Planning UPS for chest freezer, need help with inverter choice


New Member
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 (

Inverter: ????

I would love to use the one from the milk crate vid (

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 ( 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.


Photon Sorcerer
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..


New Member
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.