[Drivingforfun]

I’m aware of how various range figures and things are calculated with EVs based on their kilowatt hours but wondered something else which I don’t see mentioned

If you divide the battery capacity by the maximum output, does this give the time the car would run for while producing that amount of power, i.e. presumably at full throttle?

Taking the MINI Cooper SE which has 160KW (218bhp) power and 54KW/H battery; 54/160 is 20 mins and 15 seconds

If you multiply that by its top speed of 106mph it suggests it would go 35.8 miles at full throttle, presumably under ideal conditions

I’m aware no one would drive like that and the range is probably comparable to that of a petrol car driven at the redline, I’m not trying to criticise, was just curious

Is this all correct or did I oversimplify or something?

[Mark07]

I've heard stories where you put your foot down in high performance/thirsty petrol cars and can actually see the petrol guage go down.

We're still in the early days of EV's and tech will improve. The Ford Model T did 10-15mpg, a 2019 Vauxhall Corsa can achieve ~70mpg.

[Drivingforfun]

That's all true Mark and I tried to make that clear in my original post, I'm aware some evangelists will automatically see any curious questioning as opposition and there's nothing I can do about that, but it's really not my intention - my question was purely to ask if my maths was right or is it less simple than I'm trying to make out??

But yeah I'm well aware of mpg when driven hard, it's not unusual to get a dozen laps of a 1.5 mile track from half a tank!! 😯

[Rolebama]

I think your math is right. Most of my rc aircraft use 3.5Ah batteries powering 20Ah motors, and although they are not running flat out, around ten minutes is a safe flying time. As batteries lose power they build up resistance, so you won't get full power from them as they run down. (Some of the more sophisticated ones I use shut themselves down gradually before getting anywhere near flat to maintain integrity.)

[olduser]

Originally Posted by Drivingforfun

I’m aware of how various range figures and things are calculated with EVs based on their kilowatt hours but wondered something else which I don’t see mentioned

If you divide the battery capacity by the maximum output, does this give the time the car would run for while producing that amount of power, i.e. presumably at full throttle?

Taking the MINI Cooper SE which has 160KW (218bhp) power and 54KW/H battery; 54/160 is 20 mins and 15 seconds

If you multiply that by its top speed of 106mph it suggests it would go 35.8 miles at full throttle, presumably under ideal conditions

I’m aware no one would drive like that and the range is probably comparable to that of a petrol car driven at the redline, I’m not trying to criticise, was just curious

Is this all correct or did I oversimplify or something?

Yes that is one way of looking at the problem but in practice the cars control system will limit the maximum discharge rate anyway, I would be very surprised if the motor control system could handle the current in the way you postulate.

Discharging the battery in that way will also make it heat up, the control system then steps in and limits the discharge to prevent battery damage.

Whilst these both look like the same thing, in the case of limiting due to temperature, ambient temperature has to be taken into account and the battery my be hot due to fast charging or charging from prolonged braking.

Most EV's have an ECO mode, Normal, and Sport.

ECO - the the current from the battery is limited, and there will be maximum regeneration when braking or even just lifting off the accelerator.

Normal - maximum allowed current will be more than ECO, and there will be some regeneration when braking, and the overrun will feel about the same as a petrol engine the retardation effect coming from mild regeneration.

Sport - allows maximum current without damaging the controller or battery, still regeneration when braking, overrun the same as Normal.

All three settings are still controlled by the temperature control function.

These controls extend the cars range.

[savvy0001]

I’ve also heard similar stories about high-performance petrol cars where you can literally watch the fuel gauge drop if you push them hard. It’s a bit of a universal truth across vehicles: when you demand maximum performance, efficiency takes a backseat.

That said, EV tech is still evolving rapidly. Early petrol cars like the Ford Model T managed 10–15 mpg, but now even a small hatchback like the Vauxhall Corsa can hit 70 mpg under the right conditions. I expect we’ll see similar leaps in EV efficiency as batteries, motors, and energy recovery systems improve.