Alternator Load vs Fuel Economy.

Jeff,
A 50amp alternator at full load takes aproximately 1hp of power, modern alternators are between 80amp to 100 amp but none work on full blast ever unless you are running lots of electrical devices all at once (easy to calculate).

THe only thing where fuel economy can be attributed to a fault in the electrical circuit (ie: alternator) is the changes the ECU makes to the fuel delivery and loading to compesate for voltage drops etc, but that would not be noticeable.

I think the motors going to spin the alternator and if electricity is produced or not the dam things still going to be spun by the engine, it's not like an airconditioner where the aircon only drives the aircon pump when the aircon is actually engaged and the aircon clutch is connected/disconnected, the alternator is allways engaged and also spinning.
If it produces power is not relevant to the force applied to make it actually spin.

I'm sure it takes no more engine power to spin an alternator that IS producing power to one thats NOT producing power, how does it make the alternator harder to spin if it's producing power.
The power is produced in the alternature windings and then sent to the REGULATOR, so power is being produced even if it is not available to the battery, unless the alternator is stuffed and then the light on the dash is on...

Jeff,

Maybe it's your regulator that needs a tweak to up your preferred voltage, not an alternator issue at all.

Alternators have a whistle about them when working really hard. If it is working flat out, all that power's gotta being going somewhere. Are you always running your batteries down with accessories after the engine is turned off? If not, where is the power going?

I'm thinking if your voltage is down, I'd be checking your regulator and adjusting it if you can. Then keeping a check on the batteries to make sure you're not overcharging them.

Tim

Jeff,
Have a look at the plate on the alternator, it may give the Ampere rating. An alternator will try and supply the load asked of it, so if you run it continuously at full load it will overheat and probably die and of course the output voltage will drop due to the internal series resistance of the alternator. If you have an amp meter put it in the output lead of the alternator and see what it reads but be prepared for a reading of 80 to 100 amps. It may be safer to take it to the Auto Elect.

Cheers

Jerry

G'day Jeff, here's my 2 cents worth. Disconnect both batteries and fully charge them on a good battery charger. When you reconnect them, check your voltage then.

If it goes back to 14.1+volts, then things are fine and your truck just needs a few more good runs. If it stays the same as it is now, then look a little further.

Just a little point, how reliable/accurate is the volt meter you are using now and is it the same one you have been using all along?

Hope this helps, Cheers

Hello Jeff,
I'm going to delve into the dim distant recesses of my electrical theory here, so we'll see what comes out,
1 hp = 780 Watts, approximately.

Therefore, 100 Amps at 14.5 Volts would be,
100 x 14.5 = 1450 Watts

It would equal roughly,
1450 / 780 = 1.86 Hp, call it 2 Hp for mechanical friction, bearings, belts etc and we'd be close.

Take the roof rack off and wind up the windows for a bigger saving,

Geoff.

Mainey, every action has an equal and opposite reaction, in this case more load on the alternator creates a bigger "back" emf opposite to the flow to all the gear being run which in turn loads up the donk just that little bit.....

Hello Crew,
The way an alternator works is,
The bit that spins is called a rotor and has a pair of brass collars on it called slip rings. There is a coil wound into the rotor called the excitation fields, the wire ends of this coil are connected to the slip rings.
Carbon brushes run on the pair of slip rings and have a DC voltage applied to them.

The outer stationary part is known as the stator. It's the part of the alternator that outputs the current and voltage to charge our batteries and run the vehicle. The stator actually produces an AC or Alternating Current and this output is fed throught the diodes to rectify it into a DC voltage.

When we apply a load to our alternator the output voltage actually drops. This is where the regulator comes into the picture. It increases the current flow through the excitation fields via the carbon brushes to bring the output voltage back up to the required value. As the load on the output increases the regulator increases the excitation current until the maximum rated excitation current is reached. At about this point the alternator is producing its maximum output current too.

As the load and excitation increase, the magnetic field strength (flux density) is increasing in proportion to the current flow through the excitation fields. All this increasing magnetic field strength requires increasing levels of power to drive it.

Hence, as load on the alternator increases the power required to drive it increases.

The alternators in our power stations work in exactly the same way, except they don't have diode packs on the output. They transmit the AC output to our homes.

I've seen diesel engines stall at full load and speed on ships when someone has done something silly with the power system. This happens because the alternator has required more power than the diesel is capable of supplying. These installations will output anything up to 2,000 Amps per phase.

Hope this helps,

Geoff.