Six miles, Low Battery Warning to Turtle (Sans Effect)

thankyouOB said:

what does leveling the battery do and accomplish?

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The LEAF battery pack is made up of many battery cells. When you are charging, the charging stops as soon as any cell reaches maximum charge state. By the same token, the car is out of juice as soon as any cell reaches minimum charge state. The cells naturally charge and discharge as slightly different rates, so they tend to go out of balance over time. If the various cells are badly out of balance it can affect the total range of the car by keeping you from charging most of the cells all the way up or running them all the way down.

Balancing (or leveling) is done by charging the car all the way up, discharging the cells whose charge state is higher than the rest of the pack, then charging the whole pack up again. This puts the whole pack closer to the same charge state and increases your range a bit. The car does this automatically when it detects the problem, and it's given time plugged in to do it.

TonyWilliams said:

drees said:

Did you have any timers set for your charge last night ....

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Same timer: 12:10am-11:50am, 100%, charger has priority.
Thanks for clarifying - so it appears that you'll get balancing done any time you charge to 100% and there's enough time to level the cells out and top them off again in a charging period.

I wonder if multiple consecutive days of this results in less time between the end of the first charge and the resulting top-off charge?

I have seen the two time separated "charging Stopped" notices when charging to 100%.

A poser today:
Stopped charging message at 10 bars (80%) 12/21 5:41 PM. (About what expected)
Did not unplug and re-plug, or press override.
A second charging stopped message at 10 bars 12/22 12:10 PM - about 19 hours later.

Surely, the LEAF does not balance at 80%, does it? Would seem foolish to do so and would not accomplish much.

I don't think there was a momentary power interruption, as even my ancient VCR is not flashing.

ebill3 said:

A poser today:
Stopped charging message at 10 bars (80%) 12/21 5:41 PM. (About what expected)
Did not unplug and re-plug, or press override.
A second charging stopped message at 10 bars 12/22 12:10 PM - about 19 hours later.

Surely, the LEAF does not balance at 80%, does it?

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I've only seen multiple charging stopped messages when charging to 80% when my Blink reboots itself in the middle of the night... Could be that your 80% timer starts at 12:00 PM?

drees said:

ebill3 said:

A poser today:
Stopped charging message at 10 bars (80%) 12/21 5:41 PM. (About what expected)
Did not unplug and re-plug, or press override.
A second charging stopped message at 10 bars 12/22 12:10 PM - about 19 hours later.

Surely, the LEAF does not balance at 80%, does it?

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I've only seen multiple charging stopped messages when charging to 80% when my Blink reboots itself in the middle of the night... Could be that your 80% timer starts at 12:00 PM?

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Forget my poser.

Charge timer set to start and end at 12:10 and the car is rarely plugged in at that time. That must be it.

Bill

davewill said:

thankyouOB said:

what does leveling the battery do and accomplish?

Click to expand...

The LEAF battery pack is made up of many battery cells. When you are charging, the charging stops as soon as any cell reaches maximum charge state. By the same token, the car is out of juice as soon as any cell reaches minimum charge state. The cells naturally charge and discharge as slightly different rates, so they tend to go out of balance over time. If the various cells are badly out of balance it can affect the total range of the car by keeping you from charging most of the cells all the way up or running them all the way down.

Balancing (or leveling) is done by charging the car all the way up, discharging the cells whose charge state is higher than the rest of the pack, then charging the whole pack up again. This puts the whole pack closer to the same charge state and increases your range a bit. The car does this automatically when it detects the problem, and it's given time plugged in to do it.

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so that explains why the car finishes charging around midnight, then goes on for a short time in the early AM?
how long is the leveling charge time typically--a few minutes?

thankyouOB said:

so that explains why the car finishes charging around midnight, then goes on for a short time in the early AM?
how long is the leveling charge time typically--a few minutes?

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About 10 minutes. See charts from this thread from last January:

Charging timer: start time based on END time?

drees said:

About 10 minutes. See charts from this thread from last January:

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Which would give about 500 watts, or about 2 miles at 60mph or 3.9miles/kWh. Which wouldn't fully explain my situation.

If one cell is a lower voltage, and all the cells burn down at the same rate, when that lowest cell hits it's lowest allowable voltage, it doesn't matter how much power is left in the other 95 cell pairs... the party if over, and the car stops.

So, balancing puts in more power in the top of the charge, and allows the use of all the cells down to the depletion of the battery.

I question whether just one 100% charge every now and then is sufficient for full balancing since the amount of current that can be shunted for each cell is limited...

drees said:

Thanks for clarifying - so it appears that you'll get balancing done any time you charge to 100% and there's enough time to level the cells out and top them off again in a charging period.

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TomT said:

I question whether just one 100% charge every now and then is sufficient for full balancing since the amount of current that can be shunted for each cell is limited...

drees said:

Thanks for clarifying - so it appears that you'll get balancing done any time you charge to 100% and there's enough time to level the cells out and top them off again in a charging period.

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I have no reason to charge to 100% often, as I usually start driving with a 1500 ft. descent.

What are current opinions about frequency of 100% charging as beneficial, and if this best done at higher or lower battery temperatures?

Am I also correct in my understanding that cell balancing requires leaving the car plugged in for some time, after it reaches 100%?

edatoakrun said:

What are current opinions about frequency of 100% charging as beneficial, and if this best done at higher or lower battery temperatures?

Am I also correct in my understanding that cell balancing requires leaving the car plugged in for some time, after it reaches 100%?

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Honestly, nobody knows for sure what the best frequency is. We don't even know what cell voltage variation triggers a cell balance routine.

Once a week seems reasonable, but, like I said, we just don't know for sure. If you're not pushing the range much, I wouldn't worry about cell balancing very much.

I went through 2 consecutive nights of balancing, the first 3 hours, and the second at 2 hours. So, I recommend at least 3 hours after the 100% charge is reached. Yes, the car must be plugged in, or how else would it charge the car after the highest cells are discharged ?

The cells do not like any extreme in temperature, and the BMS will protect the battery by limiting it's power output. Above 50C/122F begins some very serious cuts in power output, and the battery pack heaters (if equipped) kick in at -20C/-4F. The batteries physically freeze at about -30C. Thermal runaway may be possible above 55C.

TonyWilliams said:

edatoakrun said:

What are current opinions about frequency of 100% charging as beneficial, and if this best done at higher or lower battery temperatures?

Am I also correct in my understanding that cell balancing requires leaving the car plugged in for some time, after it reaches 100%?

Click to expand...

Honestly, nobody knows for sure what the best frequency is. We don't even know what cell voltage variation triggers a cell balance routine.

Once a week seems reasonable, but, like I said, we just don't know for sure. If you're not pushing the range much, I wouldn't worry about cell balancing very much.

I went through 2 consecutive nights of balancing, the first 3 hours, and the second at 2 hours. So, I recommend at least 3 hours after the 100% charge is reached. Yes, the car must be plugged in, or how else would it charge the car after the highest cells are discharged ?

The cells do not like any extreme in temperature, and the BMS will protect the battery by limiting it's power output. Above 50C/122F begins some very serious cuts in power output, and the battery pack heaters (if equipped) kick in at -20C/-4F. The batteries physically freeze at about -30C. Thermal runaway may be possible above 55C.

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I guess I've inadvertently carried on a no-rebalance experiment on my LEAF, with no significant loss in range.

As I said, I always charge to 80%, then only charge to 90-100%, immediately before I take the occasional trip longer than 60 miles.

So, I don’t think I’ve had many “rebalance” opportunities, in many months.

The reason I asked about temperature, is that, I usually charge at night, and so the occasional 100% rebalance charge I will schedule in the future, would likely occur in the early morning, at 23-35 degrees F. Not a problem, as far as I can see, other than the lower (but balanced!!!) total available capacity.

TonyWilliams said:

planet4ever said:

My question was whether they started disappearing before you got to turtle, and if so, how much before........

It is interesting, though, to see that bubbles can keep disappearing while you are in turtle.

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I believe they do, but don't have concrete evidence to prove that.

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I can confirm that the power bubbles start to disappear without going into turtle mode. I was a little more than 1 mile into VLB when the furthest right power bubble disappeared.

I have also read others' similar observations.
See http://www.mynissanleaf.com/viewtopic.php?f=27&t=7022&start=30#p155180" onclick="window.open(this.href);return false;

TonyWilliams said:

Thermal runaway may be possible above 55C.

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a "Thermal Runaway" event with the possibility of flaming hydrogen venting is closer to 400° F

Herm said:

TonyWilliams said:

Thermal runaway may be possible above 55C.

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a "Thermal Runaway" event with the possibility of flaming hydrogen venting is closer to 400° F

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So, above 55C ?

:mrgreen:

edatoakrun said:

I guess I've inadvertently carried on a no-rebalance experiment on my LEAF, with no significant loss in range.

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So, you ran it all the way to Turtle? (I'm not being obtuse; just clarifying that range is how far the car will actually propel itself, and not a GOM number). The loss of range, for me, didn't show up until AFTER the LBW. Now that the cells are balanced again, I'm definitely back to proper range.

If the cells are all playing nice together, there might not be anything to balance!

Last night's charge ended at 2:49am, and again at 6:57am.... over 4 hours.

Two equalization cycles (we think) were shown in one TED Current/Power plot over time.

There was a "resting" (no or very low current) cycle of about 45 minutes, followed by a (roughly) 5 minute higher-current (charging, and tapering off) period.

The first "cycle" was followed by a second similar 50-minute cycle.

We have assumed that we observed two "balancing" cycles (after a 100% charge, I believe).

TonyWilliams said:

After the 3 hour balancing on Monday, it appears my car is back to normal. Yesterday, I drove 9 miles into LBW before getting VLB, and then drove 2 additional miles home (all at about 4 m/kWh). No Turtle and very much in harmony with the range chart.

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So to summarize your experience, Tony, you believe that the unexpected lack of "reserve" below the VLB warning that stranded you was due to the multiple opportunity-charging episodes to less than 100% during your long trip, which didn't allow for proper balancing of the cells? Now that your car has had a chance to "rebalance," you are back to having the same ~6 miles of range @ 45mph below VLB as shown in your chart?

So if I ever get really adventurous in testing the range of my car down to turtle mode like you have, in order to make the "reserve range" more predictable, I should allow the car to stay plugged in for 3-4 hours after reaching 100% to assure that it has had an opportunity for cell balancing cycles (if the pack needs them, which there is no way of knowing for sure)? It sounds like I would need to change my charging timers to ensure this would happen the night before such an adventure. At present, I have them set to only charge from midnight to 5AM, to take advantage of super off-peak rates. It often reaches 100% charge by 2-4AM, depending on the state of charge it was put away in the night before, but this would not necessarily allow the extra 3-4 hours for balancing after completing the charge--I should really allow somewhere around 8-10 hours of total charge time instead of 5 to accomplish 100% plus balancing?

Thanks for being the "canary in the coal mine" for the less intrepid of us,
TT

I'd say that sums it up. We don't (yet) have the tools to know when we're out of balance enough to seriously degrade range.

Even before my trip, I had done several quick charges in the middle of the day.

To be clear though, focusing on this event may overlook the dozens of other events where all was normal, even without time allotted for balancing.