Question about SOC

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Rickker

Rickker

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The battery SOC is readily displayed in the EV menu, as a percentage of fully charged. I am asking if there is somewhere in the system where I can obtain the actual state of charge in kilowatt-hours rather than as a percentage of fully charged? I charge at several local Level 2 public chargers and like to confirm/compare the kWh delivered by the provider to what has actually been added to the battery. The results do not always square. For example, charging from 50% to 75% at two different public AC chargers, the billing invoice should show pretty well the same number of kWh supplied. Of course a 50% reading in the Kona could mean anywhere from 50.0% to 50.9%. So, it would be helpful to be able to read the actual battery energy in kilowatt-hours. Just asking if there is a way. Thanks.
....Rickker
 
If you've set up an OBD2 dongle and smartphone you can check the changes in the energy (kWh) 'odometers', CEC and CED. The values have a resolution of only 0.5 but that might be good enough for your intentions. Cell voltage might be more accurate (see my plot of LG Chem's E63 definition) but is not easy to translate to energy.

It may not be relevant but on AC charging the efficiency of the on-board charger does vary with current. I'd guess that the published 91% OBC efficiency is at the maximum capacity. At 7 amps (230 VAC) I'm seeing it in the mid-80s. No doubt the losses are not really linear but have fixed and variable components.

LG-Chem L63.webp
 
Thanks, KiwiME, for your reply and information. I had hoped there would be an easier way. I have been thinking of getting an OBD2 dongle, but recall reading elsewhere on this forum that the related app is for an Android phone. (I use an iPhone)

Thanks also for including the graph. Very interesting. I have wondered what the battery voltage was, when the Kona goes into Turtle Mode. So if Turtle Mode kicks in at 5% SOC, then the battery voltage would be 3.4 times the number of cells, right?

Also, if the AC charging efficiency is, say 83%, does this mean that if I am paying the public AC charger for 20 kWh, that the actual amount of energy actually added to the battery is 83% of that, or 16.6 kWh?

Hope you don't mind one more question.... In addition to using public chargers, I often charge my Kona at my nephew's house using a Mustart 32 amp charger. (I live in an apartment building and hence don't have a garage or driveway) The Mustart typically runs at 7.3 kW and I record the kWh transferred each time so I can reimburse my nephew. The question is: Does the reading on the Musart display indicate the number of kilowatt-hours that left my nephew's house panel, or the amount actually absorbed by the Kona battery? Thanks in advance.
 
Rickker said:
I had hoped there would be an easier way. I have been thinking of getting an OBD2 dongle, but recall reading elsewhere on this forum that the related app is for an Android phone. (I use an iPhone) ... So if Turtle Mode kicks in at 5% SOC, then the battery voltage would be 3.4 times the number of cells, right?
Click to expand...
There's a small device you can buy that does what you want without needing to tie up a smartphone, or you can use apps that that work on the iphone with a WiFi dongle, someone else can perhaps jump in and provide a link.
In theory yes, 3.4 x 98 = 333 VDC, but when you measure it using OBD2 there is a slight load on the battery because the EV is alive so it's not technically a settled "open circuit" reading.
Rickker said:
Also, if the AC charging efficiency is, say 83%, does this mean that if I am paying the public AC charger for 20 kWh, that the actual amount of energy actually added to the battery is 83% of that, or 16.6 kWh?
Click to expand...
Correct, noting that a public charger is likely to provide enough current to get into a slightly higher efficiency, you could assume 90% at a full 32 A.
Rickker said:
Does the reading on the Musart display indicate the number of kilowatt-hours that left my nephew's house panel, or the amount actually absorbed by the Kona battery?
Click to expand...
Just what left the house. For the amount absorbed by the battery you need to read the change in the CEC value over that period. The Musart, like all EVSEs using the AC port (J1772 for you or Type 2 in my case), has no idea about the state of the EV's battery. It simply checks the ground continuity and provides a continuous signal to the EV indicating the maximum current the EV can draw.
 
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