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Discussion Starter · #1 ·
I have to wonder…
Is the Ioniq EV traction battery level gauge linear, or weighted?

It is my view that in my previous Outlander, the battery gauge was linear in that it showed the battery charge remaining as determined by voltage. This meant that if I had travelled 12 miles and still had 50% charge remaining, I would have somewhat less than another 12 miles remaining.

This is because Lithium Polymer batteries have a fairly linear discharge curve in that the voltage steadily decreases as the cell discharges.

I use Lithium Polymer batteries in my hobby (Radio Controlled aircraft), and with the packs I use, the nominal voltage of each cell is 3.7v and a fully charged cell is 4.2V. I can utilise their capacity down to around 3.4v, but do not consider the cell to be fully discharged (to a safe level) until 3.2v

In terms of useable energy, it is the Amps (electron flow) that does the work. We measure the power of this work (when working with DC current) in Watts (volts x amps).

Now say we have a 370V Lithium Polymer vehicle traction battery, the fully charged voltage should be 420V, and if we need to pull 60kW, (60,000 Watts) from a fully charged condition, we would need around 143A (143A x 420V = 60.06kW)
As we use up the capacity the voltage drops, so by the time we get down to the nominal voltage of 370V we now need 162A to achieve the same 60kW (162A x 370V = 59.94kW). Pulling 162A is obviously going to use up the available charge much more quickly.

Ultimately then, it follows that a 50% charged battery will deplete more quickly than a 100% charged battery when presented with the same power demand.
So the question remains, is the charge level gauge weighted to represent actual useable power? or simply charge level remaining?

I have not yet gone below 3 bars of charge used in order to make a valid observation myself.
 

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I think your theory looks sound, but I am not a battery expert. You can test this also without emptying your battery completely. You can compare your kilometres driven from 100 to 90% with the kilometres driven from 30 to 20%, at comparable speed/power. If your theory is right, you will drive less kilometres in the 30-20 traject.
Still I think it is a difficult job to have exactly the same conditions.


Verstuurd vanaf mijn SM-G901F met Tapatalk
 

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Battery capacity is stated in kWh, not Ah. Efficiency is rated in Wh/mi or Wh/Km. I think it is likely that the gauges are calibrated to energy, not amps or volts. My experience with the Chevy Spark EV has been that the range indicators / battery level indicators are fairly accurate... 50% means that if the same driving conditions were repeated, the same distance could be traveled.
 

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Correction : battery capacity is measured in Ah. The energy volume a battery can deliver over time is measured in Wh. Reread your fysics schoolbooks.
 

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Jesus I hope ya'll are looking at the road while doing all this "mental math"?

I think Alien-S has done the math and figured it out.
 

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Correction : battery capacity is measured in Ah. The energy volume a battery can deliver over time is measured in Wh. Reread your fysics schoolbooks.
I said that battery capacity is *stated* in kWh. Have you looked at Hyundai's specification page?

Yes, amps and volts are measured. Why would they choose for the gauges to be only voltage or Ah based, when sufficient monitoring exists to calculate real-time power and cumulative energy discharge? Alien-S has proposed a theory that is not supported by my real world experience with EV's, apparently based on the premise that the EV engineering is no more sophisticated than his RC aircraft.

The Chevy Volt, for a specific example, stores the Battery SOC in its internal computer system in units of kWh, providing the data source for the dashboard visualizations. Is it likely that Hyundai doesn't also recognize the nonlinear relationship between voltage or Ah and energy remaining, and chooses to display a gauge to the driver that inaccurately represents the remaining capacity of the battery?
 

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Discussion Starter · #7 ·
Alien-S has proposed a theory that is not supported by the real world experience with EV's, apparently based on the premise that the EV engineering is no more sophisticated than his RC aircraft.
Incorrect: First of all I was asking a question, not strictly proposing a theory. Secondly, it was based on my real-world experience of my (now gone) Outlander PHEV, the behaviour of which seemed to mimic the behaviour of my RC batteries (very similar chemistry). The last half of the PHEV's useable battery capacity emptied far quicker than the first half - consistently. Doesn't matter how sophisticated an EV is, you still need to draw progressively more amps to get the same number of watts as the terminal battery voltage drops along the discharge curve.

And I'm going to stick my neck out here and say that there is no way to truly measure the capacity of a battery unless you empty it from full and measure how much came out. Even then, there's no guarantee that you can get the same amount of energy back in when filling it back up again. Thus the only way to take a measurement of a cell's true remaining energy is to measure it's voltage and plot the remaining capacity against a voltage\discharge curve.

But I guess that you are stating that all of the EV's of which you have experience, do in fact employ some sophisticated math to ensure the energy remaining gauge remains linear over the entire discharge curve. Shame Mitsubishi didn't seem to do that on my previous car.
 

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Here is data collected from Torque Pro. From 100% to 18%, for a total of 247 km in 3 consecutive days. There are 6 trips from 40 to 44 km with similar conditions. The interesting data are the total voltage of the 96 cells as well as the SOC display.

The SOC display from Torque Pro is a bit more accurate than the car dash.

I think this fit with this thread

I will add a post with a summary.
 

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In the attach document, there is a summary.


First observation:
This shows that the display of the car gauge is proportional to the amount of energy remaining and is linear.


Second observation:
When the battery is full, the volt is 4.12V
I am a little surprised that the voltage at 100% is a little lower than 99.5%. I think it can be the temperature of the battery that makes the difference


From reference below, table 4:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


i conclude that at 4.12 volts the battery is at about 90% of the total capacity. If we calculate 28 divided by 90% = 31 Kwh.
I made a calculation test for total capacity and that gives 29.6 kWh
I think the total capacity is between 29.5 and 31 kwh.


I think it confirms the rumor of 31 kWh total capacity but not more than that.


 

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