EV Efficiency Question - hard or low acceleration
Discussion
Apologies if this has been discussed before but a search didn't throw anything up.
Assuming identical scenarios, i.e. same target speed and distance, what would consume more battery energy.
Eco mode with blunted accelerator response or sport mode with unrestricted response.
In an ICE car it's advised to get up to the target speed asap so that you can cruise and maintain a constant speed. But is this the same for EV's?
In eco mode you're accelerating the car mass for longer but using less. Compared to using more over a shorter time.
I was discussing this with a mate at work as he loves driving in eco mode all the time. Personally, for the miniscule difference (if at all), I'd rather enjoy sport mode. Most of my savings have been made by ditching the ICE so am not particularly fussed but being a nerdy engineer was interested.
Thanks
Assuming identical scenarios, i.e. same target speed and distance, what would consume more battery energy.
Eco mode with blunted accelerator response or sport mode with unrestricted response.
In an ICE car it's advised to get up to the target speed asap so that you can cruise and maintain a constant speed. But is this the same for EV's?
In eco mode you're accelerating the car mass for longer but using less. Compared to using more over a shorter time.
I was discussing this with a mate at work as he loves driving in eco mode all the time. Personally, for the miniscule difference (if at all), I'd rather enjoy sport mode. Most of my savings have been made by ditching the ICE so am not particularly fussed but being a nerdy engineer was interested.
Thanks
REALIST123 said:
“In an ICE car it's advised to get up to the target speed asap so that you can cruise and maintain a constant speed. But is this the same for EV's?“
It’s not even true for ICE cars.
There's an element of truth in it given an engine operates at max efficiency further up the rev range. Eco mode tends to labour an engine at the lowest rev.It’s not even true for ICE cars.
I'm not talking about redlining a car but making progress.
I've no idea, but it's technically quite interesting.
With an ICE there are so many variables, parasitic losses from pumps and other attached items varying with RPM, changes in friction and loading, lubricant properties, the engine mapping varying with RPM and throttle position. Theoretically (and from an pretty ignorant point of view on my part) I'd guess a pure EV should be much simpler to work this out on.
With an ICE there are so many variables, parasitic losses from pumps and other attached items varying with RPM, changes in friction and loading, lubricant properties, the engine mapping varying with RPM and throttle position. Theoretically (and from an pretty ignorant point of view on my part) I'd guess a pure EV should be much simpler to work this out on.
REALIST123 said:
“In an ICE car it's advised to get up to the target speed asap so that you can cruise and maintain a constant speed. But is this the same for EV's?“
It’s not even true for ICE cars.
Yes it is. Hypermilers in the US swear by a method of brisk (but not full) acceleration to above your target speed. You then feather the throttle so that you bleed speed slowly back down towards your target, whilst slowly increasing your foot pressure on the accelerator as the target nears.It’s not even true for ICE cars.
Assuming we are talking typical driving, ie at an average speed between say 30 and 50 mph, then all that really matters is what that average speed actually is, because for an EV, the most energy consumed is consumed pushing air out of the way (followed by drag from the tyres, and then loses in the powertrain, but those are waay lower in magnitude)
Absolute losses increase with load for an EV powertrain, because resistive loses increase with the square of current, so avoiding heavy acceleration will reduce the vehicles consumption, but those loses are of a decade lower magnitude than the basic road load (aero + rolling drag)
In reality, as long as you don't use the friction brakes, you can accel and decel at a decent rate without enormously increasing consumption. Regen braking can only return up to 70% of the energy used to accelerate the vehicles mass, so using regen IS less efficient compared to letting the vehicle coast to a halt (ie applying a "zero torque" accelerator input that is neither driving, nor retarding the vehicle), but way better than using the friction brakes to stop (0% efficient!)
In the real world however, where even the best intentioned economy driver will struggle to plan far enough forwards to always be able to coast to a halt (ie a traffic light changes to red in front of you) then using regen to stop at least recovers most of the kinetic energy in the vehicles mass.
Because an EV has a powertrain that is directly linked to the vehicles speed, unlike for an ICE where just idling the engine around uses a significant amount of power, and because the powertrain efficiency is pretty much always high, (unlike an ICE that has significantly better thermal efficiency as load increases) the concept of "coast and burn" is less useful.
It's also worth remembering just how efficient an EV powertrain actually is. For example, a really really terrible electric motor might be 'just' 92% efficient. So say a vehicle with that motor could manage 92 miles of range, even if we swapped the motor out for an impossible 100% efficient one, the car would now onlyy manage a further 8 miles of range.....
Far more important that trying to get every last percentage point of efficiency are the optimisation of auxiliary consumers (heating etc) and ensuring that the vehicle has the lowest possible road load (lowest drag). Even a 'big battery' Tesla with a 'huge' 100 kWH of energy stored in its battery is only actually carrying the equivalent of 10.6 litres (2.3 UK gallons) of gasoline. (My little battery i3, has the equivalent of 1.9 litres of gas on board, and driven carefully it can do 100 miles on that!)
Absolute losses increase with load for an EV powertrain, because resistive loses increase with the square of current, so avoiding heavy acceleration will reduce the vehicles consumption, but those loses are of a decade lower magnitude than the basic road load (aero + rolling drag)
In reality, as long as you don't use the friction brakes, you can accel and decel at a decent rate without enormously increasing consumption. Regen braking can only return up to 70% of the energy used to accelerate the vehicles mass, so using regen IS less efficient compared to letting the vehicle coast to a halt (ie applying a "zero torque" accelerator input that is neither driving, nor retarding the vehicle), but way better than using the friction brakes to stop (0% efficient!)
In the real world however, where even the best intentioned economy driver will struggle to plan far enough forwards to always be able to coast to a halt (ie a traffic light changes to red in front of you) then using regen to stop at least recovers most of the kinetic energy in the vehicles mass.
Because an EV has a powertrain that is directly linked to the vehicles speed, unlike for an ICE where just idling the engine around uses a significant amount of power, and because the powertrain efficiency is pretty much always high, (unlike an ICE that has significantly better thermal efficiency as load increases) the concept of "coast and burn" is less useful.
It's also worth remembering just how efficient an EV powertrain actually is. For example, a really really terrible electric motor might be 'just' 92% efficient. So say a vehicle with that motor could manage 92 miles of range, even if we swapped the motor out for an impossible 100% efficient one, the car would now onlyy manage a further 8 miles of range.....
Far more important that trying to get every last percentage point of efficiency are the optimisation of auxiliary consumers (heating etc) and ensuring that the vehicle has the lowest possible road load (lowest drag). Even a 'big battery' Tesla with a 'huge' 100 kWH of energy stored in its battery is only actually carrying the equivalent of 10.6 litres (2.3 UK gallons) of gasoline. (My little battery i3, has the equivalent of 1.9 litres of gas on board, and driven carefully it can do 100 miles on that!)
Edited by anonymous-user on Sunday 7th April 13:38
EV battery packs also loss more efficiency the harder you discharge. Slow progressive acceleration to a steady speed is the easiest way to achieve 'offical' rated range on EVs.
As for pure energy efficiency, this still from a Jaguar iPace video sums it up. Yet there are still people who think hydrogen is a better source of passengers vehicle energy
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As for pure energy efficiency, this still from a Jaguar iPace video sums it up. Yet there are still people who think hydrogen is a better source of passengers vehicle energy
.Durzel said:
Fascinating insight, thanks
+1Very interesting, thanks Max.
To be honest, I didn't buy an 's' to drive in eco
but have found from some very loose experiments that the biggest factor is ventilation. If I switch that off I can achieve virtually the same economy (up to 5 mi/kWh) without the penalty of terrible accelerator response.Heres Johnny said:
SOL111 said:
There's an element of truth in it given an engine operates at max efficiency further up the rev range. Eco mode tends to labour an engine at the lowest rev..
They’ve obviously named Eco mode badly if you think it’s doing the oppositePersonally I can't stand a laden pedal and from personal experience, manage to achieve close to published economy figures by driving how I like. IMHO the biggest factors are obviously not thrashing the pants off a car but anticipation and maintaining a steady speed. Taking an aeon to achieve the target speed always seemed nonsense.
I read somewhere that electric motors were at their most efficient at 75% of rated power but am not sure if this applies to EV's. If true then it makes no sense to labour an EV when, as Max_Torque has suggested, the biggest factors are drag, rolling resistance and auxiliaries.
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