alternator equals power leach

[Lunatech]

I know it is a necessary power drain.

But I was wondering if there is any reason that a system couldn’t be put into place, with a switch on the throttle cam that would at or near full throttle stop the alternator from charging, no charge =less drag. Right? But only for a short time, like for extra passing power or even for a 1320 run. Since most people, well me anyway, don’t spend a lot of time at W.O.T. I don’t think it would cause a problem with dead battery or even such a loss of power that the electronics would be affected. However, I wonder if it would cause some kind of damage to the alternator? I don't believe it is designed to be “turned off” and then back on all the time and I don’t know what would happen over a prolonged period of time. Extra wear of the belt, but probably no more than the one for the A/C.

On the other hand weather or not that would work I’m petty sure that something of this nature could be devised for the air conditioning system.

What do you think? I really want to know.

Thanks,

Bob


1990 Legacy L sedan 5MT at least 174000 mi.

[THAWA]

like a clutch system?

[Lunatech]

I thought about something like that and I think it could work well.
But it would take a bit more fabricating than I could do with my limited resources.
It also would have more moving parts and just be too complicated for my tiny mind.
However it might be better, it works for the A/C pump!

I was thinking more of a way to disconnect the alternator electrically, temporarily.

Bob

[THAWA]

I have a feeling the mechanical part of the alternator is more of an effect on performance than the electrical part.

[mTk]

yeah, simply turning off the juice won't do anything, you'd have to implement a clutch system. The alternator spins pretty damn easily as is though.

MK

[bignose]

I was told by an "alternator guy" at the local john deere repair shop that a alternator has a parisitic drag of about 7 or 8 horsepower.

If you need that 7 or 8 hp to pass someon, you should just start passing earlier.

If you need it in the quarter mile, you're just not making enough power as it is

[Finn1]

Lunatech,

If you are dead set on having the ability to turn your alternator on and off consider try this:
1) use a relay (for fog lights) that breaks the ground to the rotor from the battery then use a microswitch mounted at the throttle body, or

2) just use a small push button conveniently located to operate the "alt" relay.

:NOTE: If you try this, use a fuse in the relay circuit to save your car.

I mounted a similar relay for my A/C because I could not find the faulty one in the dash. Before when the dashboard got warmed up the compressor would not engage. When it was cool outside everything worked fine. Now, I can have cold air anytime I want!

Happy wiring,
Todd

[Lunatech]

While it is true that mechanically, the alternator does offer some resistance, I’m pretty sure that a great deal more is offered by the “effort” to charge. If you have ever jumpstarted a car you may have noticed the rescue vehicle has a decrease in R.P.M.’s when nothing mechanical has been changed, only an extra load has been placed on the alternator.

If it truly has a parasitic drag of about 7 or 8 horsepower and you could free it up for cheep wouldn’t that be cool? I mean how much does it usually cost to get 7 to 8 horsepower?

Magnecor KV85 Competition (8.5mm) Ignition Cables for Legacy 1990-1998 1.8 and 2.2 liter $99.00

The K&N panel filter is a 5-10 hp gain over stock $49.00

UNORTHODOX Ultra Street Pulley "Underdrive" provide gains of 5 to 12 HP $215.00

STROMUNG High flow cat pipe for RS, Legacy, Baja and Forester 6 to 10 hp increase $349.00

http://home.att.net/~teaguesauto/parts2.htm

MSD, Bosch, Cold air intakes, big time mufflers… The list goes on and on.

As for not making enough power to start with… WHO IS?

Thanks to every one for your responses. But just to be clear I’m not dead set on anything of this nature. Just posing a question and seeking the council of the community on this matter.





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[Legacy777]

Without dyno numbers to validate those hp gains they're worth as much as the paper they're printed on......so without documentation to backup claims, take them with a grain of salt.

[Brat4by4]

There is no gain because modern cars rely on a good electrical charge to fire the spark plugs and control all sorts of sensors. If the main power source for the car is weak or different, everything is thrown off.

[aspect]

While it is true that mechanically, the alternator does offer some resistance, I’m pretty sure that a great deal more is offered by the “effort” to charge. If you have ever jumpstarted a car you may have noticed the rescue vehicle has a decrease in R.P.M.’s when nothing mechanical has been changed, only an extra load has been placed on the alternator.

Yes, and the engine isn't getting as much power as it needs because of the additional current draw. Sorta like if you unhook the alternator....

I've never run my car without the alt, so I can't really say how well it would work, but I'm pretty much certain that disconnecting the electrical feeds would have nothing but negative consequences. If you want to free up some power, implementing a clutch system would probably do the trick, given that the car works properly with no charging.

You mention an underdrive pulley as well...this part only *slows down* the alt. Removing the connection alltogether would create much larger gains.

[professor]

7-8 horsepower would equate to over 5,000 watts. The power draw of the car in steady state condition should be under 500 watts even with all the lights on. So even taking into consideration mechanical losses and inefficiency of the alternator, there is no way that it robs that much power.

Since the alternator is an electric motor running in reverse, if you don't need to charge the battery (low amp draw), it doesn't drag nearly as much.

Not surprisingly, a good Honda gas powered generator with a 6.5 hp motor puts out around 3000W of continuous power, and the mechanical losses and inefficiency should be about the same in this system, as it is essentially similar.

So I'm estimating 2-3 hp losses, maximum.

[professor]

I found this dyno testing result comparing an engine with all accesories driven as stock, compared to the belt completely removed (thus not driving any accessories including the alternator)

Underdrive Pulleys – Our Testing
by James Walker, Jr. of scR motorsports

The Horsepower Story

With various aftermarket manufacturers claiming up to 15 horsepower gains with their underdrive pulleys, we set out to the dyno to find out how much power WE could expect on our 1999 ITA-prepped Saturn twin-cam powerplant. The results might surprise you, but here they are.

Because there were no pulleys available at the time, we went to the extreme and actually REMOVED the accessory drive belt (only for one run, of course) to see what the impact would be to ZERO drag due to the accessory drive – sort of pulleys with infinitely small diameters. We figured that if we saw a big gain without a belt, that the pulley gains would be somewhere inbetween, right?

We fired up the dyno and low and behold, removing the belt netted a whopping 3 HP (and we’re rounding UP). That's it. The number was repeatable, and even correlated to data run earlier on the doomed BMW motors - they saw similar results in their application.

So, in light of the fact that 3 HP was completely without a belt, we estimated that the best we could do was to underdrive a few components by 20% - or a theoretical 0.6 HP gain (3 HP x 0.2). After that, it hardly seemed worth it to try to custom fabricate pulleys for less than a 1 HP gain.

I know, I know – stock pulleys, like stock suspension bushings, aren’t sexy, and you can’t brag about them in the pits…but in racing horsepower talks and marketing BS walks. We chalked up this exercise as yet another learning experience in the quest for REAL horsepower. Maybe someday we’ll find some.

[Legacy777]

The one thing these guys don't get into is the weight of the stock pullies vs. the light weight ones that are typically made out of aluminum, not steel.

In thier test, putting lightweight pullies on the accessories probalby wouldn't net much hp gains over stock, however putting on a lightweight crank pulley probably would. Furthermore, they should see increases with the lightweight crank pulley while driving the accessories, and while not driving the accessories. Whether those numbers (without accessories and with) will correlate to the numbers of the stock crank pulley with & without accessories would have to be verified....