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 design 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 usually iron. For a radio-frequency transformer, the core material is usually ferrite or air. The basic property of a transformer is to change AC voltage. A transformer cannot change direct current voltage. A step down transformer has a lower AC output voltage at its secondary winding than the AC input voltage to its primary winding. Conversely, a step up transformer has a higher secondary than primary voltage. The transformer laminations or coating of shellac, enamel or varnish is to insulate adjacent turns from shorts between 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 between turns of wire can break down, causing the coil to be partly or completely shorted.

Just like a coil, you can check continuity of any primary or secondary transformer winding. The actual value of DC resistance you read is rather meaningless, but at least you will know whether a winding is open. Checking linear transformer is quite straight forward. Apply the ac voltage to the primary winding and expect output voltage at the secondary side. No or low output 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 little bit complicated. You cannot apply ac voltage to the equipment and expect the desire output at the secondary side without connect 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. Swith mode power supply 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 primary winding as secondary winding failures are exceedingly rare. How do we know which one is the primary 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 another pin of the transformer. This two pins is the primary winding of the transformer. Checking the resistance of the primary winding only can reveal whether it is open but it cannot check if it has developed a shorted winding. Only by using a ringer test you will know if it shorted or not. A shorted turn in the primary winding can cause the power section to blow.

The cheapest ringer tester that i came across is Dick Smith LOPT METER or flyback tester. Just connect the probes to the primary winding and the result are instantly seen from the Led bar graph. 4-8 bar represent a good winding, 1-2 bar represent 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 primary winding and ballast (choke).

The expensive ringer tester is from sencore equipment. Sencore LC102 and LC103C besides checking capacitor it also have the capability to check all kind of winding. Whether it is a low voltage transformer, high voltage transformer, current transformer, pulse transformer, electric transformer, custom 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 primary winding pin and connect 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 suspect a shorted winding and if the light goes off, the winding is ok.

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

Jestine Yong is a electronic repairer and a writer. For more information about electronic repair please visit his website at http://www.noahtec.com/electronic-repai r-articles.htm

---

Google News Updated : Thu, 24 Jul 2008 18:51:58 GMT Would UN Security Council Postpone Any Prosecution of Sudanese Leader? - Voice of America Voice of America Would UN Security Council Postpone Any Prosecution of Sudanese Leader? Voice of America - 1 hour ago By Joe De Capua As the International Criminal Court (ICC) considers whether to issue arrest warrants for Sudanese President al-Bashir, some are calling on the UN Security Council to block the action. Sudan's Beshir pledges peace as he leaves Darfur AFP Jordan's lower house opposes charges against Sudanese president Xinhua Hindu - Los Angeles Times - istockAnalyst.com - AllAfrica.com all 1,823 news articles Publ.Date : Thu, 24 Jul 2008 17:30:10 GMT Swimmer’s Positive Test Puts Olympic Berth Doubt - New York Times New York Times Swimmer’s Positive Test Puts Olympic Berth Doubt New York Times - 30 minutes ago By KAREN CROUSE The swimmer Jessica Hardy has not been penalized for a doping offense despite published reports that she tested positive for a banned substance. Video: Source:Hardy Tests Positive for Banned Substance AssociatedPress Sequence doesn't make Sense Los Angeles Times Gay Wired - Palo Alto Online - The Wenatchee World Online - The Associated Press all 750 news articles Publ.Date : Thu, 24 Jul 2008 18:21:30 GMT FOX News Poll: No Bounce for Obama From Overseas Trip - FOXNews ABC News FOX News Poll: No Bounce for Obama From Overseas Trip FOXNews - 27 minutes ago By Dana Blanton The significant news coverage Barack Obama is receiving on his foreign trip has not translated into a bounce in his numbers, a just-released FOX News poll shows. Wanted: 2 million poll workers for November The Associated Press Comment by Leonard Steinhorn Prof, School of Communication, American University New York Times - CNN - United Press International - PolitickerCA all 689 news articles Publ.Date : Thu, 24 Jul 2008 18:24:50 GMT South Texas begins cleanup after Hurricane Dolly - The Associated Press Calgary Herald South Texas begins cleanup after Hurricane Dolly The Associated Press - 30 minutes ago HARLINGEN, Texas (AP) - Residents across south Texas slogged through knee-deep muddy waters, tiptoed around downed power lines and dug through debris Thursday, but were thankful that Hurricane Dolly didn't pack the wallop they had feared. Video: Tropical Storm Dolly Causes Flood Worries AssociatedPress Dolly weakens, pushes inland USA Today East Valley Tribune - AHN - KIII TV3 - KVIA all 7,399 news articles Publ.Date : Thu, 24 Jul 2008 18:21:14 GMT Arizona reports first West Nile death of 2008 - Bizjournals.com TheMedGuru Arizona reports first West Nile death of 2008 Bizjournals.com - 1 hour ago Arizona has reported its first death from the West Nile virus this year. It also is the first West Nile death in the US this year. First bird in Nassau tests positive for West Nile Newsday Fighting West Nile Alexandria Gazette Packet KTAR.com - AZFamily - FOXBusiness - Boston Globe all 231 news articles Publ.Date : Thu, 24 Jul 2008 17:45:00 GMT Ford Has $8.7 Billion Loss, Shifts Away From Trucks (Update4) - Bloomberg Ford Has $8.7 Billion Loss, Shifts Away From Trucks (Update4) Bloomberg - 44 minutes ago By Bill Koenig July 24 (Bloomberg) -- Ford Motor Co., the world's third- biggest automaker, posted a record quarterly loss of $8.7 billion and accelerated a conversion to fuel-efficient vehicles to wean itself from money-losing trucks. Ford's Worst Quarter Ever BusinessWeek Ford Posts Loss of $8.7 Billion on Asset Woes New York Times Forbes - CNNMoney.com - Reuters - Los Angeles Times all 1,181 news articles Publ.Date : Thu, 24 Jul 2008 18:07:48 GMT Health Buzz: A $500 million Antismoking Campaign and Other Health News - U.S. News & World Report BBC News Health Buzz: A $500 million Antismoking Campaign and Other Health News U.S. News & World Report - 3 hours ago Billionaires Bill Gates and New York City Mayor Michael R. Bloomberg announced yesterday that they'll contribute a combined $500 million to a worldwide antismoking campaign, the New York Times reports. Video: Gates, Bloomberg Pool Riches to Fight Smoking AssociatedPress The $500 million war on smoking Minneapolis Star Tribune Reuters - Newsday - Economist - California Healthline all 639 news articles Publ.Date : Thu, 24 Jul 2008 15:43:30 GMT RSS For Web Pages Increase Traffic

PARLOT::Ebooks, Scripts, Websites, and more...

Adsense websites

Can I Use My Old Ink With My New Printer?

The quick answer is...yes and no.Consider this. How many printer... Read More

Refurbished Laptop Batteries

There are three refurbished laptop battery types, each named for... Read More

Getting to Know Inkjet Printers

Inkjet printers were born in the 1980s, replacing the popular... Read More

Expansion Cards Part 1: (of a 3 part series)

PCIThe expansion slots available on motherboards allow for a variety... Read More

Ceramic Disc Capacitor-How to Accurately Test It

The last article I mentioned about electrolytic capacitor breakdown when... Read More

How to Add or Remove an IDE ROM drive

CD ROMS - If you're adding or removing an internal... Read More

Testing Diode -The Accurate Way on How to Test Semiconductor Diode Using Multimeter

Testing diodes is different from testing a resistor because you... Read More

Ink Cartridges - A Humble Beginning

Computers and their accompanying printers were huge years ago. In... Read More

Adding USB 2.0

The process of adding USB 2.0 ports took no time... Read More

What to Do Once You Are Infected with Spyware, Ad-ware or Viruses

What to do once your PC is infected with spyware,... Read More

Pixel Disruption To Cause Nausea From User of Computer Screen

As we study the issues associated with teaching kids in... Read More

Build Your First Computer from Hardware Scratches

Wow- if you do it first time and have some... Read More

RAM - What is It & Why You Need Plenty

This is the first article in the Understanding Your Computer... Read More

Expansion Cards Part 2: AGP

Expansion Cards Part 2: AGPThe first in this series of... Read More

Inkjet Printer Tips to Select Proper Printer

If you are tight on budget, go for Inkjet Printer.... Read More

Used Laptop Computer: Your Quick Purchase Inspection Guide ? Part 4

Used laptop computers are everywhere these days. How can you... Read More

How to Change, Upgade or Remove an IDE Hard Drive

Hard drives - Hard drives are a little more complicated.... Read More

How To Stop Junk Faxes From Wasting Your Paper and Toner

Junk faxes waste the resources of every business. It is... Read More

Adding Serial Ports to a Computer with Only USB Ports

So you bought a new computer but you don't have... Read More

Upgrading, Adding or Removing a Video Card, Sound Card, or Other AGP/PCI Card

For Video cards - Most PC video cards these days... Read More

What Tablet PCs Can Do for You

Tablet PCs are great. If you are a mobile person,... Read More

A Short Introduction to Blu Ray

Blu ray is a next generation optical media format developed... Read More

Getting A Great Refurbished Laptop

Are you sick of all the high priced notebooks out... Read More

An Introduction to HD-DVD

High density digital versatile disc is a digital optical media... Read More

RFID for Beginners

RFID technology is used frequently today and has been around... Read More