Strange Battery Behavior?

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MSELeaf

Active member
Joined
Aug 8, 2014
Messages
27
Location
College Park, MD
I have a 14 mile round trip commute which is relatively flat. For the behavior that I am going to describe, the AC/heat is off, the 12V battery voltage is 13V according to LEAFSpy (12V battery not being charged), the maximum cell imbalance is 10mV (no shunted cells showing) and my driving style and average speed is consistent.

What I have noticed is when the battery is charged between 12-18.7kWh (the maximum I have now), the power usage for my commute is drastically higher than when the charge is below 12kWh. For example, during the 7mi uphill leg of my commute, below 12kWh, the power used according to LEAFSpy is 1.2kWh. However, above 12kWh, the power used is anywhere between 2-2.4kWh. When the car is in this 12-18.7kWh range, I also notice that when I am at a full stop, the Wh display in LEAFSpy is incrementing at a rate that corresponds to about a 1.8kW vampire drain! The kW display in the upper left of LEAFSpy is almost always 0 or 0.2 however the Wh display keeps going up. Below 12kWh, the Wh display does not change at all when I am at a stop. So the question is, is this normal behavior or is there something weird going on with my battery? I charge the car to 80% twice a week and to 100% about once every 2 weeks.

Thanks
 
Maybe some LeafSpy screen-shots would be better.

At a stop, you should only have the 200 watt load when not moving (no AC/Heat or battery charging). If you are getting anything else, then the creep mode is burning power basically fighting the brakes. Creep only seems to use 500 watts, so 1,800 watts seems very excessive.
 
knightmb said:
Maybe some LeafSpy screen-shots would be better.

At a stop, you should only have the 200 watt load when not moving (no AC/Heat or battery charging). If you are getting anything else, then the creep mode is burning power basically fighting the brakes. Creep only seems to use 500 watts, so 1,800 watts seems very excessive.
Click to expand...

I'm not sure a screenshot would be helpful since its the rate at which the numbers are changing rather than their actual value. But yes, according to the power indicator, when not moving, the power being used is somewhere between 0 and 200W. However, there appears to be a load somewhere else that is draining the battery that is not taken into account in this measurement.

As for the creep mode, I am fairly confident that its not fighting the brakes because the elevated trip energy usage happens even if there is minimal stopping. Just being at a full stop allows me to distinguish this additional battery usage from normal usage while driving.
 
Worrying about power usage from 1.2KW to 2.4 KW is too short a time (and power) to worry about..

Are you getting descent range on a charge? That is the measure of importance. I can blast through1.2 KW in just 1-2 miles if I am going a little uphill and stops and starts.
 
powersurge said:
Worrying about power usage from 1.2KW to 2.4 KW is too short a time (and power) to worry about..

Are you getting descent range on a charge? That is the measure of importance. I can blast through1.2 KW in just 1-2 miles if I am going a little uphill and stops and starts.
Click to expand...

Yes, you are right. I still get 75+ mile range reliably so in the grand scheme of things, this isn't an inhibiting problem. I was just curious to see if anyone had any input on this as I have been consistently seeing this behavior for about 6 months now.
 
MSELeaf said:
... have been consistently seeing this behavior for about 6 months now.
Click to expand...
Your battery and the rest of you drivetrain is perfoming normally, relax.

The Strange...Behavior you report is just the result of your LEAF's LBC (Nissan's term for its battery management system) which is producing erroneous Wh remaining data, which has you concerned.

This is why no Leaf driver should ever depend on the LBC data source for accurate calculation of either the remaining available battery capacity while driving, or the total available battery capacity as the pack ages.

Nothing new here, read my post (and those from others) from over three years ago, on this thread:

Discuss data from the LEAF Battery app, and Comparisons
 http://www.mynissanleaf.com/viewtopic.php?f=44&t=12789

edatoakrun said:
="RuneW"... is there a chance that the app is calculating something wrong? ...
Click to expand...

Probably not the app, but our LEAFs, IMO.

garygid

...For lower battery pack Temperatures, like the 10 degrees C that
you show, there is possibly some reduction in effective capacity,
just because of the lower temperature, or lower temperature
cycles in the car's recent history.

If so, then the nominal capacity might only appear after operating at
nominal temperatures...
Click to expand...

Or maybe not.

My capacity reports at app-reported temps from ~59 f to ~86 F are extremely consistent, varying only ~0.20 % since the first capacity report I got at the SF BayLEAFs meeting over a month ago. Most recently:



That being said, I think they are consistently wrong, in showing an ~12.5% loss of capacity, which has not shown up in my LEAF by either recharge or range capacity tests.

What I have seen that has surprised me is that there is only a rough correspondence between the (erroneous, IMO) loss of capacity indicated by CarWings in total kWh use from "100%" to ~VLBW (as reported less accurately, in the nav screen m/kWh and dash m/kWh reports) and that reported by the app.

For example, the app showed kWh use of 16.8 for my last 108.7 mile capacity/range test on 5/11, while CarWings reported 16.4 kWh use for the same trip.

But after multiple tests I now believe this is because the app is picking up “gauge error”, quite likely temperature dependent, in real time as I drive.

While I was running errands yesterday, the app showed increasing kWh capacity, gid counts, and negative Wh use, corresponding to increases in battery temperature reports, and the (very unusual, in my experience) increase in charge bars from six to seven.

I took this screenshot shortly after I restarted both the app and my LEAF, which had dropped to six charge bars on the restart:



Over the next ~1.5 miles, and ~ 1 hour, as I ran some errands and while I made three stop/restarts of my LEAF, I watched the charge reports by the app increase, (and at some point the seventh charge bar reappeared !) until reaching this point:



As I used WH as I drove, the negative Wh decreased, but whenever I was not driving, it continued to increase.

This was fascinating to watch, but I had to get home. As I drove further, the Wh use went positive, and
I lost the seventh charge bar for the second time after another ~6 miles just before I took this shot:

I think these observations may explain a lot about the erratic behavior of the charge bars...
Click to expand...
As an update, my pack still shows the same phantom charge on every warm day after I descend to the valley floor (~1,500 ft net) as I reported above, and by monitoring the charge accepted from the grid as measured by my utility's meter, I estimate my pack's total loss of capacity last month in the five years since delivery to be between 15% and 16% (and ~18% below Nissan's 24 kWh specification) rather than the ~28.5% capacity loss as was shown by my LBC.
 
edatoakrun said:
The Strange...Behavior you report is just the result of your LEAF's LBC (Nissan's term for its battery management system) which is producing erroneous Wh remaining data, which has you concerned.
Click to expand...

Thank you very much for this helpful information! This explains pretty much what I have been seeing.
 
MSELeaf said:
edatoakrun said:
The Strange...Behavior you report is just the result of your LEAF's LBC (Nissan's term for its battery management system) which is producing erroneous Wh remaining data, which has you concerned.
Click to expand...

Thank you very much for this helpful information! This explains pretty much what I have been seeing.
Click to expand...
Your welcome, and I suggest you continue to continue to collect as much actual data on energy use you can, rather than relying on the LBC numbers.

It is relatively harmless to rely on the LBC energy-remaining data while you drive, since, in my experience it always overestimates energy use early in a trip starting from higher charge levels, as you have reported.

So, if you rely on the LBC, your LEAF's pack will always have extra hidden capacity near the end of your charge depletion, and much more so if your trips start with a large descent as mine usually do, where the LBC's initial overestimation of Wh use is most extreme.

However, the capacity anxiety many on this forum have developed by relying on the same erroneous LBC data to determine the loss of capacity as their batteries age, seems to be quite a problem...for them.
 
While it is good not to worry about exact power measurements, there can actually be an issue where creep mode remains active even when the brake is pressed. That would show up in the power usage because the vehicle would not be moving, but power is going somewhere. In that example, to the motor and being wasted as heat since the brakes are holding the car still.

So while the phantom 1kW to 2kW power draw might be instruments issues, you can't rule out everything completely in case a real problem exist, such as the vehicle not turning off creep when the brakes are pressed down to a certain range. ;)
 

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