Hi, i have a friend that told me the more watts and power u hav the more HP u loose... He says that alternator then has to use up more power, and then u loose hp, is this true???

Thanks guys


- Nick

 

your friend.... technically maybe but if you gunna run a sytem like that you arent worrying about hp or you get a better alt.

 

I think what they are trying to say is the current draw on the electrical system will weaken the spark the engine gets from the plugs.

Kind of the same idea as old plug wires old, corroded, or dirty cap rotors and distributors can do.

I imagine to a certain extent, this is possible, since it is a drain on the electrical system.

Whether there is a perportional relationship of power to horsepower I don't know.

Good rule of thumb, if your lights don't dim as your car runs on the road with the stereo booming, you are probably fine.

Mind you this is me without coffee yet.. so..

Anyone else?

 

hey thanks guys for input so far!

 

I would be more worried about the 100lbs that the stereo gear is going to wiegh than I would about the alternator having to work a little harder.

 

i wouldnt.. this isnt gunna be a track car for me and 100lbs is only like a tenth of a sec anyways... besides if you overwork ur stack alternator youll fry it quickly

 

No, it's not losing spark power as much as it is the alternator. You need a bit alternator for lots of power, right? Well, when you're pumping the bass, that alternator will be putting quite a load (through the fan belt) onto the engine. Hence you're losing horsepower to the wheels as it's going to the alternator instead.

 

Yes, that is what I was thinking as I was reading.

 

Power in = power out. The more load placed on the alt the more energy is required to turn it.
Power loss can be calculated. i.e. if your alt's max output is 100amps @ 13.8v at 50% eff so
P=VI
1380watts = 13.8v x 100amps
so say 50% is lost to heat, etc, that alt will need 2760watts.
1 hp = 746watts

2760watts/746watts = 3.70hp

Of couse there are other factors to take into account, but you can see not much hp is used up.

 

ooh ooh ohh i learned this stuff in mah Physic Honors class this year in HighSchool... 50% loss to heat seems high but im too tired to try

 

Nothing noticable will be lost.

 

nothing noticable will be lost?

does anyone remember the formulas for jouls, HP, watts? I might have to crack my physics text book for this one....

one hp is about 735 watts? anyways....we can figure this out and get to the bottom of this...

I also have my ESA electric motor book, it's got the formulas for hp and torque ect...

 

Now I am a little lost here my friend. I recently rebuilt my alternator you see. I know there is a voltage regulation circuit in there that ensures that the right level of voltage is always going to the battery. There are some bushings and a copper part inside that these bushings ride along.

I saw no mechanizim that would cause the alternator to become harder to rotate as the voltage demand increased. Nor did the alternator appear to have the ability to speed up its rotations as power demand increased.

However I can see the regulation circuit constantly asking the alternator to put out its max voltage for overly long periods of time, causing overheating of the electronics within, and potentially causing a burnout in those electronics then of course an alternator failure.

I can also see the regulatory circuit failing for similar reasons.

Since the alternator is spun by the same belt that the water pump and the other pumps and pullies in the system are, I find it hard to picture the alternator changing speeds with the engine rotation being a constant.

Maybe it was the overheating of the alternator that you were trying to describe?

 

Yeah... that's what I said.....

But if you wanna test it, get a bass test cd and put it on pause. Floor your car and once you get going, un-pause the track and see if your wheels lock up.

But seriously, as mentioned before, weight is gonna be more of an issue than anything, and 100 lbs. is ~ one tenth.

 

Now THAT would be funny.

By that logic, if you wanted to coast down a hill without using your breaks or tranny, just crank the bass, and let the alternator drag keep you at a steady slow downward speed. LOL.

Turn the volume up to slow down and turn the volume down to speed up.




Though I think the idea is there. No, it does not really rob you of horsepower to the point where you will notice it. Yes, the wieght will be more of a horsepower (and gas milage) robbing aspect than the electrical demand on the car.


:lala:

 

ya i think the weight of the system will affect most of ur performance , more the power in the alt

 

Exactly -- the more belt-driven or electrical accessories you use (air conditioner, headlights, radio, etc...) the more load on the engine through the crank from the belts.

Edit: That said, I do not know how much load will have an effect on hp. I know A/C kills mileage but I have no idea about stereo.

 

dude if you notice one hp then you need to take some chill pills and yes 1hp = 735orso watts= 550ft-lbs/1s. really if you see a difference you are puttint in your car a 10000watt system and even at that its only like 10hp...

now about the alt drag?? slap yourself... the main problem that has anything to do with the alt is burning it up from asking to much of it..

 

Actually weight does not rob you of horsepower. A 200HP engine will put out 200HP whether it's pushing 1 lb. or 5,000 lbs. Now it can rob you of acceleration, which is what you probably meant.

I think you're a bit confused on how that works though. You're talking about how much "horsepower" the alternator produces. If you're using 735W you're robbing 1 "HP" from your alternator, not your engine. The effect is even less on the engine. Hence my original statement, nothing noticable will be lost.

 

Yeah I ment acceleration. Brain deprived of coffee again. :P

 

i was just agreeing with him... eaither way we established that the alt doesnt rob HP nor do high end stereos

 

I didn't say that a lot of power was lost through alternator load, just that some is lost.

The alternator turns mechanical energy (rotational) into electrical energy (current). It's not a perfect conversion, and you lose energy through heat loss (AKA what kills alternators).

What I was saying was that, per basic physics, the more load you demand of the alternator, the more energy it will demand from the engine. And the more energy that the engine gives it, the more the heat loss increases.

The engine will keep it spinning at a pretty constant speed, and the load effect is, as others mentioned, pretty much negligible. Yeah, it's mainly burnout that you should be concerned with.

 

buzz wrong.. dude... the alt is designed to not run at 100% for long periods of time hence the voltage regulator... if you ask 100% or 110% of it you will burn up the electronics in it thru heat and overload....

by your principle a 70 amp alt puts less strain on the engine then a 160amp alt.... which is untrue

 

That logic would require your alternator to spin faster when more load is placed on it, which is not possible since it's tied in with the engine crank spinning.

 

Right.

 

Well... perhaps I'm missing what you're stating. You said that " the more load you demand of the alternator, the more energy it will demand from the engine.", how does energy get transferred from the engine to the alternator? By rotation.

 

your not missing anything it was an easy misinterpretation to make.. i mean common sense would back up his claim but actuality crushes it.

 

The rotational speed ramains constant, it is the torque that increases. Think of the alternator as an engine in reverse. This is how electric cars have "regen" braking by turning their motor into a generator. To overcome this torque (by the way I have nop idea how much this is under full load -- could be negligible) the belt needs more force.

 

Crayz9000 is correct.

 

An alt can produce current I at X rpm. It can also produce I/n at X rpm with n being any integer. Therefore, if at idle an alt can produce 60 amps max at 13.8v, it can also produce 60/n at idle, so an alt can produce 0-60 amps of current with the same idle speed. As RPMs increases from idle, current can (not necessarily have to) increase as well. So say that same alt at 2500rpm puts a max of 100 amps out. It can also put out anywhere from 0-100 amps at 2500rpm. The closer to 100 amps produced by the alt, the more power the engine HAS TO put into the alt to produce that much power. We all know that one of the laws of physics states that power in = power out. And since on alt is not 100% efficient, it will always take more engine power in then the alt will produce as electrical current out because power is being lost do to heat, etc.. And the more current produced by the alt will require more power from the engine.

With that, if you have an alt putting out max 100 amps and replace it with an alt putting out 200 amps max, the 200 amp alt will require more power to turn from the engine then the 100 amp alt did at max power.

Whether or not the power required is noticeable or not is not the question. The fact that power loss does exist is.

Also, keep in mind 735.5 watts = 1hp(metric) and 746 watts = 1hp(US)

 

wow lot stuff im learning ,thanks so far for the input guys

 

wow......I remembered SOMETHING from college!


735......close enough for government work!



Straight out of my EASA electrical engineering pocket handbook:

HORSEPOWER
A unit of measuring the power of motors or the rate of doing work. One horespower equals 33,000 foot pounds per minute (550 ft lbs per second) or 746 watts.

ALTERNATOR
A synchronous machine used to convert mechanical power into alternating current electric power

So, it's unlikely a system will pull enough to interfere with spark, but it will put an additional load on the alternator. I'm sure it's not tlike having the A/C on, but a load......exactly how much...I'm still not sure.


The definition of foot-pound is interesting....one foot per pound or something? I never really got that one for sure....it could be one pound, one foot leverage?

is it proportional (50 feet/50 pounds) or 50 feet, one pound?

anyways, it's clear that HP is time relevant, so if 746 watts is one HP, how long can 746 watts be sustained with one HP?

during a 1/4" it might not be long enough to notice, but 746 watts used by the system (requiring more than 1 hp due to loss) will use more energy over time, if it is infact pulling a constant 746 watts....

 

FOOT-POUND
The amount of work required, in the English system, to raise a one pound wieght a distance of one foot.


nevermind...

 

Crayz9000 is 100% correct. And the people that think he’s wrong, well their wrong.
As load (electrical) on the alternator goes up, so does the load (mechanical) on the engine or what ever is turning the alternator.
Demicon, you said you that you did not see any mechanism that would cause the alternator to become harder to rotate. And that is true. There is no “mechanism” that makes it harder, it magnetic force. As current out goes up the “magnetic drag” increases as well. This “magnetic drag” is small and not really something to worry about for us, but CAN be a VARY high drag. Check out how dynamic breaking on electric motors works. No “mechanical” breaks at all but they can stop a spinning motor VARY effectively. Same idea.

 

just put some NOS and type R stickers on there, you'll be fine

 

Ah, I understand what he was saying now, thanks.

 

We need a smiley with a light bulb over it.

 

Crazy and Needaz are both totally correct, but your not going to see it unless you're putting some major strain on the system, in which case I think the alternator would go before you would see the difference.

Another way you can see it is this: A magnet is spun inside of a conducting loop, or coil. This creates a current in the coil, in a certain direction (yes, current is directional) to oppose, or balance, the magnetic field which the magnet creates. This is a natural effect. Work is actually done (mechanical) to turn that magnet inside of the coil, not because of accelerating the rotational mass of the magnet (negligable) but because there is a drag produced because of the load placed in the electrical circuit, which demands power. In the same effect, if you were to reverse the current through the coil (opposite direction), it would have, as you can probably guess, the opposite effect on the magnet inside the current. It would produce an opposing magnetic field, and would create a torque that would rotate the magnet in the same direction that the engine normally spins it, which would actually work like an electric motor and would supply energy to the actual engine via the belt. Of course, I dont think this would happen by an alternator, it's just to illustrate the concept of the magnet and coil producing current and magnetic fields. They go together, if one changes, so does the other. Now, suppose you are spinning this magent via the motor's energy by the belt, inside the coil (your typical alternator) at a constant speed, and drawing constant load from it, and you were to suddenly demand a respectfully greater load, where is this energy going to come from? Energy cannot be spontaneously created, or destroyed, and it certainly is not stored in the alternator, so it's going to have to come from the work put into turning the magnet. This increased load in current will produce a greater opposing torque than what was previously created, therefore requiring more work to be done in turning the magnet to keep it at the same rotational speed. It's hard to imagine that two things can have a 'mechanical' effect on each other like this, when they dont even touch, but they do, it's physics. Hopefully I explained that right. Now the battery also can help supply in cases of high demand like that too, so I dont think you can really count that out of the problem.

 

I retract my statement.

 

Oh no, here it comes............

 

you guys need to really take apart an alternator.. then bash yourself in the head with it... the alt can't put anymore strain on the motor than it already does meaning teh drag and motor strain are constant... you what you guys are sayin is tru then the alt would have a sort of clutch or sumthing that could actually drag the motor...

ill save you the trouble of taking apart the alt..... the alt make 100% of its power all the time..... the voltage regulation circuit cuts the power down as needed.... now commence with the bashing of your heads.

the alternator make power thru induction. pass a magnet thru a coil and it produces current. The alt doesn't know it needs to make more power... the regulation circuit does.

 

No thanks. I already took courses in engineering at the university so I know how it works. I suggest you do that same before posting about something you don't understand.

 

thanks alot but i didnt know engineers took apart cars... hmph.. well anyways im going on my 4th course of automotive at school so if you wanna talk to me i suggest you quit bashing yourself with the alternator

 

You don't know much do you.

 

well ive made it thru 4 yrs of this course. ive taken apart a few alts. so yeah i do know a bit