call it exactly what it is - "charge limit" to allow customer to set limit for whatever reason it might be, who cares really. It apparently makes EPA not to worry about it at all.
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arnis
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Re: Another reason not to charge to 100%

Wed Jan 23, 2019 12:44 pm

The higher is li-ion cell voltage, the faster it degrades. And you, my darling, can't change that.
At 80%, voltage is around 4V, at 100% around 4.1V.
So there is that.
Tesla "enforces" 90% limitation. If you set it to 100%, it will automatically drop to 90% soon.
And you, my darling, can't change that.

Also daily equalization at 99% takes a LOT of idle energy. My calculations say around 50% of
energy used gets wasted, and 50% goes in the battery (at SOC above 97%).
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Stanton
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Re: Another reason not to charge to 100%

Wed Jan 23, 2019 3:01 pm

Doesn't this sort of ignore the reality that 100% is actually more like 92-93% (at least on my Leaf)? I don't think the BMS will allow anything over 95%.
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LeftieBiker
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Re: Another reason not to charge to 100%

Wed Jan 23, 2019 3:29 pm

Stanton wrote:Doesn't this sort of ignore the reality that 100% is actually more like 92-93% (at least on my Leaf)? I don't think the BMS will allow anything over 95%.
Think of it as "Nissan packs degrade faster at sustained charge of 94% or higher." We call it 100% but most of us know it's actually lower.
All other EV offers this option under variety of names, but majority as "charge limit", while none manufacturers advertise lower range or forced by EPA to change efficiency. So the Myth is about: Nissan could not use this option, because of "something that does not exist anywhere else in observable universe". Currently, there is nothing (but old grudge) preventing Nissan from offering this option to its EV customers.
I'm still not sure what you think is a "myth." Nissan withdrew the 80% charge option in the US after the EPA lowered their overall range rating in 2013. It's true that there is now nothing stopping them from offering such an option again now, but there is no "myth" involved, just Nissan's unwillingness to change.
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arnis
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Re: Another reason not to charge to 100%

Thu Jan 24, 2019 12:40 pm

There is no such thing as "actual 100%". 100% is something somebody agreed on.
For example, Lead acid batteries can be charged way over 100%. Like 115% is easily doable.
But battery will discharge to 100% after disconnection from charger within hours.
And down to 90% within weeks. So it is just a "voltage level" agreed to be 100%.

For li-ion all chemistries are different. Those Leaf uses are agreed to be 100% at 4.2V.
Though 4.3V is easily doable, calendar life at that voltage is months, not years.
Leaf charges up to 4.13V, some may estimate that it is "up to" 93-97% of theoretical accepted maximum.
Though all this applies to ideal temperature of 25*C.


Even Li-ion cells self-discharge when charged to near 100% (maybe that is exactly why Leaf charges up to 4.13V,
just to avoid useless self-discharge zone, plus extra degradation).

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Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

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