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Automatic Grid Connection/Disconnection based on battery charge

devonsandwich

New Member
Joined
Nov 14, 2022
Messages
8
Location
Philippines
I have a residential Solar system with batteries. Most days the grid is not needed and the inverter statistics show zero energy purchased, however the electricity provider's meter, and my own independent meter shows that I'm purchasing around 1kwh/day. I've been through all of the inverter settings with my solar installer and we can't find a way to stop the power draw, without physically throwing the main power switch. I'm looking for a way to automatically cut the mains power based on battery charge. For example, disconnect from the grid while using PV or battery, when the battery gets low and there is no sun, reconnect to the grid until PV or battery is available.

I was thinking of a solar charge controller with contacts to control a contactor, or an ATS (I have an ATS that isn't being used) using only one input of the ATS and the other input with no connection. The problem I have with these options is I can't find a solar charge controller with load output controllable by battery level.

Is this a viable option, or is there a more suitable option available?
 
Lack of details means it is hard to provide specific guidance.

What inverter do you have?

Some inverters have smart load outputs that can be set to turn on at certain SoC and those could be used to drive an ATS. An example of that are Megarevo RxKLNA and Amensolar N3H-xK-US inverters which have a LOAD2 output.

Also, some inverters have dry contacts for generator starting, so you could use that to enable grid connection through an ATS or contactor.

Mike C.
 
Hi Mike, here is my set up:
2 x Deye Sun-5k-sg01lp1-eu Hybrid Inverters
2 x Lithium LifePo4 48v 300A 15Kwh batteries
15Kva Generator

The generator auto start is connected to the inverter dry contacts.
Lack of details means it is hard to provide specific guidance.

What inverter do you have?

Some inverters have smart load outputs that can be set to turn on at certain SoC and those could be used to drive an ATS. An example of that are Megarevo RxKLNA and Amensolar N3H-xK-US inverters which have a LOAD2 output.

Also, some inverters have dry contacts for generator starting, so you could use that to enable grid connection through an ATS or contactor.

Mike C.
 
Hi Mike, here is my set up:
2 x Deye Sun-5k-sg01lp1-eu Hybrid Inverters
2 x Lithium LifePo4 48v 300A 15Kwh batteries
15Kva Generator

The generator auto start is connected to the inverter dry contacts.
When do you want to use the grid and when do you want to use the generator?

I presume the following logic is what you want:

Select grid only when inverter requests generator and the grid is up.

Select and start generator when grid is down and inverter requests generator.

You could put an ATS on the grid input which selects between gird and generator. Like this one:


I think you can wire it up in such a way as follows:

If inverter is not requesting generator, the switch is connected to the generator that is not running. This disconnects the inverter input from the grid to avoid your 1 KWH per day idle drain.

If the inverter is requesting generator, and the grid is up, the switch selects grid. This provides power to the system without starting the generator.

If the inverter is requesting generator, and the grid is down, the switch stays in generator position but passes the start signal on to the generator, which then starts and provides power.

The ATS has dry contacts which can help steer the logic:

1738762270389.png

I haven't worked out the exact wiring for this, and it may require some control logic beyond what the ATS provides, but it shouldn't be too bad.

You may need a delay relay just to keep the generator from starting if the inverter asks for power and the grid is up since the switch takes a brief moment to switch to grid. If the generator waits for the start signal to be valid some short period of time, this won't be needed.

The video of the ATS switching looks very fast.

Mike C.
 
When do you want to use the grid and when do you want to use the generator?

I presume the following logic is what you want:

Select grid only when inverter requests generator and the grid is up.

Select and start generator when grid is down and inverter requests generator.

You could put an ATS on the grid input which selects between gird and generator. Like this one:


I think you can wire it up in such a way as follows:

If inverter is not requesting generator, the switch is connected to the generator that is not running. This disconnects the inverter input from the grid to avoid your 1 KWH per day idle drain.

If the inverter is requesting generator, and the grid is up, the switch selects grid. This provides power to the system without starting the generator.

If the inverter is requesting generator, and the grid is down, the switch stays in generator position but passes the start signal on to the generator, which then starts and provides power.

The ATS has dry contacts which can help steer the logic:

View attachment 275816

I haven't worked out the exact wiring for this, and it may require some control logic beyond what the ATS provides, but it shouldn't be too bad.

You may need a delay relay just to keep the generator from starting if the inverter asks for power and the grid is up since the switch takes a brief moment to switch to grid. If the generator waits for the start signal to be valid some short period of time, this won't be needed.

The video of the ATS switching looks very fast.

Mike C.
Your presumed logic of when I want to use different power sources is correct.

Here is a picture of my wiring setup.

Solar Wiring.JPG

I plan to install an ATS as shown above. Only one input of the ATS will be populated by the Grid.

It would be a big task to wire the generator into the ATS as you suggested. The generator is one floor above the inverters and the cabling goes through walls, conduits etc.

There's been a few suggestions on how to control the ATS on another thread, see below:

Cheap Option

Cheaper Victron Option

Expensive Victron Option

Very Expensive Option

Thanks for your input.
 

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