How to make calculation of low-power transformers?

In factory practice of the electrician need to manufacture low-power (to 1 — 1,5 kW) the transformer for the portable lamp, spot welding, the device, etc. often meets. We give the simplified calculation of windings and the core of the single-phase transformer providing the accuracy, sufficient for practice.

Маломощный трансформатор напряжения 100ВА

Electricians often need the low-power transformer, for the portable lamp, spot welding. It is simple to make it, relying on calculations.

Input datas:

U1 — tension of the power line, i.e. tension of the primary winding (B)

U2 — tension which is required to be received from the transformer for operation of this or that device, i.e. tension of secondary winding

I2 — current of loading of transformers, i.e. current of secondary winding (and).

Are calculated:

Однофазный двухобмоточный трансформатор.

Figure 1. Single-phase double-wound transformer.

S — transverse section of the core (cm2)

Wi — number of rounds of primary winding

W2 — number of rounds of secondary winding

d1  and d2 — diameter of the winding wire of primary and secondary windings (mm).

Procedure of payments:    

  • the scheme of the calculated transformer is formed. For the example the single-phase double-wound transformer according to the scheme provided on the figure 1 undertakes;  
  •  transverse section of the core is determined by the following formula:

where P — the power (W) consumed by the transformer from network. She from the formula is defined:

where P — the power of loading (W);

n — efficiency. the transformer which undertakes equal 0,8 — 0,9;

  • the number of rounds of the winding demanded on voltage of 1 V:

  •  number of rounds of primary winding:


  • number of rounds of secondary winding:

where 0,05U2-n — number by which it is necessary to increase number of rounds of secondary winding for compensation of voltage drop in it.

  •  diameter of the wire of secondary winding:

  • diameter of the wire of primary winding:

  •  filling of the window of transformer steel with windings is calculated; if obyomotka are not located, then the section of the core has to be increased and calculations are made again (on the increased core transverse section).

Example. It is required to manufacture the transformer for the power supply of the portable lamps of the nayokalivaniye expected voltage of 12 V if the general current of loading makes 10 A.                                                        Transformer core section:

It is possible to take transformer steel of the Sh-32 type, the set of 4 cm (5 = 12 cm' 1).

The rated number of the p:velichin 50 is mean value from which it is possible to recede in nekoyotory limits: for the transformer with good steel at careful performance of coils and windings this size can be reduced to 45 and even to 40, and at other cases can be increased to 60 and even to 70 (if bad steel with poor insulation of separate plates is applied, when winding coils in bulk or operation of the transformer without switching off for a long time).

Number of rounds of secondary winding:

Number of rounds of primary winding:

Diameter of the wire secondary обмотки:Диаметр wires of primary winding:

Check on the window of iron shows that windings with laying between them and between each layer keep within freely.

  1. Emil

    set of 4 cm (5 = 12 cm ’1). not absolutely understood this record and how as a result to make the core what it to turn out how many sheets need to be collected.

    To answer
  2. Mikula

    Long ago the simple and reliable formulas forgotten by most of electricians. Materials and good hands are necessary even for their implementation. Now the piece of the medyashka will be incurred rather in "scrap metal" on the beer bubble, than will make of it the useful thing. And more often the useful thing will be transferred to "scrap metal" and spent on drink under the slogan: Long live I chelovechestvat the imperialism, bright future of all

    To answer
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