Do not understand how Alternator low voltage load increase MPG.

[Danronian]

Originally Posted by theclencher

prolly like skirts- might show a difference over 10000m, but nothing short term

That's what I was thinking. Sometimes when I have the stereo up I think... "hmmmmm. Am I wasting more gas by doing this?" But I can't see how it could take that many more amps to power the stereo to full volume versus half volume. But I'd more be interested in the LED bulbs since they last longer (less waste) and are brighter than the OEM type. Something I'm always worrying about in my little VX next to all those HUGE SUVs out there.

[omgwtfbyobbq]

Originally Posted by Danronian

Has anyone done MPG experiments involving LED bulbs vs. regular. I wonder if there is a measurable difference, or any at all for that matter.

It depends on how gung-ho we can go and how we drive. Assuming we're good at not using the brakes, If our average speed is ~20mph it may significantly increase mileage. If we're at ~40mph, it'll increase mileage by about half of what it does at 20mph, and if we're at 80mph it'll hardly be noticeable. Assuming the car needs ~2,6,18kW at 20,40,80mph respectively, an alt runs at ~50% eff, and the average electrical load from the lights is 150W (based on this), we'll save ~300W of FF energy. So we may increase mileage by 8%,3%,1% at 20,40,80mph respectively. Similarly, an alt delete will see a greater increase in mileage w/ a more efficient driver.

[VetteOwner]

Originally Posted by Danronian

That's what I was thinking. Sometimes when I have the stereo up I think... "hmmmmm. Am I wasting more gas by doing this?" But I can't see how it could take that many more amps to power the stereo to full volume versus half volume. But I'd more be interested in the LED bulbs since they last longer (less waste) and are brighter than the OEM type. Something I'm always worrying about in my little VX next to all those HUGE SUVs out there.

yea thats what i liek about LED's. they last forever pretty much, dont get hot, alot brighter than OEM bulbs, light up quicker, might make you more visible. BUT you got the initial cost of em to factor in. id say a good estimate for just 2 brakelight led bulbs would cost $10-$15 for a pair(mayeb another $15 for multiple rear lights), $10-$15 for main front signals then add another $15-20 for all the little 194 side marker bulbs. your lookin at close to $50 for bulbs that you can get for less than $10 for all long life replacement bulbs. and how often do you break a brakelight bulb? or a turnsignal one? i think ive blown one maybe 2 in the 5 years ive had my truck...and who knows how long theyve lasted before that! so on a cost perspective, no it would take 20+ years for them to become cost effective... so thjier more of a novelty that anyhting id say...so if ya wanan do somehting that would help a bit and be safer. go ahead im not knockin them at all but if your just doing it thinking "ill never have to buy bulbs again" then maybe you should take another look....

now with the radio, yea volume doesnt change the total draw that much. (maybe 300mA at the most)

[VetteOwner]

Originally Posted by theclencher

hell i don't buy bulbs anyway, there's tons of em at the wrecking yard i frequent, they don't care about selling bulbs

haven't bought a bulb in YEARS

ohh you too? hehe yea i got enough for 50 years...same with fuses... i mean who the hell goes to a junkyard for fuses and lightbulbs!

[VetteOwner]

Originally Posted by theclencher

got a whole bucket full of em

haha same, go ta little box in the shelf thats labeled with the bulb number. (i have OODLES of 194 bulbs as they are used everywhere in my cars)

i snagged a few 12V relays (normal 1/4" spade connector kind, usuly find them on aftermarket stuff, foglights, alarm system) never have ta buy one of them...now if only i can find a scource for free 1/4" spade crimp on connectors ill be in heavn

[omgwtfbyobbq]

Originally Posted by theclencher

got a whole bucket full of em

Fasteners too!

[DracoFelis]

Originally Posted by Danronian

Has anyone done MPG experiments involving LED bulbs vs. regular.

Sorta.

Some of us have done LEDs and (anticdotally) noticed a difference in how fast the engine revs at idle when the lights are on (as well as a small difference in how far we can go on a tank of gas). However, we haven't done formal testing of that difference.

In addition, there was very active discussion/testing (in this forum) about the effect on FE of running without an alternator. This effect varied with car (some cars gaining more, and some less), but seemed to average a little over 10% better FE (at the cost of killing the batteries, but still 10%+ better FE). The reason this is significant, is that running without an alternator (i.e. ZERO electrical load on the engine) is the extreme "best case" of what you can get if/when you conserve electrical power in a car.

Originally Posted by Danronian

I wonder if there is a measurable difference, or any at all for that matter.

Oh it clearly makes a difference. How much difference will depend upon your car and your driving style.

However, a good way IMHO to estimate the difference is to compare your total before and after car watts (electrical load) to calculate what percentage (i.e. after_power / before_power) of power you are using after vs what you were using before. Because alternators are mostly linear in their behavior, you can then use that percentage number (above) to get a good idea as to what fraction of the "no alternator" gain you would get. i.e. In theory, the FE gains (of saving car electrical power) should be easily estimated by the following formula:

energy_savings_gains = no_alternator gains * (1 - (after_power / before_power))

i.e. roughly speaking, if you lowered your total car power usage 75%, than you should (in theory) get roughly 3/4 of the FE gains you would get if you went with no alternator at all.

NOTE: When calculating before and after power usage for the car, don't forget some of the "hidden" (but significant) power usages, such as the power to spark the spark plugs, and the power to run the radiator fan. And even the power to run the ECU (engine computer) can skew the numbers some.

Still "car lights" (even dash lights) can add up to a surprising large percentage of your total car electrical power in many cars (including my own). So changing those lights for energy efficient LEDs that take a small fraction as much power, can really make a (small but) noticeable difference in FE. And with the price of fuel these days, getting a few extra miles per tankful can really pay off at the pump!

[kozaz]

Originally Posted by Snax

In the case of the MR2, it would have to be driven off of the transaxle side of an inboard CV joint,

Bingo, the inboard CV Joint would not move up and down, but you would have to have clearance between it and the transmission to install a pulley.

I've also seen alternators driven by driveshafts on some motorcycle powered cars (buggies) with great results.

Thanks for the great info guys!

[dkjones96]

Why go through all that trouble? Especially for a driveshaft driven alternator.

At highway speeds you'll be in overdrive where the output shaft is spinning faster than the engine is. Like my car for example, 3,000rpm at 70mph, the overdrive gear is .78:1 making the drive shaft spin at 3846rpm. That's giving you a faster speed than the engine is running while also adding the load from the alternator and whatever extra weight your belts and pullies add. PLUS, you have more belt contact area that will cause more drag than if you left the alternator where it originally was.

Your alternator will pretty much be putting out full-charge all the time in town, especially if it's not running all the time as is the case in stop and go traffic, which will lead to premature failure more than likely due to overheating of the regulator. This will be more of an issue with people running electric cooling fans.

[kozaz]

Ok, so lets go the other way with this.

Would a higher output alternator increase gas milage? Petersons 4Wheeler or Offroad magazine (I can't remember which one) claimed this. But then again, if the truck were powering auxlliary lights and aftermarket stereo I could see where it would help.

I think my current alternator is an 80amp, but a 140amp is available.