Cell Balancing 101

[ebill3]

Equalization is not used to keep cell (pairs) from overcharging.

Sure it is, and that allows the lower voltage cells to "catch up". Just like you said.

Me thinks wordplay.

In my LEAF, 80% charge is 388.5 volts, a bit shy of 4.05 volts per cell pair.

 

[TonyWilliams]

Equalization is not used to keep cell (pairs) from overcharging.

Sure it is, and that allows the lower voltage cells to "catch up". Just like you said.

Me thinks wordplay.

In my LEAF, 80% charge is 388.5 volts, a bit shy of 4.05 volts per cell pair.

And when the DC charger starts at a low SOC, it uses 388 volts (4.05v/cell), until it ramps up to.... 394 volts (4.1v/cell). I think there's a reason for all of that.

 

[vegastar]

The DCFC here in Portugal start to lower the current around 391V and then the voltage slowly rises to 394V. I think the reason for this behaviour is because at 391V and 125A some cells may be at 4.1V allready.

 

[garygid]

One cannot regulate charging based only on Pack Voltage without
the danger of over-charging and damaging individual cells.

One must read individual cell (pair) voltages to protect the
cells that are nearest "full".

During QC, it appears (from logs) that the car specifies the current
and then the QC machine adjusts the voltage to achieve the requested
current.

With changing starting at around 120 amps, it appeared that the Pack Voltage,
as measured inside the LEAF, got as high as at least 5 or 10 volts over 400
before the charging was finished.

The car ramps up at about 0.2 amp steps every 0.1 second (2 amps per
second), starting from 0.1 amps, as I recall from the log.
The car can adjust the current 10 times per second, and terminate
the charging by requesting zero amps.

 

[smkettner]

I agree Gary. I just cannot imagine LEAF would never ever balance the cells for someone that always charges to 80%.

IMO this part of the reason I think we are locked into 80% or 100% as the only choices. Balancing is made easier with just these two levels.

BTW I have only been getting 9 bars at 80% for many days.... today it was 10 bars. I assume it balanced a bit during that last charge cycle. Garage temp was same or slightly warmer.

 

[garygid]

Or, your car might have made an adjustment in capacity,
not enough to lose a capacity bar, but enough to make the
fuel tank a bit smaller, thus making each fuel Bar a bit smaller?

Having a log of GIDs at the Bar boundaries might reveal
the adjustment.

 

[mkjayakumar]

Why do I see all three lights on (continous and not flashing) sometimes when the charging is finished. I ahve seen this both at 80% charge completion and 100% charge completion. I thought this is when balancing occurs. True ?

 

[Ingineer]

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

 

[KJD]

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.
-Phil

The LEAFSCAN sounds like it can give some good information. When can I buy one for my own car ?

 

[Ingineer]

The LEAFSCAN sounds like it can give some good information. When can I buy one for my own car ?

We are working as hard as we can on LEAFSCAN, and hope to have good news soon. Sorry, But I cannot give any hard estimates right now. Completing a large project like this takes a lot of time and resources to get right!

-Phil

 

[JimSouCal]

The LEAFSCAN sounds like it can give some good information. When can I buy one for my own car ?

We are working as hard as we can on LEAFSCAN, and hope to have good news soon. Sorry, But I cannot give any hard estimates right now. Completing a large project like this takes a lot of time and resources to get right!

-Phil

Yes, and the details all matter. Maybe the leafscan will be flash upgradable as improvements happen? EDIT, yes I see the leafscan with be upgradeable... (I also hope it will replace the need for carwings to some extent, i.e.scheduled climate timers, charge timers,etc).

 

[Nubo]

I recommend Nissan get their act together before LEAFSCAN comes out. Because there will be nowhere for them to hide.

 

[smkettner]

Or, your car might have made an adjustment in capacity,
not enough to lose a capacity bar, but enough to make the
fuel tank a bit smaller, thus making each fuel Bar a bit smaller?

You called it right. Second morning in a row with 10 bars of charge and now first morning with 11 bars capacity.

 

[LEAFer]

Here's the summation: ... 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.
-Phil

Will the BMS balance the pack if the connected (fully charged) car transitions into an "OFF period", i.e. a time of day beyond "End Time" you programmed because of (for example) ON-PEAK electricity rates ?

 

[TimLee]

Or, your car might have made an adjustment in capacity,
not enough to lose a capacity bar, but enough to make the
fuel tank a bit smaller, thus making each fuel Bar a bit smaller?

You called it right. Second morning in a row with 10 bars of charge and now first morning with 11 bars capacity.

Sorry about the loss of capacity bar
But having the car go to only 9 bars charge with 80% charging doesn't always mean immediate loss of a capacity bar.
During last summers 104F weather, my 2011 LEAF would often only show 9 bars.
But once the weather cooled down, the car has consistently shown 10 bars all winter.
And still has not lost a capacity bar.
Stoaty's battery degradation model shows I should be around 11% capacity loss, with 23 months, 3.4 miles / kWh average, at ~12,000 miles.
So with returning warm weather, there is a good chance I will lose a capacity bar before the end of summer.