Hot wire spark plug control circuit

In winter, the air in the cylinder of an ordinary diesel engine is too cold to ignite the fuel. To avoid this, a common solution is to install an electric heating device in each cylinder of the engine. This is called a "hot wire spark plug".

The attached figure is a controller circuit, which uses a simple and reliable timer circuit composed of MOSFETBS170 (T1). A short push of the S2 switch allows the power supply to quickly charge C1 through R1. When the voltage across C1 exceeds the threshold voltage of the T1 gate, T1 turns on and starts charging the large capacitor C2, while the relay RIJ1 is attracted. Thereafter, as long as the terminal voltage of C1 is greater than the threshold voltage of the T1 gate, it remains on.

The conduction time directly affects the discharge current of C2, which in turn depends on the values ​​of C1 and . The conduction time of the components shown in the figure is about 25 seconds. Therefore, pressing S2 can make the relay close for 25 seconds, so that the hot wire spark plug can obtain 12V power supply.

It is used to indicate that the hot wire spark plug is in the heating process, and LED2 is used to indicate that the heating process has ended, and a beeping sound is emitted from the buzzer PZ1, indicating that the engine is ready to start. Since the hot wire spark plug absorbs a large current when working, a car relay with a large contact rated current should be selected.