Optimizing battery life.
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KiwiME
Well-Known Member
The question came up over at the SpeakEV forum so thought I should not miss the opportunity to bore owners here as well.
It seems to me that using a simple reading of current data from any of the popular OBD apps such as Torque Pro you can quickly calculate how many full-charge-equivalent cycles your battery has endured since the BMS was last reset.
The CCC and CDC registers are cumulative coulomb odometers and represent accurate measurements of (Ah) units going in and out separately. All you need to do is add them together and divide that sum by twice the battery capacity, 180 Ah. I've plotted it out over 300 km just to show how that accumulates over SoC usage, not evenly due to regen adding to the charging accumulation, CCC.
As you can see I have only 6.75 of these cycles accumulated between my last BMS reset at Campaign 196 in Dec 2020 and about July 2021 when I took this data, about 2745 km. Extrapolating to my total odometer reading at 19,600 that would put me at ( 19,600 / 2745 ) x 6.75 = 48 cycles total.
To put this into perspective, the cell life is specified at around 1200 cycles down to 80% SoH.
One reason to plot this is that the rate can be estimated with a linear trendline. The slope of the trendline is the estimated cycle increment for every 100 SoC percent points charged or discharged, so that the slope has to be multiplied by 2 to make a full cycle, or 200 SoC points.
So, 2 x 0.659 = 1.32 full-charge cycles are accumulated every time I've utilised 200 SoC percent steps no matter how I do that, either driving or charging.
As an example, if I charge 10% then drive and use 10%, that's 20% accumulated and 0.2 x 1.32 = 0.26 cycle is used up. You might expect that to be 0.20 and it might if you were on the flat going at a constant speed.
The reason the factor is more than 1.00 is purely because of small amounts of regen occurring as you drive. I'll note that this particular 300 km drive was very hilly so the value could be lower for a Kona used on flatter roads.
It seems to me that using a simple reading of current data from any of the popular OBD apps such as Torque Pro you can quickly calculate how many full-charge-equivalent cycles your battery has endured since the BMS was last reset.
The CCC and CDC registers are cumulative coulomb odometers and represent accurate measurements of (Ah) units going in and out separately. All you need to do is add them together and divide that sum by twice the battery capacity, 180 Ah. I've plotted it out over 300 km just to show how that accumulates over SoC usage, not evenly due to regen adding to the charging accumulation, CCC.
As you can see I have only 6.75 of these cycles accumulated between my last BMS reset at Campaign 196 in Dec 2020 and about July 2021 when I took this data, about 2745 km. Extrapolating to my total odometer reading at 19,600 that would put me at ( 19,600 / 2745 ) x 6.75 = 48 cycles total.
To put this into perspective, the cell life is specified at around 1200 cycles down to 80% SoH.
One reason to plot this is that the rate can be estimated with a linear trendline. The slope of the trendline is the estimated cycle increment for every 100 SoC percent points charged or discharged, so that the slope has to be multiplied by 2 to make a full cycle, or 200 SoC points.
So, 2 x 0.659 = 1.32 full-charge cycles are accumulated every time I've utilised 200 SoC percent steps no matter how I do that, either driving or charging.
As an example, if I charge 10% then drive and use 10%, that's 20% accumulated and 0.2 x 1.32 = 0.26 cycle is used up. You might expect that to be 0.20 and it might if you were on the flat going at a constant speed.
The reason the factor is more than 1.00 is purely because of small amounts of regen occurring as you drive. I'll note that this particular 300 km drive was very hilly so the value could be lower for a Kona used on flatter roads.
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@16 cycles per year (assuming 3 years since driving car) translates into 75 years - before hitting 80% SOH.
I would love to have the opportunity to observe that occurrence
KiwiME
Well-Known Member
The link below on the Kia corporate page for British Dominica was referenced today on the SpeakEVs Kia Niro forum. I find it odd to see what are entirely-sensible suggestions on a corporate site because it can lead to more questions, complaints and liability than the typical stance of saying nothing at all.
They've already engineered the marketing, the car, the owner's manual recommendations and the warranty to maximise profit in the vast majority of consumer use cases. Kia won't want anyone knocking on their door complaining that they ran out of charge because they were following official guidelines.
But, for the diligent EV owner (at least those with NMC chemistry) it's still good advice.
https://www.kia.com/dm/discover-kia/ask/how-to-extend-ev-battery-life.html
They've already engineered the marketing, the car, the owner's manual recommendations and the warranty to maximise profit in the vast majority of consumer use cases. Kia won't want anyone knocking on their door complaining that they ran out of charge because they were following official guidelines.
But, for the diligent EV owner (at least those with NMC chemistry) it's still good advice.
https://www.kia.com/dm/discover-kia/ask/how-to-extend-ev-battery-life.html