The concepts of turbocharging and supercharging are well-known to anyone who loves cramming things into other things, which, of course, is all of us. Recently, conventional turbos and superchargers have been joined by electric versions of both. So, what are these electric versions, exactly, and how do they work?
Before we get into these, let’s just refresh ourselves with how superchargers and turbochargers work. Fundamentally, what they’re both doing is increasing the density of the air/fuel mixture that goes into an engine’s cylinder to be compressed and ignited. The higher the density of fuel/air, the more power from the ignition stroke, and the more power from the engine, even without increasing the physical volume of the cylinders.
That’s why a smaller engine with a turbo can make more power than a larger engine: it’s getting more out of every power stroke. The way this increased density is achieved is via compressing the intake air with some sort of compressor. If this compressor is powered by a belt driven from the engine, it’s a supercharger. If it’s driven by a turbine spun by exhaust gases, it’s a turbocharger.
The downsides of a turbocharger are that it takes a bit for the engine to produce enough exhuast gases to spin the turbo up to a workable level, an irritating pause known as turbo lag. A supercharger doesn’t have such a lag, but spinning the supercharger does put drag on the rest of the engine and takes a pretty significant toll on engine efficiency.
So, if assume that adding the ‘electric’ part to both of these systems is to help get rid of these downsides, then you’d be right.
There’s actually three mechanisms I want to discuss: electric supercharging, electric turbocharging, and bullshit internet scam electric supercharging.
Let’s get the bullshit electric supercharging out of the way, first. If you look on sites like eBay for ‘electric superchargers’ or ‘electric turbochargers,’ you’ll see crap like this.
That’s not a way to easily get more power from your lowered PT Cruiser, it’s a way to connect a useless bilge pump or computer cooling fan to your intake for absolutely no advantage whatsoever. All things like this, that use your car’s existing 12V electrical system to spin a ‘compressor’ are bullshit.
All they will do is put a bit more draw on your alternator to spin a useless fan that in no way has enough power to compress shit. In fact, you probably lose a little bit of power with these thanks to restricted air intake flow.
Don’t be fooled.
Now, there are real electric superchargers, and are conceptually the same as both a normal supercharger and, I suppose, the imagined way the bullshit electric superchargers are supposed to work. They still will be spinning a compressor to increase the density of air that goes into the intake, but instead of being driven by a power-sucking belt off the engine, are driven by an electric motor.
This electric motor isn’t the rinkified-dinkified 12V ones you find on eBay, but rather usually requires a 48V system. Compressing air takes an awful lot of energy, and that’s what’s made electric systems so difficult to develop.
Most batteries and conventional car electric systems simply can’t provide the volume of needed power quick enough to drive an electric supercharger. That’s why electric superchargers tend to use large supercapacitors, which can store energy and then output a lot of electrical energy very rapidly. These capacitors can also be recharged via electric and hybrid car-established methods like regenerative braking.
In fact, Mazda already uses a supercapacitor system in their i-eLoop mild hybrid system, which, while not an electric supercharger, is still a large capacitor that’s currently in production and being sold in cars, which hopefully suggests that this technology is close to migrating from the racing world to the street.
Electric turbochargers are confusing to differentiate from electric superchargers, because, really, they’re not so much electric turbochargers as they are smaller electric superchargers combined with a conventional, exhaust-driven turbocharger.
That’s because by definition a turbocharger is driven from exhaust gas; ‘electric turbocharger,’ while a commonly-used term, doesn’t really make any sense.
Essentially, an electric turbocharger’s whole point is to eliminate turbo lag and assist a normal turbocharger until engine speeds reach a point where a turbo is most efficient. To do this, an electric supercharger (which may be housed in the same unit as the turbocharger, or possibly as a separate unit driving the same impeller) is used to spin up the compressor at start and through the lower revs, and when the exhaust volume is enough, pass the work over to the turbocharger.
It’s more like an electric-assist turbo, really. The result of this hybrid system is that there’s no turbo lag, and the power benefits of turbo’d engines can be enjoyed at all engine speeds. The power requirements for the electrically-driven part of the system are less than those of having just an electric supercharger, and, since a turbo running at its ideal point is effectively capturing energy from waste gases that would be lost, the whole setup is even more efficient than electric supercharging.
So, to recap, an electric supercharger is a supercharger driven by an electric motor, from a (usually) 48V supercapacitor-based source, and electric turbocharger is an electric supercharger working in conjunction with a turbo, and an electric supercharger you find on eBay for $50 is a hunk of shit you just stuck on your engine for no good reason.
Got it? Great.