please remember
not an alternator
but a "wind generator"
useded to turn wind into electricity.

I think a few of you have this confused.
In this case, the wind will be the EXHAUST flow.
On the models i have seen, they generate 8000watts, at 15mph of wind....

Now, im not sure how many RPMS it will be turning at 15mph, but it seems the turbo would spin a ton more. Which would most likely equal out to more power being generated.

Link to wind generator.

https://www.nrel.gov/wind/animation.html

Im wondering how many rpm, the exhaust turbine would flow at IDLE, and under 2500rpm....
This would be my operating range of engine RPM.
also,

the rpm issue could be fixed with the exhaust wheel. TO turn less rpm.

As a concept I think it will definitely have it's day. Especially when paired with a low disp, twincharged gasoline engine that drives like a diesel since a turbo doesn't use all the energy from the exhaust all the time, and a supercharger is needed for more air/power at low rpm. But... It just seems like something that's not practically doable for the DIY'er. I think getting a few deep-cycle batteries and a solar charger is the ticket to the same savings in mpg w/o all the hassle.

I think you also need to consider the rotating mass of the alternator versus the mass of the compressor side turbine of a turbocharger. I've rebuilt my turbo before and the impellers are relatively light. Not sure if the alternator would spool up worth a darn and would actually pose as an exhaust restriction (trying to accelerate the large mass of the armature) giving poor performance and efficiency. I would imagine you would build up alot of pressure in the exhaust manifold (a bad thing) causing the exhaust to actually back flow into the combustion chamber diluting the incoming air/fuel charge with less than desirable results. I think you would actually get worse FE. On a regular turbo setup it requires some power to actually run the turbo (nothing is free) but the performance gains significantly offset the slight loss. On your proposed setup you would just see the loss with no performance gain (perhaps a small efficiency gain). I doubt this small gain would overcome the effort required to get a heavy armature to spool up.

Just my 2 cents worth. I've driving turbo 4 cylinders since 1985 ....

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Another 2 cents worth. A turbo doesn't make boost unless there is a load on the engine (acceleration), when you're cruising along the impellers are just spinning and not creating boost. The only way you'd create enough exhaust energy to run an alternator would be under acceleration. You'd probably have to do alot of acceleration to keep your battery charged. Heck at cruising speeds you might not even have enough exhaust energy to spin the armature and all you'll have is a highly restrictive exhaust most of the time (an impeller spinning slower than the speed of the exhaust gases would be a restriction). I'm not trying to discourage some from trying this, but I don't the effort would be worth it personally.

Some people say it would spin too fast.
Some of you say it wouldnt spin enough to generate anything because of the friction.

I do not personally feel that restriction would cause exhaust to back up. Keep in mind these things are easily turned at 10mph. Ofcourse thats with a big enough fan blade to turn it.

But i think that with the right exhaust wheel, you could get the shaft to generate enough electricity at idle.

Here is a chart for wind generators and what they produce at each MPH.

https://www.greeleynet.com/~cmorrison/windcalc.html

I have the similar idea, and some problems to deal with. 3 years have passed, and I wanna know whether your idea has come true.:)

Maybe he has realised that the mass of air hitting a 20ft diameter wind turbine at 15mph is hugely greater than that in the 2" cross section of exhaust pipe...

Which is the same as thinking you can pour a cup of water off the top of your apartment building to generate the same power as a large hydroelectric power station, because it's the same "head".

However, there should be a significant amount of recoverable energy, just have to start with something reasonable sized and work the efficiencies upwards.

What if instead of connecting the shaft of the turbo directly to the input shaft of the generator, the turbo shaft was connected to a gear that drives a chain. That chain would drive a gear on the generator. This would allow the user to tune the gear ratio and it would also cause a mechanical separation to avoid heat soaking the generator. Perhaps a clever use of ducting could also aid in the cooling of the assembly. Further, the gear on the generator could have an electromagnetic clutch so that it cuts out below turbo efficiency thereby avoiding some of the ill effects of an exhaust restriction.

Of course, the exhaust restriction would still eat some efficiency out of the motor. So would pushing a turbo be better or worse than a belt driven alternator.... It's just a really fun puzzle to think about, and incredibly difficult to pull off.

That chain drive transmission system sounds heavy, complex, and lossy. I think, when it's all said and done, this idea is barking up the wrong tree...specifically, the "more out than in" tree.

Using exhaust heat might be a way to recover some energy that's being wasted.