The best way to drain an EV? Just spank it
Never mind whacking up the heating – here's how to properly zap some electrons There’s one part of the process we currently go through when benchmarking a new car for a road test that, while necessary, isn’t formally part of it at all. And yet it’s very often one of the more revealing things we do, although I’m not sure how to regularise it or, for that matter, if we can practically take meaningful test data from it at all. Inevitably, it’s something specific to electric cars, the test procedures for which it feels like the duty of this generation of road testers to coin and assimilate. Our performance benchmarking of EVs starts with a minimum 90% charge showing and, going via acceleration tests, braking tests, handling tests and everything else, typically concludes with between 45% and 65% SoC (that’s ‘state of charge’) left. At that point, two key performance tests remain: the measurement of ‘charge depleted’ acceleration at less than 10% SoC and DC rapid-charge testing, taken from a similar level. So what’s the quickest way to turn an EV with more than half of its charge still ‘in the tank’ into one running on ‘electron fumes’? Well, there’s probably a smarter, more technical solution (although I would be surprised if you could do it in a minute at the roadside), but if you’re an Autocar road tester, you follow your instincts and simply spank it. My preferred method is to use the Horiba MIRA proving ground’s ‘number one’ circuit. It’s four lanes wide, nearly three miles around and has three banked corners. In the outside lane, you can be cornering at 33deg from the horizontal, at a ‘neutral’ steering speed (the one at which the car would steer itself around the bend) of 86mph. Set the cruise control to 90mph, then, and just let about 30 to 45 minutes fly by the window: that will usually do it. What I tend to do, however, saves some time. It’s an abuse test, I suppose. Sitting in lane four, I go through the heart of each bend at about 90mph, then accelerate hard up to 130mph along each straight (or as close to that as I can get), braking hard enough at each straight’s end to shed most of the car’s speed using the friction brakes. This is not only a very efficient way of burning through charge but also must be about the most intensive thing you can do to a battery-electric powertrain, heating the battery up to such an extent as to sternly test its cooling. Nothing has caught fire yet. The good thing about travelling at 100mph in a big circle is that cool air is never hard to come by. In any case, most EVs will, at some point in the process, automatically cap motor output in order to bring the battery temperature down, and I’ve known one or two to enter a limp mode – or simply coast to a halt – until the heat subsides. Weirdly, very few will actually tell you why they’re struggling. The Mk1 Nissan Leaf (and indeed the Mk2) had an instrument showing its battery temperature, which would inexorably climb if you covered longer motorway journeys punctuated by rapid-charging stops. Not many current EVs bother to, however. And while very few will often be driven in the way of an Autocar road tester but once in their otherwise dull and uneventful lives, I still say the gauge would be worth having. The other thing worth having, if only for the likes of us, would be an ‘empty battery to 10% SoC immediately’ button. I mean, these days it wouldn’t be an actual button, sadly, and no owner in their right mind would want to press it anyway, either deliberately or by accident (in my mind, it’s definitely marked with the ‘A’ of the Autocar masthead). But I might press it, if short of time on a testing day – even if, once in a while, it meant missing out on 130mph in lane four.
Never mind whacking up the heating – here's how to properly zap some electrons
There’s one part of the process we currently go through when benchmarking a new car for a road test that, while necessary, isn’t formally part of it at all.
And yet it’s very often one of the more revealing things we do, although I’m not sure how to regularise it or, for that matter, if we can practically take meaningful test data from it at all.
Inevitably, it’s something specific to electric cars, the test procedures for which it feels like the duty of this generation of road testers to coin and assimilate.
Our performance benchmarking of EVs starts with a minimum 90% charge showing and, going via acceleration tests, braking tests, handling tests and everything else, typically concludes with between 45% and 65% SoC (that’s ‘state of charge’) left.
At that point, two key performance tests remain: the measurement of ‘charge depleted’ acceleration at less than 10% SoC and DC rapid-charge testing, taken from a similar level.
So what’s the quickest way to turn an EV with more than half of its charge still ‘in the tank’ into one running on ‘electron fumes’?
Well, there’s probably a smarter, more technical solution (although I would be surprised if you could do it in a minute at the roadside), but if you’re an Autocar road tester, you follow your instincts and simply spank it.
My preferred method is to use the Horiba MIRA proving ground’s ‘number one’ circuit. It’s four lanes wide, nearly three miles around and has three banked corners.
In the outside lane, you can be cornering at 33deg from the horizontal, at a ‘neutral’ steering speed (the one at which the car would steer itself around the bend) of 86mph.
Set the cruise control to 90mph, then, and just let about 30 to 45 minutes fly by the window: that will usually do it. What I tend to do, however, saves some time. It’s an abuse test, I suppose.
Sitting in lane four, I go through the heart of each bend at about 90mph, then accelerate hard up to 130mph along each straight (or as close to that as I can get), braking hard enough at each straight’s end to shed most of the car’s speed using the friction brakes.
This is not only a very efficient way of burning through charge but also must be about the most intensive thing you can do to a battery-electric powertrain, heating the battery up to such an extent as to sternly test its cooling. Nothing has caught fire yet.
The good thing about travelling at 100mph in a big circle is that cool air is never hard to come by.
In any case, most EVs will, at some point in the process, automatically cap motor output in order to bring the battery temperature down, and I’ve known one or two to enter a limp mode – or simply coast to a halt – until the heat subsides.
Weirdly, very few will actually tell you why they’re struggling. The Mk1 Nissan Leaf (and indeed the Mk2) had an instrument showing its battery temperature, which would inexorably climb if you covered longer motorway journeys punctuated by rapid-charging stops. Not many current EVs bother to, however.
And while very few will often be driven in the way of an Autocar road tester but once in their otherwise dull and uneventful lives, I still say the gauge would be worth having.
The other thing worth having, if only for the likes of us, would be an ‘empty battery to 10% SoC immediately’ button.
I mean, these days it wouldn’t be an actual button, sadly, and no owner in their right mind would want to press it anyway, either deliberately or by accident (in my mind, it’s definitely marked with the ‘A’ of the Autocar masthead).
But I might press it, if short of time on a testing day – even if, once in a while, it meant missing out on 130mph in lane four.
