Simple way to measure useable battery capacity?

[evanevery]

I guess it depends what you're looking at. If you want to know the actual nuts & bolts of the battery, you're going to need to do a lot of out of warranty digging.

But if you want to know what is allotted for your use, the SOC % and kWh/100 mi are accurate. WIth a little math they give the physical amount you have available to you at any given time, plus a likely emergency buffer at 0%.

In practical use, those two numbers are quite accurate enough. At any time if you look at those numbers, plus distance traveled, and compare against detailed charging logs.. it all adds up correctly

In theory crafting, sure, the actual numbers might be different.

Also regen IS calculated in the kWh/100 mi number. If you start at the top of a mountain and coast down you WILL get a negative kWh/100 mi number, I do it every week.

I love math. I would never dissuade anyone from trying to "figure something out". So please don't misunderstand me...

I also manage analysts who quite often lose sight of the forest for the trees. Not that its not an interesting endeavor, but what are we really trying to achieve?

If we are trying to figure out the details of what Porsche has given us, then go for it! I wish you luck though, as I would be VERY impressed if you had the necessary scientific equipment or automated test environment to really do it with precision. The stuff we have in our chargers/cars is not up to that task. There simply is no reason for it. The variables we all introduce in our daily drives significantly outweigh any reason to have anything more precise than what we already have (I expect).

I believe my Taycan predicts my available range very well. (A mile is a pretty "coarse" unit of measurement). Much more so than my Tesla or any other EV I have owned (inc BMW). Porsche deserves credit for this. (mark your calendar).

But what is the point of precisely predicting the capacity of your battery, if you can not precisely control how it is expended?

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[Kingske]

I love math. I would never dissuade anyone from trying to "figure something out". So please don't misunderstand me...

I also manage analysts who quite often lose sight of the forest for the trees. Not that its not an interesting endeavor, but what are we really trying to achieve?

If we are trying to figure out the details of what Porsche has given us, then go for it! I wish you luck though, as I would be VERY impressed if you had the necessary scientific equipment or automated test environment to really do it with precision. The stuff we have in our chargers/cars is not up to that task. There simply is no reason for it. The variables we all introduce in our daily drives significantly outweigh any reason to have anything more precise than what we already have (I expect).

I believe my Taycan predicts my available range very well. (A mile is a pretty "coarse" unit of measurement). Much more so than my Tesla or any other EV I have owned (inc BMW). Porsche deserves credit for this. (mark your calendar).

But what is the point of precisely predicting the capacity of your battery, if you can not precisely control how it is expended?

Practically speaking, you are absolutely right. I am just curious to know what the useable capacity is. Your analysts losing sight of the forest analogy reminds me of statisticians in my team who analyzed and extrapolated massive sets of clinical trial data and proudly came back with a negative blood pressure as the answer.

 

[evanevery]

Practically speaking, you are absolutely right. I am just curious to know what the useable capacity is. Your analysts losing sight of the forest analogy reminds me of statisticians in my team who analyzed and extrapolated massive sets of clinical trial data and proudly came back with a negative blood pressure as the answer.

I'll add to that...

I remember a news report I saw in Canada when I was a kid (1970's?). (My parent's families are both Canadian, so I apologize in advance - (pun fully intended))

The Canadian Government spent several million dollars to find out why the unemployment rate was so high. After much time, labor, and analysis, the finding of the report was "Unemployment was High" because "People were out of Work"....

You can't make this stuff up!

 

[PanameraFrank]

@evanevery Losing sight of the forest for the trees is exactly how I'd describe most of your posts.

They wanted to know how to measure usable capacity, the method I described is how. You waxed poetic about how we can never really know the capacity and miles are crude figures. It's confusing to people coming on the forum for help and a very analyst way of looking at it. I come from more of a customer service background and frankly, there's such a thing as good enough & K.I.S.S.

Every thread on here has started becoming these massive existential debates and it's pretty tiring, hence why I post much less now. I wish we could save the more analytical/theorycrafting for certain spots, the threads @louv started are excellent treasure troves of that, instead of bloating every single thread.

 

[evanevery]

@evanevery Losing sight of the forest for the trees is exactly how I'd describe most of your posts.

Ouch! That sound like a personal thing!

 

[evanevery]

@evanevery Every thread on here has started becoming these massive existential debates and it's pretty tiring, hence why I post much less now. I wish we could save the more analytical/theorycrafting for certain spots, the threads @louv started are excellent treasure troves of that, instead of bloating every single thread.

Guilty as charged I guess.

But I thought these were discussions? I speak as if we were all sitting at a table with this community in real life. ...and I hope I brought something insightful, interesting, or helpful to the table on some occasion or another.

Unfortunately we do not have such opportunities in these times of Covid. Perhaps the limited contact imposed by Social Distancing has increased my propensity for digital communication?

I'll make an effort to reduce my "personal participation".

Thanks for your understanding.

 

[svp6]

Another way is to empty the battery. I recorded about 25 trips starting more or less at 100% and discharging down to 15-30%. You have the "energy used" in the trip meter (or if you prefer you multiply miles with KWh/mi and get the same) then solve for total capacity. Other than some weird outliers, I am getting 87-93 kWh for total capacity. Of course, the absolute way is to discharge to 1-2% then measure what you used and how much you put back in to 100% - Bjorn's style.

 

[Bill33525]

" Of course, the absolute way is to discharge to 1-2% then measure what you used and how much you put back in to 100% - Bjorn's style "

Tom Moloughney

on State of Charge has found that some cars can trave further on the first 25% of the battery than on the last 25% of the battery. Although generally not a big difference to be totally accurate draining the battery to zero and documenting a full charge is the most accurate way to determine net battery capacity. Note, the kWs into the battery should be used not the kWs on the charger screen.

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