Help stopping reverse power flow from inverter

[smonani]

Hi Everyone,

My name is Sid and I am based out of Bengaluru, India.

I would like to ask for your help on an issue that I am facing recently.

Context:
I have a battery inverter connected to the electrical system to help with power outages in the following manner:
Mains -> Main MCB -> Inverter input -> Inverter output -> Low power MCBs -> Low power devices
(parallel from main MCB output -> High power MCB -> High power devices (refrigerator, washing machine, water heater, induction stove)

In this setup, there are two parallel connections going from the main MCB output. 1 goes to inverter input, and other goes to High power MCB, onward to high power devices.

Because the inverter output is connected only to low power devices, here is what used to happen until recently when the power went out. Power to high power devices was cut, since there is nothing coming from mains, while the power to low power devices continued to be delivered uninterrupted as the inverter kicked in and started delivering power from the connected single 12v 150 Ah DC battery. This is what I wanted.

Recently however, when the power goes out, the inverter starts delivering power from it's input in addition to the output, which causes the high power devices to to start drawing power beyond inverter capacity, causing it to go in overload, and shut down.

Turning off the mains MCB and high power MCB and restarting the inverter gets it working again, but it goes into overload the moment the Mains MCB is switched on, even when the high power MCB is switched off.

I did call the company technician, and also tried a couple of local electricians. They changed the entire inverter motherboard, which fixed the problem for a few months. But the problem keeps coming back every few months.

I was considering buying a new inverter all together, but am a bit hesitant, in case I start having the same issues with that as well.

Here is some information on the inverter if it helps:
Inverter type: Sine wave
Inverter name: Luminous Ecovolt 1050
Inverter capacity: 900 VA
Rated Power: 756 W
Inverter product information: https://www.luminousindia.com/eco-volt-1050.html
Battery: Tubular 150 Ah battery
Electrical system: 240v

Ask:
In a nutshell, I am trying to stop this problem. The first option I was considering is to stop the flow of power from inverter input to high power devices. However, any other option that's not too expensive, but solves my problem is also welcome.

Is there a device that I can put between the Mains MCB output and inverter input, which will stop the power flowing from inverter to the mains when the electrical main goes out?

Thanks in advance for your help.

Regards,
Sid