SolarWise Inverters

🌡️ Over Temperature Sensor Circuit – Smart Solar Inverter Protection ☀️

In modern solar inverter systems, protecting the power electronics from overheating is essential for reliability and long life. This over-temperature sensor circuit is designed to automatically detect high temperature conditions and trigger protective actions such as fan activation or system shutdown.

The circuit is built around an NTC thermistor and an LM393 comparator:

The NTC thermistor (TH1) continuously senses the inverter’s temperature. As the temperature increases, its resistance decreases, changing the voltage across it.

The LM393 comparator compares this voltage with a fixed reference voltage generated by a resistor divider network.

When the sensed voltage drops below the reference level (indicating an overheat condition), the comparator output switches LOW.

This output is then sent to the microcontroller, which can turn ON the cooling fan or shut down the inverter to prevent damage.

To improve stability and noise immunity, filter capacitors (C18 & C19) are used at both the sensing and output stages. The pull-up resistor (R21) ensures a clean logic-level output compatible with microcontroller input pins.

✅ Features:

Accurate and fast temperature response

Automatic fan ON/OFF or shutdown control

Compact and reliable circuit design

Ideal for solar inverters, battery chargers, and power control systems

This simple yet effective design helps protect your inverter from overheating and enhances system safety and lifespan.

📞 Contact: 03214799117

Description:
>C1,C2,C3 capacitor makes RC low pass filter to clean mechanical noises and provide clean signal to MCU
Debounce time constant:
T=R X C= 10k*0.1uF=1m sec
So the input takes around 1 ms to settle, effectively removing short glitches caused by contact bounce.

>R2,R3,R4 makes pull up logic (1 continusely to mcu) when pressed button than provide 0 to MCU

As we know in C(total)= C8+C9+C10+C11+C12+C13 =>
c(total)=470+470+470+470+470+470=2820uF=0.00282F

Energy Stored:
E=1/2 CV^2=0.5*0.00282*(450^2)=285.525 Jols

Total Charge:
Q=C x V=0.00282*450= 1.269 Coulombs

Peak Surge Current:
We need the equivalent Series Resistance (ESR)
Typical 450V/470uF electrolytic capacitors(e.g Nichicon,rubycon,etc) have arount 0.15-0.25
In parrallel ,ESR divides by 6:
ESR_{total} =(0.2/6)*0.033

Now Peak short circuit current :
T_{peak}=V/ESR=450/0.033=13.636A
But this is ththeoretical Instantaneous current but its not practicle ,in practicle wiring inductance and lead resistance will limit the current to 2-5kA

Impulse duration:
Q=1.27C
Suppose I=Q/t => 1.27/2000=0.000635s= 0.635ms

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