Building a 12 volt UPS for my car hail covers...

[BigTexasFlex]

I need some help as I am endeavoring to build my first battery bank.

Namely, I am aiming to build a UPS for 2 hail covers that inflate to cover my cars. Sometimes, the hail storm can knock the power out for a few hours.

At this point, I don't see any solar aspect for this system. Just charging from the wall plug.

Each hail cover use 12 volt DC, 5 amp power supply.

I used a multimeter to determine they use about 3.4 amps each when they are running.

I am likely to buy the Fortune LiFePO4 3.2v 60AH 10C cells. I could put 4 in series to get 12.8 volts which could power these hail covers in a power outage. I like the Daly BMS 4s 12v 15 amp.

My goal is to be able to charge this pack with both hail covers running, drawing about 7 amps. Specifically, if the power to my home fails due to a storm, I want the hail covers to continue to run until the low voltage cutoff disconnects the load.

What size charger do I need to achieve this? And can I do this using the Daly BMS 12v 15 amp?

My very uninformed guess based on the schematic for the BMS is that I would need a 12v DC, probably something like 20 amp power supply to plug into the wall? That would give me head room for the hail covers to run totaling 7 amps and also the 8 amps the BMS draws to charge the bank?

If I've left out critical information, let me know. I'm very new to the DIY battery bank game.

 

[A.Justice]

A 15 amp BMS would allow you to use around 180 watts (15A x 12v DC= 180w). If the pumps require 7 amps @ 115v AC , its going to be around 800 watts of draw (7A x 115v = 805w). I would go with a higher amperage rated BMS, I wish I knew more about them, but there's tons of other people on here that could give you better advice on the specific model.

You could bypass the BMS for the blowers, but make sure you have a low voltage disconnect of some kind. Also, Make sure your inverter, or UPS, (and wiring as well) is rated for at least 20% over what you intend to be the regular use.

Those 60 AH batteries @ 12v have 720w in them as well. If you need around 800, you wont get too much time from the batteries, maybe only an hour or so of the blowers running. I would suggest getting a Kill-a-watt meter, to find out the exact consumption of the blowers, it will save you money in the long run, you will size your system right the first time. ( I wasted more than $200 on undersized batteries )

Whatever charger you get, make sure it is matched to the charge current of the BMS you decide to use. I prefer programmable chargers that let me set voltage, and amperage. I keep my LiFePo4's at around 85% SOC, to maximize the life, and safety.

I really like the CALB 100ah cells. You can get 8 of them for around $5-600 too.

Disclaimer: I work on electronics for a living, but I don't claim to know anything. Please double-check my numbers before you build or buy.

 

[wmills_92105]

You measured 3.5amps on the 12v side?