Good Q&A regarding Electric Superchargers
03-07-2005, 06:28 PM
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Good Q&A regarding Electric Superchargers
Volts and amps to horsepower
I have long thought an "electric supercharger" would be a great invention for cars. The existing solutions to pressurize incoming air (as I understand them) are below. The REASON to add air is that if you add more air you can add more fuel, which gives a bigger explosion and more horsepower.
1. Ram Air - uses a hood scoop, etc. to channel more air into the engine at speed.
2. Turbo Charger - uses exhaust pressure to spin a turbine which sucks more air into the engine.
3. "Traditional" Supercharger - belt driven by engine to spin an impeller which sucks more air into the engine.
All of these require various complicated things such as intricate plumbing - exhaust header, mounting kits, intercoolers, etc. Also known as "LOTS OF MONEY". A turbo kit for my car can run $US5,000 and more.
Why can't we just stick an electric motor inline with the air intake and call it a day? I remember reading that when cars go to a higher voltage base (than 12 volts) this will be possible. Why not today?
Well, that's what eSuperchargers.com say they can teach you to do!
Michael
Answer:
The electric supercharger is not actually a very exciting invention.
There's no laws-of-physics reason why a forced induction device has to be spun by exhaust gas pressure or a belt from the engine. An electric blower certainly can do the same job as a turbo or belt-drive pump.
The problem is getting enough pressure. The people selling cheap electric superchargers - and there are plenty of them - like to talk about the amazing air flow statistics of their ferocious blowers, but they fail to note that the static pressure capability of those blowers is not nearly as impressive. Let the blower fly around on the end of its cable, or just use it to ventilate your house, and it will indeed shift enough air that you'd think it'd have a fighting chance of doing the job of a supercharger. Actually connect it to an engine, and its flow will plummet. Merely hooking up a fan-based blower that can shift 600 cubic feet per minute (when hanging in space) to an engine that natively inhales, say, 300cfm of air, will definitely not give you one atmosphere of boost.
Forced induction for engines is, by definition, not happening at atmospheric pressure; you want boost, more air being crammed in there than you could get just from a big tube leading to the outside world. Electric blowers don't come anywhere near delivering enough compression power to make a difference to the operation of normal engines, unless the electric motor involved is so inspiringly humungous that it's got similar power performance to a real supercharger or turbocharger - and, then, it can be argued that you might as well have a real supercharger, running directly from the engine via a belt, rather than an electric motor running from the alternator which in turn is running from the engine. There's no way for that electromechanical train to be more efficient than a humble belt.
Most cheap "electric turbos" or "electric superchargers" are actually bilge ventilating fans for boats (they're meant to be preventing dangerous fuel vapour buildup belowdecks), possibly with impressive jet-engine-ish decorations, generally sold at a monstrous markup. The suspiciously cheap eSuperchargers.com proposition is different; they're charging people $US14.95 for the privilege of being told to buy a bilge fan.
The most popular electric supercharger is the eRam. It seems to actually be good for a few per cent more power on many cars ( like this one). But the eRam costs $US300, plus installation time. There are lots of other tweaks you can get for that kind of money. The difference from the eRam is small enough that your engine computer ought not to need any tweaking to deal with it - which is good, but which also indicates firmly that there's not much actually going on. Un-modified ECUs don't work right when you add a proper forced induction device to an engine, because they don't expect to see air coming in at higher than atmospheric pressure.
A more impressive system is Thomas Knight's ESC Electric Supercharger. It's got three big-___ motors driving a conventional Roots blower, and the claims made for it seem plausible enough, though I've little idea how well it really works.
The contraindications for the ESC are considerable, and such that the manufacturer doesn't recommend you buy one if you can get a regular somethingcharger kit for your car. The ESC costs thousands of dollars (around the same price as a regular turbo or even supercharger kit; it's just easier to install), it requires the installation of some extra batteries (which aren't included in the price; you may also need a high-output alternator to recharge them), and it makes a very loud noise (which you may or may not view as a drawback).
You also can't use the ESC all the time, because it drains its batteries much faster than any alternator can charge them. It's more like electric nitrous (or a switchable "Mad Max" supercharger) than like a conventional always-on supercharger. And, unlike regular whatever-chargers, the ESC doesn't run faster when the engine does; its speed is fixed, so it delivers respectable boost at low RPM but fades as you rev higher, because the engine then needs more air per second for the same boost, but is getting the same amount from the ESC.
The new 42 volt automotive electrical standard will indeed make it easier to make an electric supercharger work, because the multi-kilowatt motors required will no longer need to draw (such) horrendous currents through (such) giant cables. 12 kilowatts (an unremarkable small mechanical supercharger power consumption rating) at 12 volts is a thousand amps; you need a cable an inch thick to pass that continuously, though you can get away with mere third-inch 0 or 1 AWG cable for low duty cycle applications. A 42 volt supply would drop the current draw to a mere 286 amps. But the motors will still be big and beefy, and the other electro-charger problems will still apply.
Note that the Thomas Knight systems already run from at least 24 volts
I have long thought an "electric supercharger" would be a great invention for cars. The existing solutions to pressurize incoming air (as I understand them) are below. The REASON to add air is that if you add more air you can add more fuel, which gives a bigger explosion and more horsepower.
1. Ram Air - uses a hood scoop, etc. to channel more air into the engine at speed.
2. Turbo Charger - uses exhaust pressure to spin a turbine which sucks more air into the engine.
3. "Traditional" Supercharger - belt driven by engine to spin an impeller which sucks more air into the engine.
All of these require various complicated things such as intricate plumbing - exhaust header, mounting kits, intercoolers, etc. Also known as "LOTS OF MONEY". A turbo kit for my car can run $US5,000 and more.
Why can't we just stick an electric motor inline with the air intake and call it a day? I remember reading that when cars go to a higher voltage base (than 12 volts) this will be possible. Why not today?
Well, that's what eSuperchargers.com say they can teach you to do!
Michael
Answer:
The electric supercharger is not actually a very exciting invention.
There's no laws-of-physics reason why a forced induction device has to be spun by exhaust gas pressure or a belt from the engine. An electric blower certainly can do the same job as a turbo or belt-drive pump.
The problem is getting enough pressure. The people selling cheap electric superchargers - and there are plenty of them - like to talk about the amazing air flow statistics of their ferocious blowers, but they fail to note that the static pressure capability of those blowers is not nearly as impressive. Let the blower fly around on the end of its cable, or just use it to ventilate your house, and it will indeed shift enough air that you'd think it'd have a fighting chance of doing the job of a supercharger. Actually connect it to an engine, and its flow will plummet. Merely hooking up a fan-based blower that can shift 600 cubic feet per minute (when hanging in space) to an engine that natively inhales, say, 300cfm of air, will definitely not give you one atmosphere of boost.
Forced induction for engines is, by definition, not happening at atmospheric pressure; you want boost, more air being crammed in there than you could get just from a big tube leading to the outside world. Electric blowers don't come anywhere near delivering enough compression power to make a difference to the operation of normal engines, unless the electric motor involved is so inspiringly humungous that it's got similar power performance to a real supercharger or turbocharger - and, then, it can be argued that you might as well have a real supercharger, running directly from the engine via a belt, rather than an electric motor running from the alternator which in turn is running from the engine. There's no way for that electromechanical train to be more efficient than a humble belt.
Most cheap "electric turbos" or "electric superchargers" are actually bilge ventilating fans for boats (they're meant to be preventing dangerous fuel vapour buildup belowdecks), possibly with impressive jet-engine-ish decorations, generally sold at a monstrous markup. The suspiciously cheap eSuperchargers.com proposition is different; they're charging people $US14.95 for the privilege of being told to buy a bilge fan.
The most popular electric supercharger is the eRam. It seems to actually be good for a few per cent more power on many cars ( like this one). But the eRam costs $US300, plus installation time. There are lots of other tweaks you can get for that kind of money. The difference from the eRam is small enough that your engine computer ought not to need any tweaking to deal with it - which is good, but which also indicates firmly that there's not much actually going on. Un-modified ECUs don't work right when you add a proper forced induction device to an engine, because they don't expect to see air coming in at higher than atmospheric pressure.
A more impressive system is Thomas Knight's ESC Electric Supercharger. It's got three big-___ motors driving a conventional Roots blower, and the claims made for it seem plausible enough, though I've little idea how well it really works.
The contraindications for the ESC are considerable, and such that the manufacturer doesn't recommend you buy one if you can get a regular somethingcharger kit for your car. The ESC costs thousands of dollars (around the same price as a regular turbo or even supercharger kit; it's just easier to install), it requires the installation of some extra batteries (which aren't included in the price; you may also need a high-output alternator to recharge them), and it makes a very loud noise (which you may or may not view as a drawback).
You also can't use the ESC all the time, because it drains its batteries much faster than any alternator can charge them. It's more like electric nitrous (or a switchable "Mad Max" supercharger) than like a conventional always-on supercharger. And, unlike regular whatever-chargers, the ESC doesn't run faster when the engine does; its speed is fixed, so it delivers respectable boost at low RPM but fades as you rev higher, because the engine then needs more air per second for the same boost, but is getting the same amount from the ESC.
The new 42 volt automotive electrical standard will indeed make it easier to make an electric supercharger work, because the multi-kilowatt motors required will no longer need to draw (such) horrendous currents through (such) giant cables. 12 kilowatts (an unremarkable small mechanical supercharger power consumption rating) at 12 volts is a thousand amps; you need a cable an inch thick to pass that continuously, though you can get away with mere third-inch 0 or 1 AWG cable for low duty cycle applications. A 42 volt supply would drop the current draw to a mere 286 amps. But the motors will still be big and beefy, and the other electro-charger problems will still apply.
Note that the Thomas Knight systems already run from at least 24 volts
03-07-2005, 06:36 PM
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Hey, no **** images on this site 
03-07-2005, 06:53 PM
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