There is a long-running existing thread about this topic at Tesla confirms Model 3 will have less than 60kWh battery option
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JRP3
Hyperactive Member
You've given the Bolt the ability to use all of it's 60kWh pack size, which it won't do in the real world. If anything I would expect GM to be more conservative and use a smaller percentage of total kWh than Tesla.
This is very true, GM likes to make EVs "easy" so you just plug in and charge to "full" which they set at a safe buffer amount.
In some ways, I like GMs take on this versus Teslas. Let the engineers set the car up for proper battery management instead of making me do it. Sure I might miss out on the ability to "range" charge when traveling long distance, but then I would just work within the existing SOC range limits imposed when planning a trip.
JRP3
Hyperactive Member
I'd rather have the options to use more of the pack if I want. I like to have more control over my own vehicle, not less. It's not as if Tesla is forcing you to check your cells with a volt meter and balance them manually 
You can "GM" your Tesla if you wish, set your charge percentage at 80% or whatever you like and forget about it.
You can "GM" your Tesla if you wish, set your charge percentage at 80% or whatever you like and forget about it.
stopcrazypp
Well-Known Member
Right. I believe the default setting is around 90% anyways. No reason to cater to the lowest common denominator, when you can allow more functionality via settings.I'd rather have the options to use more of the pack if I want. I like to have more control over my own vehicle, not less. It's not as if Tesla is forcing you to check your cells with a volt meter and balance them manually
Both GM (in the Spark EV) and Tesla set the usable capacity to about 95-96% of the battery's rated capacity.
Tesla currently provides the setting to limit the recharge level to less than that. It's presumed this will also be allowable in the Model 3. We don't know if the Bolt EV will get additional settings beyond what is in the Spark EV.
Tesla currently provides the setting to limit the recharge level to less than that. It's presumed this will also be allowable in the Model 3. We don't know if the Bolt EV will get additional settings beyond what is in the Spark EV.
stopcrazypp
Well-Known Member
The reason why accessory load impacts can't simply be mitigated by efficiency improvements, esp. when done only on the locomotive side as you term it, is because accessory load doesn't scale by mile, but rather by time (it is a fixed kW load that does not vary with speed).
The Model S has a 6kW cabin heater (and separate 6kW pack heater). According to the below, average draw for cabin heater is about 1-2 kW when car has fully warmed up. So together probably a 3-4kW draw including all accessory loads.
Cold Weather Driving
Then let's go back to the post where this dicussion began.
That suggests Bolt needs 60.8kWh usable to get 215 miles of range at 75mph, and Model 3 needs 43.3 kWh usable to get 215 miles of range at 75mph (not including other loads). However, throw in the winter accessory load at 4kW and that bumps numbers to 72.2kWh and 54.8kWh respectively (the air density also changes numbers, but for simplicity I didn't factor those in).
To get back to the original topic of small vs large batteries, that would appear to be a 45kWh battery (as suggested by "small battery" advocates) vs a 55kWh battery (as I predict).
Using that calculator, I get 4.53kW (6.08hp) rolling resistance load at 75mph for 3800 lbs.
The Model S pack is around 150Wh/kg, so the additional 10kWh will weigh 66kg or 146 lbs, and I get 3946 lbs total, and 4.71kW (6.31hp) rolling resistance load. So a penalty of ~0.2kW for that extra weight.
Going back, the baseline is 45kWh (42.75 usable at 95%DOD) at 3800 lbs using 15.1 kW @ 75mph, giving 212 miles of range. With 4kW winter accessory load, that drops to 168 miles.
55kWh (52.25 usable) at 3946 lbs using 15.3 kW @ 75mph, gives 256 miles of range. With 4kW winter accessory load, that drops to 203 miles.
Note: none of the numbers above include parasitic/overhead loss (and I'm just using the 3800 lb assumption as OP did), so these numbers are not necessarily representative of the Model 3 and are only being used to illustrate the point.
As you can see, the larger capacity (22% usable gain in my hypothetical) only cost a 1.3% loss in efficiency (0.2kW out of 15.1kW @ 75mph) and this would be a great help in winter loads and makes it possible for Tesla to keep the "200 miles" promise even in slightly more adverse conditions (while a small battery would struggle).
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I'd rather have the options to use more of the pack if I want. I like to have more control over my own vehicle, not less. It's not as if Tesla is forcing you to check your cells with a volt meter and balance them manually
Ah, but based on what I have read here, if I do set it at 80% and forget it, the pack will eventually start reading less range than it actually has. To fix it, you have to do a couple of 100% charges and drive it down to let the pack re-program it's range. Sure, that's pretty easy to do, I suppose, but I will admit I do like my Volt's completely set and forget programming.
SageBrush
REJECT Fascism
(Ignoring the fact that you incorrectly rounded the Model 3's Winter range down (from 181.8) but the Bolt's range up (from 184.6... really only a 2.2 mile difference, not 4.... )
I'd also suggest your relative power draws are skewed... there's no way that the accessory draw on my Model S is 125 Wh/mi in nice weather. I'd say more like less than 50.
In any case, the point I made previously was that:
scaesare said:
While the overall driveline efficency difference in your examples is 100-(125/175)=29%, the actual overall power delta in your examples is 100-(275/325)=15%. Yet in this instance you arbitrarily suggested a 17% difference in pack size between the two vehicles.
I'd suggest that, as per my comment above, selecting a battery 17% smaller, when you know your efficiency is less than that, is not a correct selection, and your example is arbitrary.
Lets consider models using the 60KWh Bolt pack size you suggest above as a starting point but correct battey selection for the Model 3. I'll also use your same ratios of locomotive to accessory power.
If the Bolt pack is 60KWh, then given the 15% increase in overall efficiency your numbers produce, the correct battery size for the Model # should be 60 * .85 = 51KWh
Good weather Bolt:
Usable energy: 60Wkh usable
Range target: 200 miles
Locomotive power: 175 Wh/mi
Accessory power: 125 Wh/mi
Total power draw: 300 Wh/mi
Actual Range: 200 miles
Good weather Model 3:
Usable energy: 51Wkh usable
Range target: 200miles
Locomotive power: 125 Wh/mi
Accessory power: 125 Wh/mi
Total power draw: 250 Wh/mi
Actual Range: 204 miles
Using your same 20% increase in cold weather:
Cold weather Bolt:
Usable energy: 60Wkh usable
Range target: 200 miles
Locomotive power: 175 Wh/mi
Accessory power: 125*1.2=150 Wh/mi
Total power draw: 325Wh/mi
Cold weather range: 185 miles
Cold weather Model 3:
Usable energy: 51Wkh usable
Range target: 200 miles
Locomotive power: 125 Wh/mi
Accessory power: 125*1.2=150 Wh/mi
Total power draw: 275 Wh/mi
Cold weather range: 185 miles
So, the correct engineering decision in this case in my opinion is to select for the the overall power draw necessary, knowing what the accessory load percentages will require.
Of course with the Bolt's advertised 60KWh capacity, that's not usable energy as your example assumes (and same would be true for Model 3). I also believe your power draw numbers are skewed.
JRP3
Hyperactive Member
Contrived is one thing, using completely different parameters, i.e. full actual pack capacity vs usable, totally skewing any results, is another.
SageBrush
REJECT Fascism
Sigh
No one to fight with ?
You remind me of the big Sumo competition this week where the challenger charged like a bull at the onset of the match -- right past his opponent and out of the ring.
JRP3
Hyperactive Member
It's the internet, there are always plenty of people to fight with. Not sure why you seem to be upset that I pointed out two significantly different metrics you used for comparison, which rather invalidate any conclusion you may come up with.
stopcrazypp
Well-Known Member
I think his point was that for his example, the exact numbers do not matter. The usable can be adjusted and it won't really change his conclusion.
His main point was a less efficient car with a larger battery is less impacted by a fixed Wh/mi (25Wh/mi in his example, 300 to 325 for Bolt, 250 to 275 for Model 3) increase in consumption than a more efficient car with a smaller battery.
This is why we can't have nice things. Tesla has already delivered this. Leave it at the default (90%, Daily) and just use the vehicle. No fuss, no muss. Tesla's version isn't "making you do" anything.
JRP3
Hyperactive Member
Except using the larger 60kWh pack as total usable capacity ends up with the Bolt getting 185 miles of range vs the 3 getting 181 miles of range in his winter driving scenario, which projects an inaccurate picture. I'll concede that wasn't his main point.
The point is that winter weather will have a larger impact on a smaller battery car than a larger battery car, which is true. He should have used totally made up numbers to show the point and not even labeled them Bolt and 3. To pick apart one small thing ignoring the fact that all the other numbers were made up as well makes no sense. Actually I thought the most unrealistic part of his numbers is that background draw in winter weather was 1.2 times the summer weather background draw. Whereas it is several times the summer weather background draw (on the other hand it overestimated the summer background draw).
JRP3
Hyperactive Member
Red Sage
The Cybernetic Samurai
So, are you telling me to shut the [FLOCK] up, and not write my opinions any longer?
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