The most reliable relay for turn signals
As you know, all modern cars are equipped with direction indicators, which are a light bulb on the left or right side of the body or an LED. Sometimes a regular electromechanical relay fails, and getting a powerful automobile relay is not always so easy. Semiconductor devices come to the rescue - after all, to build such a relay is powerful with just a pair of transistors.The scheme is an asymmetrical multivibrator, it is included in the open circuit in series with a light bulb and a power source. When voltage is applied, the light immediately flashes. VT2 on the circuit is a field effect transistor, it is through it that the entire current of the light bulb flows. It is preferable to use a transistor with the lowest possible resistance of an open junction. Here are suitable IRFZ44N, IRF740, IRF630. If instead of a light bulb a low power LED is used, a bipolar transistor can be used, for example, TIP122.The transistor VT1 average power structure pnp, fit BD140, KT814. D1 diode can be put 1N4007 or 1N4148. The frequency of flashes directly depends on the capacitance of the capacitors and the resistance of the resistors. To increase the frequency you need to reduce the capacitance of the capacitor C2, and to reduce the frequency, on the contrary, increase its capacity. You can also experiment with the nominal values of other circuit elements and observe how the pulse ratio changes. TheFirst of all, resistors, diode are sealed to the board. After them, everything else is a pair of transistors, electrolytic capacitors and a terminal block. It is important not to confuse the transistor base and the polarity of the capacitors, otherwise the circuit will not work. When all parts are soldered to the board, it is necessary to wash off the flux residues,check correctness of installation.
Assembling the circuitThe whole circuit is assembled on a miniature printed circuit board with dimensions of 35 x 20 mm, it can be manufactured using the LUT method. After etching the tracks must be tinned, then the copper will not oxidize.
Setting and testing the relay turn signalsFor testing as a load, you can connect several high-power LEDs. The minus of the load is connected directly to the minus of the power source, and plus we start on the board. If a light bulb is used for testing, it can be connected with any polarity. We turn on the voltage and the light starts flashing immediately. The blinking frequency can be changed over a wide range, which is why this scheme can be used to find many other applications besides using the turn signals as a relay. For example, with its help you can make a rear flashing light for a bicycle, it is enough just to increase the frequency of flares by reducing the capacity of the condenser. The circuit can commute a large power - up to several hundred watts, if you apply a field effect transistor designed for the corresponding current. With a power of more than 100 watts, it is desirable to install the transistor on a small radiator, otherwise it can be heated during long-term operation.Such a scheme, in contrast to the traditional electromechanical relay, has no moving parts, so it is much more durable if used with parts of good quality. If necessary, a fuse is also included in the circuit in series with the load, indicated in the diagram as FU1. Successful assembly.
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