Can somebody with a BEV check my math for computing range?

[timbop]

I'm trying to figure out realistic range with a Mach-E standard range with both RWD and AWD configurations. It is clear that the simple single number from either EPA or WLTP calculations doesn't really help given the massive variability in EV performance based on use and conditions. It seems like the best approach is to take the range in "best case city driving in moderate weather" and apply adjustments to that to suit the situation - with the adjustments being multiplied together to get a final range number. I've already done a thread asking about "penalties" for cold, hot, and highway driving - but perhaps some of you could check my math for me?

Assumptions:

• best-case city driving should be about 10% better than the projected EPA rating
• Ford is probably going to reserve 10% of the battery as buffer
• Even with the buffer, one should not charge to more than 85% every day nor drop below 10% to protect battery longevity. Since winter affects range most, charge to 85% in the winter and 80% the other months.
• Based on the target numbers available today, the Mach E AWD has best case range of around 230 miles (10% better than projected EPA), and the RWD a range of around 255 miles

Given those assumptions, the adjustment factors suggested by others:

• 100% highway driving = .75
• 50% highway driving = .875
• summer driving (A/C and battery cooling) = .9
• winter driving (heat and battery inefficiency) = .65

Since those factors can be combined, the expected ranges per situation:

• RWD 100% highway driving in summer: 255 * .9 * .75 = 172 mi max, recommended range = 120 miles (charged to 80% and recharge at 10%)
• RWD 50% highway driving in winter: 255 * .875 * .65 = 145 mi max, recommended range = 108 miles (charged to 85%, and recharged at 10%)
• AWD 50% highway driving in spring/fall: 230 * .875 = 201 mi max, recommended range = 140 miles (charged to 80%, and recharge at 10%)

Does that make sense and are those factors reasonable, or do I have too much free time? Clearly the "best case" city/hwy EPA driving numbers will be different, but is the logic sound and are the factors mentioned all that have to be considered?

Sponsored

 

[JamieGeek]

Actually, I think you're overthinking this by quite a bit.

To get range you just need a range of mile/kWh values for various conditions (like my Bolt in the summer I can get over 4 miles/kWh and the winter I'm somewhere in the range of 2.5 - 3.0 miles/kWh). Do the math and in the summer you see I can get 240+ miles and winter between 150-180--values borne out by my GOM.

Thus to get an accurate reading on the Mach-E just guesstimate what its average power consumption will be. For the LR version Ford has said "targeting 300 miles on the larger battery in RWD" so that is 300/98.8kWh or 3 miles/kWh and some change. My guess would be that in city driving you can probably get that closer to 3.5 which would mean 350 miles...but we won't know until the car is out.

Yes I realize that I'm neglecting any buffer space that may be included in the battery by the OEM; but does it really matter? If you calculate your miles/kWh always the same (include or exclude the buffer) and always compare like with like they still will be comparable numbers.

 

[engnrng]

Good response, Jamiegeek. My EV has an EPA rated range of 258 miles on a 64 kWh battery. Calcs out to 4 mi/kWh. On my 8000 miles, I have been between 3.9 and 4.1 on almost every trip. Depending on my driving plans for the next day, I fill up when I get down to 40 to 60 miles, since my commute is 40 miles R/T. I also fill to 90% at home L2, since I live on a hill. That gives me typical battery use-range of about 45 kWh average, which is 180 miles of use between charges. If the Mach-E is expected to get only 3.0 mi/kWh, for example, on 98 kWh battery, and figuring my same refill point, that gives me about 70 kWh battery use-range, or 210 miles use between charges. I expect to do a bit better than 3.0 mi/kWh, so we'll see.

 

[hybrid2bev]

Sounds like you’re re-inventing the wheel. I’ve read that a better route planner is pretty good at range estimates accounting for elevation, wind, temperatures, and weather.

 

[timbop]

To get range you just need a range of mile/kWh values for various conditions (like my Bolt in the summer I can get over 4 miles/kWh and the winter I'm somewhere in the range of 2.5 - 3.0 miles/kWh).

What I am looking for is exactly the relative difference in various conditions you just mentioned. It doesn't matter whether you adjust mi/kwh and multiply by kwh to get miles or adjust base miles directly by the same factor - the result is essentially the same. What I am looking for is what those factors are (such as 2.5/4 = .625 and 3/4 = .75). Based on your experience, .65 seems like a good approximation for winter driving - but I'd like a sample size larger than that .

 

[timbop]

Sounds like you’re re-inventing the wheel. I’ve read that a better route planner is pretty good at range estimates accounting for elevation, wind, temperatures, and weather.

I started with that, but ABRP doesn't seem to penalize hot/cold driving nearly as much as has been suggested by anecdotal experience. Plotting a trip from charleston SC to Atlanta in 68 degrees F weather ABRP computes a rate of 2.52 mi/kwhr. At 100 degrees F it still says 2.52 mi/kwhr. At 20 degrees it only goes down to 2.38 mi/kwhr - that's only a 6% penalty. At 10 degrees F it shows 2.33 mi/kwh - only an 8% penalty

 

[JamieGeek]

What I am looking for is exactly the relative difference in various conditions you just mentioned. It doesn't matter whether you adjust mi/kwh and multiply by kwh to get miles or adjust base miles directly by the same factor - the result is essentially the same. What I am looking for is what those factors are (such as 2.5/4 = .625 and 3/4 = .75). Based on your experience, .65 seems like a good approximation for winter driving - but I'd like a sample size larger than that .

Ah but what you're really looking for is the factor for the Mach-E and you won't know that until there are some available.

Yes you can average them up across a bunch of different EV's and owner's but that won't necessarily reflect what the Mach-E does. Especially given that the Mach-E is so new: Perhaps Ford has found a way to efficiently heat the cab in the winter and thus your winter driving factor is only 10% instead of 30%...Maybe they are just going to install a Diesel heater with a small tank, then the factor for heat will be 0% !

The Focus Electric was horrible in the winter: it had two 500w glowplugs to heat the coolant that went into the heat exchanger for the cabin (that coolant also heated the batteries as well). As for heating the cabin it worked great but it could use close to 50% of the battery....

 

[timbop]

Ah but what you're really looking for is the factor for the Mach-E and you won't know that until there are some available.

Yes you can average them up across a bunch of different EV's and owner's but that won't necessarily reflect what the Mach-E does. Especially given that the Mach-E is so new: Perhaps Ford has found a way to efficiently heat the cab in the winter and thus your winter driving factor is only 10% instead of 30%...Maybe they are just going to install a Diesel heater with a small tank, then the factor for heat will be 0% !

The Focus Electric was horrible in the winter: it had two 500w glowplugs to heat the coolant that went into the heat exchanger for the cabin (that coolant also heated the batteries as well). As for heating the cabin it worked great but it could use close to 50% of the battery....

Fair point. Although, an approximation is better than the dearth of any actual information coming from FoMoCo

After all, we've got people pixel-peeping shots off of facebook trying to ascertain if there's a new doorhandle or not...

 

[JamieGeek]

Fair point. Although, an approximation is better than the dearth of any actual information coming from FoMoCo

After all, we've got people pixel-peeping shots off of facebook trying to ascertain if there's a new doorhandle or not...

LOL! Very true.

 

[theothertom]

10% buffer seems excessive (this is more than any other manufacturer that I'm aware of) but...if they do, then charging to "100%" is really only charging to 90%, which is fine. So your figures are probably too conservative.

 

[jeffdawgfan]

Not sure why you are limiting yourself to 80% charge. There are quite a few studies that it is fast charging, not charging to 100% that degrades a battery the most. We have had a Chevy Bolt and now a Leaf Plus. I charge at home to 100% any time the battery gets less than 80%. The Leaf has no battery conditioning, but accounting for energy used for the cabin heater, I don't think I lose more than 5% capacity on really cold days (Like less than freezing). Typically we just use the seat warmers if we are making a longer trip and this keep us plenty warm. The seat warmers use very little power. Back to the 80% charging, why would you leave 20% of your range lying on the table every day. I would think that charging to 100% every three days or so does a lot less degradation on the battery than charging every single day...thus that is why I charge to 100% every time battery is less than 80%. Now Fast charging, that is another topic. It is well documenting that fast charging, esp to 100% does degrade the battery much faster.

 

[timbop]

Not sure why you are limiting yourself to 80% charge.

https://www.fleetcarma.com/todays-electric-car-batteries/
https://www.geotab.com/blog/ev-battery-health/
https://batteryuniversity.com/learn/article/bu_1003a_battery_aging_in_an_electric_vehicle_ev

Sponsored