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Planning UPS for chest freezer, need help with inverter choice

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Jun 3, 2021
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I was going to build a ups for my server rack but after calculating how many batteries I would need to buy, I decided that would be a longer term project but then it downed on me to ups back my chest freezer. I have a go bit of experience with batteries form a hobby club in college but I have next to 0 experience with inverters. I current plan is this:

Batteries: 4 x 3.2V Lifepo4 100 Ah

BMS: 4s Overkill BMS (making sure it does balance the batteries correct?)

Charger: 12V 20 Amp Lifepo4 charger (https://www.amazon.com/gp/product/B...02b6cb41&language=en_US&ref_=as_li_ss_tl&th=1)

Inverter: ????

I would love to use the one from the milk crate vid (https://www.amazon.com/Inverter-600...ea257711&language=en_US&ref_=as_li_ss_tl&th=1)

but I don't like I have to turn it on manually as I want it to be a ups. I was also looking at hybrid systems but they seam overkill/too expensive for this application and what I can afford atm. This is the best one I found so far (https://www.amazon.com/POTEK-Invert...ords=automatic+inverter&qid=1622692133&sr=8-2) but I felt best to ask others on there option. I would love a inverter/charger combo for but to find pure sin wave inverter with transfer switch and lifepo4 charger for "cheap but good quality" I looks like I have to buy them separately. All the help is apricated.
 
One option would be,
1. Determine your freezer load
2. Get a charger that would carry the freezer load + 50% (so it could charge and run the freezer at the same time)
3. Run the freezer off of the inverter 24/7

The battery should stay at the voltage determined by the charger, as the charger makes up for what the freezer load is (edit) to maintain the battery voltage..
 
FWIW, I have a small 110V AC refrigerator in my RV that draw around 60W while it is running. I have (had) a nice Samlex 600W (1000W peak) inverter that would occasionally trip on overcurrent when the fridge compressor turned on. Nothing else was on the circuit, the batteries were at >80% SOC, and the inverter connection to the batteries was solid. I was stunned. Moral of the story, don't underestimate the startup surge from a compressor. I would go with a 1k inverter minimum even though it sounds crazy.
 
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