Electric mosquito coil heater

Summer is here and mosquitoes are everywhere, so electric mosquito coils are essential. So here’s the problem. The heaters that come with the electric mosquito repellent liquid on the market now generally use 220V AC, which occupies a socket and is inconvenient to move, let alone carry. After analysis, I found that the principle of the electric mosquito coil heater is very simple. The PTC resistance is directly connected to the 220V AC. The resistance increases as the temperature rises, and the power continues to decrease, and finally a stable heating temperature is obtained. Measurements show that when the cold machine is started, the maximum power of the heater can reach 10W. As the temperature rises, the power decreases. Finally, the temperature of the electric mosquito coil volatilization rod is 120°C and the power consumption is 3W. It can fully carry the load using ordinary charging heads and mobile power supplies.

The heating part uses four 5.1R 2W ​​metal film resistors, which are connected in parallel and then in series around the mosquito repellent liquid evaporation rod. Using USB 5V for power supply, the hardware limits the peak power consumption to about 5W. Although the peak power is not as good as that of the PTC heater, because the thermal resistance of the resistor itself is very small, the temperature rise process is very short, and it can eventually reach the preset temperature.

In the temperature control part, PTC resistors have their own temperature control properties. There will be a sudden change in the resistance value when the set temperature is reached, but the components are not common. Metal film resistor heating is used here, and additional temperature control circuitry is required to ensure the desired stable temperature. NTC resistance has a more stable linear change and is easy to adjust the heating temperature. A set of NTC and resistor voltage dividers are input to the forward end of the op amp, and a set of fixed resistor dividers are input to the reverse end of the op amp. The NTC is placed close to the metal film resistor. The low end of the metal film resistor is controlled by an NMOS to turn on and off. When working, the two sets of voltages are compared. When the temperature is lower than the set value, the voltage of the NTC group is greater than the fixed voltage group, the op amp outputs a high level, the NMOS is turned on, and heating begins. When the temperature reaches or exceeds the set value, the op amp outputs a low level, NMOS turns off, and heating stops. The temperature can also be adjusted by adjusting the voltage divider resistor.

The structure uses two identical PCBs stacked one above the other, connected in the middle by a metal film resistor, and the volatilization rod of the mosquito repellent liquid passes through the two PCBs. One of the PCBs is covered with components, and the other is only covered with 0R resistors as circuit connections.

After combining the two pieces

Insert electric mosquito repellent liquid

Plug in the power supply, the green light is the power light, and the red light is the heating light. The power consumption during heating is about 5W. The heating lamp goes out when the temperature is reached. In the video, measured by a thermocouple, the temperature stops heating at 120 degrees and restarts heating at 110 degrees. In this cycle, the heating temperature is basically the same as the original heater.

With short cord and mobile power supply, it is very easy to carry and suitable for outdoor use.