Exceeding the output current in power supplies indicates an increase in power consumption in the load device. Sometimes the current consumption in the load (due to a malfunction of the connections or the load device itself) can increase up to the value of the short circuit current (SC), which will inevitably lead to an accident (if the power source is not equipped with an overload protection unit).
The consequences of an overload may turn out to be more significant and irreparable if you use a power source without a protection unit (as radio amateurs often do today, making simple sources and buying inexpensive adapters) - energy consumption will increase, the network transformer will fail, individual elements may catch fire and an unpleasant odor may occur.
In order to notice in time that the power supply has entered the “non-standard” mode, simple overload indicators are installed. Simple - because they, as a rule, contain only a few elements, inexpensive and accessible, and these indicators can be installed universally in almost any homemade or industrial power source.
Simple circuit of current overload indicator
The simplest electronic circuit of a current overload indicator is shown in Fig. 1
Rice. 1. Electrical circuit of the light indicator of current overload.
The operation of its elements is based on the fact that a low-resistance limiting resistor (R3 in the diagram) is connected in series with the load in the output circuit of the power source.
This unit can be used universally in power supplies and stabilizers with different output voltages (tested under output voltage conditions of 5-20 V). However, the values and ratings of the elements indicated in the diagram in Fig. 3.4, selected for a power source with an output voltage of 12 V.
Accordingly, in order to expand the range of power sources for this design, in the output stage of which the proposed indication unit will operate effectively, it will be necessary to change the parameters of the elements R1—R3, VD1, VD2.
As long as there is no overload, the power source and load node operate in normal mode, permissible current flows through R3 and the voltage drop across the resistor is small (less than 1 V). Also small in this case is the voltage drop across the diodes VD1, VD2, while the LED HL1 barely glows.
When the current consumption in the load device increases or there is a short circuit between points A and B, the current in the circuit increases, the voltage drop across resistor R3 can reach the maximum value (output voltage of the power supply), as a result of which the HL1 LED will light up (blink) at full strength.
For a visual effect, the circuit uses a flashing LED L36B. Instead of the specified LED, you can use devices with similar electrical characteristics, for example, L56B, L456B (increased brightness), L816BRC-B, L769BGR, TLBR5410 or similar ones.
The power dissipated by resistor R3 (at short-circuit current) is more than 5 W, so this resistor is made independently from copper wire of the PEL-1 (PEL-2) type with a diameter of 0.8 mm.
It is taken from an unnecessary transformer. 8 turns of this wire are wound onto a frame made of stationery pencil, the ends are tinned, then the frame is removed. Wirewound resistor R3 is ready.
All fixed resistors are MLT-0.25 type or similar. Instead of diodes VD1, VD2, you can install KD503, KD509, KD521 with any letter index. These diodes protect the LED in overload mode (extinguish excess voltage).
Load indicator with audible alarm
The circuit and circuit board of another version of the power consumption indicator are shown in Fig. 4, a, b. This indicator has a sound alarm and, in addition, has a “memory”.
As in the previous design, the alternating voltage of the current transformer is rectified by diodes VD1, VD2, but unlike the previous version, capacitor C2 of a much larger capacity is installed in this one, in addition, the input resistance of the comparator and generator on elements DD1.1 is increased. DD1.2, which is used to save information about the value of power consumption for several minutes.
This is necessary in cases where the load is not constantly connected to the network (for example, an iron with a thermostat). If the power exceeds a preset threshold, then the generator on elements DD1.1 and DD1.2 starts working and a sound signal is heard in the phone with a frequency of about 1 kHz. This device, whose sensitivity is relatively low, should be used to indicate power consumption of 1000 W or more.
Rice. 4. Scheme (a) and circuit board (b) of a power consumption indicator with an audible alarm.
The current transformer is of a similar design; see its description in the first version. The setup comes down to selecting resistor R1 to indicate the inclusion of a load of a certain power. The BF1 phone must be high-impedance.
Literature: I. A. Nechaev, Mass Radio Library (MRB), Issue 1172, 1992.
Schematic diagrams of simple indicators of the presence of a 220V network on LEDs, we replace old neon indicator lamps with LEDs. In electrical equipment, neon indicator lamps are widely used to indicate that the equipment is turned on.
In most cases, the circuit is as in Figure 1. That is, a neon lamp is connected to an alternating current network through a resistor with a resistance of 150-200 kioles. The breakdown threshold of a neon lamp is below 220V, so it easily breaks through and glows. And the resistor limits the current through it so that it does not explode from excess current.
There are also neon lamps with built-in current-limiting resistors; in such circuits, it seems as if the neon lamp is connected to the network without a resistor. In fact, the resistor is hidden in its base or in its lead wire.
The disadvantage of neon indicator lamps is their weak glow and only pink color, and the fact that they are glass. Plus, neon lamps are now less common on sale than LEDs. It is clear that there is a temptation to make a similar power indicator, but on an LED, especially since LEDs come in different colors and are much brighter than “neons”, and there is no glass.
But, LED is a low-voltage device. The forward voltage is usually no more than 3V, and the reverse voltage is also very low. Even if you replace a neon lamp with an LED, it will fail due to the excess reverse voltage at the negative half-wave of the mains voltage.
Rice. 1. Typical diagram for connecting a neon lamp to a 220V network.
However, there are two-color two-terminal LEDs. The housing of such an LED contains two multi-colored LEDs connected back-to-back in parallel. Such an LED can be connected in almost the same way as a neon lamp (Fig. 2), only take a resistor with a lower resistance, because for good brightness more current must flow through the LED than through a neon lamp.
Rice. 2. Diagram of a 220V network indicator on a two-color LED.
In this circuit, one half of the two-color LED HL1 operates on one half-wave, and the other half on the other half-wave of the mains voltage. As a result, the reverse voltage on the LED does not exceed the forward voltage. The only drawback is the color. He is yellow. Because there are usually two colors - red and green, but they burn almost simultaneously, so it visually looks like yellow.
Rice. 3. Diagram of a 220V network indicator using a two-color LED and a capacitor.
Figures 4 and 5 show a circuit of a power-on indicator on two LEDs connected back-to-back. This is almost the same as in Fig. 3 and 4, but the LEDs are separate for each half-cycle of the mains voltage. LEDs can be either the same color or different.
Rice. 4. 220V network indicator circuit with two LEDs.
Rice. 5. Diagram of a 220V network indicator with two LEDs and a capacitor.
But, if you only need one LED, the second one can be replaced with a regular diode, for example, 1N4148 (Fig. 6 and 7). And there is nothing wrong with the fact that this LED is not designed for mains voltage. Because the reverse voltage across it will not exceed the forward voltage of the LED.
Rice. 6. 220V network indicator circuit with LED and diode.
Rice. 2. Diagram of a 220V network indicator with one LED and a capacitor.
In the circuits, two-color LEDs of the L-53SRGW type and single-color LEDs of the AL307 type were tested. Of course, you can use any other similar indicator LEDs. Resistors and capacitors can also be of other sizes - it all depends on how much current needs to be passed through the LED.
Andronov V. RK-2017-02.
About a year ago I got the idea to assemble a 12-220 volt voltage converter. A transformer was needed for implementation. The search led to the garage, where the Solntsev amplifier, which I had assembled about 20 years ago, was found. Simply removing the transformer and thus destroying the amplifier did not raise the hand. The idea was born to revive him. In the process of revitalizing the amplifier, many things have changed. Including power output indicator. The circuit of the previous indicator was cumbersome, assembled on K155LA3, etc. Even the Internet didn’t help find her. But another very simple, but no less effective output power indicator circuit was found.
Overload indicator with audible alarm
Unfortunately, in practice it is not possible to constantly visually monitor the status of the indicator LED in the power source, so it is reasonable to supplement the circuit with an electronic sound unit. Such a diagram is shown in Fig. 2.
As can be seen from the diagram, it works on the same principle, but unlike the previous one, this device is more sensitive and the nature of its operation is determined by the opening of transistor VT1, when a potential of more than 0.3 V is established in its base. A current amplifier is implemented on transistor VT1.
The transistor is selected to be germanium. From old radio amateur stock. It can be replaced with devices similar in electrical characteristics: MP 16, MP39-MP42 with any letter index. As a last resort, you can install a silicon transistor KT361 or KTZ107 with any letter index, but then the threshold for turning on the indication will be different.
Rice. 2. Electrical diagram of the sound and light overload indicator assembly
The switching threshold of transistor VT1 depends on the resistance of resistors R1 and R2, and in this circuit, with a power source voltage of 12.5 V, the indication will turn on at a load current exceeding 400 mA.
The collector circuit of the transistor includes a flashing LED and a capsule with a built-in AF generator NA1. When the voltage drop across resistor R1 reaches 0.5...0.6 V, transistor VT1 opens and supply voltage is supplied to LED HL1 and capsule HA1.
Since the LED capsule is an active element that limits the current, the LED operation mode is normal. Thanks to the use of a flashing LED, the capsule will also sound intermittently - the sound will be heard during the pause between LED flashes.
In this circuit, you can achieve an even more interesting sound effect if, instead of the HA1 capsule, you turn on the KRI-4332-12 device, which has a built-in oscillator with interruption. Thus, the sound in case of overload will resemble a siren (this is facilitated by a combination of LED flash interrupts and internal interrupts of the HA1 capsule).
Such a sound is quite loud (audible in the next room at an average noise level), and will definitely attract people's attention.
When leaving, turn off the lights.
A. MUSIENKO,
As you know, a lot of fires occur due to various electrical appliances left unattended and turned on. These include heaters, televisions, and so on. The device “When leaving, turn off the lights” - UGS-1 - is used to indicate the presence of switched on electrical appliances. It is connected in series to the circuit of energy consumers (Fig. 1).
The UGS-1 diagram is shown in Fig. 2.
When the electrical appliance is turned on, the neon light HL1 lights up. If all consumers are turned off, the neon light will not light. It is advisable to install UGS-1 near the exit door.
UGS-1 itself consumes practically no current, and the total current of consumers connected through it can reach 6 A.
Radio amateur 8/97
220 volt load indicator
The display device allows you to control when leaving home: are electrical appliances turned off from the network? If any load with a power > 8 W remains switched on in the network, then both LEDs HL1 and HL2 light up (see figure). The brightness of the glow is low at a load of 8 W (the dot in the LED is lit), so in bright light, in order to see the glow, you need to cover the penetration of bright light onto the LED with your palm. The LED(s) are installed at the front door. The conductors to them (0.2 mm) are laid under the wallpaper (due to the low current passing through them). LED HL2 can be excluded from the circuit, and if it remains, then HL1 can be installed on the inside of the door, and HL2 on the outside.
As a T1 transformer, they use ready-made ones, which have a winding with a large number of turns (2000 -3000, or maybe less) and it is possible to wind 8 - 10 turns of mounting wire of sufficient cross-section. In each specific transformer, the number of turns is selected experimentally. These 8 - 10 turns will be the primary winding of the transformer, and the secondary winding will be those that are in the finished transformer.
Different types of finished transformers were tested. TVK 70-L2 is suitable for this purpose. However, it should be noted that not all transformers work well in this circuit. The greater the load, the thicker the mounting wire for the primary winding must be taken.
Excess windings can be removed from the transformer, then there will be more space for winding the mounting wire as the primary winding of transformer T1.
The primary winding T1 is connected to a break in the wire supplying voltage to the apartment (for example, in the apartment box or in the power panel). A necessary condition for implementing such a connection is that the wire of the primary winding has a sufficient cross-section (it does not heat up under load).
Author: P. D. Rybak
Literature 1. Nechaev N. Power consumption indicator // Radio.-1986.-No. 2.
This is the simplest and most reliable network indicator I have ever made.
Previously, in order to insert a 220 network indicator into any device, you had to wind a separate coil onto a transformer or build a whole circuit of diodes and capacitors, until I came across this super simple circuit. The photo shows that the LED is connected to the socket through a resistor - brevity is the sister of talent
