Electrical Safety Monitoring of Electric Heaters
1. PCB temperature safety
Use the temperature sensor that comes with the MCU to detect the PCB temperature, and shut down and reduce power when the PCB is overheated. The protection logic is as follows:
When the PCB temperature is higher than 120°C, reduce the heating power according to the 80% derating factor, and restore the heating power when the temperature is lower than 115°C.
When the PCB temperature is higher than 125°C, stop heating, and resume heating when the temperature is lower than 110°C.
2. Medium temperature safety
Two NTC temperature sensors are used to detect the temperature of the water inlet and outlet respectively. The MCU continuously detects the rationality of the temperature sensor signal. Once an abnormality is found, it will be identified as a temperature sensor failure, which can avoid heating runaway events caused by temperature sensor failure.
When the medium temperature is higher than 70°C, stop heating, and resume heating when the medium temperature is lower than 60°C.
Note: This kind of failure indicates that there may be a problem with the system, for example: the failure of the water pump causes the coolant flow to be interrupted, or there are air bubbles in the coolant system, or the coolant leaks, and a similar dry-burning condition occurs. At this time, the user needs to correct Check and maintain the PTC electric heater in time, otherwise it may further lead to permanent failure of the PTC electric heater.
3. Current Derating
When the PTC electric heater detects that the heating current is higher than 15A and lasts for more than 3s, the current derating protection is carried out, and the heating power is reduced according to the 80% derating factor.
4. Short circuit overcurrent detection
When the PTC electric heater detects that the heating current is higher than about 56A, it will stop heating immediately after the duration exceeds about 1us, and then perform reset restart and start-up inspection actions after a delay of 2 seconds.
During the start-up inspection, if the short-circuit fault is canceled, the system can automatically resume normal operation, otherwise it will trigger the second short-circuit fault, and the system will further identify which branch has failed.
If a short-circuit fault occurs for 3 consecutive times, the system will enter the protection lock state and stop heating.
5. Long time overcurrent detection
When the PTC electric heater detects that the heating current is higher than 18A and lasts for more than 15 seconds, it will stop heating immediately, and then perform the reset action after a delay of 2 seconds, and then perform the start-up inspection action.
After detecting long-term overcurrent for 3 consecutive times, the system enters the lock protection state and stops heating.
6. High-voltage power supply voltage detection
The PTC electric heater will continue to detect the voltage value of the high-voltage power supply. When the high-voltage power supply voltage is higher than 760V or lower than 440V, it will stop heating immediately and report the abnormal fault of the high-voltage power supply voltage. When the high-voltage power supply voltage returns to lower than 750V or higher than 450V , the system automatically returns to normal working status.
7. Startup check
When the PTC electric heater is powered on or reset and restarted, if the heating power requested by the host computer is valid, the startup check process will be executed.
First, detect the total current of all heating branches in the closed state. If the current exceeds the specified value, it indicates that there is a short circuit or leakage current in the system hardware, or the current sensor detection circuit is faulty.
Then the system will supply power for each heating branch separately for a period of time, and detect whether the corresponding current exceeds the specified value. If it exceeds the specified value, it will be judged that there is an overload or an open circuit, and the corresponding heating branch is judged as a faulty branch. The road can continue to work normally.
