Range Calculations for Newbs: A Suggestion for Tesla

[SageBrush]

My wife has been thinking about taking her first long term trip alone in a non-Tesla EV, so we have been talking a lot about how much charge is needed, how long to expect to stay at a DC charger, etc.

I've been doing these sort of calcs for years so I don't usually appreciate how odd they can be for Newbs. On reflection though, I think the EV manufacturers have complicated things by showing battery SoC. It forces us to consider multiple unit conversions that are not our daily bread.

This brings me to my suggestion: Prominently display the kWh remaining instead of the SoC. Then people will only have to gain some experience to know consumption rates for different drives or conditions, and the distance they want to travel.

Example: If I travel 65 mph on a flat road, I can expect at least 4 miles/kWh.
200 mile trip ? I need 50 kWh.
If I have 45 kWh available, I have to add 5 kWh
L2 EVSE at 5 kW ?
60 minute stop.
DC charge at 100 kW ?
3 minute stop.
....
...

 

[GtiMart]

I've thought of that too, after all kWh is the unit of quantity of energy. That would relate to liters/gallons in ICE cars, but notice no ICE car shows that information. It gets more complicated with charging curves so your calculation of "time to stop at a charger" doesn't work because it depends on battery temperature, current SOC etc. Your calculation of energy needed to travel X distance is also incomplete because of temperature (heating/cooling the cabin), possible rain/snow on the road, winds etc, not even counting your own speed. Those things will screw up consumption completely, they can easily double it.

In the case of ICE cars no one cares because there are gas stations at every street corner. Once we get there with chargers it won't matter anymore. In the meantime, the best for most people (IMO) is that the car navigation takes all of those factors into account and it tells you where to stop, when to stop and for how long. They are not quite there yet but some systems are getting pretty good.

For the nerds like us who like numbers, we can do the calculations

 

[SageBrush]

Your calculation of energy needed to travel X distance is also incomplete

Incomplete for sure, but in the same way that knowing gas tank capacity and typical MPG is incomplete. The paradigm however stays the same: as you said, people are used to handling an amount and a rate.

My tank is 20 gallons, and my car usually gets 20 mpg. I can go <> far on a tank
I have $100, and my help charges $20/hour. I can hire him for ...
These are problems of a type that most people find approachable.

My wife has been trying to get comfortable with kW and kWh for 5 years now, and it is still a source of confusion for her. One thing that has helped a little is to pronounce kWh "kiwi." It reinforces the idea that kWh is an amount, just like a basket of the tasty fruit. I encourage to think of an EV eating one kiwi fruit every 4 miles

 

[Aviateur17]

I thought manufacturers were supposed to keep the size of the battery a secret? If not, then why doesn't Tesla officially advertise their battery size? Additionally, if ppl see their usable battery size decrease don't they freak out?

 

[GtiMart]

The time when you need to know all of this is in highway driving. In city / commute drives you always have enough energy for your day. Worst case your kiwi rule would work pretty well here.
With an ICE, you can pretty much estimate highway driving. Speed and the other variables do not influence consumption as much since everything else is so inefficient. In contrast, highway speed is where the EV consumption is toughest to estimate and can vary the most. Going from 60mph to 90mph doubles consumption. Driving in -15C on a snowy road doubles consumption compared to temperate summer. If you had to calculate yourself, you would need to take these into account.

Yes, people panic at the first sign of range reduction. No one wants to publish kWh capacity of their batteries for that, and also because each battery might slightly vary from the published number. On Teslas people panic because the "rated miles" changes, which is exactly the same problem. In fact, since you have rated miles, I would argue you do have kWh, as long as you know the constant Most other manufacturers show a guess-o-meter instead, which does remove the possibility to see the kWh of the battery.

 

[SageBrush]

I would argue you do have kWh, as long as you know the constant

Indeed. But then you get fools that think that value is a GOM, and complain that Tesla has a terrible GOM lol