I don’t understand EV performance! Engineers?
Discussion
Further to the Audi etron S and AC Cobra not a Cobra electric....
Why do some EVs do 0-60 in milliseconds- some in many seconds and very different top speeds yet with similar (in the ball park BHP figures or power to weight figures)
Is BHP even relevant to EVs? They don’t seem comparable/predictable to traditional ICE cars.
It used to be you would see a car- take a Golf R, 300 BHP, 1.4 tonnes, 4wd and you would know that’s 4.5 ish to 60 and 155 limited- job done.
EVs seem so variable so who can explain this to a simpleton like me?!
Why do some EVs do 0-60 in milliseconds- some in many seconds and very different top speeds yet with similar (in the ball park BHP figures or power to weight figures)
Is BHP even relevant to EVs? They don’t seem comparable/predictable to traditional ICE cars.
It used to be you would see a car- take a Golf R, 300 BHP, 1.4 tonnes, 4wd and you would know that’s 4.5 ish to 60 and 155 limited- job done.
EVs seem so variable so who can explain this to a simpleton like me?!
whp1983 said:
Further to the Audi etron S and AC Cobra not a Cobra electric....
Why do some EVs do 0-60 in milliseconds- some in many seconds and very different top speeds yet with similar (in the ball park BHP figures or power to weight figures)
Is BHP even relevant to EVs? They don’t seem comparable/predictable to traditional ICE cars.
It used to be you would see a car- take a Golf R, 300 BHP, 1.4 tonnes, 4wd and you would know that’s 4.5 ish to 60 and 155 limited- job done.
EVs seem so variable so who can explain this to a simpleton like me?!
Are you serious lol? some have more powerful batteries than others for range/performance you just convert kw to bhp?Why do some EVs do 0-60 in milliseconds- some in many seconds and very different top speeds yet with similar (in the ball park BHP figures or power to weight figures)
Is BHP even relevant to EVs? They don’t seem comparable/predictable to traditional ICE cars.
It used to be you would see a car- take a Golf R, 300 BHP, 1.4 tonnes, 4wd and you would know that’s 4.5 ish to 60 and 155 limited- job done.
EVs seem so variable so who can explain this to a simpleton like me?!
The battery pack is of huge significance as well as the motors.
Like a traditional car starting battery - only rated at 12v but the relevant bit is the cold cranking amps - try starting a car with a tiny 12v lead-acid battery.
Similarly an EV with a 300kwh+ battery pack can not only run the vehicle for longer but can also give a great wallop (technical term) of current when needed for acceleration.
That is one of the issues - a larger pack is needed not only for range but also for performance.
Like a traditional car starting battery - only rated at 12v but the relevant bit is the cold cranking amps - try starting a car with a tiny 12v lead-acid battery.
Similarly an EV with a 300kwh+ battery pack can not only run the vehicle for longer but can also give a great wallop (technical term) of current when needed for acceleration.
That is one of the issues - a larger pack is needed not only for range but also for performance.
Yeah, the point he's making is that these numbers don't add up;
Pistonheads said:
Using a traditional layout comprised of a ladder frame and composite body panels, the electric Cobra’s architecture has been adapted to accommodate its batteries and an electric motor. It produces 308hp and 369lb ft of torque, with half of that twist permanently available, enabling a 0-62mph time of 6.7 seconds and a range of about 150 miles. Those are respectable numbers for a zero-emission vehicle. Although thanks to the hardware, the EV Cobra weighs 1,250kg - about 200kg heavier than its V8 predecessor.
https://www.pistonheads.com/gassing/topic.asp?h=0&f=&t=1877663Interested in seeing examples of other EV's where you believe the numbers don't add up OP. Seems to be an issue with a single untested car made in a shed somewhere rather than something that requires further understanding?
For some of the most popular EV's
BMW i3 120ah - 170bhp - 1450kg - 0-60 7.5 seconds (117 bhp/tonne)
Audi E-Tron 55 - 405bhp - 2550kg - 0-60 5.7 seconds (159 bhp/tonne)
Jaguar iPace - 400bhp - 2150kg - 0-60 4.2 seconds (186 bhp/tonne)
Tesla Model 3 Performance - 490bhp - 1750kg - 0-60 3.2 seconds (280 bhp/tonne)
Tesla Model S Performance - 750bhp - 2250kg - 0-60 2.4 seconds (333 bhp/tonne)
Seems to all make sense?
For some of the most popular EV's
BMW i3 120ah - 170bhp - 1450kg - 0-60 7.5 seconds (117 bhp/tonne)
Audi E-Tron 55 - 405bhp - 2550kg - 0-60 5.7 seconds (159 bhp/tonne)
Jaguar iPace - 400bhp - 2150kg - 0-60 4.2 seconds (186 bhp/tonne)
Tesla Model 3 Performance - 490bhp - 1750kg - 0-60 3.2 seconds (280 bhp/tonne)
Tesla Model S Performance - 750bhp - 2250kg - 0-60 2.4 seconds (333 bhp/tonne)
Seems to all make sense?
Edited by SWoll on Wednesday 1st July 20:31
The first point of call for an "aftermarket" EV is if they motor, inverter and battery actually make the claimed power. Unlike the OE's they don't have to do any kind of certification test (eMachines get a peak (30sec) and continuous (30 min) rating when homologated for passenger car use in the EU.
Most of the time, the installer has just taken the claimed nameplate power for the motor (which is often as iffy as the claimed name plate power for an after market tuned ICE....) and said, "thats what this car makes". In reality, the installed performance may be far lower, the inverter (or battery) may not be able to deliver enough current at a high enough voltage to make the power the motor is capable of (in ideal bench top conditions) and the thermal performance is probably very poor, so after a bit of use the motor/inverter/battery overheats and pulls the power back.
And then of course, we need to talk about gearing and the road speed at which the powertrain can reach peak power, and how wide is the CPSR of the motor, ie how long can it hold on to, or close too, peak power for in terms of road speed.
Most of the time, the installer has just taken the claimed nameplate power for the motor (which is often as iffy as the claimed name plate power for an after market tuned ICE....) and said, "thats what this car makes". In reality, the installed performance may be far lower, the inverter (or battery) may not be able to deliver enough current at a high enough voltage to make the power the motor is capable of (in ideal bench top conditions) and the thermal performance is probably very poor, so after a bit of use the motor/inverter/battery overheats and pulls the power back.
And then of course, we need to talk about gearing and the road speed at which the powertrain can reach peak power, and how wide is the CPSR of the motor, ie how long can it hold on to, or close too, peak power for in terms of road speed.
It is a funny one, looking at tractive effort/gearing curves vs EV motor torques is the biggest clue why they are so fast, EV Motors make full torque at (nearly) zero rpm, ICE engines dont, coupled with gould traction control resolution keeping wheels from slipping its very easy to get a perfect launch from an EV
The variation comes with gearing - you can gear short for acceleration but loose out on efficiency at higher speeds, and cost management in the batterya nd power electronics dictating how much of the motor torque you can use reliably
And like ICE cars the motors are capable of making peak power, but only with a warm battery and cold inverter, once these overheat you derate. Your also limited on performance by the sizing of these. You could think of the battery as fuel tank/injectors so as well as capacity it has a flow rate and doesnt work well at extremes of temp, and the inverter as inter-cooler so manages the flow of power, bigger inverter more power more of the time
The variation comes with gearing - you can gear short for acceleration but loose out on efficiency at higher speeds, and cost management in the batterya nd power electronics dictating how much of the motor torque you can use reliably
And like ICE cars the motors are capable of making peak power, but only with a warm battery and cold inverter, once these overheat you derate. Your also limited on performance by the sizing of these. You could think of the battery as fuel tank/injectors so as well as capacity it has a flow rate and doesnt work well at extremes of temp, and the inverter as inter-cooler so manages the flow of power, bigger inverter more power more of the time
Gassing Station | EV and Alternative Fuels | Top of Page | What's New | My Stuff