how to use LiFePO4 for a 48V UPS battery (APC 2200Va)

prune

New Member
Hi there,
I have to change the batteries of my APC UPS 2200Va (SUA2200) AGAIN, after 2.5 years.
It is using 4 batteries, 12V 18AH (22AH on mine) in serie to form a 48V battery.
Replacement is a 300 CAN$ budget.

I'll check tomorrow the real charging voltage of the unit.

I'm looking to replace them by a LiFePO4 battery bank.
So I found some 26AH batteries on aliexpress (https://fr.aliexpress.com/item/33019600246.html) that may fit.
The idea is to build a 48V bank. According to the maths, it would be a 15 battery bank. but to better fit with leed batteries real voltage, 16 of them should be enough.

Here's some questions so far :
- should I build two 8 batteries bank with a BMS each or one with 16 batteries, and a 16 channel BMS if that exist ?
- if I build 2x 8battery bank, can I use one single 8 port BMS for both ?
- is it stupid to do that and should I just trash this unit, and buy what is needed for a far more bigger battery bank, like 10KW, and build a grid-tied battery circuit, and switch the things that need power backup to a new circuit/panel (I can still do that as my basement is still raw on concrete.wood) ? (when/if the KWh price rise in Quebec, I'll then connect solar panels)

I'm still on the learning curve... so thanks for any comment/advice.
 

SCClockDr

Solar Addict
- should I build two 8 batteries bank with a BMS each or one with 16 batteries, and a 16 channel BMS if that exist ?
- if I build 2x 8battery bank, can I use one single 8 port BMS for both ?
- is it stupid to do that and should I just trash this unit, and buy what is needed for a far more bigger battery bank, like 10KW, and build a grid-tied battery circuit, and switch the things that need power backup to a new circuit/panel (I can still do that as my basement is still raw on concrete.wood) ? (when/if the KWh price rise in Quebec, I'll then connect solar panels)
  • Before you spend:
    • What is the load (Watts) you are backing up?
    • For how long?
  • 1 16 cell battery & 16s BMS
  • NO 2x 8 cell batteries, a BMS can only monitor a single set of cells.
  • Stupid - NO.
    • If this is stationary you could do a battery box & set the UPS on top or beside them.
 

prune

New Member
UPS is a 2200Va. I'm not using all this, I do have 2 desktops, a 8 disk array, 2 monitors, a laptop, internet router/fiber/wifi.
And I want it to last as long as possible :) It can stays almost 2h with fresh lead-acid batteries with 22Ah 48V right now.

This is pure backup in case of power outage.

So, OK. one 16 cell battery + 16S BMS and trying to fit that inside the UPS or make a bigger box :)

Will the charging power from the UPS be an issue if using a BMS ? If it "disconnect" the batteries when they are full, will the BMS be fast enough to "reconnect" when the grid power switch off ?
I find almost no info of using a lithium battery on a UPS...

Thanks for your answer SCClockDr
 

SCClockDr

Solar Addict
@prune TY
Looks like it is time to break out a multimeter & check the charge voltage on drained, 50%, & 95% SOC. I'd expect 54.8v or there abouts. If the charger is a good one there will be 3 values like 57, 54, & 52 or so.
 

Maast

Compulsive Tinkerer
Your battery constant and float voltage is screwed up, take a look at this thread that tells you how to program the UPS batt constant and adjust its charge/float voltage to accommodate the slightly different voltage of a LFP battery or a large external batt bank.
 
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morth

Solar Enthusiast
I've been playing around with some Headway LiFEPO4 cells in a smaller 12v APC UPS. In a nutshell, yes, it does work. Biggest issue so far is the charging profile doesn't fully charge the batteries. Charging also takes a while but that's to be expected given the UPS thinks it's charging SLA. There's a thread on here that has details on a project that used much bigger batteries and the problems that were encountered. Longer run times are not something these UPS units were designed for. The transformers overheat unless you add cooling. The charging profiles can be changed a bit. but still not ideal for LiFePo4. This thread had a link to another site where all the gory details are exposed. I'm sure someone will post the link at some point.

Bottom line is it's doable, but many changes are needed. A dual conversion UPS would be best to to start out with since it's inverter/transformer is designed for continuous use.
 
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