TRANSFORMER

The transformer electrical component having the ability to change the voltage level and current by two coils wound around a common core or center . The core consists of a large number of plates or foils of an alloy of iron and silicon . This alloy reduces magnetic hysteresis losses ( ability to maintain a magnetic signal after removal a magnetic field ) and increases the resistivity of iron .

Operation of a transformer

The change in voltage or current that makes a transformer happens because the secondary winding is induced by a magnetic field produced by the primary winding in conjunction with the core. The change in voltage or current, delivered by the transformer is reversed, ie when the transformer increases the voltage, low current; and when low voltage, current rises. This leads to a law: the power transformer delivery, can not exceed the energy that goes into it.Although the primary and the secondary winding are insulated by cardboard, waxed paper, pressboard or plastic, the magnetic field is transmitted from the primary winding to the secondary.There is a relationship between the turns of the primary winding and the secondary winding. This relationship determines the output voltage of the transformer are equal and the relationship between the turns of the windings and the input and output voltages.When the primary winding to the secondary winding is equal (1: 1), the voltage and input current are equal to the output voltage and current. In this case the transformer only serves to make galvanic isolation, meaning that we can touch the output current without being electrocuted.By changing the turns of the secondary winding wire, change the output voltage of the transformer. Example: if every turn of the primary winding, give three laps in the secondary; would, in the case of applying a voltage of 10 volts at the input, the output would be 30 volts. And as we wind wire around the side for every three turns of the primary; in the case of applying a voltage to the input of 30 volts, we would have at the output 10 volts.

Then we will see a practical method to determine the characteristics of the transformer for your amplifier or any other device. Actually there are many ways to assess and calculate a transformer, which propose, leads easily and fairly accurately the transformer model we need.

The starting point is to determine the power delivered each amplifier channel, if the amplifier is stereo. Each channel will contribute half of the power amplifier. If it is a mono amplifier, the total power will be delivered by the only exit.

An example: having a 100-watt stereo amplifier, means that each channel is 50 watts, which means that the delivery channel power is 50 watts. In this case we use 8 ohm speakers, namely the speaker impedance RL is 8 ohms, determined by the manufacturer of the integrated output or circuit design itself.This means that the actual voltage (RMS) of the transformer needed to power the amplifier is equal to the continuous voltage that consumes the amplifier, divided by the square root of 2 (1.4141). Now, by that loss it is advisable to increase the value obtained in two or volts.

For instance; if your amplifier is powered with 34 volts DC, then the RMS voltage of the transformer is calculated as follows:

RMS voltage = 34 / √2

34 / 1.4141 = 24 volts AC

The nickel is equal to 24 volts RMS voltage =

 

These 24 volts is advisable add about 2 volts, resulting in 26 volts AC

The transformer core defined dimension. Power is nothing but the product of multiplication between the voltage and amperage of the transformer. Thus:

PT = V x I RMS RMS

 

For example in the previous case calculate a voltage of 24 volts (RMS) and a current of 5 amperes, then the power will be:

PT = 24V X = 120 watts 5Amp

TABLE AWG

The reason of increasing two volts in the secondary winding, to provide a margin loss caused by the consumption of the rectifier diodes and the natural resistance of the transformer.For your transformer respond properly and deliver the desired current, it must be built with copper wire of sufficient gauge.

How to find the wire gauge of the secondary windingTo find the proper gauge wire of the secondary winding, must find the amp consumption of the amplifier and then refer to Table AWG. In this case the amplifier consumes 5 amps we got to divide the wattage of the amplifier between the output voltage (secondary winding). If we look at the AWG table, we see that the 16-gauge wire, supports 5.2 amps, but in practice, you can use a thinner gauge, for example 17, (not more than one point lower caliber because it could overheat the transformer or not deliver the required power).It is worth remembering that if we do not use amps, simply divide the power amplifier between output volt transformer.It is clear that if the amplifier's transistors, the secondary winding has been adding amps consumed by transistors. For example, when an amplifier works with 4 transistors 2SC5200 and we know that each of these requires 1.3 amps, we have a total of 5.2 amps equivalent to 16 gauge wire.

How to find the wire gauge of the primary windingTo find the gauge of the wire of the primary winding, first we have the amperage. This is achieved by dividing the watt amplifier, the voltage between the outlet or public network in your country.In this case we have a supply of 120 volts in the public network.

RMS Amperes = Watts / Volts input

The nickel is equal to:

Amps = 120W / 120V = 1 Amp

 

120 watts divided 120 volts, equal to 1 ampere. If we look at our AWG table, the closest size is 23.

As finding the area of the transformer core 

Now the core section is related to the total power as follows:

Core section PT = √

The core section is equal to the square root of the total power.

As we saw earlier, we obtained 120 watts of power to the transformer. Then the core section should be:

√ core section = 120 = 10.95 square inches

This means that it will serve a core of 3.3 cm wide by 3.3 cm long, corresponding to a core area of 10.89 square centimeters, although not necessarily have to be square. The sheets or plates that come closest, with 3.2 inches long at its center, would place the number of sheets to give us about 3.6 cm wide to achieve that goal. Commercial formwork for this case is 3.2 cm by 4 cm which has a power output of 163 Watts. This power learned of squaring the core area.

3.2 x 4 = 12.8 cms2

12.8 x 12.8 = 163.84W

It is best to always use a core size larger than we need to be more than enough potential and not have problems to get the wire.

Measure to set the width of the core sheets or adding iron sheets…. PICTURE ANCO……

In the figures, the transformer core seen above, the core section will be the product of the length in centimeters per centimeter width shown. This should correspond to the value calculated at least, as we said before, if higher the better, because it gives a margin of power.

Calculating the number of turns of copper wire

There is a constant which is the number 42, we will not go into details about the origin of this number, since the idea is not to delve into mathematics, if not get people with little knowledge to achieve transfomradores.

To calculate the number of windings or turns of copper wire, in our example, 42 is divided between 12.8 cms2, which are the core area of 3.2 x 4.

Number of turns = 42 / 12.8 Cm2

42 12.8 = 3.28 split turns or turns of wire per volt.

This means that for the primary winding, are 120-volt outlet, multiplied by 3.28, equals 393 turns or turns of copper wire. If in your country the public network voltage is 220V, multiply 220 by 3.28 volts = 721 turns on the primary winding.

To find the number of turns of the secondary winding, the transformer 26 volts are taken and multiplied by 3.28 to obtain 85 coils or turns of wire.

Now that we know the wire sizes to use and the number of turns, we can make our Transformer

Connecting two single transformers  

In the case before us difficult to get a transformer with central TAP , an easy option is to connect two single transformers ( No Central TAP) .The figure shows how the correct connection is simple to convert our two transformers in a transformer with central TAP. Furthermore as the amount of iron plates is doubled , it is increased a little power , improving performance of the two transformers .

At other times it becomes difficult to achieve high amperage transformers and can not get the materials to do so.As a solution to this problem can be connected two transformers in parallel and so maintain double the amperage and voltage.

For example: We need a transformer 18 + 18 volts AC, with a current of 12 amps to power amplifier 300W with TDA7294.We can connect in parallel two transformers of 18 + 18V AC, with a current of 6 amps and so we get the transformer we require for this project.

If desired, you can use a program called transformer calculation, which makes the calculation work for you. For the calculations with the program out correctly, it is necessary to add two millimeters on either side of core Since the formwork where the wire is coiled wire occupies space.Another option is to use the official program from our Web site, which was created by Jaider Martinez, one of

our loyal fans. Is a free software for calculating dimensions and turns of wire gauge, by simply entering the voltage and amperage.

Examples of performing calculations for transformers

By Federico Michelutti of Argentina .

Before trying the examples we consider the following information:

Table core formworkMeasure the area of the core in centimeters. Compare the core area with the closest in the table , use this or the next largest area you need and the number of turns per volt , calculate the wire turns of the primary winding and secondary

NÚCLEOPOTENCIA MÁXIMA

VUELTAS POR VOLTIO

ÁREA Cm ²

1.6 x 1.9 9W 14 3.042.2 x 2.8 37W 7 6.162.5 x 1.8 20W 9.3 4.52.5 x 2.8 49W 6 72.8 x 1.5 17W 10 4.22.8 x 2.5 49W 6 72.8 x 3.5 96W 4.3 9.82.8 x 5 196W 3 14

3.2 x 3.5 125W 3.75 11.23.2 x 4 163W 3.3 12.83.2 x 5 256W 2.625 163.8 x 4 231W 2.76 15.23.8 x 5 361W 2.21 193.8 x 6 519W 1.85 22.83.8 x 7 707W 1.58 26.63.8 x 8 924W 1.38 30.43.8 x 9 1170W 1.22 34.2

3.8 x 10 1444W 1.1 383.8 x 11 1747W 1.004 41.83.8 x 12 2079W 0.921 45.64.4 x 9 1568W 1.06 39.6

4.4 x 10 1940W 0.95 444.4 x 11 2342W 0.867 48.44.4 x 12 2787W 0.795 52.8

As the core :Multiplying ( X) ( center width of the sheets ) by ( Y) (given by the number of caps background ), we get the area in square centimeters, the core of our transformer. Means in millimeters available which have to ( X ) are : 16 , 20, 22 , 25 , 28, 32 , 38, 44 , 50, 60 , 70, 80 , 100 .( Y) is determined by the number of plates or plates that will put one above the other.

 

 

Example No. 1: 

Admission: ( primary winding ) 220 VOutput 1 : (winding side ) 60V to 4amp

The first thing to calculate is the power of our transformer:

In this case : x 4 Amp 60V . = 240 watts

Now , if we look at the table above we find the most approximate value is 256W (These are maximum power and must be above to reduce losses )

NÚCLEO POTENCIA MÁXIMA VUELTAS POR VOLTIO ÁREA Cm ²3.2 x 5 256 W 2.625 16Thus far are the core that best suits our needs :3.2 cm X = Y = 5 cm

However; by dividing the power of our amplifier , between the input voltage , we obtain the amperage to the primary winding :

240w / 220v = 1.09 amp .

Now we look at the AWG table

Calibre Mils Circulares Diámetro mm Amperaje17 2.048 1.15 4.123 0.509 0.57 1.0

See, must use to the primary winding, magnet wire 23 gauge and 17 gauge wire for the secondary winding since this requires 4 amps.

To calculate the number of turns of the primary winding, we must multiply the Turns per volt (2.21 according to our core formwork table), by the amount of input volt transformer (voltage public network):

220 x 2.625 = 578 turns for the primary winding.

For the secondary winding, the same but with the desired output voltage:

60V x 2,625 = 158 turns for the secondary winding.

Example No. 2: 

Admission: (primary winding): 120VOutput 1: (secondary winding): 32 x 32V to 3Amp (TAP will use Central)

The first thing to calculate is the power of our transformer; In this case: 32 + 32V x 3 Amp. = 192 Watts

Now, if we seek in our core formwork table, we find the value that comes closest is: 196W, (as they are maximum powers).

NÚCLEO POTENCIA MÁXIMA VUELTAS POR VOLTIO ÁREA Cm ²2.8 x 5 196W 3 14Thus far found kernel we need, which is 2.8 cm X = Y = 5 cm

However; to divide our power amplifier between the input voltage , amperage get the value for the primary winding :

192W / 120V = 1.6 amp .

Now we look at the AWG table

Calibre Mils Circulares Diámetro mm Amperaje21 810.1 0.72 1.618 1.624 1.02 3.2

You see, we use a 21 gauge for the primary winding, and a bore 18 for the secondary winding, since this must submit 3 Amp.

To calculate the number of turns of the primary winding, we must multiply the Turns per volt (Table 3 as core formwork), the amount of input volt (public network):

120V x 3 = 360 turns for the primary winding.

For the secondary winding, do the same but with the desired output voltage:

64V x 3 = 192 turns. In this case, to reach around 96, we welded wire TAP Central, or we can wrap the wire twice and give only 96 laps, as seen in the video.

Example No. 3: 

Input: 220V (primary winding)Output 1: 24V 3 Amp (secondary winding)Output 2: 9V 1.6 Amp (additional secondary winding)The first is to calculate the power transformer to be delivered, in order to find the appropriate size core.

For this case we take the power of the main secondary winding, which is 24V x 3 Amp) = 72 watts

Then look at the core of formwork table and find the approximate value more over, that is: 96W (Note be at least 20% up, thinking of the eddy current losses).

NÚCLEO POTENCIA MÁXIMA VUELTAS POR VOLTIO ÁREA Cm ²2.8 x 3.5 96W 4.3 9.8

Thus far are the core we need:X = Y = 2.8 cm by 3.5 cm .

However; to divide our power amplifier between the input voltage , amperage get the value that must deliver the primary winding :

96W / 220V = 0.4 amp .

Now we look at the AWG table

Calibre Mils Circulares Diámetro mm Amperaje27 0.202 0.36 0.418 1.624 1.02 3.221 810.1 0.72 1.6

See, we use a 27 gauge for the primary winding 18 gauge to 21 gauge secondary winding and to the additional winding.

To calculate the number of turns of the primary winding, we must multiply the Turns per volt (4.3 per table formwork core) by the amount entered volts (voltage public network).

220 x 4.3 = 946 turns for the primary winding

For the secondary winding should do the same, but with the desired output voltage:

V 24 x 4.3 = 103 laps.

And for the additional winding, we have: 9V x 4.3 = 39 laps.

Example No. 4: 

Input: 220V (primary winding)Output 1: 33 + 33v to 3amp (secondary winding)Output 2: 12v 0.8amp (additional secondary winding)

Let's start calculating is the power of our transformer:

In this case we take the power of main secondary winding, which is 33V + 33V Amp x 3 = 198 watts.

Now we seek in our core formwork table and find the approximate value more over, that is: 231W (Note be at least 20% up, thinking of the eddy current losses).

NÚCLEO POTENCIA MÁXIMA VUELTAS POR VOLTIO ÁREA Cm ²3.8 x 4 231W 2.76 15.2

Thus we have found the most appropriate measure of core to our our core transformer:X = Y = 3.8 cm by 4 cm .

However; to divide our power amplifier between the input voltage , amperage get the value of the primary winding :

231W / 220V = 1.05 Amps.

Now we look at the AWG table

Calibre Mils Circulares Diámetro mm Amperaje22 642.4 0.65 1.218 1.624 1.02 3.224 0.404 0.51 0.8

You see, we used a .22 for the primary winding, though you can use 23 gauge, to be very little difference.We used for the secondary winding wire 18 gauge, as this winding takes 3 Amp and 3.2 Amp delivery wire 18. And the additional winding use 24 gauge wire, requiring 0.8 Amps.

To calculate the number of turns of the primary winding, we must multiply the turns per volt (2.76 according to our core formwork table), by the amount entered volts (voltage public network):

220 x 2.76 = 607.2 turns for the primary winding.

For the secondary winding, the same is done, but with the desired output voltage:

33 + 33 V x 2.76 = 182 turns. In this case, to reach around 91, we welded wire TAP Central, or we can wrap the wire twice and give only 91 laps, as seen in the video.

And we have the additional winding: 12Vx 2.76 = 33 laps.

Very special thanks Federico Michelutti of Argentina.