Hypothetical alternator question out of curiosity

Okay this is just an idea that popped in my head and it's probably not even doable.. but I was thinking of possible ideas to improve MPG and a while ago I read about how some honda 1 liter engines were getting up to 70mpg with the alternator disconected, and then I got an idea.

What if you were to take the alternator out of the engine, and then fit in a turbo, and basically use the hot side turbine to drive an ultra low torque brushless motor to create a current to charge the battery? A brushless motor could theoretically take 100,000+ rpm's right? The only problem is would it actually be doable to create enough current from it? Being burshless makes it have much less friction, and turbo's spin really fast, but the other problem is on idle, the power would drop but I don't know how much, or how doable it is. I do know that this wouldn't be an air restriction at all though, and if the motor is brushless, it will be effortless to spin, and won't overheat from 100,000 RPM if it's made well enough. Also, the bearing would be embedded in the wall of the output elbow much like a rivet would be if possible.

Problems include:

- Tolerance for the shaft would be so minimal that even a few thousands of an inch off can make the assembly pretty much explode apart
- I don't know how much current a good brushless motor would output if you drive it at say, 50,000 RPM or how much watts/amps it would provide
-I don't know how fast a turbo spools at idle vs spooling under engine load, or if it's even fast enough to be viable for this at idle.



This is a retarded diagram I made on my phone while thinking about it. The idea is probably retarded, but I thought it couldn't hurt getting input from people smarter than I am, so maybe something good will come out of it, I dunno but I'm not expecting this idea to be looked upon well. Mostly the reason I'm asking on this forum is because I have less conflict with anyone here than any forum Iv'e ever posted on <3

Interesting idea. There's only one flaw in the logic: a brush-less motor might seem like a zero friction device, and if the motor isn't powering anything, it is, but generating current through magnetic flux requires additional physical force (torque). The higher the current demand, the more torque is needed to turn the alternator.

If you were to connect an alternator to a stationary bike, you would be able to pedal very easily, until current was demanded. Then you would notice the pedaling effort would increase drastically. This makes sense when you consider that applying current to a motor results in the rotation of the armature - often with great levels of torque. Cyclists notice this when hub generators are installed on their bikes. Pedaling becomes more difficult when accessories are switched on.

A turbocharger is an efficient compressor, but does not produce any free energy, and it does not make an engine run more efficiently (no improved MPG). The only thing a turbo does is allow more fuel to be added to the combustion process, making more power and using more fuel. Powering the alternator from the turbo would in fact act as a restriction, because of the magnetic load, which would probably consume just as much fuel as a belt driven unit. And as you mentioned, performance at idle might be compromised. Turbos need to spool up to make any real torque.

Another issue would be how to store the intensely dynamic power spikes created by the constantly varying RPM of the turbo. There would need to be a special system consisting of extra batteries able to accept the charging demand. Otherwise, the current generated during high RPM throttle would be wasted, much like a blow-off valve discards the extra boost after a shift. One way would be to use a KERS type recovery system, but these are expensive, and they require a flywheel of a certain mass to be effective. Turbos and mass tend to not get along, so not sure this would work (lag city). A KERS system would probably work better in a crank-driven application, but wouldn't be needed since the crank's torque is much less dynamic compared to a turbo.

AA wrote:

Interesting idea. There's only one flaw in the logic: a brush-less motor might seem like a zero friction device, and if the motor isn't powering anything, it is, but generating current through magnetic flux requires additional physical force (torque). The higher the current demand, the more torque is needed to turn the alternator.

If you were to connect an alternator to a stationary bike, you would be able to pedal very easily, until current was demanded. Then you would notice the pedaling effort would increase drastically. This makes sense when you consider that applying current to a motor results in the rotation of the armature - often with great levels of torque. Cyclists notice this when hub generators are installed on their bikes. Pedaling becomes more difficult when accessories are switched on.

A turbocharger is an efficient compressor, but does not produce any free energy, and it does not make an engine run more efficiently (no improved MPG). The only thing a turbo does is allow more fuel to be added to the combustion process, making more power and using more fuel. Powering the alternator from the turbo would in fact act as a restriction, because of the magnetic load, which would probably consume just as much fuel as a belt driven unit. And as you mentioned, performance at idle might be compromised. Turbos need to spool up to make any real torque.

Another issue would be how to store the intensely dynamic power spikes created by the constantly varying RPM of the turbo. There would need to be a special system consisting of extra batteries able to accept the charging demand. Otherwise, the current generated during high RPM throttle would be wasted, much like a blow-off valve discards the extra boost after a shift. One way would be to use a KERS type recovery system, but these are expensive, and they require a flywheel of a certain mass to be effective. Turbos and mass tend to not get along, so not sure this would work (lag city). A KERS system would probably work better in a crank-driven application, but wouldn't be needed since the crank's torque is much less dynamic compared to a turbo.

I didn't have high expectations for the idea, but I didn't know an electric motor running as a generator needed increased torque for more amps drawn.

This means that theoretically, you have a 400 watt subwoofer RMS putting out a 60Hz sine wave setup hooked up from a DC amplifier, that it would be harder to spin the electric motor than not hooked up to it in theory because of the current draw resists the magnetic force?

Yes. The change in load might not occur immediately, because the battery will supply the current for a time, but at some point the battery needs to recharge, so the torque required to turn the alternator gradually increases, until the battery is back up to 100%. If the power drain continued indefinitely, the alternator would be required to constantly charge the battery, and would need more torque from the engine to sustain it.

In the 1L Honda engine, the torque needed to turn the alternator is a larger portion of overall engine output, so disconnecting it would make a real difference, compared to our larger 3.8L, where the needed torque is relatively small. But disconnecting the alternator isn't sustainable, so really it isn't a valid way to save fuel. The battery will need to charge again somehow. Reconnecting the alternator to a low battery presents a higher than normal load, requiring extra torque from the engine (more gas). By plugging in to the AC grid, the energy can be transferred from a lower cost source. This is the basic premise behind plug-in hybrids like the Nissan LEAF.

Men have been searching for self-perpetuating machines for thousands of years, but unfortunately they don't exist. Gasoline is an incredibly convenient and efficient way to store energy. It's about the closest thing we have to free power. The problem is, we're running out of petroleum, and the cost keeps going up. Electric powered vehicles are starting to look more and more appealing. We'll use our existing power grid for a while longer, then wind and solar will be used more and more. Someday, I think solar will provide 100% of our power needs. Then we'll finally have our magic machines that create endless amounts power on their own.

AA wrote:

Yes. The change in load might not occur immediately, because the battery will supply the current for a time, but at some point the battery needs to recharge, so the torque required to turn the alternator gradually increases, until the battery is back up to 100%. If the power drain continued indefinitely, the alternator would be required to constantly charge the battery, and would need more torque from the engine to sustain it.

In the 1L Honda engine, the torque needed to turn the alternator is a larger portion of overall engine output, so disconnecting it would make a real difference, compared to our larger 3.8L, where the needed torque is relatively small. But disconnecting the alternator isn't sustainable, so really it isn't a valid way to save fuel. The battery will need to charge again somehow. Reconnecting the alternator to a low battery presents a higher than normal load, requiring extra torque from the engine (more gas). By plugging in to the AC grid, the energy can be transferred from a lower cost source. This is the basic premise behind plug-in hybrids like the Nissan LEAF.

Men have been searching for self-perpetuating machines for thousands of years, but unfortunately they don't exist. Gasoline is an incredibly convenient and efficient way to store energy. It's about the closest thing we have to free power. The problem is, we're running out of petroleum, and the cost keeps going up. Electric powered vehicles are starting to look more and more appealing. We'll use our existing power grid for a while longer, then wind and solar will be used more and more. Someday, I think solar will provide 100% of our power needs. Then we'll finally have our magic machines that create endless amounts power on their own.

Glad I learned something today

Definitely not messing with the alternator knowing that load increases torque required to drive the generator because that just creates an exhaust restriction via the hot side turbine blade resistance.

And electric motors are cool, but somehow, it doesn't seem like it will ever be as cool as the good old smallblock making tons of power (even though I have a v6 :/ )

And only the future knows what holds our power source :o

Maybe if we ever figure out how to use dark matter, it might be viable, but until then, nuclear is very efficient at the price of security risks. We could also use frozen methane stored in the ocean floor.

It's kind of crazy to think that we can gain power from the process of two atoms fusing, using the lost mass of the two hydrogen atoms that gets converted into gamma radiation which takes thousands of years to redistribute through the layers of the star itself, and then the wavelength simply stretches out by either losing it's energy, or possibly dark energy which makes space itself expand (not really sure on that) resulting in x-rays, UV light, visible light, IR and heat, and radio/ microwaves once it gets stretched even more, then once it reaches us eventually, we create devices to turn that energy into electrical currents to be stored. And that's all because a bunch of hydrogen first formed from particals that weren't atoms yet, then gravity condensed it, superheated it with friction, then birthed stars from the heat which created new elements, exploded, made us and new stars. That really goes to show that you can't really destroy matter

hey corey, I think that your idea is actually already being used in formula 1 cars as part of their energy regeneration. so im pretty sure IT WORKS!

Yes, the new formula cars use ERS (energy recovery sys) in addition to KERS (kinetic recovery sys). The system couples a shaft from the turbo to the alternator, while remaining a conventional boost generator for the ICE. It's not a perpetual motion machine, but it does recapture some of the wasted energy that would otherwise end up as heat and sound.

So yes, I guess Corey's idea really has some merit and is being implemented. I completely forgot about this thread!