Thread: Alternator disable

How can it save fuel when mechanically its still being rotated ?

Less current
Less load
In the order of 3-5 hp

And btw I meant apply 15-16 Vdc to sense line

Oz

Less electrical load maybe but mechanical load is the same, as long as the alt is being rotated its drawing load.

Less electrical load means less mechanical draw.on the engine.

You don't get something for nothing.

Imho. Bad plan to disconnect it. You'd be better off feeding it a signal that tells it that it's making about 15v and have the boosting unit setup to cut out when the battery is showing anything under 12v.


Just remember that at the end of the day you need to charge the battery from somewhere some how. If you drive around flattening the battery and then make the alternator push bulk amps you risk burning out any number of electrical connections early.

Let's look at the truth of it tho. 15% fuel savings are unrealistic because if the alternator was doing it's.job and the battery was charged then there would only be the load of the vechile coming from the alternator which means your basically doing only one power conversion, mechanical to electrical so you get one loss. Doing it by cutting out the alternator leaves you with eventually doing mechanical to electrical, electrical to chemical then chemical to electrical and since you loose a little bit every time you convert it doesn't look like any real saving to me.

Absolutely correct Blknight.aus
The only significant load that you see on an alternator is the electrical load when the alternator is charging the battery.I would hazard a guess and say that the energy required to spin an unloaded alternator would be negligible,not even measurable on an engine in all practicality much less detected through the right foot.

How can there be less mechanical load when its rotating anyway, if i unplug the alternator its not going to spin any faster.

Up to 10%? This seems a bit pointless, no logic behind it.

Once battery is charged up and no accessories are running, alternator is just idling, there is no current being drawn from it. Except magnetic field losses, difference with alternator being switched off by above mentioned method and left as is, is very very small. Not 10% in fuel savings for sure.

If you disconnect your alternator this way, you will discharge your battery if you run anything electrical in your car, and once you turn it on, you have to charge it up again with heavier current resulting in "10%" more fuel used. Unless you want to charge your battery externally when you get home, and pretend that you have HYBRID Discovery

And for those that say that alternator still takes same power because it spins. It is much harder to rotate alternator with 20 Amps load than with 1 Amp load. Alternator uses magnetic field to create current. Higher the current demand, stronger the filed, and therefore, harder to rotate. Maybe not best choice of words, but that's what it boils down to.

Originally Posted by loanrangie

How can there be less mechanical load when its rotating anyway, if i unplug the alternator its not going to spin any faster.

Easy.

It's a rotating magnetic field as you put load on it it works as a brake and converts mechanical energy to electrical energy. Exactly the same principle as running a drill without a load on the Chuck draws less amps than when you grab the Chuck in your hand and try to slow it down, only backwards.

Here's a real world demo.

Grab one of those hand crank dynamo torches, gut it down to just the dynamo and turn it with nothing on the electrical connections. Now short the outlets and turn it again.

Or just goto any of the power/scitech style science/technology centered and jump on the bike that's got the lights on it they use to represent a powerststion generator.