Which is better: 80% charge daily vs 100% once weekly?

[VentusEU]

2) Charging the battery to 100% is good. Cell balancing only occurs over 80% SOC.

I'm new to the forum, so forgive me if this has already been covered in detail.

I'm curious about how Nissan's Battery management software performs cell balancing. I thought that "Continuous Cell Balancing" (i.e., discharging energy from the higher voltage cells into the lower voltage cells when the battery is not under load) was pretty much accepted as the best way to balance a pack of cells with Lithium based chemistry. I'm a little surprised to hear that cell balancing for the Leaf only occurs during charge at a level above 80%.

Has Nissan ever released any details of the battery management system for the Leaf? (I would certainly understand if they considered it proprietary, and haven't released any details).

Thanks,

 

[derkraut]

Welcome to the forum VentusEU. You've posted a good question. I don't know the answer, but other posters will chime in, and someone will probably know.

 

[surfingslovak]

Has Nissan ever released any details of the battery management system for the Leaf? (I would certainly understand if they considered it proprietary, and haven't released any details).

Please have a look at this older thread. Google search is your friend. No official word from Nissan on this, and many related topics, which is one of the reasons why the discussion on this forum has been predominantly technical in recent months and years.

 

[TimLee]

take it in for the 7,500 mile check-ups (which I understand includes a pack balancing charge and is included in my lease)

The Nissan battery warranty requires an annual battery test. Has nothing to do with mileage.
Required once every year.

 

[DaveinOlyWA]

I will venture to say that it is continuous.
There is no recommendation of how to charge the car "anymore" since the fast charge warning has been mitigated. Cell balancing is critical and Nissan has taken steps to insure that happens.

 

[surfingslovak]

I will venture to say that it is continuous.
There is no recommendation of how to charge the car "anymore" since the fast charge warning has been mitigated. Cell balancing is critical and Nissan has taken steps to insure that happens.

What is this in reference to?

 

[DaveinOlyWA]

No reference to anything but common sense. If a battery becomes out of balance with the pack, that imbalance willwiden each time the pack charges or discharges. So there are 2 options as i see them

1) advise user to charge in a way that balance the cells or a full charge or whatever

2) provide some sort of balancing without any special charging instructions like "to maintain cell balance, Nissan recommends charging to full at least every 30 days

There is always the "sky is falling" response that Nissan simply overlooked the need or felt it unimportant

 

[surfingslovak]

There is always the "sky is falling" response that Nissan simply overlooked the need or felt it unimportant

I'm not sure if this is in any way helpful to the question asked, and if it properly characterized what has been said here and elsewhere. There is a trend among OEMs to disclose less information, not more, and that leads to genuine confusion. Even among the staff they hire to provide support for these vehicles. When someone states that Nissan or some other OEM has not provided any information on the topic, this does not automatically imply criticism, as you seem to infer. No, it's simply a statement that qualifies the discussion among owners as "educated guesses", since no official guidelines have been provided.

Personally, I found the following quotes from Phil and Tony to be helpful, they were both posted in the thread I referenced above, and they match my experience as well. As I mentioned in my PM to you a while ago, I'm primarily interested in establishing an accurate pool of information about the LEAF. Ideally, this would be condensed to a set of best practices or recommendations most experienced owners could get behind. While many others will continue to practice their individual routine, whether right or wrong, I don't think that it's helpful to consider this forum as a prime venue for evangelism. Especially not when answering questions from new owners.

That said, it's tiring to see non-technical folks feel a constant urge to chime in, say nothing that makes sense, and go off on tangents.

The LEAF uses a sophisticated top-balance system with an array of MOSFETs that can bypass current around cells that are at a higher SOC than their neighbors, thus allowing those with lower SOC to "catch up" so that all cells have parity. This is all carefully controlled and monitored by the battery ECU located in the battery box.

How can I tell when the cells need balancing or how often should I balance the cells?
what is the proper way to balance the cells?

Cell balancing is automated. The only thing you have to do is charge the car to 100% and let it sit for up to about 4 hours. Leave the car plugged in during this time and you'll get a "top off" charge after it has discharged the highests cells during the automated process.

We don't yet have a tool to know exactly when, but it's coming (LEAFscan). When the cells aren't balanced, there will be a significant reduction in available capacity. Unless you are using the entire useable capacity, you won't know or care. I recommend once every week to once a month to allow the car to charge to 100% and give it that 4-ish hours to do the balance.

 

[DaveinOlyWA]

sorry that my technical expertise is not up to your level. the two statements you cited need clarification... maybe not to others, maybe just to me.

the first statement "seems" (since i dont really understand some of the terminology) to say that their are devices that block current to cells with a higher charge in order for cells at a lower charge to catch up during the charging process

the 2nd statement seems to say when the charge is complete, the higher cells bleed off (to the lower cells i guess) and that action causes an overall charge reduction that may require another top off?

am I even close on that?

 

[TonyWilliams]

sorry that my technical expertise is not up to your level. the two statements you cited need clarification... maybe not to others, maybe just to me.

the first statement "seems" (since i dont really understand some of the terminology) to say that their are devices that block current to cells with a higher charge in order for cells at a lower charge to catch up during the charging process

the 2nd statement seems to say when the charge is complete, the higher cells bleed off (to the lower cells i guess) and that action causes an overall charge reduction that may require another top off?

am I even close on that?

Yes, I think you got it.

 

[TimLee]

I will venture to say that it is continuous.
Cell balancing is critical and Nissan has taken steps to insure that happens.

LEAFSCAN now has a screen that shows which Balancing MOSFETs are enabled at any given time. I have seen them activate at any time, even after charging completes. While they will work anytime automatically, you will not get the full benefit of a top balance without an occasional full charge, but then again, if you only ever charge to 80%, then you probably don't mind losing 15% anyway.

Here's the summation: You don't need to do anything special for the pack to maintain itself within certain bounds, but if you want to insure that all capacity will be usable if you perform a full charge (~95% SoC), then I recommend you allow a full charge occasionally to allow the balancing to peak your pack properly. I recommend leaving the charger connected overnight after your full charge to allow for additional peaking. I've seen it restart charging up to 5 times so far.

Leaving your pack at full charge for 24 hours once in a while is not going to degrade anything, and in fact, will give you more usable range as it will stay in balance better.

-Phil

Dave your previous two part summary of how top balancing works is correct, but it clearly is NOT continuous. Phil has observed the behaviour of the top balancing with the prototype LEAFSCAN, and it only occurs following completion of a 100% charge, and apparently takes a long time if the pack has become significantly out of balance.
I plan to follow Phil's recommendation. 100% charge at the very least monthly (during cooler weather) , and leave it at 100% overnight to assure the pack is properly top balanced.

 

[DaveinOlyWA]

I will venture to say that it is continuous.
Cell balancing is critical and Nissan has taken steps to insure that happens.

LEAFSCAN now has a screen that shows which Balancing MOSFETs are enabled at any given time. I have seen them activate at any time, even after charging completes. While they will work anytime automatically, you will not get the full benefit of a top balance without an occasional full charge, but then again, if you only ever charge to 80%, then you probably don't mind losing 15% anyway.

Here's the summation: You don't need to do anything special for the pack to maintain itself within certain bounds, but if you want to insure that all capacity will be usable if you perform a full charge (~95% SoC), then I recommend you allow a full charge occasionally to allow the balancing to peak your pack properly. I recommend leaving the charger connected overnight after your full charge to allow for additional peaking. I've seen it restart charging up to 5 times so far.

Leaving your pack at full charge for 24 hours once in a while is not going to degrade anything, and in fact, will give you more usable range as it will stay in balance better.

-Phil

Dave your previous two part summary of how top balancing works is correct, but it clearly is NOT continuous. Phil has observed the behaviour of the top balancing with the prototype LEAFSCAN, and it only occurs following completion of a 100% charge, and apparently takes a long time if the pack has become significantly out of balance.
I plan to follow Phil's recommendation. 100% charge at the very least monthly (during cooler weather) , and leave it at 100% overnight to assure the pack is properly top balanced.

the parameters in how the pack is balanced maybe different between balancing at the top or balancing at any other SOC but there is little doubt in my mind that both are happening. Top balancing does enable more range simply because its enabling the cells to reach their full potential.

balancing at a lower SOC only allows longevity and stability of the pack. Both are critical processes.

the two mechanisms quoted from Tony and Phil above describe two very different events that cannot both take place at a full charge.

Scenario 1 could happen at any SOC. Scenario 2 would happen when at full charge.

**edit** although there is a HUGE variance in price and performance and specific process, battery balancing systems all work relatively the same. They work to keep the "laggards" from getting too far behind. On my ZENN, my aftermarket system only balanced connecting pairs and had the benefit of LEDs that flashed when balancing was active. Diodes were used so balancing only went in one direction. this is a cheap system and relatively inefficient system since a pair of batteries balancing may need to rebalance another pair of batteries after the first balancing is done.

now this was with lead acid but it still is a battery so the numbers are different but the mechanics are the same.

 

[TimLee]

I will venture to say that it is continuous.
Cell balancing is critical and Nissan has taken steps to insure that happens.

LEAFSCAN now has a screen that shows which Balancing MOSFETs are enabled at any given time. I have seen them activate at any time, even after charging completes. While they will work anytime automatically, you will not get the full benefit of a top balance without an occasional full charge, but then again, if you only ever charge to 80%, then you probably don't mind losing 15% anyway.

Here's the summation: You don't need to do anything special for the pack to maintain itself within certain bounds, but if you want to insure that all capacity will be usable if you perform a full charge (~95% SoC), then I recommend you allow a full charge occasionally to allow the balancing to peak your pack properly. I recommend leaving the charger connected overnight after your full charge to allow for additional peaking. I've seen it restart charging up to 5 times so far.

Leaving your pack at full charge for 24 hours once in a while is not going to degrade anything, and in fact, will give you more usable range as it will stay in balance better.

-Phil

Dave your previous two part summary of how top balancing works is correct, but it clearly is NOT continuous. Phil has observed the behaviour of the top balancing with the prototype LEAFSCAN, and it only occurs following completion of a 100% charge, and apparently takes a long time if the pack has become significantly out of balance.
I plan to follow Phil's recommendation. 100% charge at the very least monthly (during cooler weather) , and leave it at 100% overnight to assure the pack is properly top balanced.

the parameters in how the pack is balanced maybe different between balancing at the top or balancing at any other SOC but there is little doubt in my mind that both are happening. Top balancing does enable more range simply because its enabling the cells to reach their full potential.

balancing at a lower SOC only allows longevity and stability of the pack. Both are critical processes.

the two mechanisms quoted from Tony and Phil above describe two very different events that cannot both take place at a full charge.

Scenario 1 could happen at any SOC. Scenario 2 would happen when at full charge.

Phil is Dave right? Do the MOSFETS activate anytime an individual cell reaches 4.1 volts any time charging is occurring?
Without the prototype LEAFSCAN I think Dave and I are just guessing.

 

[DaveinOlyWA]

Phil is Dave right? Do the MOSFETS activate anytime an individual cell reaches 4.1 volts any time charging is occurring?
Without the prototype LEAFSCAN I think Dave and I are just guessing.

no no no... MOSFETS could care less what the voltage is. they only detect differences.

(this is a VERY untechnical explanation... so dont micromanage a response. consider the big picture first)

its like a multi segmented pool of water. MOSFETs act as gates between two segments to insure the water level is consistent. now, they do run on a voltage difference parameter. IOW, the difference has to reach a certain level before they activate. on the LEAF, i have no idea. on my super cheap ZENN, it was .1 volts which I am guessing is MUCH higher than the LEAFs parameter.

 

[thew]

I charge 80% during the Week. And 100% for the Weekend.. This way we have a Full pack for Weekend Runs. And the rest of the week, when we charge we only charge to 80%.. I believe this is the best way to go..

 

[DaveEV]

LEAFSCAN now has a screen that shows which Balancing MOSFETs are enabled at any given time. I have seen them activate at any time, even after charging completes. While they will work anytime automatically, you will not get the full benefit of a top balance without an occasional full charge, but then again, if you only ever charge to 80%, then you probably don't mind losing 15% anyway.

Dave your previous two part summary of how top balancing works is correct, but it clearly is NOT continuous. Phil has observed the behaviour of the top balancing with the prototype LEAFSCAN, and it only occurs following completion of a 100% charge, and apparently takes a long time if the pack has become significantly out of balance.

You statement, Tim, directly contradicts what Phil says in the quote. Balancing for sure happens well before the completion of a 100% charge. Balancing is simply more effective when 100% charged simply because differences in cell voltages and SOC levels is more exaggerated when the pack is either fully charged or fully discharged.

 

[surfingslovak]

Cross-posting this from another venue. The beginning of the video might be relevant to the cell balancing discussion on this thread.

High Efficiency Bidirectional Cell Balancer Maximizes Capacity and Lifetime of Series Connected Battery Stacks

 

[LUXMAN]

My guess is that Nissan has set their chargers to max out at about 98% of true 100% battery capacity and to shut down the car around 2% to prevent users from trashing their packs and creating warranty calls.

actually 93.6%

Now I am new to the forum. Leased Leaf is coming Friday 4/19 :!:

BUt it seems there is a wide ange of opinions on the battery charge. 100 vs 80%.
I have read the manual where it says to charge up when you get home. But it also says to charge a cool battery vs a hot one.
Then it says to charge to 80% at some point and 100% for max range.

Now if the charger maxs out at 93.6% and the battery maker also has a pad in there, how much capacity of the battery are you really charging too?
Sounds like a charge to 100% whenever would be fine to me. Cuz if you charge to 80%, you are getting 80% of 93.6% or some other lower number and self limiting yourself.
As I see it, if you lease, charge to 100% and see what happens. Great way to test the technology and see if you can live with it full time so you dont have range anxiety or rapair cost.
I am leasing for 2 years knowing that the range is going to be better in the 15 or 16 models.
LUXMAN

 

[surfingslovak]

Now if the charger maxs out at 93.6% and the battery maker also has a pad in there, how much capacity of the battery are you really charging too?
Sounds like a charge to 100% whenever would be fine to me. Cuz if you charge to 80%, you are getting 80% of 93.6% or some other lower number and self limiting yourself.

Please note that Phil, the person with likely most accurate information on this board, said that the maximum SOC was between 94 and 95%. 80% is just that, 80% of true SOC and not of the lower maximum. While it's good that you are leasing, and you consequently don't really have to worry about the battery too much, a lot of this has been discussed before and is captured in the Wiki. There is much less need to guess or test new technology, as you said in your post above. Perhaps it's just me, I believe that we have decent consensus on battery care and charging protocols by now. The only problem I can see is that some folks don't make much effort to quote accurate data and prefer to fly by the seat of the pants. That's their prerogative, of course, but I would advise new owners not to believe everything that's being said on some of these threads and to take this type of information critically.

My take on this is that if you don't need the full range, then charge to 80%. It's easy to override and charge to 100% when needed. If you do need the range, then absolutely, charge to 100%. It won't have much impact when the vehicle is driven daily. Just take care not to leave the car fully charged for days, weeks or months. That would be less than ideal for battery life. What has been observed so far is that the most important aspect for battery life is ambient temperature and solar loading. Park your car in the shade or in a cool garage, if possible. That will likely have more effect on battery capacity than the fairly minor difference obtained by different charing protocols over the duration of your lease. Please also note that the driving style could be a significant contributing factor.

One of the owners in LA is a gentle driver and has seen excellent battery capacity retention relative to other owners in his area. It's difficult to generalize from a sample of one, but based on prior research, aggressive driving style could be a fairly important contributing factor. I'm only mentioning it for completeness, and not to take the fun out of driving the LEAF. Please don't over-think this, the benefit over the duration of your lease might not be worth the effort.

 

[LUXMAN]

Ok. well if 80% is really 80% of true SOC, I can see the benefit.
I have a 62 mile RT commute, if the chargers at work are available I am fine with 80%, but not being able to count on it, I figure 100% out of the house would be a must.
I live in Texas and right now I have 2 other cars in the garage. Since I am leasing, not too worried as you mentioned, but the heat will be great in the summer. Also, I really take care of my cars, so I dont want to trash it in case I want to keep at the end of the lease.
I am very interested in how it pans out in terms of battery life with the heat etc, since my wife wants to go electric and get rid of her SUV. (course 2 years may no be enough)
I think a PHEV would be good for her in a couple years when they come out. Mitsubishi is supposed to have an Outlander model coming out for 2014. Supposed to drive in Series, Parallel or just EV mode. But with a 12kWh battery I bet based on size and AWD, it will ony have a 30 mile EV range. Plus, I have never heard great things about Mitsubishi quality. :roll:
LUXMAN