Do not understand how Alternator low voltage load increase MPG.
 

I understand if you disconnect the belt from the alternator you will get better mpg.

What I do not understand, is how does regulating the voltage required to keep your car running increase mpg?

I also can see replacing batteries would be a cost increase.

I've read about switching to LEDS and some newer cars that lower the amount of voltage drawn from the alternator if the car is not requiring the full amount of voltage.

I need schooling!

An after thought. What about running the alternator off one of the drive axels? It would not turn when at a stop, (battery support only) then when you drive the axles would turn the alternator.

A pulley could be machined, from the inside out, to the outer diameter of the drive axle and welded. You could hang the alternator off the body and you would not have to extend the wiring that far. Only issue is, you would have to detach your drive axle from the output flange on your transmission to change a belt.

Regards,

Ryan

I'll give this a shot, but anyone feel free to jump in and correct me if I'm wrong.
well, it's not really voltage that you're trying to decrease, the alternators output voltage should remain relatively constant, it's the amperage that you're trying to keep down. The way I understand it is that the more amperage that you are demanding from the alternator (or any generator for that matter) the more physical resistance that the alternator is presenting to the engine. So, the more amps you draw, the more HP required to turn the alternator. So the overall HP load of the alternator should (relatively) match the amperage load of your electrical system.

It's not quite like the other main parasitic accessory the a/c compressor. With a compressor it's either on or it's off. When it's off there's only a slight load due to the increase in turning the extra belt and clutch wheel. When it's on there's a lot of resistance because you're having to compress all that freon, which takes a lot of HP to do.

voltage isnt the measurment of power. wattage is. when you lower the running voltage you reduce the wattage load from most electrical devices.

runing an alternator off an axle wouldnt work because axles don't spin quick enough at slow speeds or even highway speeds to make an alternator charge. they have a certain minimum rpm as which they will charge. besides that, axles move up and down with suspension. there would be no way to keep a pulley installed on an axle inline with the alternator installed on the car.

running led's doesn't lower the ammount of voltage drawn from the electrical system, it lowers the ammount of amperes drawn. less amps couples with the same voltage means less wattage. again, wattage is how we determine load.

with that said, i think the gains from running at a reduced voltage is low. personally i don't like dim headlights and slow turning fans. i keep my system running at 14.5v.

You need to think outside the box a bit csrmel. I've seen a RWD driveshaft driven alternator work just fine. In this case, it was with an independent rear suspension, so the driveshaft did not move vertically. Likewise however, any transaxle that employs a carrier bearing and stub axle setup could easily do the same thing. In the case of the MR2, it would have to be driven off of the transaxle side of an inboard CV joint, but nonetheless, possible.

Alternator output must also be regulated to avoid overpowering whatever loads are connected - like a fully charged battery for instance.

Now I can't remember if this would be practical for anything but racing.
But you might check into some aluminum / high performance pulleys...?
They're not cheap thou, and reading up on it is fairly required.

As a general rule they weigh less, also in some cases they're a different diameter, the idea being that it reduces the accessory's rpm some.

As other have said, you want to lower the WATTS (power used) in your car, because virtually every electrical watt you draw is at the expense of putting a little more drag on the engine (and therefore a little more fuel used) to generate that extra (electrical) power. The thing you have to remember is alternators aren't simple on/off devices, they (like virtually all mechanical to electrical generators) are proportional devices (i.e. the more electrical power you draw, the more mechanical load you have on your mechanical source, in this case the gas engine). So the goal is to lower watts used.

Now: Watts (power) = amps (current) X volts (voltage)

Which means that there are two ways to lower total watts used. You can either lower the amps, or you can lower the voltage (or both). Most of us take the lowering of the amps approach. For example, using LEDs (which are more energy efficient), instead of normal car incandescent bulbs. Also turning off fans/etc when they aren't needed.

In theory you could also lower the voltage, but there are problems there. Remember, most of the car's electrical system is DESIGNED to run at 11.5 to 14.5 volts. So running at a lower voltage risks lights being too dim, problems with ignition, problems with charging the battery, etc. Lowering voltage could (in theory) save some power (watts), but in general it's likely to be more of a PITA than it's worth. And that's even more true, when you consider the power losses (inefficiency) that happens when you convert from one voltage to another using a simple circuit. i.e. if you lower the voltage in a car's electrical system without using a very fancy/decent circuit, you may actually lose more power (from the voltage lowering circuit) than you would gain by running on a lower voltage! So all things considered, I think playing with the voltage (in a car) is usually more trouble then it's worth.

However, lowering the current (by lowering the total watts of all electrical consumers in a car) can be worthwhile. And there are many practical ways to help with lowering total watts used. For example, I saved a lot of power by converting my normal car bulbs (not the headlights themselves, but most other car lights) to LED technology (which last for a very long time, and use a fraction as much electricity as the bulbs they replaced). And I've also got an adjustable radiator fan sensor, that is set to get noticeably hotter than stock (but still cool enough I don't think I'm significantly overheating my engine) before the radiator fan kicks on (thereby often saving the huge power of the radiator fans). And I generally avoid using the interior vent/heater fan, unless I really want the air blow (i.e. I don't leave it on all the time, like many drivers do), etc. And I'll only use my main headlights after dark when they are needed for seeing (and even then I avoid the extra power hungry "high beams", except when I actually need that extra light), and instead only use my (energy efficient LED) secondary lights if/when I just want other cars to be able to see me!

The point is, such electricity saving tricks can make a noticeable (if not huge) difference in FE, because using more electricity in a car really does translate into slightly more fuel used as well (as the electricity has to come from somewhere, and that "somewhere" is extra mechanical drag on the gas engine).

show me a drive shaft driven car alternator that works just fine.

In racing you change pulley sizes on the crank, waterpump. alternator to slow down the water pump to prevent cavitation at high rpms and lower the alternator draw at high rpms. Increases horsepower...usually run no fans except in 12 and 24 hour enduros for the same reason.

https://www.jalopyjournal.com/forum/s...ad.php?t=53403

https://www.pembleton.co.uk/bulletinb...d87f7db9c5b37c

https://forums.hybridz.org/showthread.php?t=88805

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.

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. :(

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.

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)

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!:confused:

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):thumbup:

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:D

Fasteners too!

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.

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!

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!

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.

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.

kozaz,

I wouldn't go installing a higher output alternator in an effort to save fuel. Unless you need it to run a bunch of upgraded electrical items.

My understanding is, the alt's amp rating is it's maximum output. Measured at some particular rpm of course, but I don't know precisely. From my experience, alt output seems to reach it's max at something like 1.5 x the idle speed. Designed that way because if it's say, an 80A alt, and you NEED 80 amps, they can't build it so you have to get up to 6K rpm to get those 80 amps. You need them at 2K rpm just like you would at 6K. At idle the output can presumably be allowed to drop a bit (??) because the car won't spend much time at idle.

Anyway, the actual load the alt places on the engine at any given time
[which is what determines how much fuel need it's creating]
is mostly proportional to the actual electrical load the alt is "serving". That is, computer + injectors + ignition + fans + lights etc.

I'm sure that an alt with greater capacity, such as a 140A vs. 80A, will have a larger base mechanical load that's always present (which would hurt you if you install it). Because it will be heaver, and so will probably need more mechanical energy just to keep it spinning even if there would be zero electrical load on it. (That's where the mechanical load on engine isn't exactly proportional to the electrical load on the alt)

Of course if you've put in upgraded electrical everything plus a "bouncer" hydraulic suspension just for show and need to power all that stuff - then that's another story. But you probably wouldn't do those mods you' if you're trying to get better fuel economy.

I kind of like the idea of using a Sterling engine to drive the alternator.
The Sterling would re-use the waste heat from the engine and cause little loss of efficiency. The numbers seem to work too for a normal car.

For example: 15 hp is used for driving the car forwards which means about 45 hp is wasted as heat. If we could suck up 25% of this for the Sterling engine (11,25 hp) and we managed 20% efficiency (very realistic), we still get 2.25 hp to drive the alternator, which seems about right.

I saw a reference to a system like this somewhere but it was for big trucks.

With some optimizations, the total efficiency would be much better and we would get an electrical surplus. With a hybrid system (like Hondas' IMA) we could use the power to offload the combustion engine even more.
The biggest practical problem is the availability of high output, low weight, Sterling engines. There really aren't any smaller ones above 1000W on the market :( It will also be much easier to experiment with this kind of system in a boat than a car due to space constraints and legal matters...

No kidding. Using the copious amounts of automobile waste energy has been the goal of 1000's of tinkerers and dreamers. Significant wasted energy includes brake energy, coolant heat, and exhaust heat. So far the only waste energy that automakers have been able to recover on a commercial (i.e. economically viable) vehicle is brake energy, i.e. in hybrids.

Aside from cost, another trouble with stirling engines is weight. A simple (non-pressurized) stirling engine capable of ~2 kW weighs hundreds of pounds.

Turbos would perhaps count as being powered by waste energy.
Putting a turbine in the exhaust stream and connecting the output to the crankshaft also works. This principle was used on at least one aircraft engine (WWII?). I also saw some reference to something that looked like this on a current truck engine. They used both a turbo and another turbine for crank augmentation. For the aircraft engine, I saw a figure of 8% improvement in power if I remember correctly.
Sorry for running off-topic...

Turbo to crankshaft - slick!
You'd have to gear it down like crazy I think - the rest of it is just a matter of finding places to route the belts etc.

Maybe this needs a new thread?

"turbocompounding" has been around a loooong time; i don't know why it isn't in more widespread use. :confused:

Same d**n reason that all our cars are set up for "performance" instead of safety, fuel economy and reliability. :mad:

https://www.greencarcongress.com/2005...veloping_.html

BMW puts a steam engine in the exhaust system and reclaims 80% of the exhaust heat. This yields 14 hp on a 1.8 liter 4 cyl engine.