Toroidal Transformer Winding

[Adabella Frierdich]

Im partially rewinding a toroidal transformer just for the pure thrill of controlling the output voltage. I'm sure I'll get over it, but for the moment that prospect is pretty exciting for some reason :)

On the outside and between the primary and secondary windings, the transformer is wound with a clear plastic tape (no adhesive backing) that is 12mm wide and 3 mils (0.003") thick. I'm sure it performs a mechanical protection role and given its inter-winding appearance an electrical insulation role as well.

I notice the tape is pretty stiff (not floppy or stretchy to speak of) and holds the kinks from its original winding position pretty clearly. It occurred to me that it might be some sort of heat-shrinkable tape that stiffens and holds bends once it's been shrunk. That would make some sense I suppose because the shrinking would insure the winding underneath was tightly bound and less likely to become noisy or whatever.

According to DuPont, the dielectric strength of (their) mylar is about 4kV/mil at this thickness, so half-lapped and double wound as mine was, it provides a heck of an insulating layer, almost 50kV nominally.

I ran over it with the heat gun afterward and it tightened right up the few edges that were not quite flat. I can't tell the difference between this one and the others I have that are factory fresh. Except for the yellow mylar tape which I went a little crazy with; I was worried it wouldn't hold when I shrunk it again but that didn't seem to be any problem at all. I'll probably pull most of that off before I wind the secondaries; might as well keep it looking professional :)

I manufacture toroidal transformers commercially. All the toroidal transformers we make and the ones I've seen from other manufacturers use a clear mylar film for insulation. It isn't heat shrinkable by design or during the manufacturing process. The stuff we use is 50um thick and usually wound with a 50% overlap.

I have no idea where a hobbyist would buy it - I have trouble buying it in suitable quantities as a manufacturer. My supplier wanted me to order 1000 rolls of one size - I negotiated it down to 300 by telling him to throw the rest away (since the material is cheap but the freight is not). Perhaps try asking a local toroidal transformer manufacturer if they will sell you a roll.

I am done primary winding today of my toroidal core. Attached photo of transformer below. 755 turn of 0.914 mm magnet wire. Core size before winding OD-100mm, ID-60mm, Ht-50mm (M4,CRGO). Sir when I test for secondary voltage I get 2.7 volt on 10 turn of magnet wire. why I get less volt per turn. Because before making the primary winding I done partial test on core, wind 10 turn for secondary, I get 3.2 volt. And I am winding center tap for this transformer of 35-0-35 using dual winding method (2 wire at same time, bifilar.) If I want lower voltage from same winding can it be done? e.g for 25-0-25?

A smaller transformer can be used if the load is intermittent. Because the output power in this case significantly exceeds the nominal power, the secondary voltage drops below the voltages given. The voltage drop increases proportionately with the current being drawn.

The secondary voltages and currents are valid for normal output power. At partial load, the output voltage, as a function of transformer size, will be accordingly higher. The below figure shows the voltage increase for Talema standard toroidal transformers for partial loads.

As can be seen from the graphs below, Talema standard toroidal transformers are designed for a temperature rise of 60 C to 70 C at nominal load. When choosing a transformer size, the ambient temperature and heat sink coefficient of the mounting place must be taken into consideration. Figures show the typical temperature change which occurs as a function of output power or overload.

An autotransformer allows smaller dimensions and a more economical overall design in cases where galvanically separated windings are not required. The same transformation of voltage and current can be obtained with a single winding autotransformer as with a normal two winding transformer. There are two major differences:

Autotransformers have lower leakage reactance, lower losses, smaller excitation currents, and they can be smaller and less expensive than dual winding transformers when the voltage ratio is less than 2:1. And, of course, they provide no isolation.

The characteristics which give the toroidal transformer advantages also contribute to a disadvantage: high inrush current with initial application of power. Talema is successful at designing transformers with low inrush current.

where Vp-pk is the peak primary voltage, and Rp is the DC resistance of the primary winding, depending on the power capability of the transformer, and on how strongly the core was magnetized. This inrush current peak occurs for a short time during the first or second half period of the power sine wave.

The purpose of these devices is to cut off the transformer in the event of overheating. The one-shot fuse is used primarily for protection from internal transformer faults, tripping at a preset temperature. The auto-resettable thermal switch provides intermittent protection from internal transformer faults and external overloads. This device opens at a preset high temperature and closes at a preset lower temperature. These devices are mounted internally to the transformer and wired in series with the primary or secondary winding.

Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.

A toroidal transformer is a type of electrical transformer constructed with a torus or donut-shaped core. Its primary and secondary windings are wound across the entire surface of the torus core, separated by an insulating material. This configuration minimizes the magnetic flux leakage. Therefore, a toroidal core is regarded as the ideal transformer core design.

Toroidal transformers are suitable for sensitive and critical electronic circuits because of several advantages over traditional square and rectangular-shaped transformers. Some of these advantages are high efficiency, quiet operation, minimal heat generation, and compact size. They are mostly seen in power supply systems, audio systems, control equipment, power inverters, and other electronic devices.

Before going into the specifics of toroidal transformers, it is best to first understand the basic operating principles of electrical transformers. An electrical transformer is a passive machine that transfers electrical energy from one circuit to another using a magnetic field to induce an electromotive force. This is done while the circuits being electrically isolated from each other. Transformers are used to increase (step-up) or decrease (step-down) voltages without changing the frequency of the electric current.

The magnetic field involved in electromagnetic induction is typically from an electromagnet with a varying electric current. This varying electric current is commonly known as alternating current (AC). As the electrical current is generated and collapsed continuously at a given frequency, the magnetic field is also created and collapsed the same way. This magnetic field with varying amplitude induces an electric current to a second conductor. The induced electrical current in the second conductor has the same frequency as the electrical current from the electromagnet circuit.

A magnetic field with varying amplitude is not the only way to induce a current. A magnetic field can be imagined as a field with many lines of induction. Making the conductor "cut" through these magnetic field lines can generate an electric current. This phenomenon is seen in electrical generators.

The simplest transformer is a single-phase transformer. It has two electrical coils called primary and secondary windings. The primary winding is where the power supply is connected, while the secondary winding is where electricity is induced. These windings are wrapped in a closed-loop magnetic core.

The two windings are not electrically connected but are coupled by a magnetic field. Voltage can be increased or decreased in the secondary winding by altering the number of coils of a winding relative to the other. Since the transformer is considered a linear device, the voltage generated in the secondary winding can be predicted by determining the ratio of the number of turns of the windings. The result is known as the turns ratio (TR).

Simply put, power is obtained by multiplying voltage by the current. A transformer without any losses can be considered a constant power device, meaning the generated power in the secondary winding is the same as the power supply in the primary winding. Thus, to increase the voltage, the current must be decreased, and vice versa.

Core losses are from hysteresis or eddy currents. Hysteresis is due to the power required to reverse the magnetic field as it changes direction. This is given off as heat, which will then be dissipated from the machine. Eddy currents, on the other hand, are produced by the magnetic field from the primary winding within the core and are not part of the current generated for useful work. They are minimized by using laminated cores.

Copper loss is due to the resistance of the copper windings. All conductors have electrical resistances that cause a voltage drop as an electrical current passes through them. This loss cannot be easily reduced since it requires increasing the cross-section of the conductor. Consequently, this will require a larger and more expensive transformer. This loss causes a release in energy from the windings in the form of heat.

Stray loss is from the leakage of the magnetic field that influences other conductive parts of the transformer. Since this magnetic field is weak compared to what is present in the iron core, the eddy currents produced by stray magnetic fields cause negligible effect.

3a8082e126