Hello homemade radio amateurs!
In the process of amateur radio activities, there is often a need for heating, for example, to seat heat shrinkage, or to warm up an etching solution for printed circuit boards. For different needs, heating to different temperatures is required, respectively, and the heater must be universal, allowing you to regulate the temperature over a wide range. Ideally, the range should also cover the melting temperature of the solder in order to solder the printed circuit boards. At the same time, the design of the heater itself must be reliable and safe, both electrically and thermally, so as not to accidentally get burned. As the basis for the design, the author uses a rectangular-shaped aerated concrete block with heating coils inside. This material is a dielectric and is not afraid of high temperatures.
The power of the heater, and, accordingly, the maximum temperature will depend on the spirals used, or rather, on their resistance. In hardware stores, you can buy ready-made sections of spirals designed for various capacities, given their low cost, it is more rational to use ready-made ones than to wind your own. By combining several spirals by serial-parallel connection, the final power can be varied. It is advisable to use several coils that evenly cover the bottom of the base and provide the same uniform heating. Also, ready-made heating elements can be used as a heater, for example, from an iron or an electric kettle. The author installed spirals corresponding to a power of 2 kW, which is quite a lot and will provide a maximum heating of the platform up to 500 ° C. If such high temperatures are not required, you can install a heater for 200-500 W, during operation, the temperature can in any case be adjusted. Photo of the installed spirals below.
You can simply connect the spirals to the 220V network, they will simply heat up to their maximum and the temperature will be set at the same level. You can significantly expand the scope of the heater by installing a power regulator, the diagram of which is shown below.
Compared to a thyristor one, such a regulator is a little more complicated, but it provides significantly less noise. The principle of operation is very similar to a conventional PWM regulator, which are used when regulating DC power. The NE555 microcircuit here serves to generate rectangular pulses, while the variable resistor P1 regulates the duty cycle of the pulses – that is, the duty cycle, and, accordingly, the useful power, which will be dissipated in the form of heat on the spirals. The NE555 connection scheme is absolutely standard, it requires a minimum of elements in the harness, any details will do, if only they correspond to the ratings. The right side of the circuit is power, has a 230V mains voltage input, and also shows the contacts for connecting the heater (HEATER contacts). In fact, the heater will turn on and off several times per second, in time with the pulses from the generator. It commutes to heat a powerful BT138-600 triac, rated for a current of 12A and a voltage of 600V. If the heater is designed for a maximum power of 500 W or more, then a radiator should be installed on the triac; when a large current passes, it can heat up significantly. Optocoupler MOS3043 serves for galvanic isolation of the power part of the circuit from the logic one. The supply voltage of the circuit is 8-15V, limited by the supply voltage of the NE555 microcircuit. The current consumption is 20-30 mA; any power supply unit or AC adapter is suitable for power supply. You can use a transformer with a diode bridge-rectifier connected to it as a power source.
Considering the high power of the heater, the design must be reliable and solid. A body is built around the aerated concrete “bath”, a protective mesh is mounted on top of the heaters on ceramic supports so that no debris can penetrate to the spirals. Above are fastened runners-holders, on which it will be possible to put the object to be heated. On the front panel there is a knob – a power regulator, and a toggle switch. If you want and have a good thermometer, you can graduate the scale of the pen by indicating the values in degrees. Or completely display the thermometer display on the front panel in order to see the current temperature in real time and adjust it to the desired level. Thus, an interesting and necessary heating device has turned out, which will certainly find application in radio amateur affairs. Happy assembly!
Hello homemade radio amateurs!