Battery "balancing" at an 80% charge

[DaveinOlyWA]

I am still not convinced this extra charge cycle is part of any balancing cycle. I think balancing happens during the main charge.

I speculate the top off is from voltage or temperature changes after the battery settles down then the BMS just decides it is not quite to 80% given the new measurements. Has anyone actually tracked voltage and temperature after a charge?

And I might be totally off base also

i have to agree with at least part of your statement. it seems this "recharge" happens frequently in warmer places but not cooler places so guessing temperature is in the equation somehow.

i get text msg notifications of charge complete and have never gotten a double message. so it does happen but seens to only happen in certain circumstances and balancing should be happening in all circumstances to one degree or another

 

[DaveEV]

I cannot imagine that the battery is NOT balancing its cells even at 80% charges. Cheap battery chargers for radio control planes/cars' packs balance cells all throughout the charge, why would this multi-thousand dollar system not do the same?

Good point. I've got this inexpensive $45 battery charger to charge the LiPo and NiMH for my various toys and I always use the balance charge mode when charging my LiPos. You can see the difference in individual cell voltage if you don't use the balance mode, but when you charge in balance mode, it keeps the cell voltages very, very close. Granted, these cheap LiPo packs I'm using are very unlikely to be closely matched so they'll likely go out of balance fairly easy especially since they get pushed much harder than the pack in the LEAF (I will charge them at up to 2C and discharge at an average of 2C with peaks much, much higher than what the LEAF pack sees).

 

[Ingineer]

I can assure everyone that the Leaf pack does balance throughout the charge, even when under 80%. A restart after 80% is rare though. The most accurate balance is going to come from a full charge.

Let me remind everyone, you do not need to worry about it, or have a special charge regimen. I advise a full charge at least once in a while, say once a month minimum, but if you don't need the range, only charge to 80%.

You'll get maximum charge (range) when you need it if you occasionally perform the top balance. Other than that, it doesn't have much impact on battery life/health, as the automatic systems keep it in-line.

-Phil

 

[ebill3]

I can assure everyone that the Leaf pack does balance throughout the charge, even when under 80%. A restart after 80% is rare though. The most accurate balance is going to come from a full charge.

Let me remind everyone, you do not need to worry about it, or have a special charge regimen. I advise a full charge at least once in a while, say once a month minimum, but if you don't need the range, only charge to 80%.

You'll get maximum charge (range) when you need it if you occasionally perform the top balance. Other than that, it doesn't have much impact on battery life/health, as the automatic systems keep it in-line.

-Phil

Thank you for your clear and concise post. This puts the issue at rest, at least it does for me.

Bill

 

[Stanton]

I got double "charge complete" messages for only the second time I can remember, and it was last night. I completed a (timer bypass) charge to 100% last night, then received another "charge complete" message over 7 hours later! Temps here have been MUCH colder the last few days, which means I've been @5TB's for the longest stretch since last Spring.

 

[DaveinOlyWA]

I got double "charge complete" messages for only the second time I can remember, and it was last night. I completed a (timer bypass) charge to 100% last night, then received another "charge complete" message over 7 hours later! Temps here have been MUCH colder the last few days, which means I've been @5TB's for the longest stretch since last Spring.

do you have any capacity bars missing?

 

[TonyWilliams]

I got double "charge complete" messages for only the second time I can remember, and it was last night. I completed a (timer bypass) charge to 100% last night, then received another "charge complete" message over 7 hours later!

That is the most time I've ever heard! I went 4 hours and about 50 minutes once, but that was after multiple partial charges at low SOC.

 

[DaveinOlyWA]

I got double "charge complete" messages for only the second time I can remember, and it was last night. I completed a (timer bypass) charge to 100% last night, then received another "charge complete" message over 7 hours later!

That is the most time I've ever heard! I went 4 hours and about 50 minutes once, but that was after multiple partial charges at low SOC.

any capacity bars missing?

any way to measure the amount of charge between the two "charge complete" notifications?

is it possible you simply received duplicate messages? I get duplicate messages from AV for same charging session and they can come anywhere from a few hours apart to a day later...

 

[TonyWilliams]

any capacity bars missing?

I've not lost a capacity bar on either of the two LEAFs that I've driven over 35,000 miles. But, that has nothing to do with losing battery capacity (15% loss on previous LEAF with 25,000 miles and 10% loss on current LEAF with 10,000 miles).

any way to measure the amount of charge between the two "charge complete" notifications?

Blink EVSE's give that data.

is it possible you simply received duplicate messages? I get duplicate messages from AV for same charging session and they can come anywhere from a few hours apart to a day later...

Anything is possible, but I'm not following your thought process. I don't have an AV unit, and I've never gotten (to my knowledge) a duplicate message.

The charge events are the final "top off" after the cell balancing routine. Obviously, the longer the balancing takes, the more time there is between charges.

 

[LEAFer]

I got double "charge complete" messages for only the second time I can remember, and it was last night. I completed a (timer bypass) charge to 100% last night, then received another "charge complete" message over 7 hours later! Temps here have been MUCH colder the last few days, which means I've been @5TB's for the longest stretch since last Spring.

When you say "(timer bypass)" are you implying that you pushed the "timer override" button ? And if so, was there ALSO an active (overlapping) timer set at any time during the period of being plugged in ? What were the (over-ridden) timer's settings ? Were you charging at L1 or L2 ?

 

[DaveinOlyWA]

Tony; why are you talking about capacity loss when responding to my question concerning charge balancing? lets just stick with that for now

do you have any capacity bars missing?

assuming its possible that capacity bars "could" be missing due to heat and "might" be returning due to cooler weather or at least some capacity is coming back is it possible the EVSE charged the pack to full and the pack cooled lowering SOC so EVSE restarted charge

any way to measure the amount of charge between the two "charge complete" notifications?

I guess i could have skipped the next question if i knew this one. some have reported a spike in charge which would imply that charge was restarted for some reason. wondering if he got the same info and how much charge is this? since most reported a pretty small amount

is it possible you simply received duplicate messages? I get duplicate messages from AV for same charging session and they can come anywhere from a few hours apart to a day later...

obviously if charge was transferred above then this would not be a duplicate message but asking this simply because its easier to get more info at one time instead of piecemeal

 

[TonyWilliams]

Tony; why are you talking about capacity loss when responding to my question concerning charge balancing? lets just stick with that for now

do you have any capacity bars missing?

assuming its possible that capacity bars "could" be missing due to heat and "might" be returning due to cooler weather or at least some capacity is coming back is it possible the EVSE charged the pack to full and the pack cooled lowering SOC so EVSE restarted charge

Because you asked if there were any battery capacity bars missing? I don't believe that reduced capacity batteries will get anything back in cold weather. Do you have a link to a study ever done anywhere to suggest otherwise?

What does that have to do with cell balancing?

 

[DaveinOlyWA]

Tony; why are you talking about capacity loss when responding to my question concerning charge balancing? lets just stick with that for now

do you have any capacity bars missing?

assuming its possible that capacity bars "could" be missing due to heat and "might" be returning due to cooler weather or at least some capacity is coming back is it possible the EVSE charged the pack to full and the pack cooled lowering SOC so EVSE restarted charge

Because you asked if there were any battery capacity bars missing? I don't believe that reduced capacity batteries will get anything back in cold weather. Do you have a link to a study ever done anywhere to suggest otherwise?

What does that have to do with cell balancing?

it doesnt afaic. i dont believe these restarts have anything to do with balancing.

the amount of charge a battery can hold varies due to many outside conditions and temperature seems to be the biggest one. i am not likely to be convinced anytime soon that the battery pack in question decided 7 hours later that balancing was needed.

i dont have the ability to determine any very small charging events but in 21+ months this double charge complete has never happened to me so that tells me that i need to investigate the notification system a bit better.

i guess another question is did this notification come from carwings? (the only one i have which may explain why i dont get them...carwings may simply discount the events as inconsequential...who knows what carwings is thinking?)


or does it come from your EVSE? maybe the parameters of the alerts is the issue?

 

[TonyWilliams]

it doesnt afaic. i dont believe these restarts have anything to do with balancing.

Ok, we'll just have to disagree there. What do think happens after cell balancing discharges the highest cells to match the lowest cells (unless you don't believe that happens)? The pack just stays at the lower voltage, or the BMS orders a top off charge?

the amount of charge a battery can hold varies due to many outside conditions and temperature seems to be the biggest one. i am not likely to be convinced anytime soon that the battery pack in question decided 7 hours later that balancing was needed.

You're right; it didn't decide it needed balancing then. It decided it needed a top off charge AFTER balancing.

i guess another question is did this notification come from carwings? (the only one i have which may explain why i dont get them...carwings may simply discount the events as inconsequential...who knows what carwings is thinking?)

I don't use CarWings at all (not directly, anyway... Yes, I send charge status messages through text message or other app). Yes, CarWings should send a charge complete message each time. Again, I use the Blink charge events.

You seem to be convinced, for whatever reason, that something quite well known doesn't happen. I guess because you haven't observed it. Don't know what to tell you.

The car gets charges to complete cell balancing, and it ain't gunna get any more capacity when it's cold.

 

[DaveinOlyWA]

so you dont think its strange that only some of us are seeing this restart scenario. people with 20 months on their LEAF seeing it twice?...

i can think there could be a lot of reasons why i dont see this. i am not using blink. its not often that my car is still plugged in 7 hours after charge is completed. (average time is 3-4 hours though...) for all i know, my EVSE is powering back up after a charge is completed and putting a bit more in there and carwings is simply not reporting it.

now, i do know that carwings reports every charge stop no matter how brief. my Son occasionally has problems getting the handle to click into place so i will get 2 or 3 "charge stopped" messages in rapid succession.

as far as balancing? i think it happens all the time which could explain why these restart scenarios are so infrequent. they could be happening only when the pack was unable to balance itself when the first charge cycle was completed.

 

[TonyWilliams]

as far as balancing? i think it happens all the time which could explain why these restart scenarios are so infrequent. they could be happening only when the pack was unable to balance itself when the first charge cycle was completed.

Yes, it happens "all the time"; you seem to discount that time after the balance at 100%.

 

[smkettner]

I don't think the additional charge has anything to do with finding unbalanced cells and running through an additional algorithym to balance.

I think balancing takes place during the main charge. I believe if the voltage settles a bit or the battery cools a bit the BMS just decides to top it off due to the new data.

 

[Nubo]

I think it's been said that the shunt for individual cells (cell-pairs)? is of a fairly modest current. So it would seem reasonable that an imbalance could be greater than what the shunts could deal with during a charge cycle and require extra "bleed time" before applying a finishing charge.

 

[smkettner]

That might be possible. My point is that a person does not need to leave the vehicle plugged in for an extended period to have the cells balanced. I would like to assume if balancing continues after charging has initially completed it will do same even if unplugged. And it would seem most balancing would occur during the initial charge.

 

[DaveinOlyWA]

That might be possible. My point is that a person does not need to leave the vehicle plugged in for an extended period to have the cells balanced. I would like to assume if balancing continues after charging has initially completed it will do same even if unplugged. And it would seem most balancing would occur during the initial charge.

true true. you would just have slightly less than a full charge. its strange that it happens at all when one of the battery performance "stars" is how often one tops off or starts charge with SOC over 80%. wondering if the test can tell the difference?