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Apartment Emergency Backup with all in one inverter charger

Mingo

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Nov 26, 2022
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I have a Growatt spf 3000tl lvm-48p and an Orient Power LiFePO4 Battery 5.12KW 48V100AH Wall-Mounted/Powerwall that I would like to install in an apartment to be use as backup when there is a power outage.

It is my understanding that this all in one inverter/charger has an ATS built in.

No solar inputs will be connected as this will be mounted inside an apartment.

Looking at my breaker panel, all my critical loads are on one leg and my intent is to use only 120V.

I have seen videos and builds for standalone off grid units and split phases with solar.

But as a single phase configuration with electrical grid as the main source and battery as emergency backup, I haven't seen much.

My question is on the ac input and output under UPS feature as the intent is to use the electrical grid and when there is a power outage, critical loads are automatically powered by battery and when the power gets back, all the loads goes back to the electrical grid and charges the battery.

For this configuration, do I need to create a sub-panel and add a 40A breaker for the AC output coming from the inverter on one side and add the critical loads breakers coming from the Main Breaker Panel to this sub-panel on the second leg of the sub-panel? If this is the correct way, would the AC input from the inverter need to go directly to the main panel in a separate breaker for when the power gets back, it can charge the battery?

Or, can the ac output from the inverter be wired directly to one leg of the main breaker panel and add a new breaker for the AC input on the second leg?

Any information or assistance would be greatly appreciated.
 
My question is ... do I need to create a sub-panel ...Or, can the ac output from the inverter be wired directly to one leg of the main breaker panel and add a new breaker for the AC input on the second leg?

A breaker's job is to protect the wire. I know by itself that sounds a bit flip, so let's walk through it.

Inside the walls of your apartment reside the electrical wires and they have different gauges that will overheat and possibly catch fire if too many amps are run through them (e.g., a short circuit occurs). The breaker is sized to the wire gauge to prevent too many amps from traveling through the wire.

Let's assume there are four critical circuits you want, one of which has a 20 amp breaker and three that have 15 amps. 20 + 3x15 = 65 amps. Does that mean you need a 65 amp breaker from the load center to the inverter? No, you need to look up the maximum throughput the inverter can handle. If it's a 3000W inverter it'll probably only be rated for 25 to 30 amps, possibly a bit more if it's intended to be used as a UPS. It also means that the circuits converted over can only ever have a combined load <= the inverter's maximum throughput (although with a manual Circuit Transfer Switch style configuration you can switch between the load center or the inverter).

So, for the UPS configuration you want, you'd install an appropriately sized wire to the inverter, and connect it to an appropriately sized breaker for that wire in your load center.

Each of the critical circuits transferred to the inverter needs to be individually protected by a breaker sized for the wire. The existing breaker size tells you how many amps the wire can safely carry (where I live that can be a deadly assumption, always actually best to check the wire gauge). The breaker should be as close to the power source (e.g., the inverter) as you can get it.

If it is a 120V inverter it should look something like:

1669897960695.png

Whether its a subpanel off the inverter like a Circuit Transfer Switch or a DIY version using DPDTs and breakers, typically it isn't important except for any local codes. If it's a 240V inverter you'd need a double-ganged breaker in the load center and you may run into load balancing issues as without a neutral forming transformer typically each inverter leg can only supply 1/2 the rated amps with 120V loads.

Hope that helps!
 
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Thank you for the guidance.

I made sketch of what I intend to do based on the guidance provided.

Do you see anything wrong or something that I should incorporate?

The intent is to use the battery/inverter in UPS mode for when the power goes out, those critical loads expected to be relocated to the sub-panel are energized and when the power comes back, the charger charges the battery.

The sub-panel itself is for 120volts only. I plan to install a 60 Amp, 2 spaces, 4 circuit panel. Only 3 20 amp breakers will be moved to this sub-panel (lights + outlets, refrigerator, and microwave). Lights and outlets were wired in the same loop. Old apartment.

Any thoughts or feedback would be greatly appreciated.

IMG_20221205_162233651.jpg
 
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