Current or power consumption indicator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The proposed device is intended for light indication of the consumed current (and, accordingly, power) by a load connected to a 220 V lighting network. It is included in the break of one of the network wires. Features of the device - the absence of any additional power source and galvanic isolation from the network. This was achieved by using high-brightness LEDs and a current transformer.

Fig. 1

The diagram of the indicator is shown in fig. 1. It consists of a current transformer T1, two half-wave diode rectifiers VD1 and VD2 with smoothing capacitors C1 and C2. Series-connected LEDs HL1 and HL4 are connected to the first rectifier, HL2 and HL3 are connected to the second one. Trimmer resistors R2-R4 are installed in parallel with the HL1-HL3 LEDs. With these resistors, you can set the output current of the rectifier, at which the corresponding LEDs start to shine.

When the load current flows through the primary winding of transformer T1, an alternating voltage appears in the secondary, which is rectified by both rectifiers. The indicator is configured so that when the load current is less than 0,5 A, the voltage at the rectifier outputs is not enough to light the LEDs. When the current exceeds this value, a weak but noticeable glow of the HL1 LED (red) will begin. As the load current increases, the rectifier output current also increases. If the load current reaches 2 A, the HL2 LED (green) will turn on, at a current of more than 3 A, HL3 (blue) will light up, and when the current exceeds 4 A, the white HL4 LED will light up. Experiments have shown that the indicator is operable up to a load current of 12 A, for domestic conditions this is quite enough, while the current through the LEDs does not exceed 15 ... 18 mA.

Fig. 2

All elements of the indicator, except for the transformer, are installed on a printed circuit board made of fiberglass laminated on one side, the drawing of which is shown in Fig. 2. The device uses tuning resistors SP3-19, capacitors - imported oxide, diodes can be used with any low-power rectifiers, LEDs - necessarily with increased brightness.

The current transformer is made from a step-down transformer of a small-sized power supply (120/12 V, 200 mA). The active resistance of the primary winding is 200 ohms. The windings of this transformer are wound in separate sections, which simplifies rework. Its primary winding will become the secondary winding of the current transformer T1, and the secondary is removed and the primary winding wire is wound instead. For the above parameters of the indicator, the number of turns of the primary winding is three, the wire must be in reliable insulation and designed for the mains voltage and current consumed by the load. For the manufacture of a transformer, any low-power serial step-down transformer is also suitable, for example, from the TP-121, TP-112 series.

To calibrate the indicator scale, you can use an AC ammeter and a step-down transformer with a secondary winding voltage of 5.6 V and a current of up to several amperes. The device being adjusted, the ammeter and the load are connected in series to this winding - a variable resistor with a resistance of 10.15 ohms and a power of 25 watts. By changing the resistance of the load resistor, the required current is set and the trimming resistors achieve the ignition of the LED corresponding to this current.

Fig. 3

The appearance of the mounted board is shown in fig. 3. The transformer and the board can be placed at a great distance from each other. By changing the number of turns of the primary winding of the current transformer, it is possible to rebuild the indicator to a different current indication interval. This device also allows you to indicate the power consumed by the load in the range from 100 W to several kilowatts, for this the LED scale should be calibrated in units of power.

Author: I. Nechaev

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