Battery Capacity Question

[marccbr]

I wanted to see if my calculations are correct. I am using the Android app with bluetooth connection to the OBDII sensor. I charged to 100% capacity and got a reading of 18.8 Kw. So given I started with a 24 Kw capacity minus the 7% that is not used(5% on the max side and 2% on the minimum sides) that would leave me 22.32 Kw when it was new. Since I am at 18.8 Kw now that would mean that 18.8/22.32 = 0.84 which would mean that I currently have 84% of the capacity that I started with so I have had a 16% capacity loss, right?

 

[GregH]

I wanted to see if my calculations are correct. I am using the Android app with bluetooth connection to the OBDII sensor. I charged to 100% capacity and got a reading of 18.8 Kw. So given I started with a 24 Kw capacity minus the 7% that is not used(5% on the max side and 2% on the minimum sides) that would leave me 22.32 Kw when it was new. Since I am at 18.8 Kw now that would mean that 18.8/22.32 = 0.84 which would mean that I currently have 84% of the capacity that I started with so I have had a 16% capacity loss, right?

Without knowing how that "18.8" number is being calculated by the app, I have no idea what this means. On the most part we use Amp hours to measure battery capacity as kWh vary based on a number of factors (including how you drive!) A healthy Leaf battery is in the 66-67Ah capacity range.

 

[marccbr]

It is the LEAF battery app that is available here on this forum. I'm not sure how it does the calculation, does anyone else know how this app does the calculation?

 

[GregH]

It is the LEAF battery app that is available here on this forum. I'm not sure how it does the calculation, does anyone else know how this app does the calculation?

I'm guessing it's multiplying the Ah capacity by some assumed voltage.. That's usually how kWh capacities are measured. Take the Ah capacity and multiply by the "nominal" voltage. What Ah capacity does the app show for your car?

 

[marccbr]

Just went thru the screens and it is showing a reading of 55.93 AHr and Capacity of 84.42%

 

[marccbr]

The defaults for the app are #AHr = 100% is set to 66.2556 I assume that that is the battery capacity when it was new and Nom. Voltage is set to 360.0 not sure what this is since I am not an electrical engineer just a software engineer.

 

[marccbr]

What is also weird is that I have not lost any bars at all.

 

[TomT]

The first bar goes way after 15% so, if your numbers are correct, you are near the threshold of it disappearing...

What is also weird is that I have not lost any bars at all.

 

[GregH]

Just went thru the screens and it is showing a reading of 55.93 AHr and Capacity of 84.42%
The defaults for the app are #AHr = 100% is set to 66.2556 I assume that that is the battery capacity when it was new and Nom. Voltage is set to 360.0 not sure what this is since I am not an electrical engineer just a software engineer.

The only actual number coming from the car is the Ah capacity (55.93Ah).. everything else is being calculated by the app and varies depending on how you have it set it up. The "Capacity %" is just the Ahr/66.2556 = 84.42. If you wanted you could change this number to anything you wanted.. change it to 67.3620 which is the max on a 2013 car.. or set it to 66000.. or set it to 55930 and watch your capacity degrade from where it stands today at 55.93.. It's totally arbitrary and up to you.

Similarly the kWh of a pack is the Ahr capacity times the app's assumed nominal voltage of 360.. so 55.93 * 360 = 20.1. Not sure where 18.8 comes from.. there is probably some other assumption about unusable capacity on the low end.

So far the only capacity related numbers we've seen FROM THE CAR are the Gids at a full charge (or "80%" charge), the Ahr capacity (in Ahr) and the "health" percent which we're not entirely sure what it means... it seems to track Ahr capacity for mildly degraded cars but gets really low for cars with a dramatically lower Ahr capacity (cars that have lost capacity "bars")

All that being said 55.93Ah is getting down there.. People have reported losing their first bar in the 54-56Ah range..

YMMV.

 

[surfingslovak]

The only actual number coming from the car is the Ah capacity (55.93Ah).. everything else is being calculated by the app and varies depending on how you have it set it up. The "Capacity %" is just the Ahr/66.2556 = 84.42. If you wanted you could change this number to anything you wanted.. change it to 67.3620 which is the max on a 2013 car.. or set it to 66000.. or set it to 55930 and watch your capacity degrade from where it stands today at 55.93.. It's totally arbitrary and up to you.

Greg, that's correct, the nominal voltage came from an AESC data sheet. Jim made it user-adjutable via preferences, but I doubt that many people tweaked this value. If memory serves, Jim subtracts a certain amount of energy held in "reserve", which is another user-adjustable setting. I agree that only Ah and SOH should be used to judge the health of the pack. Everything else was apparently designed to aid the driver with range estimates. That said, a Nissan engineer experimented with the app recently, and liked the idea of delivering a range prediction based on user-adjustable energy economy. Who knows, perhaps it will help facilitate some rethinking and future changes to the GOM.

 

[marccbr]

Thanks everyone for there inputs. That clarified quite a bit for me.

 

[TonyWilliams]

... a Nissan engineer experimented with the app recently, and liked the idea of delivering a range prediction based on user-adjustable energy economy. Who knows, perhaps it will help facilitate some rethinking and future changes to the GOM.

With the resistance from the several developers here to such a tool, I'm stunned that anybody from Nissan would find value!!!

 

[sparky]

... a Nissan engineer experimented with the app recently, and liked the idea of delivering a range prediction based on user-adjustable energy economy. Who knows, perhaps it will help facilitate some rethinking and future changes to the GOM.

Maybe they took a hint from Tesla.
I've found Tesla's "rated range" gauge quite accurate. Saturday, I did a roundtrip from SoCal to Fremont and back in one day (TESLIVE).
Used all the Superchargers between home and there and mostly drove 75. But, when I backed off to about 310 Wh/mi, "rated range" moved in lockstep with my distance driven. This allowed me the peace of mind to consider skipping a Supercharger stop knowing that I could get to the next one by just backing off on my speed and minding the energy graph.