LuchoTurtle
commented
6 months ago I'm not super familiar with UPSs to begin with but it seems you aren't the first one to think about using 12V batteries to emulate them:
- https://www.quora.com/Can-we-use-a-car-battery-as-an-uninterruptible-power-supply-UPS-backup
- https://www.quora.com/Can-a-car-battery-be-used-as-a-backup-for-an-inverter-home-UPS-system-Are-there-any-problems-with-using-a-car-battery-in-this-way
- https://www.quora.com/I-have-a-UPS-It-uses-a-12V-7AH-battery-Can-I-use-a-12-V-90AH-battery-instead-If-this-is-done-will-it-damage-the-UPS-as-well-as-the-computer-connected-to-it
The only problems that may arise with using LiFePO4-based batteries are:
- depending on the load (and the capacity), they may not last long.
- unlike marine batteries, for example,
LiFePO4batteries don't like being discharged deeply and stay discharged for long periods of time - it will affect the lifespan of the battery. Just like the ones found in computers, they like to be in-between 20% and 80% charged.
Other than that, the other caveat that I can think of currently is if there are no problems with the battery being charged and discharged at the same time. In my personal experience, I haven't had any problems with it. And according to https://www.reddit.com/r/amateurradio/comments/itng4x/charging_and_running_off_a_lifepo4_battery_at_the/:
As others have stated, your answer is really to use an appropriate charge controller with your battery.
Let me clear up, from a basic electronics perspective, why you are probably seeing people talk about not being able to charge and discharge a battery at the same time. In principle, a battery can only be charging or discharging at any given time. A battery itself cannot do both at the same time. If you hook a load and a charger directly up to a battery, the battery will be charging or discharging depending upon the current supplied by the charger and current drawn by the load. If the charger is supplying more current than the load is drawing, the remaining current will charge the battery. Inversely, if the load is drawing more current than is being supplied by the charger, then the battery will discharge to supply the additional current needed.
Charge controllers are primarily used to limit the current supply to a battery during charging so that the cells in the battery are not over supplied. Solar controllers also do a voltage conversion to properly charge connected batteries and supply power for loads.
So you should be golden.
At the end of the day, a battery pack is a battery pack. If you're using it just as a fail-safe so you have Raspberry Pies running at all times even if the power runs out, a 12V battery should do quite nicely. With the one we've built, it surely last a long time. Every time it is "out on the field", it lasts the whole day and we still have juice in it after it's done.
So you should be fine, though if you're running low-consumption products like those, I feel like doing a 280Ah 12V battery is waaay too overkill. It's heavy (20KG with BMS), you'd need an inverter and basically you'd have to create a power bank like we did, which I believe doesn't really make sense if you just want it to power a handful of tiny electronics. Lower capacity would be recommended (I don't know if there are any cells that have low capacity, so beware that you may enter the 18650 batteries rabbithole, which is actually neat because you spotweld them together to basically make a cell).
nelsonic
Busy researching buying a UPS for our home server which we really want to keep online as it runs a few vital services ... 💭
Would much prefer to build something using an array of LiFePO4 cells than the crappy cells most commercial UPS come with.
Basically just want to be able to connect a battery bank into an electrical socket and power a couple of Raspberry Pis (or other low power consumption boards). Then if (when) the power is cut, they fail over to using the battery power (till it runs out while sending alerts) 🚨
Is this a use case you have considered ?