Please tell me, what factors determine the secondary output current of a 220V/12.5V transformer?

一沙一世

Please tell me, what factors determine the secondary output current of a 220V/12.5V transformer? [Copy link]

 

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I would like to ask, what factors determine the size of the secondary output current of the 220V/12.5V transformer? As shown in the figure below, the output current of this transformer is within 500mA. What factors limit its output current to within 500mA?

maychang

What factors determine the size of the transformer secondary output current?

Determined by the cross-sectional area of the primary and secondary conductors of the transformer.

In fact, to be more precise, it is determined by the copper loss of the transformer.

Going further, it is determined by the heat dissipation of the transformer.

damiaa

The original poster can pay attention to the production method of the transformer, how to choose the primary coil, secondary coil and magnetic core, and how to wind it.

High frequency transformers can also be wound by yourself.

However, I asked the transformer manufacturer to help me wind the samples, or the chip manufacturer's laboratory to help (I don't have the equipment and I'm too lazy to do it).

一沙一世

damiaa posted on 2023-6-3 09:37 The OP can pay attention to the production method of the transformer. How to choose the primary coil, secondary coil and magnetic core, etc., and the winding method. High-frequency transformers can also...

Thank you. The ratio of the primary and secondary coils determines the voltage ratio of the primary and secondary, but does not determine the upper limit of the secondary current? Now I want to ask what factors determine the current size of the secondary coil. Please answer this. Thank you

damiaa

Yishayishi published on 2023-6-3 11:02 Thank you, the ratio of the primary and secondary coils determines the voltage ratio of the primary and secondary, but does not determine the upper limit of the secondary current? Now I want to ask about the secondary...

After the transformer is wound, the upper limit of the output current is determined after connecting to the standard voltage.

If your load has a large power, it will not be able to carry it. It will show a drop in output voltage... etc. In short, it cannot carry the load.

All power lines have a load limit, including the mains: the voltage will drop at 10 pm when the power consumption peaks. If your mains power generation capacity is sufficient, this phenomenon will be alleviated. This is also the reason why power outages are required.

一沙一世

maychang posted on 2023-6-3 09:12 [What factors determine the size of the secondary output current of the transformer] It is determined by the cross-sectional area of the primary and secondary wires of the transformer. In fact, it is more accurate...

Thank you very much. Another decisive factor is magnetic saturation. When the current reaches a certain value, the magnetic field strength generated no longer grows upward, and the magnetic saturation occurs.

maychang

Yishayishi published on 2023-6-3 13:51 Thank you very much. Another decisive factor is magnetic saturation. When the current reaches a certain value, the magnetic field strength generated no longer grows upward, and magnetic saturation...

Magnetic saturation determines the upper limit of winding voltage but has nothing to do with current.

For example, the transformer in the first post has a primary rated voltage of 220V effective value. This value is determined by the number of turns of the transformer primary winding, the cross-sectional area of the core, and the saturation flux density of the core.

Can this transformer be used for AC 110V 50Hz? Absolutely, but it is a bit wasteful and does not give full play to the capacity of the transformer. But it must not be used for 380V 50Hz. If the primary is connected to 380V, the core will enter saturation, the no-load current will be very large, the transformer will heat up too much, and will eventually burn out.

maychang

Yishayishi published on 2023-6-3 13:51 Thank you very much. Another decisive factor is magnetic saturation. When the current reaches a certain value, the magnetic field strength generated no longer grows upward, and magnetic saturation...

Saying that magnetic saturation limits the maximum current shows that you haven't figured out how transformers work.

maychang

Yishayishi published on 2023-6-3 13:51 Thank you very much. Another decisive factor is magnetic saturation. When the current reaches a certain value, the magnetic field strength generated no longer grows upward, and magnetic saturation...

[When the current reaches a certain value, the magnetic field strength generated no longer grows upward and the magnetic field is saturated. ]

You think that when the current reaches a certain value, the magnetic field strength will no longer grow upward. This is because you do not understand the two concepts of magnetic field strength and magnetic flux density. Even for ferromagnetic materials such as the silicon steel core of the small transformer in the first post, the magnetic field strength is proportional to the current no matter how large the current is. However, the magnetic flux density is no longer proportional to the current after it reaches a certain value, but grows at a rate that is [slower] than the current change. This is magnetic saturation.

maychang

Yishayishi published on 2023-6-3 13:51 Thank you very much. Another decisive factor is magnetic saturation. When the current reaches a certain value, the magnetic field strength generated no longer grows upward, and magnetic saturation...

[When the current reaches a certain value, the intensity of the magnetic field generated no longer grows upward and the magnetic saturation occurs].

Your statement assumes that the high current is the cause and magnetic saturation is the result. In fact, when the primary of the transformer is connected to an AC voltage, magnetic saturation is the cause and the high current is the result. You have reversed the cause and effect relationship.

Gen_X

This is a different "industrial frequency" transformer with a core made of multiple layers of silicon steel sheets.

The power of the transformer is determined by two parts:

1. The cross-sectional area of the core (the tongue in the middle of the E-type). This area determines the maximum working power, which is the magnetic saturation limit mentioned above. It is generally determined by the material, stacking form, etc. In addition to not being able to increase power, it will also generate unnecessary harmonics and heat when it is close to saturation.

2. According to the power determined by the cross-sectional area above, choose the appropriate primary and secondary wire diameters. Generally, the current can be calculated according to the power and voltage, and the appropriate wire diameter can be found according to the current. The wire diameter mainly determines the current and heat generation as well as whether the space can accommodate it. If it is too thin, the power is insufficient and heat is generated. If it is too large, the coil will not be able to fit.

led2015

The structure of the transformer, core material, turns ratio, input voltage and load impedance will all affect it.