Grid tie transfer switch

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Jan 6, 2021
Good morning all from sunny UK (today at least)

Sorry been away a few months, ebike builds have taken up almost all of my time..

I have finally managed to get enough usage usage estimations from my current set up to start and build my whole home battery backup system.

I know that we use a smallish amount of power per day 9.9kwh and have already got a very tiny 750w grid tie setup on the roof which generates a max of 30Ah at 90v DC which is then inverted to 249v and goes directly to our consumer unit (this was installed when the house was built and no more room on the roof for panels)

The grid tie inverter is a measly 700w inverter which I have built a battery and that's working well.

The next phase is to add a second solar array that covers the house energy needs.. But I need to make sure that when the grid goes down that we have an auto transfer switch that switches of the grid to avoid any potential back feeding.

Because in the last 7 times its gone down, it will keep coming on and offline for about 30 mins before it is stable, I am looking for a way to do as follows.

Detect no grid power and switch off the incoming grid... Detect grid power is back live and wait say 30 mins for stable power and switch back in...

My plan was to have an ATS that has grid power one side and nothing on the other so if grid goes down it just switches off and my inverter then feeds the house

Does this sound viable or do the ATS have to have a connection both sides?

Roland W

Oct 9, 2017
Does this sound viable or do the ATS have to have a connection both sides?
If you are looking to use one of those simple ATS, you need input on both sides, as the motor which will rotate the mechanical dial needs to get power from the "R"eserve Source when power on "N"ormal Source is lost. In your case you would connect the Grid to Normal and the solar inverter to Reserve. So when the grid goes down, the ATS would rotate to the R side within a few seconds. The question is just, how you will delay the move to N side again for 30 minutes after power on grid is restored. I do have a over/under voltage relay in my system, which will wait for 30 seconds after power has stabilized.


Oct 8, 2016
A grid tie system will do this automatically without issues. Ie when the grid is down it wont back feed at all. So not sure what you are looking for?
You cant feed your house with a grid-tie only system. You need to have one with battery and if its properly set up with the legal aspects your problems wouldn't be a problem. For example if my grid goes down and up 100times in 20 minutes it doesn't matter because i will have power in my house based on using the load port on the inverter and the grid-tie side connects/disconnects as is.

So i would like to explain a bit further why you have problem and what it is that you try to do. You say something about built battery but it sounds like you have hacked something together with those kind of GTIL inverters or something?

Neither less for just delaying grid its not a big issue. Just have a contactor in between with a delay that never can engage until the timer have been on for 30 minutes and you are good to go. This is how you do it with generators or on unstable environments where you don't want to switch to often.

One of my videos: