Running my house on batteries at night

G’day all,
Thanks in advance for any ideas.
I have a grid tied Enphase solar system and would like to be a little more independent from the grid at night.
Here is what I have.
I have an AC300 and 3 x B300 that I would like to tie into my sub panel inside my house. Air con, oven and dryer have their own circuits running from my main breaker panel so the inside sub panel is running all my outlets and lighting.

Here is what I want.
I would like to tie the AC300 into my sub panel so that during the day it charges and the entire house runs off the sun but at night when I stop producing solar, I would like to “automatically and uninterrupted” switch over to the AC300. Then again in the morning, “automatically and uninterrupted” switch back to grid tied solar.
What parts would I need and how would I wire this up? I have some ideas but putting it all together is hurting my brain


So basically you want the grid to turn off when the sun goes down, The AC 300 will pick up the load and then when the sun comes up the grid will turn back on and your grid tied system will charge up the AC 300 and back feed the grid if theres power left over?

Almost yes. I want the grid to turn off only to the sub panel, so I can still have AC and oven from the main breaker when the sun goes down.
I guess it should also switch back to grid at night if the batteries run low.

Is there such a thing as a smart load switch with a programmable timer, or the like?


Im not aware of one specifically but there has to be an option out there. what your asking for isnt that difficult.

From what I understand, plugging your sub panel or transfer switch into the 30 amp outlet of the ac300 and connecting the power chord to grid power and running in ups mode it would do what you are asking. I think the ac300 does what you want without needing anything else.

You need to program the ac300 under the ups parameters to your desired requirements, time of day/battery percentage to run on grid or ac300.

Your heavy amp usage appliances such as a/c, oven, dryer stays on your power grid/main panel and not managed by the ac300 ups mode of operation.

You need to get very familiar with the ac300 ups operation modes.

Also you probably should get the 30a power chord. your power consumption would be limited to what the ups power offers basically around 30a. Grid power Pass through??

I think I am understanding what you’re saying but let me clarify one thing. An ATS is supposed to sense the loss of power on one side and automatically switch to the supplemental power. If I have grid power on all the time on one side of the ATS and programmed the AC300 to supply power at a set time, would that not be trying to fight the ATS?
I must be missing something
Cheers, J

If you have not already I would suggest reviewing the ac300 manual the section on ups operations I think on page 28. There are 3 modes and the one on custom setting may be what you want. Both my ac300s are set to standard ups by default with its default values. I have not tested the ups functions. Maybe someone else on this forum can give you their experience. Otherwise you will need to experiment.

I do know that when grid power is restored, I do get an issue where the ac300 throws errors and shuts down the ac inverter. The errors must be cleared manually and the ac inverter turned back on manual locally on the unit. Cannot clear errors or turn on inverter remotely.

I did want to have the ac300 run certain circuits during the day to offset grid electricity usage in order to lower my electric bill. And switch those circuits onto grid and recharge the ac300 at night when grid electric cost is lower.

The ac300 can detect when it has lost power from the power charge plug from the grid and switch to battery backup. That is from the ups settings. You call it ATS/ automatic transfer switch?? I believe all three ups modes provide switching to battery power when it detects grid unavailability.

I was thinking the same thing in regards to it would use the UPS functionality to pick up the load but I still see the need for the grid to turn off in order for the AC 300 to take over. The grid and AC 300 cannot be in parallel. Its one or the other, not both at the same time.

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What about an ATS in reverse so that the grid is on the “backup” side and the AC300 is on the “grid” side, so to speak? Would that be an option?


I am no expert on this and may not have it properly stated. You mentioned you have solar and grid power. During the day, for lights and outlets you want to run on solar when there is enough solar and switch to battery/ac300 when not enough solar Or run on AC300 at night when no solar. Doesn’t matter there is no solar.

I think there is a UPS mode to set Priority (PV) solar charging and SOC/state of charge/power chord charging. plus there is scheduled time usage for the ac300 to supply power. I would think Set solar to be priority like 60% and SOC maybe 40% (I am guessing, you need to determine the values). I think solar priority 60% says to leave 60% of batteries charge to be solar charged.

This way, the AC300 charges through its power charge chord using grid electricity when at 40% or below and charge via solar when above 40% leaving 60% to be charged using the solar input charge cables?? You need to find a way to feed the AC300 solar input ports from your solar. I would power your subpanel with the AC300 and let it supply power to that all the time. Unless you also want to use scheduled timing to power the subpanel. This way the AC300 batteries will have a state of charge to power your subpanel. Unless both solar and grid loses power. Then when the batteries drain, the AC300 will shutdown. I hope I stated the scenario properly and again this is just my understanding and not any real experience on my part.

I just re-read page 28 more carefully. UPS Time control is I think what you need.
To do what I said in my prior post I think
You can set charge time - when to charge from grid. I would set this 24 hours
discharge time - when to run loads using batteries from ac300. I would set it 24 hours
SOC low - battery state of charge when to stop powering load. I would set at 5% or 10%
SOC high - at what battery state of charge not to use grid charge and only use solar charge.
I would set at 40%

Thanks mate. I will read (and re-read) the manual on the weekend and see if this might work for the timer portion of my idea. I still need a way to switch off the grid at a set time in conjunction so as not to have the grid tied solar and AC300 fighting each other for dominance at that set time.

I think without a switchable ats similar to a whole house natural gas generac generator that can switch the source of power to the load, the option might be to move the solar panels to connect to the ac300 and use the ac300 to always run the lights and outlets. Since it can take in both solar and grid. It might not be a great option and you might lose some power. You might purchase another ac300 and run split phase with the fusion box to double the watts from 3000 to 6000.

After all this discussion with you, I might start using the ups time control myself to run my lights, outlets and furnace during the day and use the ac300 grid pass through to run that load at night through my public electricity.

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if you plan to use the fusion and power it at all with grid power you’ll need to get the “AC Charging Cable for Split Phase” which is not yet available even though the AC300 has been out for a bit now. I’m waiting for that cable to be available to order myself.

Yeah true. Someone made their own split phase charging cable. I am not 100% sure about the phases. I called my electric company and learned that offsetting electric usage requires a different rate plan. The rates are not that great but if you use electricity when you are not supposed to, it is real expensive. 3 or 4 times the normal rate plan. Air conditioning will kill you on the plan. The savings is a about 3-4 cents per KWH. I learned my electric supplier was charging a high rate at 20 cents per KWH. I switched to a provider that now charges 7 cents per KWH. Key lesson, always look at what they are charging and what rates are available by the different providers.

So my AC300’s will only be used when I have a power outage. I also have a Costco dual fuel 7500 watt generator. I am in the midst of converting the Firman to be Tri fuel and also be able to run on natural gas. I will be installing an exterior natural gas quick connect hook up in the next couple of weeks. I purchased a Garettson propane/natural gas regulator or the generator. Will see if it will work. All this for contingency. But the weather is getting more severe and power outages will be more common.

I have the two AC300 units and the P0030 Fusion Box Pro set up for split phase 240 VAC power for my home. I had to buy the materials build the split phase grid charging cable myself.

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I’d like to purchase one of those homemade fusion box ac300 ac input cables from you

is that a 30amp or 50amp cable?

Going along the idea of the AC300 UPS modes you mentioned, I found this YouTube video on how to set it up.

Not sure if the Home Panel is an automatic switch or a manual switch (and it’s always out of stock anyway), but I did get in contact with another company, GoPower, and their 30a and 50a transfer switches can be set up to <=10ms with a jumper inside. I need an ATS and a breaker panel as it turns out