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Lithium for UPS

I think you will have better luck if you charge the LFP batteries to about 14.0 and disconnect the charger. Restart charging at maybe 13.2 volts. I don't think the existing charging system in the UPS is doing you any favors. Probably killing the SLA batteries too.

I would probably be inclined to build my own UPS system.
scanning the boards here looking for 'replace apc ups LiFePO4 Battery'
not seeing anyone marketing this yet??Running 2 or 3 ups units and 2 year the SLA replacement's are more money every few years
I don't want to hack up the old apc to much more adding the outboard connector is easy,
the older models can be started without Ac from the grid.
what's the lifePO4 really need to see to keep it happy in this roll inside as UPS service ??
14.6 charging volts? wont the BMS inside a typical 12v pack do the rest ?
My 1500 apc ups is beeping and needs it now.
 
scanning the boards here looking for 'replace apc ups LiFePO4 Battery'
not seeing anyone marketing this yet??Running 2 or 3 ups units and 2 year the SLA replacement's are more money every few years
I don't want to hack up the old apc to much more adding the outboard connector is easy,
the older models can be started without Ac from the grid.
what's the lifePO4 really need to see to keep it happy in this roll inside as UPS service ??
14.6 charging volts? wont the BMS inside a typical 12v pack do the rest ?
My 1500 apc ups is beeping and needs it now.
For long term UPS service keep your LFP closer to 13.80 charging voltage, 13.50 for float. Possibly equalize at 14.20 once a month.
This should last a decade if cycled every day. Even longer with minimal cycles. I wish I knew a charger that could be programmed to these specs.

14.60 volts is for speed charging.
 
Over the 20 UPS I have converted to LFP, I have found the charging voltage and Low voltage disconnect, very conservative and well inside the parameters of LFP.

Mostly APC
 
scanning the boards here looking for 'replace apc ups LiFePO4 Battery'
not seeing anyone marketing this yet??Running 2 or 3 ups units and 2 year the SLA replacement's are more money every few years
I don't want to hack up the old apc to much more adding the outboard connector is easy,
the older models can be started without Ac from the grid.
what's the lifePO4 really need to see to keep it happy in this roll inside as UPS service ??
14.6 charging volts? wont the BMS inside a typical 12v pack do the rest ?
My 1500 apc ups is beeping and needs it now.
I know @Gazoo built his own UPS, you might ask him for his thoughts. He seems very satisfied.
 
scanning the boards here looking for 'replace apc ups LiFePO4 Battery'
not seeing anyone marketing this yet??Running 2 or 3 ups units and 2 year the SLA replacement's are more money every few years
You won't find a LFE battery that is compatible.

14.6 charging volts? wont the BMS inside a typical 12v pack do the rest ?
No. The BMS will not have anything to do with charging other than being a protection device. There are hacks and workarounds to get a UPS to work with LFE. I don't know off hand where they are but I have seen them.

I bought a cheap UPS from China to use with my LFE cells. One could also use an inverter/charger for a UPS. Most will accommodate LFE chemistry but check to be sure. Also too high a float voltage will shorten the life of an LFE battery. All of my cells are floating at less than 3.39 volts which is a bit more than I would like, but it's the best I can do with the UPS I have.
 
Please quantify.
Hi @smoothJoey
I dont have the numbers on hand. But I can explain my reasoning.

I checked 3 UPS models for charging and low voltage:

APC 650 12v
APC Pro 1000 24v
Triplite 750va 12v

with 12V models I found they charge at 13.8 -14v and low voltage disconnect >11v
With 24v Models 27.6v and low voltage disconnect >23v

So, With those charging voltages averaging 3.45v per cell, I found them perfect for a 3-5 year life expentancy for a Second life LFP Cell.
Remember LFP (LiFePo4) nominal voltage is 3.2v

I Just buy these models and insert the battery for friends and family.

I have done one-off larger UPS, with Lithium Ion 3.7v and daly bms (2 of them) in series for 48v.

This Forum helped me allot in the begining (early 2021), trying to give back to the comunity.
 
I've been using 7s7p on APC 1500(s) and 14s13p on an APC 3000 for a couple of years now.

The APC 1500(s) charge up to 27.7v (+/- just a bit depending on different APCs). Charging is 2-3a range, so about 80w. 27.7v/7 = 3.96v/cell for lithium-ion and 27.7v/8 = 3.46v/cell for LifePo4.

At the low end, my APC tests cut out right at 21v. This is 21v/7 = 3.0v/cell for lithium-ion and 21v/8 = 2.625/cell for LifePo4. It can be just a little lower on some APCs.

Lithium-ion works OK. And at 3.95v/cell, there's a good deal of power in them as a reasonable replacement for lead acid as far as run times if the power goes off. Here's a chargery 8t screen on a 7s7p sitting in an APC 1500. (I'm not using the shunt)
1638396051497.png

In one of my APC 3000(s) I have 2 separate / independent 7s7p(s) - just like you would have 2 separate 24v lead acids - and here's a pic of voltages. What's interesting is that over several months the independent batteries will drift and I have to manually discharge one to bring it back inline - else it will actually charge up over 4.2v/cell. In the pic you can see one is 27.4v and the other is 27.1v.
**I wonder if this is why lead acid fails over time?
1638396286351.png

And then I did a 14s12p and rewired it a bit to just have 1 x 48v connection - and this works very well!
1638396494683.png

Here's the stabilized voltages of the 14s12p on the APC3000 (shown above) - e.g. 55.53v overall and 3.96v-3.97v/cell after balance.
1638396882908.png
 
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