Calculating Your Ideal EV

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danrjones

Well-known member
Joined
Apr 17, 2019
Messages
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Location
Ridgecrest, CA
I did some napkin math and was able to calculate the near perfect EV, in terms of range and charge speed.

If you take the high voltage technology from something like the Taycan, but you use Tesla efficiency, and you oversize the battery, you can get some interesting results.

If you look at charging curves, the Tesla 3 LR can hit 250kW on V3 but only for a short time - 5% to about 25% then starts to ramp down. The Taycan charging curves I found manage to charge at 250 kW from 5% to about 50% then start to ramp down.

The Tesla S with 370 miles of range has a battery of 100 kWh. The Taycan will have a range around 220ish miles when rated, and it has a battery of 93.4 kWh. So there is a large efficiency difference but also the Taycan may have a big portion of its battery locked off.

So I want to keep that 370 miles of range but maximize that 250+ charge speed. If we design a vehicle that only allows you to use the battery from 10% to 60%, we would need a battery obviously twice the size. So you would have a 200 kWh pack with the first 10% locked off, and the last 40% locked off. But if I understand correctly, a battery that is twice the size could possible accept twice the energy. So if the Taycan can take 250 kW right now, a battery pack twice that size could theoretically take 500 kW if you could keep it cool. Individual cells would still be getting the same amount of power as the 100 kW battery at 250 kW, just there are twice the cells. Using EA chargers as the current max, our car with the 200 kWh battery could then take the max of 350 kW for that allowed 10-60% section of the battery with no ramp down. Simple math gives us a recharge time of 17.1 minutes to "fully" charge the battery for 370-ish miles. That's pretty good! I've taken the liberty of a few assumptions but it presents an interesting example. Right now it would be too expensive and you'd have to fit it all in the vehicle. Online data says Tesla battery cost is currently 110ish per kWh, so a 200 pack would be $22,000. So perhaps that's not so outlandish after all?

True, if they unlocked the top of the battery you would end up with 500+ miles of range. I guess it would be a marketing thing, but to be able to say the battery charges "fully" in 17 minutes for 370 miles of range would be a big deal. And if somehow you could supply 500 kW, it would "fully" charge in 12 minutes for aprox 370 miles of range.

Is this crazy talk or the future?
 
This article has a lot of good data and is where I got much of my numbers:

https://jalopnik.com/an-extremely-detailed-look-at-the-porsche-taycans-engin-1837802533
 
Bigger batteries charge faster, all else being equal.

Congrats to you and Jalopnik for figuring this out too.
 
Your sarcasm aside, I think most people here know that, but most everyone else does not. To most non EV-ers, it seems counter intuitive that a bigger battery charges faster (and it especially charges faster if you look at in terms of miles per minute). I had this same discussion with coworkers, and had to explain why bigger was faster.

But my real question was what people here would draw up as their ideal EV in terms of charge speed, battery size, locking off part of the battery, so forth. To me it looks like 500 kW charging is fully possible, down the road. Your opinion might differ.
 
My ideal EV gives me enough time to pee and stretch before it starts nagging me to get going. My Tesla Model 3 LR is borderline. For example, I was looking into driving to Colorado Springs from my home in Albuquerque. It is a 6 hour, 370 mile drive and the car requires 11 minutes at a charging stop. I don't know if I can only stop for 11 minutes over six hours. I may have to find a CHAdeMO station
 
I think we understand, you love Tesla, we get it, But for some of us they really are not upto ICE when it comes to travel.

I did a trip with my son in my truck to Grand Tetons and Yellowstone this summer. Our campsite was over 900 miles from home. Because of my work schedule, we had to do the trip in one day each direction. It was a long day, but with a ICE vehicle totally doable.

How long would the same exact trip take in the BEST EV right now?

TFL has been testing their Tesla 3 and now X. The X was doing great until they started to tow. They had planned a trip out and couldn't make it. The range of the X plummeted to about 125 miles per full charge while towing. They basically figured that for every 1.5 hrs of driving they would need about an 1 hour and 15 minutes of charging. That's ridiculous, and they felt so to, and had to abandon the attempt.

It all depends on your lifestyle and what you want to do. But for some of us, EVs are not there yet, and so I'm curious what people would need. For SageBrush, they are fine now. For me, not even close. Give me some slack, its an exploration in math and concept, not a knock on Tesla Sagebrush. I'm looking at what it would take to get parity with ICE.
 
I'm curious what people would need.
I told you.

... of course I was only talking about my usual driving during the year. Did you want to include corner cases ?
I've thought about a nice trip around the world in an EV. I would tow a semi-truck with a nice yacht inside, which would tow a nice dreamliner jet in case I got tired of driving.

But EV is just not up to the task. <<<sigh>>>

its an exploration ... I'm looking at what it would take to get parity with ICE.
The answer is trivial:

33 kWh a gallon
Refueling at 600 gallons an hour

20 GW charger before differences in efficiency are accounted for.
Call it 10 GW
 
SageBrush said:
The answer is trivial:

33 kWh a gallon
Refueling at 600 gallons an hour

20 GW charger before differences in efficiency are accounted for.
Call it 10 GW

Energy wise that sounds correct. But most EVs are far more efficient. The model X has a range of aprox 325 miles and a battery of 100 kWh. That gives it a tank equivalent to what, about 3 gal of gas. That is probably one reason TFL had such issues towing - the EVs are so efficient that you toss a trailer behind them that is not efficient and the energy stored is not enough. For truck users that want to tow, they are going to need a lot more.

But for a mileage equivalent, say to a 30 mpg car, it would be close to 2.77 GW (using the model X). That's clearly a lot more than my hypothetical 500 kW. But who knows what the future will bring. Still, for ME, 10-12 minutes for 370 miles is a pretty good goal to fully replace an iCE. And a charging network to support.
 
GRA said:
Seems like we're in more or less complete agreement on what's needed for full ICE replacement. I'd even say 600 miles wouldn't be amiss, to allow for degradation and HVAC use. For full replacement I want at least four hours at 75 mph (80 mph preferred) plus at least a 30 mile reserve at the same speed with all the allowances as above, for at least 12 and preferably 15 or better yet 20 years. As a battery with that kind of longevity seems unlikely, I'm a big believer in battery leasing to keep the overall size/weight down. Let the leasing company worry about degradation.

If anyone comes up with a battery that will allow the full capacity (minus reserve) to be routinely used without hastening degradation, and which will last the car's lifetime, the total range can be reduced accordingly. And range can be traded off against charging speed to some extent, but as charging speeds that would replicate liquid/gaseous fuel energy replenishment times (<=5 min. to provide above range, which would require at least 1,200 kW) aren't likely anytime soon if ever, range is more critical. I don't mind stopping for 30-40 minutes every four hours or more as I can combine that with eating, but I'm not going to want to do that every two hours (or less) as is currently the case under those conditions. At least, it is in a BEV at an affordable price.

Yes, thanks. I'm curious what people would accept for towing.
 
I don't tow, but I suspect two hours with <=15 min. recharge to do the same again would work for many weekend trips, say from the Bay Area up to Tahoe. When the Model X came out and we first started to get test reports about its range deficiency as a tow vehicle, I asked a dive buddy who regularly tows his RIB down to Monterey and back from Oakland (ca. 110-120 miles one-way) with his V-8 4Runner if he was able to do the round trip un-refueled, and he said it would be very close. He doesn't bother, and gets gas somewhere in Monterey or on the way back. But it takes a lot less time, as in addition to the short refueling time he can just pull through the pumps rather than block several and/or have to un-hitch, which are the all too common cases at SCs/QCs due to their lack of pull-through spaces.

Of course, that's a single sample for routine weekend use. I'm sure there are people hauling big boats or trailers over long distances who'd want more range.

At the moment, I don't see any BEV as an adequate ICE-replacement tow vehicle for more than occasional weekend use on short trips. As is the case with delivery/distribution versus long haul trucks, I think the current technology ZEV long distance tow vehicle would have to be an FCEV, unless/until battery energy densities, prices and charge rates radically improve. But both the infrastructure and (vehicle and fuel) pricing would have to be improved to make FCEVs a practical answer.
 
danrjones said:
Still, for ME, 10-12 minutes for 370 miles is a pretty good goal to fully replace an iCE.
.
TFL reported 1 kWh/mile to tow. If that is a reliable benchmark for you then you are waiting for a 2 GW charger. A GWh battery should do the trick. Of course you might encounter headwinds, elevation, or have a hankering to go 80 mph so I recommend a 2 GWh battery and a 4 GW charger.
 
danrjones said:
But for some of us, EVs are not there yet, and so I'm curious what people would need.
Looks like you are more interested in corner cases that show "EVs are not there yet". Towing a trailer is something not many people do.
 
jlv said:
danrjones said:
But for some of us, EVs are not there yet, and so I'm curious what people would need.
Looks like you are more interested in corner cases that show "EVs are not there yet".
.
Yep. That is why I mock him.
Towing a trailer is something not many people do.
.
Actually, it is pretty common, albeit for a small fraction of total miles driven. Once in a while, an ICE is the right tool
 
SageBrush said:
jlv said:
danrjones said:
But for some of us, EVs are not there yet, and so I'm curious what people would need.
Looks like you are more interested in corner cases that show "EVs are not there yet".
.
Yep. That is why I mock him.
Towing a trailer is something not many people do.
.
Actually, it is pretty common, albeit for a small fraction of total miles driven. Once in a while, an ICE is the right tool

It's not a corner case at all. A big chunk of the country drives trucks. Just look at the sales of vehicles in the USA right now. If you want main stream adoption you need to look beyond just how you think people should drive. There was over 2.4 million trucks sold in 2018 in the US. And long road trips are still part of the american vacation.

As far as you mocking people whom have different ideas than you, I'd guess it's a character flaw. If you think the thread is dumb feel free not to post.
 
An EV truck is do-able.
A truck able to tow a big brick 370 miles at 70+ mph with 10 minute charge from empty is not.
That is just trivial arithmetic

Of course normal people might consider starting each day with a full charge, towing a more Aerodynamic load, or driving slower but this thread is all about you so the arithmetic is for you.
 
The trailer TFL tried to tow was only something like 3k lbs. Not heavy at all as trailers go. Everyone in my neighborhood has a trailer. I have a tent trailer.

The idea of the thread is simply to see what people want. I dont mind disagreement but there really is no reason to put others down.

Let people dream man.

Besides, just a decade or two ago an EV doing 370 miles was "impossible". Now it's a Tesla model S.
 
danrjones said:
The trailer TFL tried to tow was only something like 3k lbs. Not heavy at all as trailers go.
.
Weight is a minor issue unless climbing

By physics, mass*G*ƒ
Something on the order of 120 Newtons so about 54 Wh/mile. The other ~ 500 Wh/mile in the TFL episode was Aero and climbing at speed. They did not know how to extrapolate the consumption graph so they bailed.
 
Whatever way you want to slice it, it was a pretty moderate trailer. Taller than a tent trailer, shorter than a full travel trailer. I know at the start they pulled a bunch of gear off the roof. Without collecting data on hundreds of trailers it's hard to say for sure, but I'm guessing it's a fair representative for medium trailers.

They were using 900 to 1000 watt hours per mile. So clearly a 100 kWh pack is not big enough. Supposedly Tesla is paying around 110 and VW recently said they have the cost below 100 per kWh.

So if you tripled the battery size, and could package it, you are looking at 30k in battery costs for a tesla that can tow 300 miles. If a tesla truck ends up around 80 to 100k, that might be possible.

I watched EESTOR for years on ultracapcitors. They failed but humans can be quite clever and find solutions when either money is to be made or they are forced to innovate.

Graphing out fast charger speeds by year and seeing where that trend line is going would be interesting.
 
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