Trying to automate inverter/charger and solar panels for partial off grid during the day

[Yoyi]

Hello and thank you for receiving me in this forum. I have a 1.35kw solar setup, with four 225 amp batteries on a 24 volt configuration, a Powmr 60 amp mppt and a 3.6kw pure sine inverter/charger.

I am have the idea of automating this off grid setup (that is really not an off grid setup, but just for the convenience of lowering a bit my utility bill when the sun is shining -not for real off grid use during the night unless we have a power outage - and they tend to be common) and have some questions:

I have a Din Rail DC programmable timer (30 amp), that I have not yet installed but am concerned that using it during the day, since I live in the Caribbean there is normally a lot of sunlight, but there are cloudy and rainy days at least during part of the day, when using it arbitrarily to shut off the utility power I understand it may harm my batteries, since it would not be helping me in regards to voltage. So I am thinking of adding a 50 amp Automatic Transfer Relay (MOES) to automatically change from my solar panels to utility power when the battery voltage is low during the day (yes, during the day because of cloudy moments of the day that could harm the batteries).

Any experience with what happens to that automatic transfer when it is manually switched to off? Will it only provide battery power, for example, or in what setting will it stay?

If I were to use both the programmable timer as an on/off switch (NO or NC configuration?), and add the Automatic Transfer, what would be the configuration and could I specify that only at certain times of the day the Automatic Transfer will work as it is designed to work (changing from battery power to grid when the battery voltage is low)?

Currently I have to manually turn off the Inverter/Charger breaker for it to change from utility to inverter mode, and turn on the solar panel breaker (since this inverter/charger adds unwanted electrical charge in parallel with the mppt controller to my batteries), and I have to be on the lookout for battery voltage, and in the afternoon change it back again.

Please let me know if this combination of timer and automatic transfer is useful in this setup, or if some kind of LVD and contactor relay, or dc relay to turn off the solar panel input with another timer would be recommended also or instead. Since I recently purchased this inverter/charger I am not planning to change it to an solar inverter with hysteresis, etc.

I appreciate in advance your answers,
Yoyi

 

[sunshine_eggo]

This seems overly complex. If you have an inverter/charger, you may have the option of simply falling back to grid if battery voltage drops to X. When the inverter is receiving AC input, it is charging batteries AND passing through grid power to your loads.

What inverter?

 

[Yoyi]

Thank you for your reply. The inverter is a Powertek L-UPS SW3600 (chinese but good quality and sold in the Diminican Republic, Venezuela - Latín American countries) and the issue is that it has a low voltage disconnect of 20 volts, which I find can harm the batteries. I want to be able to establish the low voltage cut off for protection by some means.

 

[sunshine_eggo]

Thank you for your reply. The inverter is a Powertek L-UPS SW3600 (chinese but good quality and sold in the Diminican Republic, Venezuela - Latín American countries) and the issue is that it has a low voltage disconnect of 20 volts, which I find can harm the batteries. I want to be able to establish the low voltage cut off for protection by some means.

Yeah, if it's not adjustable, that's too low.