Custom Made Isolation Transformer

One of my ERG member from Iran that had bought my ebooks successfully built an isolation transformer with the help from his friend. This is the email he wrote to me
Refer to your new smps repair book and the importance to have a isolation transformer first i decide to buy one but i could not found any in the town ready to use therefor the only way was to make one
by assistance one of my friend mr esmaili he has transformer shop he made one transformer 1:1 220 to 220 volt for me and then i assemble the other parts inside. and out side of a metal box
i put voltmeter range up to 250volts and ampere meter range up to 5 amp on/ off switch /fuse ac cord pilot lamp on the panel also i fixed the transformer with 4 screw in the bottom of the box 220 volt out let is on the front panel that is safe 220 volts ground free total cost me 50 usd and from now i work in safety

What Is Toroidal Transformer

Here is a good explanation taken from Wikipedia:

“Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or perm alloy wound into a coil, powdered iron, or ferrite. A strip construction ensures that the grain boundaries are optimally aligned, improving the transformer’s efficiency by reducing the core’s reluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core. The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed, and also provides screening to minimize the core’s magnetic field from generating electromagnetic interference.

Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (see “Classification” above).

Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to a megahertz, to reduce losses, physical size, and weight of switch-mode power supplies. A drawback of toroidal transformer construction is the higher cost of windings. As a consequence, toroidal transformers are uncommon above ratings of a few kVA. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.”

For your information I’ve seen Toroidal transformer in Computer subwoofer speaker system but not on any Monitors or even Computer SMPS

Transformer or Inductor

Once in a while i do get question like how do i know whether the component is a transformer or an inductor since both of them have similar shape? For your information in certain electronic equipment like the Samsung CRT Monitor the inductor (wrapped like a transformer) almost have the same size as a transformer! The first thing that i told them was to check on the marking on the circuit board. If it start with a “T” letter then it is a transformer and if it start with a letter “L” then it is an inductor.

Generally the transformer have a bigger size than inductor and assuming if there is no marking on the board then i guess you have to look at the circuit from behind. This will require some experience to identify the diffrences between the transformer and the inductor circuit. Transformer primary winding will usually have a transistor (fet or bipolar) to drive the winding while inductor is usually a bit direct which mean there will be an input and an output especially in the RFI filter circuit AC SUPPLY side.

Take a board now as a test and start to see the difference between a transformer and an inductor. If you have question about this topic please feel free to leave your comment below

Testing A 240V Transformer

The best way to test a 240v linear transformer is to power on. Of course you can test the ohms of the winding for the primary and secondary side but measuring the input and output voltage by far the most accurate method. You must have the courage to test it if you are a beginner or else get someone who has experienced in the electronic repair field to guide you.

Place you analog or digital meter to the input of the transformer and make sure there is 240v entering in. If no voltage then begin to troubleshoot upward until you managed to find the fault. Assuming the input measured 240v, now you have to check the output. If the linear transformer output stated 9 v ac then you should expect a little higher ac at the output (say may be 9.8 vac and etc). Once you got the ac voltage rating then you would know that the transformer actually working. Note: please do not perform this kind of test on switch mode transformer because if the switch mode transformer do not have load on it, it will blow the whole power section

TRANSFORMER DESIGN AND APPLICATION HANDBOOK

TRANSFORMER DESIGN AND APPLICATION HANDBOOK

Electric Power Transformer Engineering

Electric Power Transformer Engineering