Electrical Terms



QUESTION : (1) What is the voltage of a single cell in a multi cell wet cell 12v battery as used in most cars?

A 12v battery consists of 6 cells producing slightly over 2v each. These cells are connected in series to produce 12v. The leading and trailing cells have an external (+) positive terminal and a (-) negative terminal where battery leads power up the entire vehicle circuits with 12v.


QUESTION : (2) What is meant by the term voltage drop?

Voltage drop occurs where the resistance in a circuit is great enough not to allow the flow of 12v from the battery source. The voltage drop could be the result of bad connections or high resistance in the electrical wiring. This voltage drop will increase as the circuit heats up lowering the performance of the electrical component.


QUESTION : (3) Around what voltage should an alternator be producing to charge a 12v battery?

An alternator charges around 14v so as to be able to overcome the battery voltage and deliver a charging voltage. Any higher than this will overheat the cells and boil out the water. The electrolyte (electricity conducting fluid) as used in wet cells is usually made up of 33% sulfuric acid and 66% distilled water.


QUESTION : (4) What are these terms measuring, volts, amps, watts and ohms?

Volt … is a measurement of the electrical potential of a power source.
Amp…is the measurement of strength of the electrical current flow.
Watt…is the measurement of the electrical power required to operate a component.
Ohm…is the measurement of the resistance of a conductor (To calculate the minimum size of a fuse and wiring for a particular component you simply divide the wattage by the voltage and that gives you the amperage. Eg if you are fitting 2 x 150 watt driving lights on a 12v system you will design the circuit with 30-amp fuse and 30 amp wire to power the relay and lights.) 300 w divided by 12v = 25 amps. required to operate these lights.


QUESTION : (5) What is the basic difference between DC (direct current) and AC (alternating current)?

Direct current (DC) flows in one direction only from positive (+) to negative (-) while alternating current flows in both directions in a cycle between (+) and (-).


QUESTION : (6) With reference to a diode in an alternator, what is its function?

A diode is an electronic one way switch that allows the flow of current in one direction only. In the function of an alternator the diodes convert the generated alternating current (AC) into direct current (DC).


QUESTION : (7) What is the purpose or function of a relay in an electrical circuit?

A relay is a switching device that is used so the control switch of a component does not have to carry the current required to operate that particular component. The advantages of using a relay to operate electrical components is that the switching side of the circuit can be of much smaller capacity than if the component was switched directly from the control switch. The load required to operate the component is connected to the battery source through a heavier circuit that is switched at the relay. The result is good current flow with little voltage drop and higher performance of the component.


QUESTION : (8) What is the basic difference in the method of power generation between an alternator and a generator?

The operation of an alternator and a generator both rely upon passing a stator or armature through magnetic fields the main difference is that a generator uses permanent magnets to supply the magnetic field where the alternator uses electromagnets to supply the magnetic field.
One advantage of a generator over an alternator is that a generator will supply generated current even when connected to a fully drained battery but an alternator in the same situation will not as it needs the field wire to be energised.


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