Using NE555 to make a car food warmer

This food and beverage warmer is very useful for people who frequently work in the car. It can keep your tea, coffee or food in a warm state, convenient for taking at any time, but consumes very little electricity.

The circuit is very simple. Use a common 555 timer to connect to the oscillator mode. The two diodes IN4148 connected in reverse can adjust the duty cycle of the output waveform together with VR1. The current capacity of Darlington power transistor T1 is 5A, and the output power can be greater than 60w. The discrete components selected in the figure can make the frequency of the 555 oscillator output close to 1Hz. R1 and VR1 can adjust the duty cycle of the output waveform. The larger the duty cycle, the higher the temperature of the heater.

The heater can be connected in parallel with up to 5 10W heating wire elements HC1~HC5. Therefore, the maximum power of the heater is 50W. The temperature of the heater can be controlled by switches S1~S4. As switches S1~S4 are disconnected in sequence, the current consumption becomes smaller and smaller. Therefore, the heat control is very flexible. The rated current capacity of S1~S4 is 6A.

The circuit can be mounted on a normal PCB board, and a thick heat sink should be used for the power transistor. The heater circuit should be isolated from the 5 heating wire elements. Connect the two parts with two wires that can carry 6A current. Place the heating wire elements under a rectangular aluminum or steel plate with a thickness of at least 1mm. Don't forget that the metal heating plate should be electrically insulated. The heater can be powered by the 12V battery in the car. When the battery is connected to the circuit, the connecting wire should have an appropriate current capacity.