With this tester, you can assess the capacity of Inverter to handle the load. It gives a warning beep, if the inverter load exceeds above its load handling capacity. Inverters are available in different ‘Size ratings’ from 50 VA up to 50000 VA. VA indicates the ‘Size’ (capacity) of the inverter which represents its maximum load capacity. Commonly available inverters are 500 VA, 800 VA, 1000 VA, 1500 VA etc. An inverter needs Peak or Surge power and Typical or Average (Usual) power to handle the load. Peak power is the maximum power that an inverter can supply usually for short time. If the load increases above the rated capacity of the Inverter, it will over load the inverter that may leads to its permanent damage.
The circuit senses the current passing through the Ampere Meter connected in series with the Battery Negative and Inverter Negative. If the load is within the handling capacity of the inverter, say 400 watts for a 500 VA inverter, current flowing through the meter is low and if the load increases, there is a corresponding current flow through the meter and the circuit senses this increased current to activate the alarm.
To compare the current through the meter, a Differential Amplifier built around IC1is used. Since the current flowing through the meter is too low, the voltage developed will also be very low. The differential amplifier amplifies this minute voltage to give a high output around 2 volts (as set by VR1).This is used to control the Schmitt trigger built around IC2. When the voltage level in the Trigger input of IC2 (Pin 2) is less than 3 volts (as set by VR2), output of IC1 remains high which lights the Green LED and inhibits the buzzer and Red LED. This indicates that the Inverter load is not high. When the load increases, the current flowing through the meter also increases and the output of IC1 gives more than 3 volts which changes the output of IC2 to low. Red LED turns on along with beeps from the buzzer. This indicates that the inverter is overloaded.