[Schematic Review] Semi-automatic switching: Grid - EcoFlow

[glebkooo]

Hello.

Please help review the following idea / schematic. The main questions - is it actually safe.

What I want to achieve is to charge EcoFlow Delta 2 when the household is connected to grid, and power the household from EcoFlow's inverter during blackouts.
I have a 2 pole mains breaker separating the apartment from grid. So when grid goes off, I turn the breaker off, then connect EcoFlow's inverter output directly to the wall socket and turn it on. When power from grid becomes available again, I turn inverter off, unplug it's output from wall socket, plug the EcoFlow's "charger" cable to wall socket, and, finally turn on the mains breaker.

I want to somehow automate this plugging and unplugging. I am not allowed to change the wiring in the apartment, because it is rented. So I cannot use Automatic Transfer Switch there.

The idea is to use 2NC-2NO 25A Contactor driven by a Controller (Isolated AC-DC converter + MCU + Relay).
When Controller is powered off, the EcoFlow charges from mains thru the normally closed contacts.
When I turn on the EcoFlow's inverter it starts powering the Controller. If Controller detects there is no mains (using Optocoupler) - it turns on the coil of contactor, and the latter one disconnects EcoFlow's charger and connects the household mains to the inverter. Of course, I need to switch mains breaker off before that.

[jwet]

Below is a link that summarizes the National Electric Code in the US for such circuits.  What you have looks safe in general.  You might want to get your design figured out in detail and do a failure analysis.  Allow any component to fail and see what the effect is.  If there is a single fault that can cause an unsafe condition, it should be eliminated.  For example, what would happen if the opto that sense the grid being out didn't operate?  etc, etc.

Be very careful, a lot of electrocutions have been caused with switchover circuits.  Its a special danger to linemen working outside your house if you are not isolated from the grid.  You should be an "island" when in an emergency.  I see you're in Ukraine and circumstance might be difficult, it likely won't be you that gets hurt, it might be an innocent family member.  Tag out switches and breakers very explicitly and keep people out of them.

https://windsorlocksct.org/wp-content/uploads/2020/09/generator_requirements.pdf


You can read the requirements above- it looks like you understand the problem.

The ampacity of the wiring has to be chosen and circuits must be fused properly- generally only certain loads are powered by backup power.  Circuits should (but don't have to) operate automatically.  Usually, emergency loads are segregated into a seperate box that is powered by the aux power source.

There has to be a positive means to permanently isolate the generator from the power grid.  This is usually a removable disconnect block.

Also- there may be a loop in your system where the inverter could be running and charging its own battery unless the changeover switch won't allow this - is this possible- it shouldn't be.

[themadhippy]

So when grid goes off, I turn the breaker off, then connect EcoFlow's inverter output directly to the wall socket and turn it on. When power from grid becomes available again, I turn inverter off, unplug it's output from wall socket

please dont tell me your using a plug to feed power into a socket,such devices are known as widow makers for a very good resaon

[leham]

Doesn't the ecoflow have a UPS function.
Why not just use that and put the important stuff you'll need in a blackout on its output.

The average apartment size there is 57 sqm, I'd take the mess of cables (that could be tidy) over back feeding your apartment and possibly introducing hazards to you or someone else 

[glebkooo]

Thank you for detailed answers!

The first thing I am planning to do before implementing that, is to consult an electrician, maybe he would propose a better and safer solution.