[myself6]

Fine....

Then please enlighten me. ANYONE...


Under what conditions does the electrical load of an alternator make it harder to turn the rotor?

Is there some type of buildup of the magnetic flux field that works against the rotation of the rotor?


Im willing to admit I don't know something but ONLY if you can adequately explain it.

[Jonx6]

And I’m not talking about the permanent magnet fields; I am talking about the electrically created ones.

[norwaypinesavage]

An alternator consists of a rotating magnetic field inside several coils of wire. The rotating field generates electricity in the coils. Even at a constant RPM, if the voltage regulator senses the need for more electrical output, it increases the strength of the magnetic field. Therefore, it takes more torque to turn the field, and hence, more engine power to turn the alternator. The input energy to the alternator is directly related to the output energy that the alternator is making. More energy out requires more energy in, even at a constant RPM.

[JAKraig]

Ok, I will give it a try.

Creating electrical current is similar in many ways to pumping water.

The generator is analogous to a water pump. The electrical load is analogous to a nozzle on the end of a hose.

When a water pump turns without the hose nozzle open there is no flow (current). When the nozzle opens a little a little work is being done by the pump. Kind of like a light dimmer, when the lights are low very little electricity flows through the lights. If you open the nozzle all the way the pump has to do a lot of work.

If you have ever listened to a high pressure spray washer as the wand valve is opened and closed you would understand in a second. When the wand is closed the motor does not sound loaded, as soon as the water valve is opened you hear the engine bog down until the governor opens the throttle and helps the engine catch up with the required load.

Exactly the same thing happens with electricity. When the light dimmer is only on a little bit there is very little electricity flowing and the generator does very little work, turn the dimmer on all the way and a lot more electricity flows therefore more work.

I hope this helps.

[Final Authority]

I don't know if anyone tried to explain why an alternator becomes harder to turn with an increased electrical load but I will try.

Think of a load on the alternator as a demand for current, forget voltage. Current is the same when measured from any place in a circuit so the current going through the main fuse box is the same as the current in the stator of the alternator (if the stator is the output winding). As more current is demanded by turning on lights for example more current must surge through the alternator and that current comes from the induction caused by the rotor, which is energized by the battery/electrical system and spun by the engine. If the engine did not spin there would be no induction and no current but in an alternator there is a greater reluctance for the rotor to spin as the current increases. A simple example test would be to take a model or toy DC motor and hold in your hand and spin it, then connect the electrical leads together and give it another spin. You will find it harder to spin it when connected. Now, take a voltmeter and attach it to the leads and give it a spin. You will get a voltage generated. Now spin it faster and you will see a higher voltage. Since the circuit has a resistance a higher current (faster spinning) will cause more voltage to be generated as the equation for this is V (or E)=I*R or voltage is current times resistance. So in a car, increasing load is reducing resistance while the voltage regulator is maintaining voltage the current must go up. The load on the alternator goes up, the reluctance to turning goes up hence the power to generate the electrical power must go up.