Sunday, March 10, 2013

How an Inverter Functions How to Repair Inverters General Tips

It is rather futile discussing how to repair DC to AC inverter until one becomes fully informed regarding how does an inverter work. The following content walks you through both the aspects which can prove very useful to any electronic technician.Stages of an Inverter

As the name suggests DC to AC inverter is an electronic device which is able to convert a DC potential normally derived from a lead-acid battery into a stepped-up AC potential which may be quite comparable to the voltage that is found in our domestic AC outlets.

Although repairing sophisticated inverters are not easy and requires expertise in the field. Inverters which provide sine wave outputs or the ones which use PWM technology to generate modified sine wave can be difficult to diagnose and troubleshoot for the folks who are relatively new to electronics. However, simpler inverter designs that involve basic operating principles can be repaired even by a person who is not specifically an expert with electronics.

Before we move into the fault finding details it would be important to discuss how does an inverter work and the different stages normally an inverter may comprise:

An inverter normally may be divided into three important stages viz. oscillator, amplifier and the transformer output stage.

Oscillator: This stage is basically responsible for the generation of oscillating pulses either through an IC circuit or a transistorized circuit. These oscillations are basically the productions of alternate battery positive and negative (ground) voltage peaks with a particular specified frequency (number of positive peaks per second.) Such oscillations are generally in the form of square pillars and are termed as square waves, and the inverters operating with such oscillators are called square wave inverters.

The above generated square wave pulses though are too weak and can never be utilized to drive high current output transformers. Therefore these pulses are fed to the next amplifier stage for the required task.

Booster or Amplifier (Driver): Here the received oscillating frequency is suitably amplified to high current levels using either power transistors or Mosfets. Though the boosted response is an AC, but is still at the battery supply voltage level and therefore cannot be used to operate electrical appliances which work at higher voltage AC potentials. The amplified voltage is therefore finally applied to the output transformer secondary winding.

Output Transformer: We all know how a transformer works; in Ac/DC power supplies it is normally used to step-down the applied input mains AC to the lower specified AC levels through magnetic induction of its two windings. In inverters a transformer is used for similar purpose but with just opposite orientation, i.e. here the low level AC from the above discussed electronic stages is applied to the secondary windings resulting in an induced stepped up voltage across the primary winding of the transformer. This voltage is finally utilized for powering the various household electrical gadgets like lights, fans, mixers, soldering irons etc.

DC to AC Inverter, Repairing Tips

In the above explanation a couple of things become very critical for obtaining correct results from an inverter. Firstly the generation of the oscillations, due to which the process of voltage induction is able to take place across the windings of the transformer. The second important factor is the frequency of the oscillations, which is fixed as per the country’s specifications, for example countries that supply 230 V, generally have a working frequency of 50 Hz, in other countries where 120 V is specified mostly work at 60 Hz frequency.

Sophisticated electronic gadgets like TV sets, DVD players, computers etc. are never recommended to be operated with square wave inverters. The sharp rise and fall of the square waves are just not suitable for such applications.

However there are ways through more complex electronic circuits for modifying the square waves so that they become more favorable with the above discussed electronic equipment. Inverters using further complex circuits are able to produce waveforms almost identical to the waveforms available at our domestic mains AC outlets.

How to Repair an Inverter

Once you get well versed with the different stages normally incorporated in an inverter unit as explained above, troubleshooting becomes relatively easy. The following tips will illustrate how to repair DC to AC inverter:

Inverter is “Dead”: Check battery voltage and connection, check for a blown fuse. If that’s OK, open the inverter outer cover and do the following steps:

Locate the oscillator section; disconnect its output from its preceding stage and using a frequency meter confirm its proper working. No frequency or a stable DC indicates a possible fault with the stage. Check its IC and the associated components for the remedy.

In case you find the oscillator stage working fine, go for the next stage i.e. the amplifier stage. Check each device using a digital multimeter, you may have to completely remove them from the board for the particular tests. If you find a particular device to be faulty just replace it with a new one.

Sometimes transformers also become the major cause for a malfunction. Check for an open winding or a loose internal connection in the associated transformer. If you find it to be suspicious, immediately change it with a new one.

Although it wont be that easy to learn everything about how to repair DC to AC inverter from this chapter itself, but definitely things will start "cooking" as you delve into the procedure through a lot of practice and some trial and error.

Still have doubts...feel free to post your specific questions here.

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