Alternator Mods
 

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?

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.

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.

... 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.

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.

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.

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.

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.

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.

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.

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?

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.

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 :eek: 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...:D since im running a "lighter" alt the 6lb battery i found will work perfectly for the system also

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!

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!

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

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. :turtle:

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!

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 ;-)

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.

I couldn't agree more. :thumbup:

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. :cool:

Has anyone tried replacing the rectifiers with Schottkys if they aren't already? That should halve the rectification losses since the forward voltage drop of a Schottky diode is about half that of a regular diode.

what if you put an air conditioning compressor clutch on the alternator and hooked that up to an openguage or something that tracks instant MPG's and had it engage only when the MPG were above a certain amount. this would disengage the clutch whenever we accelerate or drive up hills or such when any extra load on the engine hurts us the most.

Agreed. I am on time-of-use so night time charging via a timer switch will be dirt cheap. I have a solar panel to integrate into my trunk that will keep the battery topped off during the day (15w). Should mitigate any issues in most commuting situations.

I plan on leaving the alternator installed so I can belt it up if need-be, but how do i go about finding a belt the appropriate length for just my water pump and main crank pulley? The tensioner on most cars is integral to the alternator bracket instead of the water pump, so i need a way to tension the belt properly. ideas?

Yes ! Lower amperage ones ! Use teh lowest amperage alternator possible and forgert all those "luxury" things like power windows, A/C, etc

Denis

Just use an underdrive pulley
 

Why dont you just use an underdrive pulley system? That reduces drag on all driven components and should help with mileage while keeping battery fully charged.

it would help, but not every company makes them for every car. Ford Aspires and Chevy Metros never really made it in the import racing scene. The thing is that its a confirmed 10% increase in mpg's in some vehicles to not run an alternator at all. That is a very tough number to beat with any other method, or combined methods (other than driver mod)

When you remove a watt from the load on the alternator you remove more than one watt from the engine load
the stronger the field the stronger the resistance to the engine
As long as the field is off the alternator is nothing but a flywheel and an extra pulley. But when accelerating you still have that extra rotating mass to contend with and even at constant rpm with no load you still have the belt friction loses

The problem with removing it is that single 12V battery is not enough power to drive with
you will go dead fairly soon
Modern cars are simply not designed to conserve electricity
There is probably a two hundred watt draw on your 12V system with out even the headlights on

You can fix that by replacing brake, dash, cab and running lights with LEDs
You can probably fit about thirty watts worth of photovoltaic panels on even a small roof
And adding an extra battery to run in parallel with your original will more than double available range

decreasing belt leach is easy as lightening up a load. alternators are a must for a more efficient engine, but you can still make lighter pulleys at a machine shop even underdrive pulleys.
aluminum instead of steel always works better (depending on the car)

lighter pulleys is a lighter load on the belt.
whether a/c is on or off it will always draw from your engines power same with power steering. (always an option to remove a/c and p/s)

or you can go all out an start putting panels all over your car. might as well just convert it to electric.

I have looked at this and concluded that the cost per cycle of a deep-cycle battery make it not cost effective.

For example in the UK, a deep cycle battery like the "red top" would cost £140 and if you got 500 cycles out of it, that's about £0.3 per cycle, or 0.3 liters of fuel's worth just for the capital cost of the battery. That ignores charging costs, which are low from the grid -but a decent charger will cost something.

What would make it worth it, is if you had regen. braking and an electric assist motor, and could use the energy for more than just starting the car the next day.

I was surprised that the battery would only hold 600Wh, by my calcs equivalent to 55 ml of diesel...

I found a super easy way to reduce the load on my alternator. I bought a $10 solar panel and threw it on the dash. 1W...not really because solar panels are rated at no load.
i'll just fill my dash with them...
but then where will i put all the empty McDonalds containers?

Schottky diode's can be scavenged from a computer switching power supply
hmmm, silicon carbide Schottky diodes... Now i need a Scangage and a spare alternator.

Pwm?
 

I'm wondering what if we use a PWM at the alternator rotor coil...

Hmmmm... Any ideas??

"Knock yourself out.."

You might find it interesting that one of the european manufacturers, BMW or MB, I don't remember which, is installing a slightly larger battery and only allowing the alternator to go into charge mode during coastdown or braking periods. Except if the battery charge begins to get "too" low.

Modern day solid state alternator voltage regulators are already of the PWM "switching" type, just as were their forebears, the old mechanical relay type regulators.

Apply full battery voltage to the rotor winding, wait the few milliseconds for the battery voltage to rise to setpoint, open the circuit, wait for the voltage to decay, repeat as needed.

I much like the idea of a switching alternator... although I believe it should be accompanied by a mechanical continuously variable pulley as well, which would be designed to keep it at its most efficient RPM, regardless of engine RPM.

Also, it should work when the engine is at idle speed, since during idle, you're burning fuel for nothing anyway. (Unless you're coasting with the engine on, but the engine still isn't DOING anything for the fuel it's consuming.)

For an electronic controller, "Idle speed" is defined as "particular idle speed while at 0 load and 0 TPS reading." (For automatic vehicles, change "0 load" to "limited braking load" due to it being in gear.)

I have a 75 Amp alternator. If I currently EOC 30% of the time, with lights, ecm, and radio on, draw must be like 40A or less since I've never had a charging issue. I'm curious as to how much exactly it draws, though. Time to find an ammeter that can handle 60+Amps, or try a few fusible links.

Something to note.... the AD244 alternator GM uses in several fullsize rigs puts out around 200A at idle, and slopes off to 145A around 1900rpm. I have no idea why it does that, but I plan to swap to it on my truck to support all the offroad aux lighting.

Anybody understand the principles better than I?

That's odd... normally, alternators increase their amperage output while accelerating.

I figured out that I have over-charge protection on my Honda's new alternator, simply b/c when I rev it to 6500RPM, the alternator light comes on. It stops charging so that it doesn't overdo itself. I think that's LOL-able.

No no no, not the voltage regulator... ;)

I mean the rotor coil. The one that spinning in the alternator... :D

Any thoughts?? :)

I was wondering about this myself.

There seems to be a flaw to this logic. An alternator is NOT a generator. It has no permanent magnets. It is very similar to an induction motor, such as what you would find on a vacuum cleaner. But when there is no power going to the field coil, there is no magnetic resistance, only frictional resistance. And the alternator only draws its max output when the field coil is strengthened by the regulator.

Instead of alternator mods, worry more about reducing the electric load, as he pointed out. An alternator is designed by manufaturers to be very efficient, but the electric loads are not entirely efficient.

If you want to reduce the alternator load, put in a bunch of solar panels on the roof and dashboard.