Why do ppl think that more electrical current draw == more drain on engine?
 

I just noticed this in the post about the alternator. The alternator is always going to require the same amount of energy, regardless of how much is being put out.

no.

No? Thats the job of the regulator. The alternator is not going require more energy under higher load. The regulator ensure that the unused current is disappated. If the car is attempting to use more current than it rated for, it will either be unavailable or burn out the regulator if the engine is revved high enough to produce the required current.

no again. think of it this way. if there is an electrical load, the alternator will offer some 'drag'. under a no or little load condition, the alternator presents less 'drag'. reluctant to use the word resistance in this electrical context.

I disagree.
http://www.alternatorparts.com/understanding_alternators.htm

Looks like I'm correct. The alternator is always generating the same amount of current in synch with the RPM's of the engine. There is no additional load as the current increase, merely less current is disapated.

The only job of the regulator is to turn on and off the field windings inside the alternator based on battery voltage and turn off the charge indicator light on the dash.
If you think there is no draw from the alternator turn on all the electrical accesories in your car and note the rpm drop.

The alternator is a magnet and a bunch of wires going around in a circle. If the wires were generating current (electro magnet) then it would cause the magnetic fields of the natural and electro magnet to interact with each other and perhaps add to the load on the engine.

[edit]
Ah see here I am thinking of a generator. So the alternator is an electromagnet and a stator. I see as the load increases the regulator increases the current in the electromagnet there by increasing the physical resistance of the rotor interacting with the stator. Now I see. How is this more advantageous than a generator? Heat issues with the disappation of the extra energy?

Why do you need a 10 hp motor to turn a 5200 watt generator? You could probably spin the armature by human power without a load, but plug in a heater and you're not going to spin it.

Winmutt, the force required to spin the alternator is DIRECTLY proportional to the instantaneous electrical load on the system.

The magnet you talk about is the field, it's an electromagnet controlled by the regulator. I guessing the "bunch of wires" is the stator it's stationary. When a conductor passes through a magnetic field you get current. Thats how an alternator works.

Which is why regererative braking works on EVs and hybrids.

Sixto
... stay tuned

Think of it like this.
 

a generator/altanator uses electromagnets to convert mechanical energy into electrical energy.
the more electrical load on the altanator, the stronger the current passing through the windings, hence the stronger the magnet will be pulling against the iron stator. the stronger the magnetic field, the more hp is required to turn the winding.
directly proportional to power used. perhaps you are correct in that the altanator is designed for a specific power output, and that output will not change by rpm, but the regulator will drop in and out the field based on demand.
Hmm, perhaps you are confusing power with amperage... the same 14.4 volts will be produced no matter how much you turn the rpm's due to the VOLTAGE regulator bringing in and out the circuit.
imho
John

Your right, I didnt realize the strength of the magnet changed :).

Early alternator-equipped Harley-Davidson motorcycles did have this property, as they used a permanent-magnet field and a shunt-type regulator. However, even with these, you could install an aftermarket regulator which did not shunt the excess current, and thus would free up just a bit of power.

But even typical automative generators would control the field current to affect the output voltage, which does cause the input power to be somewhat proportional to the output power (there is always some loss). All automative alternators that I've ever seen do this.

A good example that an alternator puts more load on the engine when providing more power is seen on modern cars too, when I jumpstarted a car with our minivan, when cranking the car I was jumping, the van raised its RPM's on its own by probably 300-400rpm to compensate/produce extra power. The car's computer saw the huge power draw, and rev'd the engine in response, it then dropped back to normal idle when the load was gone. Pretty cool. The van itself is junk, but I thought the high tech compensation was cool. :D ;)

I can tell on my SD when I power on the CC, rear window defroster, headlights, etc...the rpms do drop by 50 or so, you can tell by the sound.


Here's an idea, put a huge amp capacity alternator on your car, then fully load it, and try a 0-60 run, compare it with the times with no load on the alternator. :D A 120+ amp one can sap over 10hp off the engine under heavy load....