Does an Alternator Need Power to Work?
It’s not immediately obvious why the alternator shouldn’t power up without having to ignite your vehicle, but on closer inspection of the internal workings of the automotive mechanical system, it’s quite clear that, given enough time, it can’t work without it.
There is a reason we are advised to keep jumper cables on us at all times when we are on the road. More than it is about preparing for the worst, the concern is supported by the underlying physics of vehicles.
If you have a vehicle, you may think that the battery powers the electrics in your car, but that’s not the case. The battery provides electricity needed for the starter motor to start the car.
When the car is running, the alternator generates energy to feed the electrical system and charge the battery. The alternator used to be called a generator, and it works in a similar way.
In this case, a car’s internal combustion engine spins pulleys under the bonnet, which turns the pulley on the alternator and creates energy.
How it works
An alternator works together with the battery to supply power for the electrical components of the vehicle. The output of an alternator is direct current (DC).
When the alternator pulley is rotated, alternating current (AC) passes through a magnetic field and an electrical current is generated. This is then converted to DC via the rectifier.
Advancements in technology have meant that alternators have changed vastly in the last 50 years. Originally, alternators were only used to generate current which was controlled by an external regulator.
The introduction of a built in regulator, in the 1990s, used the warning light to excite the alternator and start the charging process.
Many modern vehicles adopted a load request type charging system with the introduction of smart charge systems and CANBUS systems which are now widely being used. These systems are controlled by the vehicle Engine Control Unit (ECU).
As the vehicle demands more load the ECU sends a signal to the alternator requesting it to start charging. The alternator has to cope with varying electrical loads and adjust its charge rate accordingly.
This alternator rotor is driven by constant speed drive and this drive gets mechanical power from gas turbine engine, the
refore it only follow that said alternator does require a power but mechanical. Regarding speed control, if alternator is designed for constant frequency power out put obviously it has to be driven at constant speed.
Old version AC generator that has built in DC motor/AC generator motor part being common, part of it is an armature with commutator segments for motor function and the other part is rotating field for alternator function, the DC supply is given through slip rings to produce rotating field and AC output is derived from stator winding of that alternator section.
It is understood that in order to derive out put from a machine power is essential for the rotor to rotate either mechanical or electrical .
So, does it?
Yes—and no. But really, yes. The alternator (most, anyway) does not have permanent magnets as part of its field magnets (stator). The field magnets are electromagnets, so need some “juice” to produce a magnetic field, through which the armature can move to produce electricity.
If you had an alternator attached to a totally dead battery, and spun the alternator, it would not charge the battery. If the battery has a slight charge, or you jump start the car, it will energize the stator enough to get things going.
An alternator cannot ‘sustainably' generate power without a battery as it uses the back load to generate the electromagnetic field needed in place of the magnets in a generator.
So the next time you consider testing out whether you can drive without your battery, think again.