The principle of controlling the current of the secondary winding of a transformer, by means of regulating the primary current, is not new. Nevertheless, I would like to share the experience of using such a scheme.

The great advantage of the circuit is that there is an adjustment of small currents that take place in the power supply circuit of the primary winding. Accordingly, the cost of power elements is much lower.

At the end of the article is my YouTube video on the application of a similar circuit on a load transformer.

The same thyristor KU202 costs only 50 rubles. If a circuit with thyristor control of the secondary current were used, one would have to fork out for a T-122, the cost of which is already 250 rubles. And this is provided that the current in the secondary does not exceed 20-25 A.

And so ... Cheap KD 202 in a diode bridge, yes KU 202. And you don’t even need to put them on radiators. The currents are small 🙂 The rest is a trifle. Doesn't count!

Diodes on the secondary - this is already from your needs. If you are not going to exceed the load of 10A, then those indicated in the diagram will go. If you need something more powerful - the store will help you!

However, it is worth remembering that all primary winding controls are under mains voltage of 220V and touching them is life-threatening. Therefore, you need to pay special attention to the placement of all elements - do not allow them to come into contact with the metal case of the device!!!

The variable resistor must be fixed on the dielectric surface of the panel, and the adjustment knob must be made of plastic!

Below are two oscillograms taken on the secondary winding: with the position of the variable resistor close to the minimum and maximum.

A few years ago, based on a similar circuit, I made a load transformer with primary adjustment. The scheme then was slightly different from the one above. If you are interested in my review “Which scheme is better: in this article or in my YouTube video?”, So I will tell you that I liked this scheme more - it works more stable.

That loader I used (and still use) to test circuit breakers. The loader is capable of delivering more than 100 amps on the secondary. But in this mode, I use it for a short time (up to 10 seconds), because. the cross section of the secondary wire is 16 mm2.

In a long-term mode, without any special overloads, it stably holds currents up to 60A. Thus, I check the operation of the thermal protection of the machines. Compliance 1.2 In.

Examples of applying this scheme (links):

Do-it-yourself load transformer. With thyristor control on the primary winding.

Testing wire connections Which connection is more reliable How to connect wires