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Inverter size/type? 2 freezers, refrig, electronics

Rottweiler

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Joined
Oct 29, 2020
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I'd be grateful for a recommendation on inverter size.

This will receive it's primary power from the grid. The solar panels will keep the batteries charged if the grid fails. I don't want the batteries to discharge unless the grid fails. I think this means I need an All-In-One as I'm basically building a largish UPS.

Load (steady state, 120VAC):
  • Refrigerator: 219VA, 198W
  • Lg freezer: 130VA, 119W
  • Sm freezer: 124VA, 121W
  • Electronics: 101VA, 82W (server, network gear)
Total: 574VA, 520W

The startup current on the 3 motor-driven appliances is obviously the big issue. What size inverter should I look for?

I'd like an inverter that can be monitored over the local network (but not necessarily cloud connected). This is all housed in an out-building and no-one is there most of the time so a local monitor panel isn't much help.

Inverter recommendations?
 
Other than the remote monitoring, I would recommend a LF inverter/charger with solar input, and grid charging from aims/samlex/sigineer etc... the all in ones aren’t really suited for motor surge duty. For that type of load, a minimum 1500 watt design would be best... battery storage becomes an issue with continuous loads... so you need to calculate the total daily Wh consumption... the freezers should have stickers stating average Wh... but plugging in a killowatt meter and measuring actual use for a few days will tell you precisely how much splatters you need to buy.
 
... a LF inverter/charger with solar input, and grid charging from aims/samlex/sigineer etc... the all in ones aren’t really suited for motor surge duty. ...
Thank you. I must be confused on the terminology. I thought the definition of "all in one" was that it had both solar and grid charging capability. What's the proper term for what I'm looking for in a charger-inverter?
 
So long as power (grid or inverter) is always at the output, the three refrigerators will never try to start during the same 1/4 second, and 1500W is probably sufficient for the largest. I've measured 5x nameplate rating.

If power was off during a night and PV panels were used to recharge battery, when it reached the point of inverter turning on again, all would have their thermostat switches on, drawing starting current simultaneously.

Are your wattage values operating current measurements under nominal conditions (comfortable house, refrigerator/freezer already cold inside?) What are nameplate ratings? If 500W was the sum of nameplate ratings, I'd say an inverter capable of 2500W surge for a second would be needed to start them.

I measured a small window air conditioner with current probe and scope. Starting current was 5x rating, running was 1/2 rating. It wasn't working hard; room temperature on both sides.

This "inverter charger" listing is a steal:


Sunny Island, 6kW output (11kW surge), 120V, charges 48V battery from grid and produces AC

It does not include PV, which you haven't mentioned. If for extended power outages, you might want PV panels and a charge controller (or all in one inverter which includes PV charging)

You'll need to consider average power draw, but consumer labels for full size refrigerators show about 500 kWh/year, 1500 Wh/day average around the year.


Running refrigerators overnight requires a fair amount of battery capacity. Multiple days even more so. You are better off turning them off at night, because ice is cheaper than batteries. Just run when the sun shines.
 
The power numbers above are straight off my Kill-A-Watt (after the surge current subsided). The nameplate rating on the refrig is 7.20A (864VA) which sounds more like surge current. Nameplate on the lg freezer shows 5A (600VA). Both numbers are 4-5x what I measured.

These are located in a non-temperature controlled shop, so seldom are operating under optimum conditions.

It's a good point if they were all off and wanted to start at the same instant. In that situation I'd need to bring them up one at a time.

The PV is "Phase II". First I want a grid-fed battery backup. Then get some PV for extended outages. (But I have a generator to cover that eventuality for now.)
 
The nameplate rating likely includes defrost heater and possibly icemaker (heater), but wouldn't include motor starting surge.
I've taken a few running measurement for fridge/freezer, defrost, and the window air conditioner. Surge only for the A/C. Running power for the compressors was in the 200 to 300W range. Average consumption was more than the newer, more efficient models.

That Sunny Island I linked would probably cost $1500 with shipping. Four 12V, 100 Ah AGM about $1200 (5kWh total, 3.5 kWh usable). MPPT charge controllers range from $200 to $1000. Large PV panels can be had for $0.15 to $0.50/kW plus freight shipping. Maybe 2kW delivered for $1000, generating around 10 kWh/day average.

That would be a very capable system, able to run additional loads. My system is larger, using grid tied PV inverters for net metering (rather than PV charge controllers), and backs up the whole house during grid failure.

Then there are smaller all-in-one at lower prices. They can work if they support enough PV for your loads. It is battery to run at night that gets expensive, so "load shed" of the refrigerators after dark would be more economical.
 
Wow, I love your precise calculations. I wish I was on your level. My father and I recently ordered our first pack of solar panels,and my mother recently bought a new air freshener here https://buyersimpact.co.uk/ and for the first test of solar panels, we decided to use it. Given that we were getting energy into the batteries, for some reason we couldn't transfer electricity to the air freshener, although, it works perfectly.
 
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