Thoughts on 80% Charging

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Bob

Well-known member
Joined
May 24, 2013
Messages
305
Location
New Hampshire
I've been thinking about charging a lot recently. My 2013 has the option of long life charging to 80%. Is this a good idea? Here's my thoughts.

Charging to 80% is less chemical stress on the battery. That's why Nissan first made the mode.
Charging to 80% is more likely to give you range anxiety because you have...less range.
Charging to 80% looks worse in range statistics. We think that's why Nissan eliminated it.
Charging to 80% takes less time. That last 20% of charge takes much longer.

But charging to 100% includes cell balancing. This means stopping the charge process, measuring each cell, and then draining charge off of the cells that are too high so that they are all at the same state of charge, then finishing the charge. It could also be a smarter algorithm that shuffles charge from one cell to another.
Radio-controlled device fanatics claim that cell balancing is critical for long battery life but I've yet to see data.
Cell balancing gives you the most range, because you aren't limited by the weakest cells. All cells are roughly the same.
Cell balancing may give you longer battery life, because no cell is over-charged or proportionately harder worked. That could be another reason why Nissan might have eliminated 80% charging.
Cell balancing wastes energy because it involves discharging batteries to get them into balance. I have no idea if this is significant but it probably is not wasting very much energy.
Cell balancing also could reduce the life of certain cells because it discharges them during the balancing process.
If you occasionally charge to 100%, you may get the same balancing benefits as always charging to 100%.

Some reading on cell balancing:
http://www.ti.com/lit/an/slyt322/slyt322.pdf" onclick="window.open(this.href);return false;
http://www.mpoweruk.com/balancing.htm" onclick="window.open(this.href);return false;
http://mocha-java.uccs.edu/ECE5720/ECE5720-Notes05.pdf" onclick="window.open(this.href);return false;

What do you think? Is any of this wrong? Am I over-analyzing? Please share your thoughts.

Bob
 
Bob said:
Am I over-analyzing?
Yes! And I love it! :D
Bob said:
Is any of this wrong?
I only see a couple of things I would nit-pick:
Bob said:
But charging to 100% includes cell balancing. This means stopping the charge process, measuring each cell, and then draining charge off of the cells that are too high so that they are all at the same state of charge, then finishing the charge.
The shunts are typically active during nearly every stage of charging and discharging, but I agree that a better job is done after charging to 100%.
Bob said:
It could also be a smarter algorithm that shuffles charge from one cell to another
I've made this suggestion myself! Someday perhaps there will be a BMS that does this to get that last 0.25% of efficiency!
Bob said:
Radio-controlled device fanatics claim that cell balancing is critical for long battery life but I've yet to see data.
Here is a presentation that makes a strong case for a BMS.
Bob said:
Cell balancing gives you the most range, because you aren't limited by the weakest cells.
You are ALWAYS limited by the weakest cell. What balancing does is prevent you from being limited by a cell with a higher SOC and/or a cell with a lower SOC.
Bob said:
All cells are roughly the same.
Normally. I do find that when it is extremely cold they seem to differ due to having different thermal environments. This effect is not so noticeable in more temperate weather.
Bob said:
Cell balancing also could reduce the life of certain cells because it discharges them during the balancing process.
I doubt it. The shunts are only about 1A, IIRC.
Bob said:
If you occasionally charge to 100%, you may get the same balancing benefits as always charging to 100%.
I agree, and that's what I do. But with the 2011/2012s, it takes a couple of trips to 100% to regain full balance. With a 2013, I think the charging algorithm can get it done in a single charge to 100%

But I rarely ever even charge to 80%. Typically I will charge to 60% or so. I target a charge percentage which will return me home right around 30% so that the car usually sits around that SOC.

One other observation I have is that much of the degradation I see with the 2011 appears to be at the top end. I say this because battery voltage drops down very quickly when fully charged. Average cell voltage will get below 4.0V in less than about 0.5 miles, even at no load. This observation agrees with slide 14 in the presentation that I linked above. Basically, with a 2011 I can get a bit more capacity by charging at L1 instead of L2. This gives the BMS more time to balance the cells, but it also allows the cells to get to a higher SOC even though they have higher resistance than when new. Again, I think the MY2013s and beyond have largely addressed this issue by allowing the charger to go all the way down to ~600W output power at the end of the charge cycle.
 
RegGuheert said:
But with the 2011/2012s, it takes a couple of trips to 100% to regain full balance.
Hmm, at least with my LEAF I can't see any significant difference even after multiple 100% charges. Maybe because you usually charge to even less than 80%?

RegGuheert said:
One other observation I have is that much of the degradation I see with the 2011 appears to be at the top end. I say this because battery voltage drops down very quickly when fully charged. Average cell voltage will get below 4.0V in less than about 0.5 miles, even at no load.
I notice this too, but not to that extent. What I notice is that 100% settles to 393V (4.094V/cell) when it used to charge to 394V (4.104V/cell). 80% is 386V (4.021V/cell) and I'll see the pack quickly drop down to 389-390V (4.05V/cell) after a couple miles of driving, but 4.02V at rest would still come at around 80% SOC. I'll try to double check next time I charge to 100%.

RegGuheert said:
Basically, with a 2011 I can get a bit more capacity by charging at L1 instead of L2. This gives the BMS more time to balance the cells, but it also allows the cells to get to a higher SOC even though they have higher resistance than when new. Again, I think the MY2013s and beyond have largely addressed this issue by allowing the charger to go all the way down to ~600W output power at the end of the charge cycle.
If you have an EVSEUpgrade, or OpenEVSE, you can dial it down to 120V / 6A or 720WAC and get a nice long charge, but I've tried that a time or two and still haven't seen a big difference on my '11. Maybe I'll try it again as it's been a while.

Anyway, to answer the OP's question - I wouldn't sweat any 80/100% balancing issues, even charging to only 80% the pack seems to stay balanced enough to avoid any major loss of range due to imbalance and at least on a '13+ LEAF, a single 100% charge appears to work well enough to ensure a good top-balance when done.
 
drees said:
Maybe because you usually charge to even less than 80%?
Perhaps so.
drees said:
RegGuheert said:
One other observation I have is that much of the degradation I see with the 2011 appears to be at the top end. I say this because battery voltage drops down very quickly when fully charged. Average cell voltage will get below 4.0V in less than about 0.5 miles, even at no load.
I notice this too, but not to that extent. What I notice is that 100% settles to 393V (4.094V/cell) when it used to charge to 394V (4.104V/cell). 80% is 386V (4.021V/cell) and I'll see the pack quickly drop down to 389-390V (4.05V/cell) after a couple miles of driving, but 4.02V at rest would still come at around 80% SOC. I'll try to double check next time I charge to 100%.
It is about 1/2 mile to the stop sign at the end of my road. The road is almost completely flat to that point and I often drive very gently. I do tend to look at the meter when I stop there, particularly if I have charged to full before the trip. That is my gauge. The SOC meter is usually already below 90% at that point, but never below 80%. But I generally am seeing voltages right around 4.0V. Perhaps I am looking at the lowest cell voltage instead of the average and that is throwing me. I'll try to make more meaningful observations at that point of me trip in the future.

Unfortunately I didn't have the meter when the car was new, so I only have my recollections of when I would lose charge bars. I used to be able to travel over 10 miles on the first (12th) charge bar when full and balanced. I seem to remember going almost 12 miles one day. Now it is a challenge to get beyond seven.
drees said:
If you have an EVSEUpgrade, or OpenEVSE, you can dial it down to 120V / 6A or 720WAC and get a nice long charge, but I've tried that a time or two and still haven't seen a big difference on my '11.
That would be nice! I do have an EVSEUprade, but mine is the Rev. 2 version which delivers 16A, but it is earlier than the 20A one which offers adjustable charging rates.

One trick I use in wintertime (with L2) is to turn on the climate control when there is about one hour of charging time remaining indicated on Carwings. That does a decent job of slowing the charging rate and also warms the cabin! However, the air conditioner uses so little power that this trick does not do much to help this time of year.
RegGuheert said:
Maybe I'll try it again as it's been a while.
I need to make a fairly long drive next Tuesday which I had made exactly one year (and a couple of Ah) ago. On that trip, I was able to drive an additional 10 miles after arrival and was still above VLBW. I intend to charge with L1 the night before the trip. It will be interesting to see if I can achieve a similar result this year.
 
I had a 2013 loaner about a year ago. It had less than 3000 miles on it, was set to 80%, and had about 11% degradation. No QC. After charging it to 100% a couple times it regained about 5%. I suspect the car sat on the lot a while, but the moral of the story is that charging to 100% did provide some battery conditioning.

Also for what it's worth our 2013 has been charged nearly daily to 100% just prior to takeoff for the past year. 28k miles and 3% degradation. 63.99ahr
 
Phatcat73 said:
I had a 2013 loaner about a year ago. It had less than 3000 miles on it, was set to 80%, and had about 11% degradation. No QC. After charging it to 100% a couple times it regained about 5%. I suspect the car sat on the lot a while, but the moral of the story is that charging to 100% did provide some battery conditioning.

Also for what it's worth our 2013 has been charged nearly daily to 100% just prior to takeoff for the past year. 28k miles and 3% degradation. 63.99ahr

I definitely see this same thing in my 2013. If I charge to 80% for a while (and I do it for regen availability, not long life) I will see a definite reported drop in capacity. But when I charge to 100% for a few days it climbs back up to around 64 ahr (20K miles so far).

I have also notice that doing a QC will almost always INCREASE the reported capacity for a while.
 
epirali said:
I have also notice that doing a QC will almost always INCREASE the reported capacity for a while.
I see that with my 2011, also. Unfortunately, the closest QC is about 40 miles away so it doesn't happen that often.
 
Phatcat73 said:
Also for what it's worth our 2013 has been charged nearly daily to 100% just prior to takeoff for the past year. 28k miles and 3% degradation. 63.99ahr
epirali said:
I definitely see this same thing in my 2013. If I charge to 80% for a while (and I do it for regen availability, not long life) I will see a definite reported drop in capacity. But when I charge to 100% for a few days it climbs back up to around 64 ahr (20K miles so far).
I have noticed this with my 2013 as well. I wanted to do the 80% charge for regen as well (city driving with lots of 4-way stops), but noticed my ahrs were dropping (down to 59.25) when only charging to 80%. Now that I'm in WI, I charge to 100% and have ahrs back to around 61.05. Still well below you guys and with far less miles (just over 5k now) but mine did sit for over a year on the dealer lot, so that may be the price I am paying.
 
Phatcat73 said:
the moral of the story is that charging to 100% did provide some battery conditioning.
I think the moral is that the BMS system can get pessimistic if the full SOC isn't used regularly, but it shouldn't result in any significant real-world loss. It is interesting that the '11-12 with all updates doesn't seem to report the same drastic capacity swings, the '13+ BMS is a step backwards in this area.
 
drees said:
Phatcat73 said:
the moral of the story is that charging to 100% did provide some battery conditioning.
I think the moral is that the BMS system can get pessimistic if the full SOC isn't used regularly, but it shouldn't result in any significant real-world loss. It is interesting that the '11-12 with all updates doesn't seem to report the same drastic capacity swings, the '13+ BMS is a step backwards in this area.

I agree with you, in that I think the full and QC are probably changing the estimation by BMS much more than any real change. It would take some serious testing to prove this.
 
One of the things we talked about in the very early days of the board is the way that computerized BMSs will lose track of the actual battery capacity and state of charge if the system isn't 'exercised' regularly. This seems to be recognized by Benz - before the annual battery test they want the battery discharged to below 40% and then charged to a full 100% prior to the eval. This is similar enough to the BMS 'drift clearing' process for laptops that I'll bet that's the reason for the requirement.
 
AndyH said:
One of the things we talked about in the very early days of the board is the way that computerized BMSs will lose track of the actual battery capacity and state of charge if the system isn't 'exercised' regularly. This seems to be recognized by Benz - before the annual battery test they want the battery discharged to below 40% and then charged to a full 100% prior to the eval. This is similar enough to the BMS 'drift clearing' process for laptops that I'll bet that's the reason for the requirement.
The iMiEV used to have a similar requirement for it's BMS IIRC - might still have it?

At the very least the '11-12 LEAF doesn't seem to respond much to a full discharge/charge routine, either because it's generally good at tracking changes in battery capacity, the '13+ LEAF seems to have a lot more variance in the reported Ah of the pack. It's also interesting that the reported Ah of the pack doesn't necessarily track GIDs all that well, either on the '13+ LEAF - look at how many new '13+ LEAFs have reported 56-58 Ah through LeafSpy, but also have a completely normal GID count.

Anyway, the only easy way to confirm actual pack capacity is to drain the pack and recharge while counting kWh into the pack. Also need to keep things like input voltage/current as similar as possible when comparing.
 
I've got a 2015 with no option for 80% charge, so perhaps I'm in a different situation, but I really think that the only drawbacks to 100% charging comes from (1) leaving the car at that high % for a long period of time and creating extra heat on the pack. (2) The added cost of electricity during the top end re-balancing. (3) The lack of regen when driving from 100-85%.

In my case we charge up most of the time for free at my wife's work, she plugs in after lunch so that we have a full charge just before she leaves, and we do the round trip to home and back the next day, arriving back at her work with about 30% charge left. I think that cycling through regularly is perfectly fine for the pack.
 
With our 2012, I mainly used 80% charge but made sure to do a 100% charge at least once a month for balancing. With the 2015 I don't bother trying to circumvent the default 100% charge, but I do still use an end-time charge timer to minimize the time spent sitting at 100%. Even though my driving requirements haven't changed and 80% was more than adequate, I still find that psychologically it's more pleasant to start the day with 100% charge. :)
 
I also charge my 2012 to 80% typically, to 100% a couple of times a month. I can get what I need done with 80, and being in the computer field I have seen for many years what happens to laptops that are maybe in a different circumstance, but killed by overcharging. Manufacturers have settings for docked laptops to maintain 50 to 80% charge as a result of this issue.
 
I'd be curious as to how much energy is stored in a typical laptop battery vs its design limit. For example, a Leaf has a 24kWh battery however at 100% charged only holds 22kWh. Thus there's 10% overhead which may be enough to prevent damage.
 
Phatcat73 said:
I'd be curious as to how much energy is stored in a typical laptop battery vs its design limit. For example, a Leaf has a 24kWh battery however at 100% charged only holds 22kWh. Thus there's 10% overhead which may be enough to prevent damage.

Batteries for small consumer products are generally subjected to murderous SOC percentages on both ends, in order to boost run-time claims. 18 months later when the consumer replaces the battery (or device), they complain that batteries suck, and don't realize the device designer is the one who killed their battery.
 
excuse my language but WTF is charging to 80%?

Forgive me, but I'm about to delve into math, numbers, and lies.

First off my 2012 SL charges to "full" when leafspy says the SOC is 91.9% to 92.x% but that is always below 93%.

Now I just tonight told my car to charge to "80%" with a charge timer and less than an hour later it stopped charging.

* 75% https://www.nissanusa.com/owners/vehicles" onclick="window.open(this.href);return false; says the state of charge is 75%

* 75.1% leafspy says 75.1%

- leaf manager gives a range (70.8% to 77.9%)

- the target for stopping charging was 80% but nothing I check says that.

* 82% openwings says 82%

- Nissan Leaf android app says miles range or time to full charge (no % there)

I know the 2013 and newer has a dash SOC %, I don't know how far dash SOC diverges from leafspy SOC. I do know that leafspy SOC is linear and all the others are "lying" at the top end and bottom end of the scale.

For now I'm going to say "charging to 80%" is really charging to 80% of max which in my case is 75%.
 
Got a screenshot?

On my '11 "80%" charge, SOC is always 79.9X%. "100%" charge is usually around 95% SOC, but I've seen it as low as 89% on occasion.
 
Back
Top