[ishiwgao]

great stats! very informative.

just a recommendation though. the graph regarding electric car range vs weight, I would suggest you change the y-axis title to energy per range, rather than charge per range (i would prefer energy per distance though).

I'm sure everyone knows what you mean when you say charge, but maybe it's better to use a simpler word rather than an incorrect technical term.

 

[Sparweb]

Done!
Thank you. I realized you were right even before I finished reading your post.

 

[kennybobby]

Great study you have done and interesting data, thanks for sharing your research--it will be a very useful reference.

One annoying thing about microsloft excel graphs is the ugly gray background that makes it difficult to read--but that default can be changed to white or no fill, look for 'format plot area'. You wonder who was the idiot that thought it was a good idea, just try plotting one out and waste ink on that background...

 

[Sparweb]

Thanks kennybobby
I agree that the colors in Excel are bad, but I think they are worse now, with those faded pastels...

 

[Karter2]

Interesting data.
Im not sure that "Wh/mile vs vehicle weight" is a valid comparator as there are so many factors to influence Wh/mile beside weight..
EG...
Aero design
Drive type..AC, DC, gearing, etc
Test routes
Speed
Etc

 

[brian_]

Im not sure that "Wh/mile vs vehicle weight" is a valid comparator as there are so many factors to influence Wh/mile beside weight..

I agree that weight is not a strong factor, which is why the increase in consumption with weight is a shallow slope. The slope in the "blue" category is shown as steep, but there is very little correlation; the Tesla correlation is strong, but the slope is shallow.

Mass affects energy required to accelerate, but EVs make some of that back on deceleration and any vehicle makes some back when coasting down.
Weight (a consequence of mass) increases rolling drag, but aerodynamic drag is a more important factor and adding battery to the same body doesn't change the aero drag.

 

[kennybobby]

i think weight is a first-order factor to consider and definitely a good metric.

Look at the yellow line for Pb batteries, typically the oldest diy projects out there. To get more range additional cells would be added; but this increased the weight and subsequently the energy consumption, as seen by the steep slope.

With the availability of LiFePO, diy conversions could be done with less weight in the pack. For the blue trend line there is a dramatic change in slope compared to the yellow, but the general principle applies that a lighter car uses less energy per distance.

The OEMs can do better than diy, but the slope is still in the same direction: more weight uses more. Even for the "tesla" class, heavy uses more.

so from these charts it's clear to see that weight is a primary factor for consideration of average expected range and energy consumption. Plenty of same-route testing of this has been done over the years by jack over at EVTV.me for various conversions, various pack sizes and cell types. He came up with the 10% rule of thumb on consumption versus weight: a well-done 2500 lb Li-cell conversion could expect to get 250 W-h/mile

 

[jonescg]

Here is an interesting link:
https://www.elektroauto-news.net/2017/gewicht-keine-entscheidende-rolle-reichweite

Basically weight doesn't really impact range - rather the amount of battery. Because batteries can range from lousy (lead) to outstanding (Li-NMC) weight is something of a secondary issue.

Energy density (Wh/l) and specific energy (Wh/kg) are what determines a long range car, and Wh/l is probably the more important. If it doesn't fit, it won't matter how heavy it is.

Some cells offer great power density (W/l) and specific power (W/kg) but always at the expense of energy.

Below is a little charge I've been compiling. Basically you can have power or energy, but the bleeding edge is both.

 

[ishiwgao]

Here is an interesting link:
https://www.elektroauto-news.net/2017/gewicht-keine-entscheidende-rolle-reichweite
Below is a little charge I've been compiling. Basically you can have power or energy, but the bleeding edge is both.

all the batteries seem to lie on a line that lies between 100Wh/kg 3000W/kg and 280Wh/kg 300W/kg, except for FEP9050135. May I know what cell is that?
tried googling for that but came up empty

 

[jonescg]

all the batteries seem to lie on a line that lies between 100Wh/kg 3000W/kg and 280Wh/kg 300W/kg, except for FEP9050135. May I know what cell is that?
tried googling for that but came up empty

It's the same pouch cell I use in Voltron Evo - 30C continuous, 60C burst. Its energy density is not the greatest, but at least the low impedance makes for a fairly efficient cell.
https://endless-sphere.com/forums/viewtopic.php?p=1269272#p1269272

 

[Karter2]

Basically you can have power or energy, but the bleeding edge is both.

Yes, but few need that "bleeding edge" combination.
For example that 18650BE , with a low specific power, is basicly the cell Tesla use ..to give one of the best performing EVs available in terms of power and range.

 

[brian_]

He came up with the 10% rule of thumb on consumption versus weight: a well-done 2500 lb Li-cell conversion could expect to get 250 W-h/mile

As a really rough guide - which is what a "rule of thumb" is for - the weight serves as an overall indication of size. The heavier EV will typically be wider and taller as well, so it has more aero drag and more of everything that consumes energy.

 

[Sparweb]

Thanks for all the feedback.
I'm surprised at the attention you have given to the 18650 cell. Definitely a critical factor in the construction of so many LiPo battery packs, but is it the chemistry, or the packaging of these cells that matters most?

In my study, it didn't seem to matter what system voltage was chosen; AC or DC. With the vast majority in the ~140-200 DCV range there are not enough very high/very low examples to use for comparison.

If anyone knows of some well-documented examples in the forum or the EV Garage of high-voltage and/or AC drives I'd love to see how they look relative to the typical DC drives. I did find a couple, but they are extreme examples with very powerful traction motors (~300kW) so I don't think they are representative.

 

[jonescg]

I work in a field where we use 18650s, so I have done a stack of work on them recently. Data was easy to come by.

The chemistry has made the biggest difference moving from LiFePO4 to LiCoO2, LiNiMnCoO2 and LiNCA. But cylindrical Li-ion cells consistently offer better energy density (by volume) than pouches.

DC motors are less efficient than AC motors, but you could argue with the money saved by installing a DC motor you can afford more battery

My race bike is high voltage AC but it's probably not much use to your comparisons (being a motorcycle, and a racing machine, efficiency was the #3 priority).

 

[Sparweb]

i think weight is a first-order factor to consider and definitely a good metric.
Plenty of same-route testing of this has been done over the years by jack over at EVTV.me for various conversions, various pack sizes and cell types. He came up with the 10% rule of thumb on consumption versus weight: a well-done 2500 lb Li-cell conversion could expect to get 250 W-h/mile

I haven't watched enough of EVTV to have found any episodes with road mileage tests, but since you mention it, I'll go back and have a look.

About the 10% rule of thumb: my collection of numbers doesn't support that. No claim to a scientific basis here, but of what I've seen on EVTV, they can't either. My list comes from builder's own claims, and of the 20 cars I put in, only 4 can claim they hit the 10% rule. The rest are like 12% to 13% or more.