Testing a Transformer - How To Accurately Test A Transformer

There is two types of transformers in the market- linear transformer and switch mode power transformer. The transformers compose is different. Sometimes it is just referred as ac transformer. Linear transformer mostly used in radio, project kits, Vcd and etc while switch mode transformer can be found in Monitor, Tv, Fax and so on.

A transformer consists of two or more coils wound on the same core. For power transformers, the core material is commonly iron. For a radio-frequency transformer, the core material is commonly ferrite or air. The basic asset of a transformer is to change Ac voltage. A transformer cannot change direct current voltage. A step down transformer has a lower Ac yield voltage at its secondary winding than the Ac input voltage to its customary winding. Conversely, a step up transformer has a higher secondary than customary voltage. The transformer laminations or coating of shellac, enamel or varnish is to insulate adjacent turns from shorts in the middle of winding. I will not go too details about how transformer work and transformer calculation as you can read more details from most electrical and electronic transformers books.

How to test transformers: Transformer failures are relatively rare in most electronic equipment, compared with other components. If too much current goes through a coil or winding, the winding heats up and can either open up completely, or the insulation in the middle of turns of wire can break down, causing the coil to be partly or thoroughly shorted.

Just like a coil, you can check continuity of any customary or secondary transformer winding. The actual value of Dc resistance you read is rather meaningless, but at least you will know either a winding is open. Checking linear transformer is quite straight forward. Apply the ac voltage to the customary winding and expect yield voltage at the secondary side. No or low yield voltage means the transformer winding has open or shorted winding. Look for any evidence of overheating, such as darkened or blackened areas or a burnt smell.

About how to test a power transformer-it is a dinky bit complicated. You cannot apply ac voltage to the equipment and expect the desire yield at the secondary side without join together to load otherwise over voltage will happen (because you have removed all the secondary load) and will blow the power section which consist of power fet, pwm ic and etc. Switch mode power contribute are designed to run with load while linear transformer can be test without load.

The best way to test a switch mode power transformer is first remove it from the board. Check only the customary winding as secondary winding failures are exceedingly rare. How do we know which one is the customary winding? Trace from the big filter cap the positive pin to see where the circuit goes. It will go to one of the pin of the transformer. Then look for the power fet middle pin which is the Drain and it will lead to other pin of the transformer. This two pins is the customary winding of the transformer. Checking the resistance of the customary winding only can retell either it is open but it cannot check if it has advanced a shorted winding. Only by using a ringer test you will know if it shorted or not. A shorted turn in the customary winding can cause the power section to blow.

The cheapest ringer tester that i came over is Dick Smith Lopt Meter or flyback tester. Just join together the probes to the customary winding and the follow are promptly seen from the Led bar graph. 4-8 bar report a good winding, 1-2 bar report partial short and if the led goes off means there is a heavy short in the winding. Besides checking the transformer it can be use to check B+ Coil, horizontal yoke coil and flyback customary winding and ballast (choke).

The expensive ringer tester is from sencore equipment. Sencore Lc102 and Lc103C Besides checking capacitor it also have the potential to check all kind of winding. either it is a low voltage transformer, high voltage transformer, current transformer, pulse transformer, electric transformer, convention transformer this equipment will be able to check and test it.

If you do not wish to invest on this tester you may use a light bulb to check it. remove one of the customary winding pin and join together a 60 watt light bulb. One end to the circuit while the other to the transformer pin. If the bulb light and didn't goes off guess a shorted winding and if the light goes off, the winding is ok.

Transformer heal is not easy and it require a good skill to do it. Most of the transformer repairer adored to rewind bigger winding such as fan, car alternator and starter. Switch mode power transformer is a dinky bit difficult to rewind because of the small size and low price.

Testing Coil - 3 uncomplicated Methods To Accurately Test Any Coils Or Inductor

Testing coil is very easy compares to checking three leads components such as Scr, Fet and etc. In general, a coil consists of many turns or wire wrapped nearby a tasteless core. The core could be made of iron or even air. When an electric current passes straight through the coil, a magnetic field is produced. A coil in some respect s acts just opposite a capacitor. A capacitor blocks Dc while allowing Ac to flow straight through it; a coil allows Dc to flow straight through it while restricting Ac current flow. Another name for a coil is an inductor.

Coil or inductor can be test using an analog, inductance or a coil meter such as the dick smith flyback tester. A coil that is small in size, I would normally just test it with analog meter and you could check it on board too. Set your analog meter to X1 ohm and place the probes across the small coil. The meter should show some reading (or continuity) and this proved that the coil winding is okay. Small coils seldom spoilt because it have less winding compares to big coils where it could have many turns of winding and chances for it to go shorted is very high.

Testing bigger coil or inductor such as the computer monitor B+ coil, you need an inductance meter to find out the exact inductance value which is in the unit of henry (h). From experienced using an inductance meter to check coils to see if it good or bad is not recommended because a shorted coil (shorted in the middle of winding) could have a good inductance value and you would miss out checking a bad coil. Unless you want to use the inductance meter to presume the reading and do rewinding, looping and etc on that coil. I would only test a big coil with dick smith flyback meter. Any shorted winding in it could be for real detected by this meter.

Now is the time to share my true case example- a computer dealer send me a monitor for repair with power blink symptom. normally I do not level away repair the monitor but I would first use the flyback tester to scan all the major coils (smps, flyback, b+ coil and horizontal deflection coil) before using my digital or analog meter to do testing. When measuring the B+ coil, the Led lights went off and it suppose to show at least 5 Led bars and above. Upon soldering out the coil, I did not see any burn mark at the winding or loop and in fact it looks shiny. Because I trust the meter, I opened up the winding and to my surprised the internal winding had burnt into crisp but the outer winding looks good indeed! A new B+ coil restored the monitor to life.

By using a flyback tester for testing coil, it has helped me to search many shorted coils in switch mode power transformer traditional winding, B+ coil, flyback transformer traditional winding and horizontal deflection coil. The flyback meter can even be used to check the condition of ballast in fluorescent lamp too!