Power Inverter with Li-ion voltage range

Thread Starter

CarlPace

Joined May 3, 2022
20
Novice learner here. I recently had the misfortune of having my EV die (Ford Focus Electric), but therefore DIYer's dream of inheriting 430 prismatic 15Ah Li-ion cells. I've already safely extracted about 25 of the cells for my own devious purposes.

My first idea was to make a portable backup battery that could buy me about 2 hours of refrigerator runtime in case of a blackout, or about 1.5 hours of running my small window air conditioning unit. So far I've got the charger, BMS, case, and cooling solution figured out. All of which were fun learning experiences.

My stumbling block has been the power inverter. Since most seem designed to run off of lead acid/car batteries, they have an upper voltage limit of around 14.5V, but when my back is fully charged it will be closer to 16.8V.

I've been able to find some suitable inverters, but they're overkill (both in power and budget) for the project. I only need 600W continuous, as my air conditioner tops out at 480W. My one thought was to simply use a buck converter to get the voltage down to inverter-friendly levels when its at full capacity, but most have max current limits that are too low, as I would prefer to have 50A to be safe, even though I would only be drawing a max of 40A. Perhaps I could run multiple converters in parallel?

Some basic info about the battery:
Cell's nominal voltage: 3.7V
Cell Capacity: 15Ah
Configuration: 4S4P
Cell Discharge Rating: 1C
So, battery capacity 888 Wh

Any ideas that don't involve throwing gobs of money at the project? Aiming to learn. Thanks.
 

Thread Starter

CarlPace

Joined May 3, 2022
20
Hah! This is why I should come here first before thinking for two days in the wrong direction... Thank you.
 

LowQCab

Joined Nov 6, 2012
4,029
Unfortunately,
Lithium-Batteries don't like working in a fully-Charged-state for long periods of time.

That's part of the reason why Lead-Acid--Batteries are still very popular,
they operate best when being maintained in a fully-Charged-state.

Lithium-Batteries are a poor choice for a UPS application.
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