Simple battery backup for house

[corn18]

Just in exploration phase. I have a full Victron setup in my 5er that I wish I had in my house. But I don't. House has 200A mains service with a 50A subpanel for the generator hookup. Manual interference switch from mains to genset. The genset is a Westinghouse 9500W/12000W (surge) 240V/50A on natural gas. This works fine but man is it obnoxious when that beast is on. The subpanel includes the heat pump for air conditioning.



I installed an Emporia Vue energy monitoring setup and learned a lot. The interesting part is that my house basically has an idle use of 600W. That's with some lights on and a TV. Unless one of the big loads kicks in, it pretty much draws from 400W to 1200W (if all the fridges are running at once). That seems like something that a battery backup system could handle with aplomb. My 5er could handle that for a long time, maybe forever with the solar.

I am thinking a simple battery backup system could easily handle these loads.

EXCEPT

I want to be able to run the air conditioning. Heat is gas so no problem there. The 3T heat pump draws 6000W on startup (I installed an easy start) and 2000W running. This is the same issue I have with my RV. Easy to handle everything and run forever until you introduce an air conditioner. In winter, the battery backup would be all we need and use the generator to charge the batteries (no solar).

I'm stupid when it comes to residential stuff so what would be a good way to handle this? Primary backup is batteries and if I want to run the aircon I have to start the genset. All of the loads in the subpanel are 120V except the aircon.

Our power outages are 10 per year for 2-6 hours. Worst case was 16 years ago when the remnants of a hurricane came up to Ohio and power was out for 3 days.

 

[chrisski]

Sounds like you could take a 30 amp or 50 amp plug to a critical load panel and use the RV instead of a generator. I think this could be more trouble than its worth. I have a 50 amp plug to the generator portion of my Home install, but don't see a situation where I would ever plug my RV in to run the house.

I installed an Emporia Vue energy monitoring setup and learned a lot. The interesting part is that my house basically has an idle use of 600W. That's with some lights on and a TV. Unless one of the big loads kicks in, it pretty much draws from 400W to 1200W (if all the fridges are running at once). That seems like something that a battery backup system could handle with aplomb. My 5er could handle that for a long time, maybe forever with the solar.

I would recommend doing an energy audit based off the bills in these down months. My 3000 watt inverter on my RV could handle parts of my load. I use 24 kWh - 40 kWh per day in the low energy parts of the year. The big thing my RV could not handle is

1) The electric Oven.
2) Having battery power overnight. I do have 13 kWh in the RV, but this won't last the night for me.

I have a critical loads panel that the RV could handle, but the really big winter loads, the electric car charger and the oven are not on that. I have about 300 watts of draw on this critical loads panel. Another thing I'd have to change is I have a 120 volt inverter and would need to go to 240 v split phase.

Primary backup is batteries and if I want to run the aircon I have to start the genset.

Is starting the generator this way practical? I have AC 24 hours a day in the summer that is probably on 20 hour a a day. This is three months of my year.

I want to be able to run the air conditioning. Heat is gas so no problem there. The 3T heat pump draws 6000W on startup (I installed an easy start) and 2000W running. This is the same issue I have with my RV. Easy to handle everything and run forever until you introduce an air conditioner. In winter, the battery backup would be all we need and use the generator to charge the batteries (no solar).

You may want to look at the locked rotor amps of the heat pump. Could take a bit of an inverter to get it going. The easy start may or may not help enough with the inverter.

Although my air conditioner uses 4000 or so watts with no real way I can measure the start up amps. The 4000 watts my inverter can handle. I can look at the sticker and see the LRA is 109 amps at 240 volts, which is way above the surge rating of my inverter. That is around 24 kW of surge. For the first few weeks I did run the AC off the inverter using the batteries from 4 pm to 7pm, but stopped when my lights have started to flicker more when the AC kicks on.

I was going to install an Easy Start on mine, but when I popped the cover, there was already a hard start and four capacitors. Beyond my capabilities.

 

[corn18]

The easy start tells me the locked rotor amps after install. Sticker on heat pump said 78A factory LRA. Easy Start is reporting 25A after install.

Now that I am looking at my outage profile of 10 outages a year for 2-6 hours, why not just move the aircon back to the mains panel and use the sub panel as a critical loads panel? We can survive 2-6 hours without ac. For our outages, 5,000Wh of batteries on a 3000W single phase inverter would be all we need. Power up the genset to recharge the batteries if needed.

Would be easy to hook the aircon back up to the subpanel if we hated not having it.

 

[Browse]

I went through this exercise, but in the reverse. My Honda couldn't start my 4 ton HVAC even with an EasyStart installed. My first option was to purchase an inverter portable AC. That worked fine for a bit and it's nice to have the option to cool a single area during an outage without spending a lot on energy.

The second option was to get an inverter and battery system with a high surge capacity for starting large inductive loads like the compressor in the condensing unit. The Growatt 12k is a low frequency model with very high surge capability, and this can start the whole house HVAC if needed. For longer outages during a heat wave, I intend to run on the Growatt, using the Honda to keep the batteries charged up. I purchased a Chargeverter for this so the Growatt wouldn't try to pass through the power from the generator. I can use the same interlock connection for either the generator or the Growatt to power the house by using a jumper between the two outlets, but usually the generator feeds the Chargeverter.

 

[chrisski]

Power up the genset to recharge the batteries if needed.

For our outages, 5,000Wh of batteries on a 3000W single phase inverter would be all we need.

Will the inverter take a single phase ? Mine won’t .

You seem to have a decent plan.

 

[corn18]

What would happen if I leave the aircon

Will the inverter take a single phase ? Mine won’t .

You seem to have a decent plan.

Not sure. I am not smart unless it's an RV. Whatever a simple Victron inverter/charger takes I can provide from the monster outside.

 

[corn18]

Here's a really dumb question: what happens if the power goes out while the heat pump is on, then the 120V inverter takes over and only supplies power to one leg of the heat pump? I'm thinking I could just turn off the heat pump breaker before I manually transfer to the inverter which works great for me but is definitely NOT wife proof.

 

[corn18]

The more I think about this, the more irritated I get with myself. I spent $1900 on the big genset and a soft start. Just to be able to have air conditioning. If I just remove the heat pump from the sub panel, I can power all the sub panel loads easily with just my 2500W Champion inverter generator which is uber quiet. Then spend that $1900 on 5000Wh of batteries and an inverter/charger. I always buy before I think.

 

[corn18]

The simplicity of this sure makes it appealing. Ima gonna abort for now.