Does alternator load increase engine load?

[Mudderoy]

Having an interesting, on going, discussion with a friend.

In my mind it's very clear that as electrical load increases on your alternator the engine has to do more work to turn the alternator.

My friend disagrees. He says there is no connection between electrical energy and mechanical energy.

I've been researching online and I can't find a 100% credible source for the answer.

I thought since it was just a spirited conversation between myself and my friend, you guys (and gals) might want to join in.

[4.3LXJ]

Tony, this one belongs in a high school physics class. First fundamental law of the universe IIRC. Energy is neither created or destroyed. So, according to this law, the energy in burning gasoline is converted into rotational energy which is transferred to the alternator which is converted to electricity. Also, the total energy of an alternator is dependent on rpm. It cannot put out as much amperage at 50 rpm as 2500 rpm. To get to maximum output, it needs more rotational energy from the engine to do so. If not, it in essence could produce maximum current at rest with no mechanical input. Also on a more practical note, when smogging last time I had to tell the tech that when the fans kick on it might kill the engine before the idle air controller can compensate for the increased demand for mechanical energy from the engine. It did it right then and he said, I see what you mean. Love that 250 amp alternator

[Mudderoy]

Tony, this one belongs in a high school physics class. First fundamental law of the universe IIRC. Energy is neither created or destroyed. So, according to this law, the energy in burning gasoline is converted into rotational energy which is transferred to the alternator which is converted to electricity. Also, the total energy of an alternator is dependent on rpm. It cannot put out as much amperage at 50 rpm as 2500 rpm. To get to maximum output, it needs more rotational energy from the engine to do so. If not, it in essence could produce maximum current at rest with no mechanical input. Also on a more practical note, when smogging last time I had to tell the tech that when the fans kick on it might kill the engine before the idle air controller can compensate for the increased demand for mechanical energy from the engine. It did it right then and he said, I see what you mean. Love that 250 amp alternator

Yep, I agree, but the person was very sure of their view on this, so I thought the only proper thing to do would be to research it. I couldn't find anything from a completely reputable source online though. Wouldn't be the first time I was certain and turned out to be wrong either. ;)

[4.3LXJ]

Can't argue with the fundamental laws of the universe

[4.3LXJ]

There may be a point of confusion on his part. Back when there were generators instead of alternators, if you were stuck in stop and go traffic you could drain a battery because the generator needs to turn at a fairly high speed to put out enough current if say you run the headlights or heater fan. The advantage of the alternator is that it puts out max current at a fairly low speed, just above idle. That is why there is that small pulley on there. So it will put out as much at say 1K rpm as 3K rpm. But it still takes energy to make it turn and at a speed too low it will be like the generator and be inadequate

[OrangeXJ]

He says there is no connection between electrical energy and mechanical energy.

This is absolutely wrong. The more electrical energy needed the more mechanical is needed. I have a lot of experience with generators. A lot of commercial engines are rated with KW kilowatts instead of HP. If you took an engine rated for 7KW generator it will not fully run a 20 KW gen set. Look at a KW to HP conversion table to prove this.

[4.3LXJ]

Good point

[denverd1]

yep, energy is transferred, not created

magnets and brushes create forces the alt/engine must overcome. tell your friend he's wrong

[denverd1]

another way of putting it: on some very high output alts, they run 2 v-belts off the crank to the alt. why wouldn't one belt work? and why spin the damn thing in the first place?

[4.3LXJ]

another way of putting it: on some very high output alts, they run 2 v-belts off the crank to the alt. why wouldn't one belt work? and why spin the damn thing in the first place?

So if we could get it to work without spinning, what would happen if we spun a battery? :D

[denverd1]

So if we could get it to work without spinning, what would happen if we spun a battery? :D

according to muddy's friend, it would recharge!! In my case, I would ruin another pair of jeans with battery acid....

[denverd1]

Tony, did you win?

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