battery capacity +- over 1kwh ??
- Thread starter evboy
- Start date
Help Support Chevy Spark EV Forum:
You are not loosing anything 
I believe two factors are at play:
1- The numbers themselves
Calculating a battery % used and kWh used is not trivial, there is no exact method to do that (that I know of).
So whatever method is used by GM to evaluate these number is likely imprecise. By how much I dont know, but it is there.
2- Imprecision in the reading itself
The number only show full percentage points, and the kWh only go to 1/10 of a kWh.
So when you look at a number that says 13%, it could be anything from 13% to 13.9%, and that for each of the 3 numbers, so if the there percentage number are being used, this carries a possible error of up to 2.7%!
In the same way when you read 13.3 kWh, it could be 13.1kWh, or 13.19 kWh
To eliminate one of the imprecision, you can write down the numbers when either the % or the kWh just changes to the next one up. At that time the imprecision is only on the other one.
For example:
- If you catch the kWh when it just changes to the new higher number, you know that one is right, but the % may be underestimated, which will lead to an extrapolated capacity that will be Over estimated.
ie: when the kWh just turns to 9 kWh, you note the percentages and they amount to 50% that would mean a capacity of 18kWh, but in fact the actual % could be as much as 52.7% which would mean a capacity of 17kWh
- If you catch the % when it just changes to a new higher number (assuming only the driving one is the only one), you will know the % is right but the kWh may be underestimated, which will lead to an underestimated battery capacity.
ie: when the % just turns to 50% (assuming only the driving one is there), you read a kWh of 9 kWh, that would mean a capacity of 18kWh, but in fact the actual kWh could be 9.09 which would mean a capacity of 18.2kWh
I have now gathered numbers every 5% for 5 charge and discharge cycles, and I ended up with numbers ranging from 18kWh to 15.8kWh.
That said, when I plot these numbers, I can see the trends. The Fluctuations get smaller when the number are read at higher percentage use (as the relative imprecision decreases), and I can deduct an average from these which is around16.4kWh
The way to do that is to make a reading when the battery is over 50% used, observing when the number changes to minimize reading errors.
Do that for at least 5 charge discharge cycles
Then put these numbers in Excel and create a line graph
Then use Xcel trend line feature to plot the trend and it will give you an idea of where the truth probably is.
Then forget about all that and start enjoying your car. Knowledge is important, but can be crippling if it becomes obsessive
I believe two factors are at play:
1- The numbers themselves
Calculating a battery % used and kWh used is not trivial, there is no exact method to do that (that I know of).
So whatever method is used by GM to evaluate these number is likely imprecise. By how much I dont know, but it is there.
2- Imprecision in the reading itself
The number only show full percentage points, and the kWh only go to 1/10 of a kWh.
So when you look at a number that says 13%, it could be anything from 13% to 13.9%, and that for each of the 3 numbers, so if the there percentage number are being used, this carries a possible error of up to 2.7%!
In the same way when you read 13.3 kWh, it could be 13.1kWh, or 13.19 kWh
To eliminate one of the imprecision, you can write down the numbers when either the % or the kWh just changes to the next one up. At that time the imprecision is only on the other one.
For example:
- If you catch the kWh when it just changes to the new higher number, you know that one is right, but the % may be underestimated, which will lead to an extrapolated capacity that will be Over estimated.
ie: when the kWh just turns to 9 kWh, you note the percentages and they amount to 50% that would mean a capacity of 18kWh, but in fact the actual % could be as much as 52.7% which would mean a capacity of 17kWh
- If you catch the % when it just changes to a new higher number (assuming only the driving one is the only one), you will know the % is right but the kWh may be underestimated, which will lead to an underestimated battery capacity.
ie: when the % just turns to 50% (assuming only the driving one is there), you read a kWh of 9 kWh, that would mean a capacity of 18kWh, but in fact the actual kWh could be 9.09 which would mean a capacity of 18.2kWh
I have now gathered numbers every 5% for 5 charge and discharge cycles, and I ended up with numbers ranging from 18kWh to 15.8kWh.
That said, when I plot these numbers, I can see the trends. The Fluctuations get smaller when the number are read at higher percentage use (as the relative imprecision decreases), and I can deduct an average from these which is around16.4kWh
The way to do that is to make a reading when the battery is over 50% used, observing when the number changes to minimize reading errors.
Do that for at least 5 charge discharge cycles
Then put these numbers in Excel and create a line graph
Then use Xcel trend line feature to plot the trend and it will give you an idea of where the truth probably is.
Then forget about all that and start enjoying your car. Knowledge is important, but can be crippling if it becomes obsessive
how about i charge to 100%. clear the odometer and c how many miles i get of actual driving. when the warning comes up and says charge if i got about 70 miles than the battery is good since i like to go a little fast. as long as im getting about 70 in todays weather i should be good.scrambler said:You are not loosing anything
I believe two factors are at play:
1- The numbers themselves
Calculating a battery % used and kWh used is not trivial, there is no exact method to do that (that I know of).
So whatever method is used by GM to evaluate these number is likely imprecise. By how much I dont know, but it is there.
2- Imprecision in the reading itself
The number only show full percentage points, and the kWh only go to 1/10 of a kWh.
So when you look at a number that says 13%, it could be anything from 13% to 13.9%, and that for each of the 3 numbers, so if the there percentage number are being used, this carries a possible error of up to 2.7%!
In the same way when you read 13.3 kWh, it could be 13.1kWh, or 13.19 kWh
To eliminate one of the imprecision, you can write down the numbers when either the % or the kWh just changes to the next one up. At that time the imprecision is only on the other one.
For example:
- If you catch the kWh when it just changes to the new higher number, you know that one is right, but the % may be underestimated, which will lead to an extrapolated capacity that will be Over estimated.
ie: when the kWh just turns to 9 kWh, you note the percentages and they amount to 50% that would mean a capacity of 18kWh, but in fact the actual % could be as much as 52.7% which would mean a capacity of 17kWh
- If you catch the % when it just changes to a new higher number (assuming only the driving one is the only one), you will know the % is right but the kWh may be underestimated, which will lead to an underestimated battery capacity.
ie: when the % just turns to 50% (assuming only the driving one is there), you read a kWh of 9 kWh, that would mean a capacity of 18kWh, but in fact the actual kWh could be 9.09 which would mean a capacity of 18.2kWh
I have now gathered numbers every 5% for 5 charge and discharge cycles, and I ended up with numbers ranging from 18kWh to 15.8kWh.
That said, when I plot these numbers, I can see the trends. The Fluctuations get smaller when the number are read at higher percentage use (as the relative imprecision decreases), and I can deduct an average from these which is around16.4kWh
The way to do that is to make a reading when the battery is over 50% used, observing when the number changes to minimize reading errors.
Do that for at least 5 charge discharge cycles
Then put these numbers in Excel and create a line graph
Then use Xcel trend line feature to plot the trend and it will give you an idea of where the truth probably is.
Then forget about all that and start enjoying your car. Knowledge is important, but can be crippling if it becomes obsessive
SparkevBlogspot
Well-known member
- Joined
- May 25, 2015
- Messages
- 498
Scrambler is mostly right. Lack of digits is one problem, but it seems the reading is momentarily incorrect when using lots of regen. I noticed this going down a long hill (about 30 minutes worth). But when back on flat road, reading came back in line with what was measured.
There's also the question of power. LiIon, like all battery types, are rated at certain kWh at some discharge current. Since real-world driving makes the current go all over the place, I don't expect the kWh to remain the same. How much it varies will depend on your driving (which you can measure) and battery discharge capacity characteristics (which only Chevy / battery maker knows).
But in general to get better reading, you need to take many points in one discharge to most of battery capacity scenario (ie, 100% down to few %). To take the readings, it's best to have a video camera (ie, dashcam) recording it, and process it later. In signal processing, averaging is like low pass filtering which cuts down on noise, which the uncertainty can be treated as noise. Technically, it should be uncorrelated Gaussian noise, but it should be close enough.
If you have a video clip and you are handy with scripting, you can pick out % and kWh from every frame (frameserver is your friend), giving you literally tens of thousands of points. Timing on video cameras are typically less than 100 PPM (0.01%). Then you'd have very accurate battery capacity measure for that particular driving scenario.
If you did this for extremes, one for constant 24 MPH windows closed etc. and one in very cold weather with full heater and windows open at 90 MPH, you'd have boundaries of capacity variability.
There's also the question of power. LiIon, like all battery types, are rated at certain kWh at some discharge current. Since real-world driving makes the current go all over the place, I don't expect the kWh to remain the same. How much it varies will depend on your driving (which you can measure) and battery discharge capacity characteristics (which only Chevy / battery maker knows).
But in general to get better reading, you need to take many points in one discharge to most of battery capacity scenario (ie, 100% down to few %). To take the readings, it's best to have a video camera (ie, dashcam) recording it, and process it later. In signal processing, averaging is like low pass filtering which cuts down on noise, which the uncertainty can be treated as noise. Technically, it should be uncorrelated Gaussian noise, but it should be close enough.
If you have a video clip and you are handy with scripting, you can pick out % and kWh from every frame (frameserver is your friend), giving you literally tens of thousands of points. Timing on video cameras are typically less than 100 PPM (0.01%). Then you'd have very accurate battery capacity measure for that particular driving scenario.
If you did this for extremes, one for constant 24 MPH windows closed etc. and one in very cold weather with full heater and windows open at 90 MPH, you'd have boundaries of capacity variability.
The only meaningful stat is how far you can actually drive on a full charge. And even that will vary depending on temperature, climate settings, average speed, etc. The battery usage percentages and battery state of charge indicator that we see are all estimates and lack precision, so variation should be expected in your calculations. That's on top of the variation caused by the factors I listed above.
Bottom line: if the car is able to carry out your mission each day, who cares what the battery capacity is? It's either enough for you, or it's not. And, if at some point it's not enough, then you bring it in for service and GM will use their more advanced tools & tests to determine if the battery has lost 35% of it's capacity.
Bottom line: if the car is able to carry out your mission each day, who cares what the battery capacity is? It's either enough for you, or it's not. And, if at some point it's not enough, then you bring it in for service and GM will use their more advanced tools & tests to determine if the battery has lost 35% of it's capacity.
when i charged up last night, 18.20 kwh was put in when full. i dont know if thats accurate either. i did get 68 miles on the odometer. that seems decent for the weather, 60's, and a slightly heavy foot. if i had 18 kwh capacity, i would get 72 miles at 4 kwh which seems to be my average. i had 68 but i wasnt going to let it go to zero so i pulled into the station. u figure i had at least 4 miles left if i pushed it. thats 72. the screen was showing 7 minimum.
MrDRMorgan
Well-known member
The Chevy dealer should have test equipment to accurately determine the actual capacity of the battery.evboy said:
evboy said:
Here you go, everything is fine, breathe deeply (you seemed to be getting a bit intense for a moment)
Joke apart, you look just fine if you got 68 miles with a screen showing 7 left minimum (the middle number would actually be better to use), then you actually had at least 75 miles range on that trip with these driving conditions.
When you say your average is 4kWh, I suppose you meant your average is 4 Miles per kWh (which is 72 miles for 18 kWh)
If you use your trip odometer to check your average miles per kWh on each trip, and it is consistent, and if the Guess O meter Middle number when fully charge also becomes consistent, then you can use them to corroborate your other calculations.
For example, Now that I have driven my Spark for over 5 cycles, my average has stabilized to 5 mile per kWh, and when fully charged the guess O meter middle number is consistently showing 83 miles range.
That means 83 / 5 = 16.6 kWh capacity, which matches the fluctuating average I get from the extrapolation of % and kWh used, which was ranging from 18kWh to 15.8kWh but showing a Trend-line of 16.4 kWh (close enough to the 16.6 I just mentioned)
Bottom line, there is no exact way to know with the tools at our disposal, but cross referencing the various information we do have, you can get a pretty good idea of where you are, and then sleep better at night knowing you own a great and fun car to drive
scrambler do u clear your odometer to see if u can actually get 83 miles of actual driving before pulling in for your next charge. btw, how r some of u getting 6 miles per kwh. you drive like grandma or is the cali weather really making that big a difference. i guess i will c in april when we get good weather out here.
I dont drive until stranded, but the amount of miles I have driven plus the reminder estimate does stay pretty consistent with the initial range estimate (so long as my driving stays the same).
As far as getting 5 mile per kWh, I drive smoothly, so yes I probably drive like a granpa compared to you, and yes I am in California so the temperature is good, and finally, I drive 60% city 40% highway with usually a max of 60 on highway, so all that contribute to my 5 m/kWh.
As far as getting 5 mile per kWh, I drive smoothly, so yes I probably drive like a granpa compared to you
, and yes I am in California so the temperature is good, and finally, I drive 60% city 40% highway with usually a max of 60 on highway, so all that contribute to my 5 m/kWh.btw, when the heat hits 110 in vegas in july, will the thermal management system turn on by itself to cool the battery without being plugged in. i wont be able to plug it in when im at work in the daytime. does it have to be plugged in for the TMS to work.
If I recall reading on the volt, If the car is off and not plugged in, The AC will come on to cool the battery, but only if you have enough charge (like 50 or 70%)
But what I also read is that the full TMS does not run when the car is unplugged and turned OFF
Someone who knows better may chime in.
But as soon as you turn on the car or plug it in, it will activate battery conditioning.
But what I also read is that the full TMS does not run when the car is unplugged and turned OFF
Someone who knows better may chime in.
But as soon as you turn on the car or plug it in, it will activate battery conditioning.
No TMS when not powered on or plugged in.scrambler said:
I have read a Tesla will use battery power to run TMS but only when SOC is >80%.
You don't want to leave your car at a hot or cold airport and return to find it used up the SOC just sitting there.
SparkevBlogspot
Well-known member
- Joined
- May 25, 2015
- Messages
- 498
The worst combination is full charge + hot temperature. If you have it about mid-level in hot sun, it is bad but not as bad (whatever that means).
But if you charge to full, unplug, let it sit in 110F, the battery will degrade almost as much as Nissan Leaf. I say "almost", because
a) SparkEV cools the battery while charging, so that initial temperature after unplugging would be cooler than ambient. Leaf battery would be far hotter than ambient, because battery charging incur some loss as heat.
b) the liquid in SparkEV battery TMS will have some thermal momentum, delaying reaching the ambient temp; drawback is it cools down less quickly than Leaf, but most people plug-in by then, which cools the battery MUCH quicker than Leaf.
I harp on Leaf (probably true with eGolf as well), because it is the absolute worst in hot weather. The worst thing you can do with Leaf is to plug-in at hot weather. That will not only increase battery charge (degrade) in hot ambient (more degrade), but charging loss will add even more heat to the battery (much more degrade). It's a textbook definition of poor engineering. Frankly, I'm amazed how anyone can drive the Leaf in hot climate of AZ, NV, even some parts of CA.
In contrast, the best thing you can do for SparkEV in hot weather is to plug it in, charging or not.
But if you charge to full, unplug, let it sit in 110F, the battery will degrade almost as much as Nissan Leaf. I say "almost", because
a) SparkEV cools the battery while charging, so that initial temperature after unplugging would be cooler than ambient. Leaf battery would be far hotter than ambient, because battery charging incur some loss as heat.
b) the liquid in SparkEV battery TMS will have some thermal momentum, delaying reaching the ambient temp; drawback is it cools down less quickly than Leaf, but most people plug-in by then, which cools the battery MUCH quicker than Leaf.
I harp on Leaf (probably true with eGolf as well), because it is the absolute worst in hot weather. The worst thing you can do with Leaf is to plug-in at hot weather. That will not only increase battery charge (degrade) in hot ambient (more degrade), but charging loss will add even more heat to the battery (much more degrade). It's a textbook definition of poor engineering. Frankly, I'm amazed how anyone can drive the Leaf in hot climate of AZ, NV, even some parts of CA.
In contrast, the best thing you can do for SparkEV in hot weather is to plug it in, charging or not.
SparkE
Well-known member
If you live in a hot area, during hot season you can use 'charge during off-peak' setings to leave car plugged in but not charging so TMS will be active (IF you have access to even just 110V plug during the day).
That variation is consistent with the 125 data points I collected:evboy said:
http://www.mychevysparkev.com/forum/viewtopic.php?f=7&t=4610
At high SOC the TMS will activate to keep the battery from overheating and being damaged, even if the car is not plugged in. But, the battery has a lot of thermal mass. So, it would take a while baking in the sun before the battery reached a critical temperature and the TMS kicked on.
Similar threads
