Energy vs %SOC or Wh / 1%Soc

Energy vs %SOC or Wh / 1%Soc

I am collecting data of energy (Wh) for 1% Soc. It could also be Wh per bar. I hope to record the degradation of battery pack in time. But data are erratic for now. There is variation but I don't know yet what are the variables: energy spent faster or slower ( speed, head or tail wind ) , temperature or others. I have to wait till next summer to check it out. If you have any opinion or data about it, it would be nice te exchange.

First test with a new battery pack in temp around 0°C ( 32°F), at around 60 kmh ( 40mph). Each line is as follow:

Bar ** %SOC ** WH cumul ** Difference ** Per 1% SOC

First day

16 ** 100 ** 0
15 ** 92% ** 1210Wh ** 1210 ** 151.2
14 ** 85% ** 2281Wh ** 1070 ** 152.8
13 ** 80% ** 3041Wh ** 760 ** 152.0
12 ** 75% ** 3807Wh ** 766 ** 153.2
11 ** 70% ** 4574Wh ** 767 ** 153.4
10 ** 65% ** 5319Wh ** 745 ** 149.0
09 ** 60% ** 6069Wh ** 750 ** 150.0
08 ** 55% ** 6827Wh ** 758 ** 151.5

Second day: Number of bars and % soc increased during night, giving less Wh per bar.

10 ** 65% ** 0435Wh **
09 ** 60% ** 1093Wh ** 658 ** 131.6
08 ** 55% ** 1760Ww ** 667 ** 133.4
07 ** 50% ** 2418Wh ** 658 ** 131.6
06 ** 45% ** 3078Wh ** 660 ** 132.0
05 ** 40% ** 3735Wh ** 657 ** 131.4
04 ** 34% ** 4509Wh ** 774 ** 129.0
03 ** 28% ** 5288Wh ** 779 ** 129.8
02 ** 22% ** 6050Wh ** 762 ** 127.0
01 ** 17% ** 6695Wh ** 645 ** 129.0
00 ** 12% ** 7330Wh ** 635 ** 127.0
--- *** 10% ** 7588Wh ** 258 ** 129.0

As we can see it is quite regular on the whole scale. Any difference of 2-3 Wh has no mathematic significance since it is difficult to note the exact number of Wh on the go, at the exact change of %Soc.

I just saw that Malm is running at 108 Wh / 1% Soc. It is quite low compare to mine, which is between 128 Wh and 160 Wh, depending upon what ??? I will find out in a couple of month when weather will improve.

108 against 132 for 1% of SoC. Approximately 18% loss in 4 years (maybe a little more, because my 0% SoC could be 2,75 V in the weakest cell, and 3,3 V in a new one.)

Not bad, when compared to the Nissan Leaf here in Portugal. With 4 years like mine, and the same millage, most of them had lost at least 2 bars, so lost at least 21% of its original capacity. Some of them lost three bars (less 26%-30%).

Malm, your 108 appeared to be low compare to my 150Wh which would give a total capacity of 15 kwh to the pack. I don't question your hability to evaluate the capacity of your pack, considering your experience with this car and much more km ( mine has only 16,000 km). It is very informative to have your datas from one of the oldest I-miev. I am awaiting for data on the degradation of your pack as it ages in the future.

One question concerning your number ( 108 ) between 50 and 55% soc, is it always this number or does it fluctuate. Is it regular in the same conditions and/or fluctuating in different conditions of Temp, wind, speed ? As you know mine is fluctuating and I will try to find out why, so to establish a comparaison test of future degradation.

My first 2 year old pack seemed quite good with 143 to 158 Wh per 1% soc. I will compare it with my new pack this summer, in the same conditions and same itinerary.

My weakest cell is at 3,6 volt at 4% soc.

Pier said:

... There is variation but I don't know yet what are the variables: energy spent faster or slower ( speed, head or tail wind ) , temperature or others.

Click to expand...

I'm always bemused by those of you who willingly drive your packs to extremes in the interest of science, unlike some of us who hover over the battery pack like a mother hen. Whereas I see temperature being a significant factor in capacity measurements and perhaps should be noted as part of the datataking, is there any evidence to suggest that heavier loads (e.g., high speed) vs. very-light loads make a difference?

Pier said:

Malm, your 108 appeared to be low compare to my 150Wh which would give a total capacity of 15 kwh to the pack. I don't question your hability to evaluate the capacity of your pack, considering your experience with this car and much more km ( mine has only 16,000 km). It is very informative to have your datas from one of the oldest I-miev. I am awaiting for data on the degradation of your pack as it ages in the future.

One question concerning your number ( 108 ) between 50 and 55% soc, is it always this number or does it fluctuate. Is it regular in the same conditions and/or fluctuating in different conditions of Temp, wind, speed ? As you know mine is fluctuating and I will try to find out why, so to establish a comparaison test of future degradation.

My first 2 year old pack seemed quite good with 143 to 158 Wh per 1% soc. I will compare it with my new pack this summer, in the same conditions and same itinerary.

My weakest cell is at 3,6 volt at 4% soc.

Click to expand...

I measure 108 Wh - 1% SoC WHEN CHARCHING. Canion gives me that result WHEN CHARGING (and this value is very stable). When discharging, the value is higher, for sure, and may fluctuate. 1% SoC, seen with canion, is not the same thing when charging or discharging.

I will try to get a number of Wh/1% Soc when discharging of my car. I believe I will get a number between 120 to 130Wh/1% SoC.

I saw by Canion 577 Wh consumed between 50% and 45%. So 115 wh/1% SoC (less the I expected). Less 23%/24%. My car assumes to have less 23%/24% battery capacity then a new one.

I will try to make a discharge from 100% to 0% and see what rests in the battery, to check if the value is well calculated. If 0.0% SoC happens when voltage of the weakest cell is low then 3,3 V, then I will say that the value of 115 wh/1% SoC is right.

Answer to Joes

Don't be stupefy Joes, to me this battery pack has to be used --- not using only 50% as the volt do. In every day errand, I keep it between around 30 to 50 % soc, never a full charge for long but just before leaving. But many times I need to drive 80, 100 and even 120 km (75 miles), so I use most energy from the pack, but rarely below 10% soc. I see here a 5% soc new pack, the lowest cell is at 3.73 volt wich is far from the bottom 2.75 volt. This I-miev looks like an egg but not necessary to brood it like a hen.( Hic !!)

This car would be useless using only 50% soc.

For the possible difference between heavy and light load, I don't know yet, but I will make many test before having more than an opinion. For now there is the possibility that a heavier load, by lowering fast the voltage, might induce a temporary lower energy per 1%soc. (??). Slowing will increase back the voltage, so the erratic measurement. But not sure about it. It all depends upon the way the car computer make calculations.

Answer to Malm:

A fast vérification gives a reading of 121,5 Wh / 1%soc on re-charge. It is regular at the middle of scale around 50% soc, so the number for 1% is the same number for 5% divide by 5. Done at around minus 5°C. I suppose it increase with temperature. According to Canion, 7A and 2.5 kw IN. Also 3.1kw 240 volt at the wall. It probably also depends on speed of charge.

Verification at 120 volt 860w at the wall. About 84 Wh / 1%soc, with variation from a pourcentage to the other, between 40 and 44. Same temp around 60%soc. Canion gives 1.2A and 0.4kw IN.

108 versus 121,5 Wh. Only 12% difference within 4 years would be very good.

Some more data for those interested : a few examples of Wh per 1% Soc, to show how irregular the data are without knowing why. Since in constant driving conditions, the data are regular on the whole scale , I decided to make calculations for older data, dividing WH Out by % Soc used with my old battery pack.

1- 156 Wh / 1% Soc, Soc from 100% to 20%, medium headwind, speed 70kmh avg 59, Temp 20°C (68°F).
2- 145 Wh / 1% Soc, Soc from 100% to 23.5%, med tail wind, speed 80 kmh avg 69, T° 26°C.

3- 152 Wh / 1% Soc, Soc from 100% to 17.5%, light head wind, speed 65 kmh avg 57, T° 12°C (54°F).
4- 143 Wh / 1% Soc, Soc from 100% to 8.5%, light tail wind, speed highway 105 kmh avg 97, T° 21°C.

These driving without stopping except some red light.

Here are few shorter runs without stopping :

A- 153 Wh / 1% Soc, Soc from 100% to 67%, LM head wind, speed 90 kmh avg 65, T° 10°C.
B- 161 Wh / 1% Soc, Soc from 63% to 33%, LM tail wind, speed 90 kmh avg 68.4, T° 12°C

First run with my new pack in december:

X- 135 Wh / 1% Soc, Soc from 99% to 5%, Light head wind, speed 90,60,50 at the end avg 55.4, T° -2°C

And a few more lately this march :

5- 153 Wh from 100% to 37% soc, strong head & tail wind , avg 56.5 kmh, -2°C.
6- 128 Wh from 100% to 46% soc, M h&t wind, avg 56.7 kmh, -12°C.
7- 144 Wh from 100% to 24% soc, M h&t wind, avg 59 kmh, -3°C.
8- 159 Wh from 100% to 59% soc, L h&t wind, avg 59 kmh, +2°C.

Malm wrote : « 108 versus 121,5 Wh. Only 12% difference within 4 years would be very good.»

Indeed, it would be very good, but I hope my number will increase with higher temperature. It was -5°C while charging.

Having performed capacity tests on batteries as well as individual lithium cells for years, I've been thinking about the efforts of all us CaniOn owners with our i-MiEV -

What is it we're trying to achieve with this datataking?

Simply to ascertain if, and by how much, our vehicle's battery is degrading over time.

What parameter are we interested in?

Kilowatt-hours

What conditions do we need to control in order to obtain repeatable results?

Temperature and battery current

How do we do that?

By performing controlled discharging and recharging tests while recording current, battery voltage, kWh, SoC, and temperature, using CaniOn.

How can we perform controlled discharge and recharge?

I am aware of only these:

Charging: using L1 or L2, with the ac charging current set by the EVSE. CaniOn shows the dc current flow but I am unclear whether this is current into the battery or current into the 'system'.

Discharging: the only static test I can think of is running the vehicle heater, even though it may not be a steady-state load. In the case of discharge, I don't think it matters where the current is going (e.g., some of it into the car's 'system'), as long as it is being measured coming from the battery.

Note that I am discounting discharge while driving, because current magnitude while driving is an uncontrolled variable. We may have identical kWh between tests, but they may be achieved using radically different currents.

I recognize that Lithium battery capacity is less sensitive to current draw than lead-acid batteries; however, if we are attempting to establish a baseline and then perform another test at a later date, then current should certainly be a controlled variable to ensure identicity between tests.

Before we start taking lots of datapoints, perhaps it may be worthwhile having a discussion first?

Pier, since you started this thread I will be happy to move this question to a different (or new) thread if you wish.

Edited Once

Of course Joes, you can delete this thread. It is not very useful since BlueLightning with help from Xavier and Martin went much farther on the subject of battery capacity and degradation.

JoeS said:

Before we start taking lots of datapoints, perhaps it may be worthwhile having a discussion first?
Pier, since you started this thread I will be happy to move this question to a different (or new) thread if you wish.

Click to expand...

Pier said:

Of course Joes, you can delete this thread. It is not very useful since BlueLightning with help from Xavier and Martin went much farther on the subject of battery capacity and degradation.

Click to expand...

Pier, I'm sorry I did not make myself clear: your thread I consider a good contribution to our knowledge base about our i-MiEV, and I would not like to delete it.

All I was suggesting is that we first discuss the methodology and, if possible, perhaps agree on a standardized procedure for determining our i-MiEV battery capacity.

Yes I like this thread to.

I agree we need to all play the same game befor we can compare scores.

We are all using Canion and a Imiev that's a start. Now I don't think it makes much differance if you measure 1% or 100% as my tests have shown me the isn't much error in just multiplying a 1% data and comparing it to large % scopes. It saves time and a 1% data point can be measured very quickly.

I do believe the lithium cells will perform different based on temperature. Some data being take at -5C and others at +35C would not be a fare comparison. Performance suffers in the cold.

Discharge whrs/1% increase on Canion gives different results to charge whrs/ 1%. I agree with this.

Today I will share my results (2012 Imiev 25,000km, QLD Australia hot climate though I do my best to keep the cars battery cool) Charging with 2.2kw EVSE. Discharging with heater. (Charging and discharging with pack around 50% SOC)

1% Discharge = 154whrs

1% Charge = 110whrs

Share your 1% results.

Edit: I think discharge whrs/1% using the heater at similar ambient temps (or batterys temps) is the best comparison. As the kind of EVSE output you are using looks like it has an effect on the results. But stationary load (heater) results should be comparable for 1% on Canion.

Kurt

I will do the charge test in my i-MiEV. Surprised with yours 1% charge value. 110 Wh is a low number. My value, is about 108 Wh, so almost the same thing, but mine with almost 5 years and 84.000 km. And the last value I saw in my battery, from june this year, was 35 Ah.

My discharge value was 154whr/1%

Your taking about charge value.

Yes that's why I don't pay attention to the charge number as the range of the car hasn't changed from new and my discharge number is very similar to others with packs that have little to no capacity losses.

Kurt

Your data being as follow:
1% Discharge = 154whrs
1% Charge = 110whrs. Share your 1% results.

I do this test from time to time to get data for future reference. Up to now, it is not very regular, so it is difficult to draw conclusion, but on the long term we will see a constant I believe.

Here is a result: At 20C bat temp., and around 50% soc :

1% discharge = 151 Wh / 1% soc.
1% charge = 115 Wh / 1% soc.

Pier

Sorry, I wanted to say, my charge value is 108 Wh - 1% SoC. I corrected my last post. Again, 108 looks very similar.

115 is also a low number, I have no doubt that there will be some of us with 124 Wh, or even a higher number. I have no doubt that two years ago my value was over then 125 wh, 1% SoC.