You may have noticed automakers offering an extra boost of performance to owners of electric vehicles. Mercedes, Tesla, Polestar, and others are all doing it over the air. Another 68 horsepower for just $1,195 may sound tempting in your new Polestar 2, but how does it work?
EVs are not like internal combustion cars that are effectively hardware-limited to a certain amount of output in stock form. By changing a few settings in the inverter of an EV, it’s possible to unlock more power without any bolt-ons, albeit with limits.
Electric drivetrains revolve around voltage and current—the latter is expressed as amps. Current in an electric motor translates directly into torque while voltage determines your motor speed. Increasing current for a given motor speed means more wattage (horsepower). It’s truly that simple. Voltage in a traction system remains relatively constant for a given state of charge, so altering the current is how electric cars get more or less power to the ground.
The safe limit for an electric drivetrain to sustain is called the continuous current rating. Current creates heat, but as long as that heat can be managed, it’s all gravy. Measure the heat and you can limit the current to safe levels. Nothing gets melted, there’s no loud popping, and no dashboards turn into Christmas trees.
Without proper cooling, failures inside a battery module like this BMW unit could be catastrophic.
More is often possible, though, and this is where burst current enters the picture. This is a level of amperage higher than the continuous rating that can be held for a limited amount of time before the temps get out of control. If you have a complex and capable liquid cooling system for the motor, battery, and inverter—as most EVs do—you can do this with some degree of freedom.
Assuming an automaker has tested the thermal limits associated with briefly increasing current and is confident they can be handled, you have your power-increasing over-the-air update ready to ship.
The true limit is really battery chemistry. Most automotive batteries can provide an immense amount of power in a burst. Just cross a wrench between the positive and negative leads in your own vehicle’s 12V battery to witness this (no actually don’t) however the drivetrain could be incapable of handling it in a plethora of key areas. A connector, contactor, or other component might fail under the stress.
Individual battery cells are capable of extreme currents in automobiles, but everything that carries the associated heat must be up to the job, too.
Finding the bottleneck isn’t straightforward for some automakers. Ford Mach-E GTs recently had serious issues because people were flooring it for too long. It seems like Ford wasn’t measuring heat in the right place and therefore its stated horsepower limit for the Mach-E was not actually sustainable. In other words, it was running too many amps. That was the first time I had ever seen a recall for something like that.
The potential for power-adding OTA updates is still huge, though. As technology advances, I would expect to see more of this going on. In the end, there’s really no reason not to do it if it can all be managed safely.
It may sound like a scam that OEMs aren’t giving you everything the car has out of the box, but it’s ultimately up to you to decide if a small gain in performance is worth further investment in the car. Personally, I’ll keep my cash unless a power upgrade comes with hardware improvements to things like the cooling system. There’s still no beating physical upgrades, as much as some car companies may want you to think otherwise.
Photo credit: BMW, Polestar
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- Source: https://www.motor1.com/news/702927/electric-vehicle-ota-power-boost/
