I want my 281!

[vegastar]

21.74 kWh at the wall from turtle to 100% is very low. I got 22kWh from (right after) VLB to 100% (and it is consistent accross more than 10 events) , and 25,5kW.h from turtle to 100%. One time, 5km after VLB I got 23.2kW.h. I usually get 277 gids, but if after 30 minutes I force a new charge it goes to 281.

In my opinion you should go to a Nissan dealer check the battery. Probably there is a bad module reducing the capacity of the whole pack.

 

[TickTock]

21.74 kWh at the wall from turtle to 100% is very low. I got 22kWh from (right after) VLB to 100% (and it is consistent accross more than 10 events) , and 25,5kW.h from turtle to 100%. One time, 5km after VLB I got 23.2kW.h. I usually get 277 gids, but if after 30 minutes I force a new charge it goes to 281.

In my opinion you should go to a Nissan dealer check the battery. Probably there is a bad module reducing the capacity of the whole pack.

Thanks, I was hoping to cross check with others. I *did* take it to the dealer and they assured me the battery was fine. Instead of service, I was given a pamphlet on how to drive efficienty. Gee, thanks. Maybe I'll try a different dealer.

 

[Gonewild]

What dealer did you go to?

 

[garygid]

Ask the dealer if they can provide a printout of all 96 cell-pair voltages.

Also ask if you can come in almost full, get the printout, and return later (almost empty) for another printout.

If they have never done that with their "Consult III" diagnostics machine, offer to help them learn more about EVs, using your LEAF for the tests.

 

[vegastar]

If the pack is top balanced, then the weak cell(s) can be detected with an almost empty pack. According to the service manual there is a procedure for that:

1 - Discharge the pack until the minimum cell voltage reaches 3,712V
2 - Check total battery Voltage (A) and Maximum cell voltage (B)
3 - Obtain cell voltage loss judgment value:

Cell voltage loss judgment value = (2.5 x A - 0.144 x B) / 96

where

A = “TOTAL BATTERY VOLTAGE” (V)
B = “MAXIMUM CELL VOLTAGE” (mV)

4 - Obtain all 96 cells voltages and if any of then is lower than the cell voltage loss judgment value, than it must be replaced.

 

[TickTock]

Interesting. What section? Did it indicate what value would warrant replacement? I wonder if this minimum and maximum cell voltage is being broadcast on the EV can (IOW, already captured in my logs if I can figure out where). Something to look for.

Unfortunately, when I went to the dealer I had to go to work so couldn't hang around to interact with the servicemen when they actually started work on the car (not sure they would have been happy about it if I had). I was very specific in asking for the readout of all 48 cells (and they even wrote that down), but when I got back they simply told be they ran the full diagnostic and the tool didn't output any report on all the cells (and I could increase my miles by coasting). They were very friendly about it, but worthless none-the-less. At least they didn't try to charge me anything.

 

[vegastar]

It is explained in EV Battery System, EVB.pdf, page 66. There are 2 methods, one where the cell voltage loss judgment value is obtained from consult and the one with the formula I gave.

The value that would warrant replacement is in the formula. Imagine that when the weakest cell is at 3712mv the total battery voltage is 360V and the maximum cell voltage (strongest cell) is at 3790mV. The cell voltage loss judgment value would be:

(2.5 x 360 - 0.144x3790)/96 = 3,690 V

Then check all the cell voltages. In this case, as the weakest cell is 3,712mV it is OK. But if the total battery voltage was 365V and the strongest cell 3810 mV, the cell voltage loss judgment value would be 3,790V and at least the weakest cell would be replaced.

Unfornately the (low) knowledge of the dealers is the same around the world. Do they read the Service Manuals?

 

[DaveEV]

Unfornately the (low) knowledge of the dealers is the same around the world. Do they read the Service Manuals?

That might require them to do some homework (read the service manual) and then actual work (run the test)!

 

[Danal]

This is consistent with how the Owners Manual describes the fuel bars. Since the battery has lower capacity at cold but doesn't lose charge when it cools, the same charge indicated a higher fraction of the new lower/cooler charge capacity.

I read about this behavior of lithium-ion before, but dont really understand how it works.. supposedly if you charge a lithium-ion to full in hot weather and then take it to a cold location the battery is suddenly overcharged.. but I dont think it hurts anything.

That is my understanding. When the temperature drops after 100% warm charge, it will be effectively over-charged (beyond what was set as the 100% charge level). Presumably, Nissan has accounted for this in their 100% set point to allow some room for the temperature fluctuation.

Lithium based batteries are "absolute voltage" devices. The exact voltage varies with chemistry, but when we say 'overcharged' we really mean 'over the voltage at which irreversible harm will occur to the cell due to a breakdown of the barriers in the electrodes, and/or molecular structures of the compounds in the electrolyte'. That exact voltage varies with temperature, and the key factor is that this damaging voltage goes DOWN as temperature goes down.

So, for example, if you charge a given chemistry Li battery that's specified for 4.235V at 20C, and then drop the temperature to 10C, that battery is now over-voltage for that temperature, and irreversible reactions occur that have the effect of lowering the available capacity at the next charge/discharge cycle. Fortunately, these same reactions reduce the voltage in the resting cell, so it doesn't just "eat itself" down to zero.

And, yes, anyone who deploys batteries for outdoor use puts some margin into their battery management system to define "full charge" voltage as somewhere less than the 20C voltage for that chemistry. I'm sure Nissan did the same.


This article doesn't much mention temperature, but it does show the electro-chemical potentials and mention the irreversible reactions: http://en.wikipedia.org/wiki/Lithium-ion_battery#Electrochemistry" onclick="window.open(this.href);return false;

 

[Herm]

Thanks Danal.. so if the battery is kept at a lower constant temp then it will have a lower capacity?

 

[DaveEV]

Thanks Danal.. so if the battery is kept at a lower constant temp then it will have a lower capacity?

Yes, Lithium based batteries hold / release less energy at lower temperatures as their internal resistance increases.

Higher temperatures increase capacity but increases the rate at which the battery ages.

 

[evnow]

I've not seen any change in SOC # at full charge (280) - between now when the garage temperature is around 50 and in summer at a temperature around 70.

I also haven't seen the 80% charge comeup with 11 bars. My Odo is about 5,750 miles.

 

[garygid]

evnow, you do have the "New-Bars" firmware update, right?

 

[Danal]

Thanks Danal.. so if the battery is kept at a lower constant temp then it will have a lower capacity?

Yes, if you were to charge the battery to the max V at the lower temp, and charge it to a higher V when warmer.

However... if you designed your battery management system to always charge to a V that allows the pack to be 'fully' charged and then cooled without harm, then you are always using the same V and therefore the same capacity. You are "leaving some capacity on the table" when the battery is warmer, to protect it when it is cooler.

Note that a BMS cannot (safely) measure the pack temp and charge accordingly. At least not where I live. I have seen -100 deg F swings in 24 hours or less... -70 deg F in 1 hour.

 

[Danal]

I've not seen any change in SOC # at full charge (280) - between now when the garage temperature is around 50 and in summer at a temperature around 70.

I also haven't seen the 80% charge comeup with 11 bars. My Odo is about 5,750 miles.

I wouldn't expect to see SOC change with temp, for the reasons measured in my prior post, Nissan is very likely holding back the max resting V to something safe for a cold pack, regardless of current temp.

Also, realize that SOC is not something that can actually be measured. You can measure resting V, amount in or out over the last few charge/discharge cycles, things like that. But you cannot directly measure SOC in a cell. At least not without breaching the bag and examining the anode/cathode/electrolyte. So, whatever the CAN bus "GID" is, it is either calculated from prior cycles, or resting V related, or some combination of these.

And, even if you charged a Li pack to a resting V appropriate for warm, and measured that V, and chilled the pack, you won't see the V drop as the pack chills. At least not much. All that will happen as you pass down through the temp where that V damages the pack is those chemical reactions in the pack... the V won't go anywhere (which is the problem, really).

 

[Brightonuk]

I am assuming that all the previous post are for 2011 cars?

I am in florida and although it has been chilly 55-60 at night when I charge I always charge to 100% and I always get 277 never more never less.
I have even charged during the day 70 degrees ave and 277 is the majic number.
I have not tried a forced charge as yet.

My car was delivered in mid December so I assume I am running the latist firmware.

I was wondering is any other drivers have an SOC meter hooked into a 2012 and what they numbers they are getting on a full charge.

Does that extra 4 gids translate into usable milage or is it just a number that we think should be the standard, as regardless my GOM acts the same every day in how fast it drops from 116 miles (Full charge) to 96 after 3 miles

 

[garygid]

Your readings (277 gids) are reasonably normal for cold weather and/or lack of equalization.

Warm weather and equalization will probably give you 281.

Nothing to worry about now.

So far there are no reported differences in Battery & SOC between the LEAF 2011 and 2012 models.

Note: The top 5% of the indicated "soc" does not hold a lot of Energy - that is also normal.

Caution: The low 10% (or 15%) of the indicated "soc" MIGHT not take you very far either, at least occasionally.

Equalization: Leave the car connected for 2 or 3 hours after the normal "finish" of charging to 100% (to give the car time to equalize the cells). Do this on several occasions (when charging up to 100%, after using a significant portion of the charge), and then occasionally thereafter.

 

[Brightonuk]

Thanks G

The car is always charged overnight at least 5 times a week it is left plugged in for a good 6 hours after the charge has competed how does one know if the batteries are equalizing?

 

[garygid]

Tough to tell when equalization is happening without logging the current into the car or battery.

After charging, the car will appear to "rest" for about 45 minutes, then "charge" again for a few minutes. On a log/chart of current, one can see the "spikes" at about 50 or 55 minute intervals.

Using the SOC-Meter to Log the EV CAN bus would capture the data, and then CAN-Do can show the graph of Pack Current.

During the "rest" period, the higher-voltage cell-pairs are being discharged (slowly) to bring their voltage down closer to the other more-average cells. Then, everything is charged back up a bit, raising the average just a little.

So, your 277 is likely temperature related.

Cheers, Gary

 

[DaveEV]

The car is always charged overnight at least 5 times a week it is left plugged in for a good 6 hours after the charge has competed how does one know if the batteries are equalizing?

Here's how we think it works at a high level:

The car will balance the cells after a 100%/full charge is complete if it detects that some cells are still undercharged too much. No balancing occurs unless you charge to 100%.

After 2-3 hours of discharging the highest charged cells (it's a slow process), it will start charging again to bring all the cells up. This charge will take 15-30 minutes.

There's a couple ways of detecting the top-off charge:

1. Monitor charging current using a TED or similar.
2. Enable charging stopped notifications - you'll get one after both the first charge stops and after the top-off charge.