Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

[oil pan 4]

Originally Posted by Frank Lee

F.Y.I. I've seen a credible analysis that says vehicle-generated electricity costs 4x what household electricity does... car probably costs 5x what it does at the outlets in my house!

You are right on. With a good diesel generator setup it costs 4 to 5 times more to generate power than to buy it from the power company. Gasoline generated power costs even more.

[Tesla]

Originally Posted by Frank Lee

F.Y.I. I've seen a credible analysis that says vehicle-generated electricity costs 4x what household electricity does... I saw the figures he used to do that calc; my electricity is much cheaper so the electricity I use in my car probably costs 5x what it does at the outlets in my house!

I would say that this point is debatable, esspecially when you add the conversion from household electricity to battery, that would add another loss.
If the study was done assuming ideal load conditions, then household electricity is probably far cheaper, but add low load, no load and peak load conditions into the mix and the story may be different.
What is the cost measure? If I run my vehicle on renewable fuel that I produce then that would be free.
How was the comparison done, electricity in a vehicle is only a minor part of vehicle cost.
There is a big movement towards decentralised electricity production in the sustainable building area, where electricity generation is incorporated into building design using gas or diesel as fuel supply, these are large commercial & residential buildings.
So maybe the National grids aren't as efficient as we may think.

[mikehallbackhoe]

I don't like the idea of not having 14 volts for the ignition. what about running two systems? Run the ignition with the alternator, using a motorcycle battery, and a larger pulley on the alternator. run the rest of the car with a deep cycle battery. even if you completely drained the deep cycle battery the car would continue to run. the larger pulley on the motorcycle ,just running the ignition system, would take less fuel to run than the alternator with a regular pulley.

[Nerys]

what does the ignition care if its 13.8 or 12.8 volts ? theses cars take CRAZY little power ESPECIALLY the ignition.

My first day with the car the alternator slowly died and I did not realize it. I noticed the head lights getting dimmer and dimmer. odd.

the battery was so dead when I turned it off to try and figure out what was wrong it would barely even CLICK when I tried to restart it. did not even try to crank.

I figured it was that dead so stopped on an incline pop the clutch got it started.

I almost made it home then a cop saw me turning the headlights on and off. on when other cars nearby off when not.

eventually I could only accelerate with lights off and just barely. too much gas and it sputtered for lack of power.

I never knew a car could run on so little power :-) amazing little critters.

I would leave the pulleys in place. and simply reattach the belt if I ran low on power (such as needing headlights and blower for an extended period of time)

the ignition is the least of my concerns. the only 3 things that really take power in this car are the starter - blower on high - headlights.

and even the starter is likely the lowest power one of the lot :-)

plus with dual deep cycle batteries I will see far less voltage drop and far greater efficiency from the batteries.

[MetroMPG]

Does the alternator even care what size pulley is on it? Won't it just strengthen the field current to compensate for reduced RPM?

If that's the case, except at very low alternator RPM, I don't believe there's anything to be saved by underdriving the alternator.

[mikehallbackhoe]

I may be wrong but I assumed if the alternator turned slower, it would put out less power. if that is the case, the ignition system probably doesn't use much electricity. would the alternator use much energy just charging just the ignition ? if that is the case, you might not need the larger pulley. the plus side would be you could drive as far as you want without losing spark.

[Frank Lee]

Underdriving the alt = less losses from the alt fan; also bigger pulley = less belt hysteresis; but most of all, like engines, there is a max efficiency range of rpm and load for alternators and it's 2000-2500 rpms and about 40% of rated output. Alternators are normally spinning 2-3x faster than that at cruise.

[brucepick]

Originally Posted by MetroMPG

... If that's the case, except at very low alternator RPM, I don't believe there's anything to be saved by underdriving the alternator.

I think that's right, as far as the electrical aspect goes. Mechanically, I think that with the engine spinning the alt at lower rpms, the alt's purely mechanical load on the engine would be reduced by whatever percentage you reduce the alt's drive ratio. I'm talking about bearings, belt friction, that stuff. Those are the engine loads you can't remove by only disconnecting the alt electrically, you can get rid of that load by removing the belt or likely reduce it by underdriving the alt.

Likely the alt's max amps output would be reduced at the lower spin speed. If you have a 70A alternator and you ask it to deliver only 30-40A, it will deliver them just like before. You might not get the full 70A if you ever "ask" for it (cabin fan, headlights, and kicka$$ stereo all running at max). With an underdrive or with stock drive pulley, output is reduced near idle speed rpms; you can see that on a voltmeter at idle.

If you're hypermiling you're likely already working to reduce electrical system load; you probably won't need the max limit of what the stock alternator was able to do. Until your uncle rides with you and expects the full luxury treatment.

[Mario_Marques]

One important question, does your alternator has clutch assisted pulley?
Do you have hidrailic assisted steering?
Thanks.

[Nerys]

I was wondering exactly that for a different reason.

I was wondering what it would take to replace the crank pully with a AC CLUTCH pulley.

this way I could simply turn it off and leave the belt etc.. intact and with the flip of a switch engage the clutch and engage the stock pump and alternator.

is that possible? how might I go about that?