Battery "balancing" at an 80% charge

[vrwl]

So yesterday, after my brief running around town (25 miles or so), I got home and plugged in my car to the L1 Trickle charge to recharge it. I have the timer set up to charge to 80%. At around 10:30pm last night, I got a message on my phone that charging was completed. Ok, good, I just left the plug in the car as usual and did nothing about it. Then at 12:00am, I got ANOTHER message on my phone saying that charging had completed.

I've read several times in the forums that people have wondered whether this balancing effect would occur at 80% charges, but I hadn't yet read any reports about it happening. This is probably the 3rd time I've had it happen on my car with an 80% charge (always on the L1 Trickle charger), where I get a second message about charge completion an hour or more later after the first charge finishes. So I wanted it report it to you all.

 

[davewill]

How is your timer set up? If it's from midnight to midnight, then what happened was the start time of the timer caused the charge to start back up. It quickly decided it was already at 80% and stopped. You might want to change your start/stop times to some time in the daytime (like noon to noon) when you're unlikely to be plugged in.

 

[ebill3]

Yep, I'll bet davewill hit the nail on the head. My timer is set noon/noon and the car is often still plugged in at that time. The first time I got the second message, I was at a loss until a MNL member set me straight.

 

[dandrewk]

Quick slightly OT question: I rarely charge to 100%, but I have noticed that when I do I get two "charge completed" messages with varying intervals. Is the second message telling me the Leaf has "battery balanced" and is back at 100%? If so, can I assume the longer the interval between the messages, the more balancing was required?

 

[RegGuheert]

Is the second message telling me the Leaf has "battery balanced" and is back at 100%?

I would say you can assume it went through a balancing cycle, but I would NOT assume it is fully balanced. IME, it generally takes a few trips to 100% to get the pack fully balanced.

If so, can I assume the longer the interval between the messages, the more balancing was required?

I don't know the answer, but I always assumed that the system was waiting for the pack to get to a full "rest" condition and for the temperatures of all the cells to be the same. That way, when it started balancing it was doing it based on measurements of the cells with them all in a similar condition.

 

[DaveEV]

As others have stated - it was probably just your charge timer clicking over that caused the momentary 12am charge. I've never witnessed the car coming on again to top-off during after a 80% charge (OK, when the Blink used to crash in the middle of the night it would do that).

As far as amount of time required to balance - Phil has said that balancing can basically occur at any time, though I would imagine that any balancing at 80% is minimal at most as it's difficult to determine how out of balance the cells are the closer to the middle of SOC the pack is.

The other day I charged to 100% for the first time about 6 weeks. Out of curiosity about 15 minutes before I left and about 40 minutes after the 100% charge had stopped, I started charging again to see how much more energy the pack would hold. I didn't let the car finish topping off, but it did charge for 11 minutes and put another 0.4 kWh into the pack before I stopped it to leave which indicates to me that definitely some balancing had been going on.

The first 80-100% charge put in 4.509 kWh and took 1h 13m. The topoff put in 0.413 kWh and took 11m (all data recorded by Blink).

 

[vrwl]

How is your timer set up? If it's from midnight to midnight, then what happened was the start time of the timer caused the charge to start back up. It quickly decided it was already at 80% and stopped. You might want to change your start/stop times to some time in the daytime (like noon to noon) when you're unlikely to be plugged in.

Ahhh, that might be it. Normally my charging doesn't complete BEFORE midnight, but I plugged it in earlier than usual yesterday so it was done earlier and then it probably tried to restart again after midnight. Ok, I'll change the times to prevent that from happening. Thanks for the suggestion.

 

[GerryAZ]

I believe balancing can happen at any charge level. I have been analyzing the recordings made with my Fluke 289 and current probe (recording intervals of 5 to 10 seconds during the full charge cycle) to try to fill in my missing charge records. In one recording of charging from shutdown (below turtle), the current went to zero after a few minutes of charging, ramped back up for a few minutes, dropped to zero for a few more minutes, ramped back up, and stayed at the full 15.6 amperes until reaching 100% charge. I have also noticed the ramping down of charging current at intermediate charge levels and near full charge. I believe this is the BMS balancing the cells whenever it determines they need to be balanced. I typically discharge the battery to near LBW or lower and charge to 100% so the cells seem to stay balanced with very few balancing events. I notice more tapering or ramping of current (which I assume to be cell balancing) if I recharge from 40 or 50% SOC.

Once I get the "charging complete" email, I have never had the charging start again by itself so I think the multiple charge complete emails are coming from timer settings or perhaps brief power outages.

Gerry

 

[dandrewk]

Once I get the "charging complete" email, I have never had the charging start again by itself so I think the multiple charge complete emails are coming from timer settings or perhaps brief power outages.

Gerry

If you are referring to 100% charges, I can tell you that -clearly- is not the case. I have only one timer, end time only at 7 AM seven days a week. I have gotten those two email message every time I charge to 100%, and have never gotten them for any 80% charge. The interval between the email vary, with longer intervals coming when I have gone weeks between 100% charges.

 

[GerryAZ]

Once I get the "charging complete" email, I have never had the charging start again by itself so I think the multiple charge complete emails are coming from timer settings or perhaps brief power outages.

Gerry

If you are referring to 100% charges, I can tell you that -clearly- is not the case. I have only one timer, end time only at 7 AM seven days a week. I have gotten those two email message every time I charge to 100%, and have never gotten them for any 80% charge. The interval between the email vary, with longer intervals coming when I have gone weeks between 100% charges.

That is really interesting. I always charge to 100% and leave the EVSE connected until I leave the house in the morning and I have never received an extra "charge complete" email. I wonder if I have different software versions.

Gerry

 

[dandrewk]

Once I get the "charging complete" email, I have never had the charging start again by itself so I think the multiple charge complete emails are coming from timer settings or perhaps brief power outages.

Gerry

If you are referring to 100% charges, I can tell you that -clearly- is not the case. I have only one timer, end time only at 7 AM seven days a week. I have gotten those two email message every time I charge to 100%, and have never gotten them for any 80% charge. The interval between the email vary, with longer intervals coming when I have gone weeks between 100% charges.

That is really interesting. I always charge to 100% and leave the EVSE connected until I leave the house in the morning and I have never received an extra "charge complete" email. I wonder if I have different software versions.

Gerry

Just a guess, but if you always charge to 100%, perhaps little or no balancing is done. Or maybe two messages only get generated if external current is used in the pack balancing.

 

[Ingineer]

I have seen charging restart after an 80% stop on several occasions, but it's not as common as when it does a "full" (~95%) charge.

-Phil

 

[DaveEV]

That is really interesting. I always charge to 100% and leave the EVSE connected until I leave the house in the morning and I have never received an extra "charge complete" email. I wonder if I have different software versions.

Just a guess, but if you always charge to 100%, perhaps little or no balancing is done. Or maybe two messages only get generated if external current is used in the pack balancing.

That would be my guess - if you always charge to 100% the pack doesn't get unbalanced enough to trigger a top-off.

I have seen charging restart after an 80% stop on several occasions, but it's not as common as when it does a "full" (~95%) charge.

Out of curiosity, what kind of timer settings were you using when you saw that? Originally I was on a 12-5am timer, but now I'm on a 5:45am end-only timer I doubt you'd ever see the car top-off using an end-only timer.

 

[Ingineer]

I didn't set the times, I left them at default (12:00am?) and set the 80% option. It charges as soon as I connect, at any time, to 80%. When it does restart, it's been roughly 4-10 hours after charging ceased the first time, and not on any particular hour boundary. There was no power failure.

Next time I see it, I will document it carefully.

-Phil

 

[GerryAZ]

As noted in my earlier post, the charging current has dropped to zero for a few minutes at a time (which I assume to be BMS-initiated cell balancing), but I have never received an extra charge complete email associated with it. I agree that my 100% charging combined with relatively deep discharges probably tends to keep the cells balanced without frequent BMS cell balancing cycles. I will be following this thread to see what others report.

Gerry

 

[planet4ever]

I've kept all my "Charging stopped" and "Charging Complete" emails for the past 14 months. I normally use an 80% end-only timer set for 6 AM or 7 AM, because that is when my electrical rates go up. I'm retired, and a night-owl, so I rarely use the car before noon. I just reviewed those emails, and there is not one "Charging stopped" that I can identify as being due to balancing.

I occasionally override the timer to charge to 100%, and have 30 "Charging complete" emails. Of those, three appear to be due to balancing, happening in the night 3:18, 0:44, and 2:35 after an earlier "Charging complete" email. I don't have any way to monitor energy use at the wall, and I don't have CarWings data (or even know if it would contain any clues), so I can't verify that balancing was happening.

Those emails seem to be nearly void of information, apart from their time stamp. (Well, OK, they do tell you number of bars. Whoopee. :| ) Think how nice it would be if they could say something like, "An estimated 12.3 kWh was added to your battery in 4:08 hours of charging."

Ray

 

[DaveinOlyWA]

Once I get the "charging complete" email, I have never had the charging start again by itself so I think the multiple charge complete emails are coming from timer settings or perhaps brief power outages.

Gerry

If you are referring to 100% charges, I can tell you that -clearly- is not the case. I have only one timer, end time only at 7 AM seven days a week. I have gotten those two email message every time I charge to 100%, and have never gotten them for any 80% charge. The interval between the email vary, with longer intervals coming when I have gone weeks between 100% charges.

That is really interesting. I always charge to 100% and leave the EVSE connected until I leave the house in the morning and I have never received an extra "charge complete" email. I wonder if I have different software versions.

Gerry

plus one. i get text msg alerts when charge is stopped, completed or whatever and have never received a double "complete" msg. and the text msg alert is pretty sensitive.

back when my Son first started plugging in the LEAF for me he had trouble making a good connection and there would be times i would get 2-3 stop msgs because he would not have a good connection. he now looks for the flashing lights

 

[EatsShootsandLeafs]

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?

 

[Stanton]

I'll throw this out there: I can only remember getting a "double charge complete" message ONE time in over a year of ownership, and it was a couple of weeks ago on an 80% charge (I have a daily 6am "end only" timer set). Coincidentally, that was the only time in a couple of months that I got a 10 bar @80% charge instead of 9 bar @80% charge. I have charged to 100% before and since (most recently this past weekend, where I purposely left it plugged in to balance since the temps have moderated), but have NEVER received another "double charge complete" message.

Seems unusual that I have NEVER required balancing in over a year of ownership. Was the one a couple of weeks ago a fluke? Did it for some reason notice that I didn't get a 10 bar charge (for only one day)? I still have 12 capacity bars (and get decent range), but still see 9 bar @80% charges.

 

[smkettner]

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