Hi,
I've been lurking a long time, but still far from a chance to start an EV build of my own. Instead, I've been collecting info from the experts here. Then I realized that some of my research on DIY EV's might actually be worth sharing.
I've been comparing groups of EV's, looking for trends and similarities, and I found a few. I put a lot of the data from the EV Garage into a spreadsheet so that I could compare the battery pack size, motor power, range and so on. I also added data from production EV's for comparison. I hope you find these comparisons interesting.
Both graphs are grouped into four distinct types:
1) DIY lead
2) DIY LiPO
3) Production EV's
4) Tesla (a class of its own).
I plotted trend lines because there's a lot of scatter in the data - but actually a lot less scatter than I expected, and the points for each "technology" are definitely grouped. They also tell a bit of a story of technical progress as EV's become more capable.
The DIY lead is obviously the past, and here's a clear illustration of why. To get any range requires an enormous amount of battery mass, but soon mass of the the batteries overwhelm the mass of the car.
Close together are the DIY LiPO and production EV's. The production EV's have a slight advantage, but there is considerable overlap. It is clear that the DIY builders have access to technology that is similar to the technology being used by the major automakers. Note that I haven't included any DIY builds that use production vehicle drivetrains or batteries. That could be a 5th technology group but it might also have been confusing. So no DIY Tesla drivetrains in a Mazda Miata in these graphs.
Then of course, there's Tesla. By these comparisons they really stand out, although I must give a shout for the proud little Chevy Bolt which has slipped into the Tesla pack by these measures.
If anyone wants to see the original spreadsheet, they can download it here:
http://www.sparweb.ca/EV/Design/EVs_Garage_Comparison.xls
I tried to upload the whole thing to Google sheets - but I can't make a graph to save my life on that site. And if anyone finds any errors or would like me to consider something else, I'm all ears.
I hope that plots like these will be helpful to people who are considering what kind of range and pack size they should expect and/or aim for in their conversions. Getting good, reliable data is hard. I have to rely on the claims of builders, but you know, we're not all scientists. Take comfort that we shouldn't believe the range values from the OEM's, either.
For instance, I've seen people suggest that a 3000 pounds DIY car might get 300 Watt-hr per mile, but I haven't seen a credible example of that in a DIY car, but a production EV can do it.
I have also seen people limit their DIY build to about 60 Amp-hours of battery pack in a fairly heavy (4 seat) car. That is fine if they didn't really want a lot of range or had a limited budget, but the experience of others shows that a DIY project can reach 20% or more of the car's weight in batteries, with a payoff in driving range that beats many production EV's.
Overall, I'm still very impressed with what DIY EV builders can achieve. Their results can equal and in some cases even beat the major OEM's is just amazing, and I look forward to the day I can join the club!
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