Alternator Mods

[Unklecueball]

Hey there,

I am really loving the site, btw! Some really great info on here and everyone seems to be pretty cool.

My question is on alternators. I am reading about the drag it puts on the engine, people wating to upgrade to LED lighting, installing cut off switches and deep cell batteries, etc. Now I am a mechanical novice when it comes to autos. I understand the basics of how things work but I am by no means an expert. I know that the alt pulls power from the engine just like the AC does when it kicks on. Does the alt drag more on the engine with each extra amp it produces? If so, if you could turn it off and let it "free wheel" any guess as to what the increase in FE would be?

[BITBY]

I've been lurking here for a little while, but just registered and this is my first post.

Alternators don't operate like A/C compressors do. An A/C compressor has a clutch bearing, which when disengaged (no A/C) spins freely without resistance...that being said, removing the accessory belt on engines where the water pump is not a crank-driven accessory is somewhat common in drag racing for that very reason; less resistance on the engine.

If you so desire to bypass the alternator for brief periods, keep in mind its the alternators job to maintain current charge in the battery while powering the vehicle's electrical system; taking it out of the equation leaves the battery, and any fuel savings you may experience may be trumped by a much shorter battery life.

[SVOboy]

There is more drag based on how much it's putting out, but the main thing, I think, is just that it's always there, which is why a lot of people disconnect it.

[Shawn D.]

Originally Posted by BITBY

... any fuel savings you may experience may be trumped by a much shorter battery life.

... and reduced FE. It used to be common to run without an alternator in certain racing circles, but it was found that the reduction in ignition efficiency (~14V from the alternator vs. 12.6 from a fully-charged battery) actually hurt power. Thus, I'm dubious that disconnecting the alternator is a good idea.

[elhigh]

I'm getting ready to pull my engine fan to switch to an electric fan; it'll drag more on the alternator but I'm certain that I'll land on the positive side of that equation. Switching out lights, when and if that ever happens, will make up some of the deficit - not much, rarely driving in the dark.

Hear's a thought, though: I've considered switching my alternator out to a high-output version, which I know would probably add drag to the engine regardless of whether I add loads, but then switch to underdrive pulleys to slow it down. My main goal here isn't reducing drag as much as reducing noise. There isn't a lot of noise insulation in my old stripper truck, and that little fan doing its thing has to be making a fair amount of racket. Slow it down and the noise gets lower. Any opinions?

This is all blue-sky of course, those alternators are couple hundred bucks and I'm not Daddy Warbucks.

[ebacherville]

the energy efficiency from a electric fan is its only doing any work when its needed.. even a good clutch fan is always adding some drag to the system..

truly if you can drive with no alternator or mod it to run only in situations where power is truly wasted, i think you'll get gains from it.

[AnDoireman]

Are there low resistance alternators on the market at all? Although I'm sure if there are, they'd be rather mainstream in the eco modding communities.

[jamesqf]

Originally Posted by elhigh

Hear's a thought, though: I've considered switching my alternator out to a high-output version, which I know would probably add drag to the engine regardless of whether I add loads...

Actually, it shouldn't add much load, if any. When the alternator isn't producing energy, you just have friction losses from the belt & bearings. That's going to be pretty much the same with a high-output version.

As for finding one, scan the junkyards for old cop cars.

[1GCRXHF]

The "friction" in the alternator actually charging is the magnetic resistance the active circuit is supplying. The resistance is the current voltage the battery sitting at in the circuit. Generators (like your alternator) and electric motors are the same thing, the difference is the polarity of the circuit. If you hook up your alternator straight to your battery it will run; The engine has to overcome this force in order for the alternator to charge the battery, because it actually has to spin the alternator the OTHER way, in order put the battery in a charging state. I think the only way you could get less resistance from the alternator running would be to go with a low amperage unit. Adding a larger output alternator would be the exact same as installing a larger electric motor for your engine to fight. If you did your wiring right and went minimalist on your electrical goodies, you could easily get away doing this. Take a good look at anything that uses electricity in your car, and remember that every single milliwatt you is energy derived from your gasoline. Use less power, use less gasoline.

[getnpsi]

cop cars actually have smaller pullies that increase the output at idle. the upgraded cop package of the 80s on fords became the mainstram parts in the 90s as ecus, nice radios, power windows etc used more juice and became more "standard equipment."

to see a real gain you either need to use the smallest alternator you can get away with, OR use a high power alternator that only runs when you are decellerating. i dont know how to take one apart (and get it back together) to put a switch to turn off the field. there is a thread about it and from what i see is they just remove the darn thing and run a bunch of deep cell batteries. If someone is a rebuilder they can probably do it. id pay a guy to put some sort of switch on there to operate it by choice.

[AnDoireman]

Does the prius use an alternator along with its regenerative brakes? I assume it does... but does it do so in an efficient or interesting way if so?

[jamesqf]

Don't know about the Prius specifically, but the Insight does get all its electrical power from the motor/generator. It charges the 144 volt main battery, then a DC/DC convertor shifts some down to 12 volts (actually around 13.6, to keep the small 12 volt battery charged) to run the standard electrical accessories.

[Kaneda]

ive asked similar questions for my crx project... ive been looking at the aviation world... there are a few companies that offer 35-45 amp alts.(some higher) that weigh in at 4-6lbs thats shaving some 10lbs off my honda alt... and only losing 20amps output... but im also going minimal on my electronics... my massive stereo system will include: an ipod and plug speakers... since im running a "lighter" alt the 6lb battery i found will work perfectly for the system also

[TomT]

Running the engine just off the battery will shorten the battery life.

Draining down the battery and then periodically turning on the alternator to recharge it might shorten the life of the alternator. (A new ACDelco alternator for Unklecueball's '06 Aveo is $390 per RockAuto.com)

Modern cars like the Aveo already use the smallest, lightest, lowest output alternator possible.

Turning off major electrical accessories when stopped at a light would increase gas mileage because the engine would not have to automatically speed up to avoid stalling. But turning off headlights at night might be risky!

[gascort]

Like others have said, reducing accessories reduces the magnetic field and thus resistance within the alternator, raising FE. My friend had a HUGE (like 2000W) stereo in his car; when he turned his amp on, it was like a "slowness switch".
FYI - a car's electrical system (necessary stuff like ecm, ignition, sensors) is typically somewhere around 300-400W without lights, radio, etc. Newer cars are more than older cars I'm sure.

Noone's mentioned using a deep cycle battery and a plug-in charger. This is what I'm planning on doing; running a kill switch on my car and when I'm commuting 15 miles to and from work, running on straight battery when I can. The alternator sees no extra duty and the deep-cycle battery is made to be discharged and recharged with minimal sulfation. Electrical power is more efficiently produced in a power plant than in your car, and with current prices, it's way cheaper too!

[Katmandu]

Originally Posted by 1GCRXHF

Take a good look at anything that uses electricity in your car, and remember that every single milliwatt you is energy derived from your gasoline. Use less power, use less gasoline.

Come on now. Get a grip. You guys are "SPLITTING HAIRS" worrying about alternator drag and it's effects on MPG.

These alternators are so small to begin with that they do enough just keeping your battery charged.

If you're willing to risk a DEAD battery (out in the middle of nowhere) for the sake of increasing MPGs. Knock yourself out.

Medication for OCD is cheaper than AAA and a new battery. Just think of all the time/energy/$$ you'll spend just to save (1) MPG.

[gascort]

Originally Posted by Katmandu

Medication for OCD is cheaper than AAA and a new battery. Just think of all the time/energy/$$ you'll spend just to save (1) MPG.

Time/Energy shouldn't count - this is a hobby for most of us, probably including you!
That said, the $$ aspect of this is very important to many of us, and it's what will allow us to spread the word on Ecomodding.

I'm personally on a pretty tight budget. All the mods on my car have to be cost effective if I'm going to do them. I'm willing to invest money if it is likely to pay itself off in ~6 months at $5/gal fuel. Most of my mods so far are with free stuff I got, stuff I found in the trash, or things I had lying around. Time invested is my only cost, and it's fun!

[Gregte]

Saving a few 'milliwatts' of power is ridiculous. It takes a whole 746 watts to equal 1 horsepower. A few thousandths of an HP is not worth considering. Just slowing down a fraction of a MPH will gain you much more.

Also, a higher output alternator should not put any more load on your motor. The post earlier that said that an alternator will operate like a motor and turn against your gasoline engine is incorrect. Therefore it is also incorrect to assume that a high output alternator will be more of a load (backwards turning resistance) on your engine. A high output alternator will only be more of a load than a standard output alternator IF or when your car's electrical system is demanding the extra output.

I think there is more misinformation floating around in the field of electrical circuitry than any other part of auto mechanics. I also think that it is in part due to the incredibly poor wiring diagrams that are in many automotive service manuals. They are often only good for identifying wire colors to the various components. They are very poor at depicting an actual circuit as such and this I believe contributes greatly to the misunderstanding of what a circuit is and how electricity works. Anyway, that's my opinion ;-)

[garys_1k]

The alternator "mod" I'd like to see would involve back-driving the unit with power to turn it into a motor. Charge up a super-capacitor when slowing down and use that power when accelerating -- sweet!

It'd be complicated, but not impossible. You'd have to have a variable frequency inverter drive the coils, not something I'd know how to do.

[Katmandu]

Originally Posted by gascort

Time/Energy shouldn't count - this is a hobby for most of us, probably including you!
That said, the $$ aspect of this is very important to many of us, and it's what will allow us to spread the word on Ecomodding.

I'm personally on a pretty tight budget. All the mods on my car have to be cost effective if I'm going to do them. I'm willing to invest money if it is likely to pay itself off in ~6 months at $5/gal fuel. Most of my mods so far are with free stuff I got, stuff I found in the trash, or things I had lying around. Time invested is my only cost, and it's fun!

I couldn't agree more.

That's why I posted what I did. If one was to run down your battery out in the middle of nowhere (because of "trying" to save $$ on fuel), you would be LOSING much more $$ in the process.

Like I said, a tow from AAA ($60+) and the time/energy (also worth $$$$) to recharge/replace one's battery ($50+) HAS to be taken into consideration.