Alternator driven behind transmission.(Separate thread)

[dwtaylorpdx]

So the premise is that if you drive the alternator from the axle instead of on the engine and if you put a switching circuit on the accelerator pedal to control when the alt charge to only happen off throttle, you might save energy. Maybe add a circuit to the brake lights to trigger full charge when braking to maximize the use of the parasitic nature of the alternator.

You can buy rear drive axle mounts from Jegs and Summit as well as other stock car sources. They use the pinion seal bolts and a strut to the rear cover bolts to mount them. Easily built as well.

A pulley could be sandwiched behind the CV on a FWD car, and a simple steel mount from the transmission bolts and any other convenient spot. A mitsubishi forklift alternator strikes me as the best option, they are tiny, relatively inexpensive and light weight and produce about 45 amps.
If you were really lucky you could install a fwd alternator backwards and it might be close enough to use some spacers to line it up with the drive axle cv at the transmission end...

This method works especially well on a race car where the engine is revving beyond what alternators really like to turn. (Like 7500+) But the speed increase it allows down a straightaway is measurable. Which implies a savings in power lost to the alternator thats pretty impressive.

Dave

[RobertSmalls]

An axle-driven alternator is perfect for some types of racing, because you want any power-sapping accessories off during acceleration, and they can turn back on after you're up to speed.

It's less perfect for ecodriving. The dealbreaker for me is that the alternator would be on during EOC, which would slow you down faster, and thus reduce the number of engine-off opportunities during your trip. There's also the fact that your alternator would be spinning at 12000 RPM on the interstate, potentially for hours on end. I bet it takes substantial power just to turn an alternator that fast.

I really like the idea of intelligent alternator on/off. There may be clever ways to set up a simple circuit to automatically turn the alternator off and on at the right time. I suppose you could monitor throttle position, EGR operation, voltage, or other parameters. However, the most intelligent control would come from a toggle switch mounted next to a voltmeter on the dashboard. ;-)

[dwtaylorpdx]

? Ok maybe I'm doing the math wrong, but the axle spins about 1/3 to 1/4 the speed of the engine. Assuming a engine rpm of 2500 at cruise that would put the axle RPM at about 1000 rpm. The engine pulley is about 4 in in diameter and the alt pulley is about 2 so the alt spins 2x the engine rpm so that 5000 at cruise. So we are spinning the alt 20% of the rpm it normally turns.

Your right it would be some load at EOC, but I'm thinking there has to be a simple way to disengage the alt when coasting, Maybe use a maf sensor and a solid state relay to cut the power from the alt? Hmm.

Dave

[Frank Lee]

You have to do different math between FWD and RWD cuz the FWD axle you tap into is after the diff and the RWD is before.

[shovel]

I really believe that beyond turning the magnetic field on and off within the alternator, there's really not much to gain here at all. I'm not trying to be negative, all ideas deserve some consideration. I just think the old saying "nothing's ever been so simple that some fool couldn't make it more complicated" applies here. Engage and disengage the alternator's field coil - or better yet build an arduino project that regulates the field coil's strength in conjunction with the alternator's regulator... and you've got all the gains you're reasonably going to get.

Then dedicate the rest of your creative energy to aero and weight loss.

[extragoode]

I agree that this isn't as complicated as it's being made out to be. My ideas on this last time it was talked about were 1) put relay inline with brake light circuit so the alternator only energizes during braking, just like real regen braking. 2) put another relay in electrical system that energizes the alternator when the system voltage drops to a certain level, like 11 volts. I still think this is all that needs to be done. This way you're only charging if you're braking, so you're wasting that momentum (energy) anyway, or when you're on the highway cruising, since you haven't been braking enough to keep the voltage up.

[metroschultz]

I have seen one car where the owner regulates the alternator with a continuous duty solenoid.
Solenoid in circuit with the battery charge cable.
Solenoid off = no drag from the alt.
Solenoid on = drag from alt.
Works for him, he sees 5% gain in FE from alternator-less driving.
I will see of I can find the thread he started,

[rgathright]

Originally Posted by metroschultz

I have seen one car where the owner regulates the alternator with a continuous duty solenoid.
Solenoid in circuit with the battery charge cable.
Solenoid off = no drag from the alt.
Solenoid on = drag from alt.
Works for him, he sees 5% gain in FE from alternator-less driving.
I will see of I can find the thread he started,

I agree with your statements.

Rather than putting an alternator on your driveshaft, take the more direct route of removing the alternator completely. Put a Group 31 Gel Cel in your trunk or truck bed. I got a range of 150+ miles out of 2006 Jeep TJ I-6 from this modification and saw an increase in MPG as well.

Turning an alternator on and off while spinning puts a tremendous strain on the diodes inside the alternator and will "pop" them quickly.

[dwtaylorpdx]

The main reason I was talking about this mod is that on a race car, this one mod makes a easily measurable difference at high RPM, so the assumption is that it somehow lowers engine load without actually modifying the alternator system other than location, if a car goes faster the easy assumption is its less parasitic at the lower RPM but would still charge the alternator. Removing the alternator is not an option on many cars. But reducing its use still is. You can protect the diodes with caps, not that hard.

Of course it simply may not pay off at the lower rpms on the street. May make way more sense to just increase the alternator pulley size to slow it down./

Dave

[dwtaylorpdx]

Originally Posted by Frank Lee

You have to do different math between FWD and RWD cuz the FWD axle you tap into is after the diff and the RWD is before.

True, it would turn slower. Likely only charge at 30MPH or something..?

Hmm.

Dave