Questions on a backup system

Jdoyle7Jdoyle7 Registered Users Posts: 1
I'm looking at putting in a small backup power system. I need to run 2 refrigerators, a chest freezer, small tv, dvd player, and 6 cfl lights. I plan to run one refrigerator or the freezer at a time maybe 2 at the most. For now I want an AGM battery, inverter, and charger that I can power with my generator. I would like to add a charge controller and panels later.

The fridge/freezer are all rated at 4.7 amps at 115v (540w), the TV & DVD are 100w together, the 6 CFL lights are 78w total. I figure about 718w total.

I was looking at the Exceltech XP-1100 12v inverter, and two 31 series AGM batteries. I can get Duracell 31DTMAGM (20 amp hour rate is 105) batteries locally. I'm not sure what to get for a charger. I have a 5500w genset that would be powering the charger. I'm also not sure how long it would take to charge 2 batteries. I saw the AGMs need to be charged at a c20 rate which I figure is about 5 amps (105 / 20), but the smallest charger I found on the website was the Iota 15 Amp 12 Volt. I'm also not sure how long I could run on 2 batteries. I'm figured 40 hours at a 5 amp draw but I'm not sure if I did that correctly. The equipment would be located in my basement. The main purpose of this setup is to save gas when I need to run the generator during power outages. I'd like to run the genset only to charge the batteries or when I need to pump water. Any help would be appreciated.


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Questions on a backup system

    Welcome to the forum.

    You are actually looking for a very large back-up system if you want it to run two refrigerators, one freezer, and so forth.

    Never mind what the numbers on the things say: go buy a Kill-A-Watt meter and actually test their consumption. You will be surprised, probably appalled. A refrigerator alone can use up 1200 Watt hours per day. That "hours" part is vital to the formula. On a 12 Volt system that number represents 100 Amp hours of battery capacity, meaning a minimum 200 Amp hour battery to run one refrigerator for one day. In AGM terms that's something like this:

    Or two GC2 (flooded) batteries from the local warehouse store for a fraction of the money.

    The Exeltech will just about start most refrigerators (their start demands can be very much over 1100 Watts).

    My advice would be after you measure the actual power usage of the things you want to keep running you go out an invest in a Honda EU2000i inverter-generator. Less money, won't rot, no place near as noisy or hungry as the 5500 Watt gen you've got. It will also run many water pumps. I know because I have done exactly this, using it to keep refrigerator and freezer cooled down on a rota, pump water (1/2 HP surface pump) when needed, and run the entertainment otherwise.

    Battery + inverter back-up is very expensive. If you have frequent/long outages it may be worth the investment. Otherwise it rarely is.
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