Problems in main AC power line 


The environment around an electronic equipment can affect the way the equipment operates. An electronic equipment may be affected by radio interference and power-line problems in the electronic environment. Electronic equipments may also be affected by temperature, humidity, etc, in the physical environment. You might expect the power company to guarantee smooth, uninterrupted, electrical power. Unfortunately, the conditions in the power lines to your home or office are constantly changing. Power problems can be divided into two main category, that is:-


1) Overvoltage

2) Undervoltage


Overvoltage = can be again divided into two types, spikes and surges.




A spikes is a very short burst of high voltage which can disrupt the operation of any electronic equipments. Some small spikes are caused by switching equipment, including motor controllers. When lighting strikes the power system, it can cause very large spikes.


The effect on electronic equipments varies with the size and power of the spike. A typical spike may have a fairly high voltage (5000 volts or more). Small spikes usually do not damage the components, but spikes caused by lighting can be much more powerful. It can burn the complete PCB of any electronic equipments. As you are troubleshooting, whenever you notice that many parts are damaged, in different parts of the equipment, suspect lighting damage.




These are overvoltage that last for more than one cycle. Surges are caused when some heavy electrical load is suddenly switched off. Surges can cause damage in many equipments.


In case the overvoltage is very severe, it can slip through the power supply and can blow up the components inside the equipment. A continuous high voltage can damage the power supply itself.


Spikes and surges are generated by the switching off of high power motors and other inductive appliances. All electric motors and transformer generate fields that store energy. When one of these appliances is switched off, the magnetic field collapses and as a result the stored energy having no other place to go, come down the power line as a spike.


Relatively small motors like those used in refrigerators, photocopiers and air-conditioners can also lead to spikes of thousands of volts.


Spikes and surges damage any equipment on a cumulative nature. When a number of spikes and surges get through, first the component and then the electronic equipments fail. Spikes and surges are the main cause of destruction of the electronic equipments.



Undervoltage = can be further divided into three categories, sags, brownout and blackout.




Sags are undervoltage that last for more than one cycle. Sags can slow down the computer disk-drives, leading to data errors and can cause head crash making permanent data loss.




Brownout is the low voltage condition that can be present even for several hours. This is often created when the power demand exceeds the capacitor of the power generator. Brownout can also cause many problems. Fortunately, high or low voltage problems can be tackled by using some good quality voltage regulators.




Blackout is the complete no-power condition. Sometime sudden power failure can bring about wastage of time, money and resources.


The interrupted process may have to be restarted from some earlier stages or sometimes even the complete work may have to be redone right from the beginning.




Any signal present on the power line besides the expected alternating current of 50 Hz is called the noise. Noise usually consists of short term over and under voltages. Any noise entering a computer brings about data errors. If the noise is strong enough, it can get past the power supply and create false digital '1s' and '0s' and can confuse the computer such as cause the computer to produce a bad bit of data. A few of the letters in a word-processing file may be incorrect, or some of the numbers in the spreadsheet may be wrong.


There are several different types of noise. Radio-frequency interference (RFI) is caused by radio or television sources, or even by other computer equipment. If your equipment is located near a radio or television transmitter, the power or signal lines may pick up enough of the radio or TV signal to cause problems. A weaker source, such as a wireless telephone, fluorescent lamp, lamp dimmer, or a car ignition system, can cause similar problems if it close enough to your equipment. Radio energy drops off very quickly as you move away from the source.


Electromagnetic interference (EMI) can occur when computer wiring runs too close to equipment that produces an electromagnetic field. As the magnetic field changes, it can 'induce' false pulses into nearby computer wiring. Again, this effect drops off sharply as you move away from the source of the EMI. EMI can be a problem when two wires run beside each other. A signal in one wire can create a changing field, which then induces a signal in the other wire. The effect is stronger when the wires are close together and when they are parallel for a distance. Large electric motors can create powerful electromagnetic fields and may cause EMI problems. Electric motors, which may cause EMI, are found in various kind of equipment-refrigerators, air conditioners, washing machines, furnaces, copier, elevators, machine tools, and so on.


Harmonic Distortion


Harmonic distortion is the deviation of the power supply waveshape from a pure sinewave. It can disrupt the operation of some sensitive device like computers and communication equipments.


Click here for more details on How to repair SMPS Power Supply Repair Guide


Author By : Jestine Yong


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