Why is forced induction always mechanical?
 

The only popular forms of FI are superchargers and turbochargers. Why (besides some crappy bogus stuff on ebay) aren't there any electric compressors that run off the battery (or some other electrical supply)?

With an electric compressor you're not tied to engine RPM or exhust flow / turbine size. Also it doesn't put extra load on the engine (powering the super or reducing exhust flow).

If you're eating from the battery, then it'll cause the alternator to kick into overdrive, but there are other ways to get power (ie. charge battery over time with regeneritive brakeing / exhust turbine like a turbo, rather than alternator).

Seems to me that getting variable level of boost on demand (without the worry over overboost) would make an electric forced induction system popular... so why aren't there any? There must be an electric compressor out there that has enoguh airflow / pressure for the cost of a good turbo/super.

It's simply a matter of the power requirement to run an electric SC at anything like the boost you would need to compete with a turbo or SC . You would need either a huge alternator or a big ass battery (or both)- just not practical .
I do think there would be a place for an electric SC that can flow enough to boost low end to mid range torque on the Renesis - but it would do nothing at the top end which is where most of us want the extra.

I did a little more looking around at the electric super-charger scams (some im prepared for some flames)... and yes... they're shit... but i dont see why someone couldnt make a GOOD one.

It wouldnt work if you were constantly at full boost, but considering that you usually aren't... you store up energy in the battery gradually as you drive, and you use all that energy in bursts when you run the compressor.

you can assist the alternator with regeneritive breaking (or if you're worried because there probably aren't any performance brakes that have regen braking out there), put a small turbine in the exust, like a turbo, that generates electricity. That way you dont need some monster alternator. regeneritive breaking especially.

just curious, at sealevel with no boost, how much airflow does the renesis need?

There was a local company here in San Antonio that had a Electric Supercharged Civic and it was fairly fast but their kit was like $10,000 estimated and sort of unreliable and added a ton of weight to the car. It ended up being a one off thing and the idea failed. I tried to search for it right now could not find any info on it.

It's called NAAAWZ

Thats exactly what I was thinking as soon as I read the topic.

For electric boost they go from mechanical to electrical and back to mechanical...
It involves two losses so it can't match the efficiency of the direct mechanical link.
Maybe once we can directly move air using electricity we'll get a non mechanical FI... with no moving parts ;)
The big advantage of electric boost would be the decoupling of the boost pressure from the engine RPM...

Its all about the losses associated with converting energy. Both superchargers and turbos us energy already created by the engine to spin a turbine or blower. With an electric solution you would have to convert that energy to electricity, store it, then convert it back to a physical motion to turn a turbine. Everytime you convert it you lose energy and as such lose effeciency.

And then there is weight. To store that energy would require a battery(s). Also a supercharger uses a fair amount of HP to get turning. An electric motor capable of producing the 30-60hp needed to spin a gearbox and turbine would be heavy as hell!

I would like to see a hydraulically powered supercharger. Either have exhaust gas or an electric motor turn the hydraulic pump. Draw from a small reservoir of oil which supplies oil through oil lines that in turn power a small hydraulic motor that turns the compressor wheel. I think it would eliminate some packaging restraints. It's all a fluid power link. The only thing is hydraulic pumps don't like variable speed so an electric motor would be more conducive to turning the hydraulic pump unless you have the electric motor cut-out once a certain RPM is reached once appropriate exhaust pressure builds. But that might make an overly complex system as compared to a plain ol' turbo charger.

i dont know . its not necessarily less efficient. the electric assisted steering is more efficient than the regular power steering AND it saves weight.

This is true, you will lose energy that way.
However, if you're using regeneritive breaking... you're using energy that would have been lost anyways. And if you're using a turbine in the exhust, and it is variable geometry, you can make it spin at the most efficient speed, rather than the speed that will produce the most boost.

but the biggest thing is, you're building potential energy in the battery over time, to be used quickly in bursts. Sure, its a bit less efficient... but because you're using stored energy you're going to have more than enough. over-all you'll get worse gas milage, but the inefficiency isn't going to hurt performance (which is what matters here).

I didn't realize it took so much. I find it hard to believe that a turbocharger can generate 30-60HP to run a compressor, but i guess it could happen.

You're right, it would be heavy... but people who run nitrous don't seem to mind a big-ass tank in their car, so i didn't think it'd make that much of a diff. I don't think it'd be hundreds of pounds worth of heavy.

Too bad no one picked up the last two sentences...

running an alternator needed to power such a device would be just as parasitic as a supercharger

Remember, You need energy to create energy!

Like i've said before. the alternator is constantly generating energy to recharge the battery. You aren't constantly at full boost. You store energy over time, and then use it in bursts with the compressor.

You aren't running the compressor directly off the alternator.

Sure, in the grand scheme, you lose a bit of gas milage... but since when do people who mod for power really care about that?
With an electric compressor, you'll get boost that isn't tied to exhust flow, turbo size or engine RMP, and you'll get it immediatly, whenever you want.

is this really not do-able? I can't believe that an electric engine couldn't drive a turbo's compressor. How much power does it take to drive one of em, and how much airflow does the renesis need?

There are good electrical superchargers out there. The Thomas Knight company is one of them. The best way to find them is to google and look for the review articles. There are just too many of the bogus ebay type ones out there.

you have to take into effect the bigger (read: more parasitic) alternator you will have to run and you will run more of it, you would be suprised how much more amps you would be pulling with an electric compressor

its not like turbos or superchargers are always at full boost either, most super kits have a bypass while the engine is in vacuum.

say you want to turn on your compressor at low rpm's for a kick in the pants, you are going to drain your battery and overstress your alternator at low engine speeds, so you would need a bigger one. Im not sure you understand the limits of electrical storage and how much stress your stock alternator is under with just your headlights, a/c, and stereo on.

is it doable? absolutely, is it going to work like you want it to? kinda. will it give mechanical FI a run for its money? in your dreams

the problem with electric compressors(legitimate ones) is that you cant generally run them for more than a few seconds at a time. Essentially you'll spend 2-3 times the money to end up with the same result as a much cheaper and less intrusive NOS setup

Would that be much of a problem, given what you say just after?


As you drive, you store energy in your battery, using the alternator (or regeneritive breaking / other means). Then you boost when you need it. it sucks out part of your battery... but you're not doing full boost for long.

You're not powering the compressor directly from the alternator, so the alternator doesn't have to be powerful enoguh to run the compressor.

Pair it up with regeneritive breaking (which is powerful and has the added benefit never locking your breaks), and i think you'd probably take much of the load off the alternator. Not that i've ever heard of regen braking kits for cars lol.

of course, there are variable geometry turbos that also reduce lag and are better across a wide RPM range, but those dont seem popular either. Or atleast aren't advertized as such. but thats a whole other topic :p

It would make the RX-8 sound like 2 hairdryer instead of 1.

wrong, that is exactly what you are doing. It is not two separate systems, the battery and alternator are linked at all times. as soon as you start drawing juice from the battery the alternator kicks in to replace what you are taking, and I just dont think you realize the size of a battery and alternator that you would need. you can only crank the rx-8 engine over about 15-20 seconds before your battery is gone, how many seconds you think you can spin your compressor with that little juice? especially at the speeds you need to make positive boost. using brakes to charge your battery can top a system off, but you wont be using the brakes and compressor at the same time, and short of a huge, heavy, expensive battery, you will drain your 12v before you can go through 2 gears

the main argument I am boiling down to here is that the alternator you would need to run, would suck up more horsepower at a constant speed, than any benefit you would get from on demand FI; however it seems to me that you refuse to listen to anyone on this board trying to describe logic in automotive and electrical engineering, and are more interested in arguing any point with the same old sentence about store power in a battery and use brakes to charge it.

What's in a (user)name?

you need at least something around 50kw just to run a supercharger. do you think your small battery and alternator can do that? can you imagine how thick the wire is gonna be just to handle 30kw at 12V? 2500 freaking amps, you need metal rods to handle that current. :bowdown::bowdown:

You'd have to be running the system at hundreds of volts to be practical

I think one of the biggest problems that hasn't been addressed is the rechargeability of the battery. You can't just keep dumping in charge and pulling it back out as that'll massively shorten the lifespan of the battery. You'd need a special kind of battery (meaning expensive) to deal with memory issues and to hold enough charge. Perhaps a bank of the Tesla or Tango ones?

That said, if an electric-driven supercharger could be made to work, it would be pretty neat, as you could easily switch the blower on and off at your leisure. Picture your RX-8 whirring down the road when some schmuck in a 350Z or Mustang tries to race you. You reach up, flip a switch Speed Racer-style, and leave him eating your dust.