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Discussion Starter · #1 ·
How do you figure that increased demand for amps places an increased load on the engine??? The alternator is not like the a/c where it is engaged by a clutch. A 100 amp alternator has the capabiltiy of making 100 amps only, but does not mean that it will do so unless demanded. You do not place any more strain on the motor if you want 20 amps or 100 amps. The alternator spins freely and the load to the engine never changes. The wound wire that rotates past the magnets induces a current that produces power for your car. Let me know otherwise if you think I am wrong.
 

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RE: For all who posted on loading the alternator&l

"counterelectromotive force"
Run yer car on a dyno with all the electrical accessories off, and record the rear wheel hp available. then do it with all the accessories running. If it's an accurate dyno you WILL notice a difference. A 100 amp draw on an alternator will show up as LESS than 2HP I believe, as that's the equivalent of 1200 watts. You get nothing for free. It's physics. "spinning freely" it does do, but the mechanical force required to turn the rotor windings past the lines of force created by the stator increase porportionally with the load induced. BTW, this is how an "eddy current dynomometer" measures HP...
 

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Discussion Starter · #3 ·
<b>RE: For all who posted on loading the alternato

I have a '76 280z with a pretty serious stereo system in it.
I have about 450 watts rms clean. By my math, the system draws about 80 amps peak. When the bass hits, the engine RPM actually dips. I don't think that would happen if the alternator wasn't placing a load on the engine.

--Jeff--
 

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thanks for reminding me, maui!

Yes, as I went back and read a few more of the posts, let me clarify: it is sort of a moot point UNDER NORMAL CIRCUMSTANCES. Alternator loss will be small, as stated, 1-2HP. It IS a loss. But to really drive the point home, there once was a rally 510 with a killer light bank, and we had to adjust the idle speed UP to keep the lights FROM KILLING THE ENGINE if they were all flipped on at once. Thinking another way in the AC world, then a 10,000 watt generator (16HP usually) would work just fine if the engine was replaced with a 5HP engine. No increased load on the alternator/engine? Wrongo...
 

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Discussion Starter · #5 ·
RE: For all who posted on loading the alternator&a

Rule of Thumb Stuff:

1 Hp = 746 Watts approx.

100 amps x 14VDC = 1400 Watts

1400 Watts/746 = 1.88 Hp

or about 2 Hp.

Typical Hp for 280ZX, non-turbo, 5-speed: 160 Hp

(2Hp / 160 Hp)* 100 = 1.25%

which explains why the full load alternator doesn't seem to "load" down the engine.

As Tony D. says"you don't get something for free..."

Mike 280ZX
 

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Discussion Starter · #6 ·
<b>Nothing like the Real world</b>

Good follow-up posts. Short and to the point.

Isn't 240 Turbo supposed to be a phd student in EE or something and worked at Nasa before?? No wonder them rockets blow up so often. Hehe.
 

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RE: Nothing like the Real world

I don't think 240z turbo is the same 240turbo we have all come to know and love. The post was too nice!! And anyway 240turbo (James) is hard at work trying to get his car running. I talked to him Saturday and he said he was on a deadline and his car would be on the road in two weeks.
greg
<a href="http://www.flash.net/~joeao/greg/zcar.html"71 240z</a>
 

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RE: Nothing like the Real world

I'm glad someone looked up the .75kw to hp conversion factor. I was too lazy to go to the bookshelf! :)
 

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Discussion Starter · #9 ·
<b>IE not EE</b>

You miss the point. OK brainchildren, I will give you the explanation tomorrow if you promise to be good. So put down your physics books and outdated dictionaries with the words "electromotive force" and get a good night sleep.
 

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I'll sleep on it.

IE, doesn't that involve stopwatches and anti stress padding? ME? Weapons, CE:Targets, IE: Weapons Factories. Couldn't resist...
besides, CEMF sounds so cool...
 

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RE: I'll sleep on it.

What was the point, anyway? I thought someone said the alternator didn't put a load on the engine. I thought the idea was that the stock fan is overkill, sucking power we need for smoking donuts, and that the electric fan used less, as it wasn't spinning all the time. Even when it was spinning (and drawing 100 Amps!) it would only use 2HP, or 1.88 if you have the calculator. In other words, the electric fan is less of a draw than the stocker with a siezed clutch, but it's still a draw. We got tangled in extremes, and it's not good, eh? Like I said earlier, the ammount of HP draw by the alternator is MINIMAL, even under full load, but it does use the torque of the motor to generate the electrical power we use. The voltage regulator will saturate the field windings to compensate for voltage drop, and cause more A's to compensate. Or was it V's? We digress...
 

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Discussion Starter · #12 ·
RE: Hey ther 240 Turbo!

You're big time wrong, man!!

Still I want to strike up a conversation with you about converting my '72 Z into a Turbo, and I think you're probably one of the most knowledgeble ones on that subject.

But back to alternators:

The alternator does not "spin freely" it just feels that way when you turn it by hand at a snail-pace compared to its speed while the engine is running. And just because the parts inside are not touching, that doesn't mean that drag doesn't increase as the load increases. Think of the reverse: your starter motor. Within the inside of the starter-motor itself, the armature and coils don't touch - and yet the electro-magnetic force created is enough to crank your engine over!!! Saying an alternator doesn't cause drag when creating electricity is like saying a starter doesn't cause force when provided electricity. Or think of a typical eletric fan motor. When you turn the switch from Low to High on a house fan, doesn't the fan speed up? Isn't that because extra electricity created more force? A generator is the opposite of a motor. Instead of electricity creating force, force is creating electricity.

Enough said!

John M
 

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Discussion Starter · #13 ·
Hey Jeff!!!

Your car's RPM isn't going to dip from just 80 amps, accept maybe at idle. Your tach will fluctuate down though because of the slight drop in eletrical voltage in yur system as the Bass thuds. Don't damage you hearing.

John M
 

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Discussion Starter · #14 ·
RE: Hey Jeff!!!

An alternator will absolutely draw power off of you engine. The electricity going through the alternator is like a magnet and slows it down, therefore costing horsepower.
 

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THIS IS GETTING TEDIOUS

Has everyone forgotten about the battery? The alternators function is to charge the battery. All the devices (like an electric fan) draw current THROUGH the battery. It acts as a buffer (when propery working) in the electrical system of the vehicle. None of these devices directly interact with the alternator making this supposed increased resistance a moot point. B.T.W. the analogy of a motor and an alternator is invalid - yes a motor produces torque but it is taking IN electron flow to create a field as opposed to an alternator that is exciting a coil to cause electrons to go OUT. This output is more affected by motor speed than by load (another fact everyone is missing). And with regard to the fellow who is seeing his rpm drop when he has large transients travel through his subwoofer - consider it just might be a VOLTAGE drop in the electrical system causing the coil VOLTAGE to drop? Slap a vom (preferably analog) on your coil positive and ground, crank your system with some White Zombie and watch for fluctuation.
 
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