Converting an uninterruptible power supply to LiFePo4: what do you need to know?

[@fathergratwick]

Anything over 3.365v is not ideal for lifepo4 cells...seems that bms had setting for lipo caells (3.7nominal)

[@michaellesage]

Have you done a rundown test, i.e. pulling 200 Watts (or 500), how long your unit stays on for? I'm trying to figure out how efficient (or inefficient) UPS's are in getting power from batteries to the load (i.e. how long should a UPS run with a 24v 100 amp hour LiFePo4 battery at say a 200 watt, 1.5 amp load - got only 45-50 mins with 75 amp hour Sealed Lead Acid)?

[@Den_Electro_channel]

I did not conduct any experiments on this UPS, since it is not my device. But I tested my UPS. True, there I changed the battery to 12 volts. part 1 kzbin.info/www/bejne/aZXRmKqqiNGriZY part 2 kzbin.info/www/bejne/qGrJoIWso62bn9E

[@fernandofrediani9010]

I have replace my UPS battery for a Lithium one, but the issue is that as it has a lower nomimal voltage, 11.1V, at some point the UPS thinks it is out of charge while it still has charge to give and starts to beep quicker in a out of charge state. How is it possible to fix that ?

[@Den_Electro_channel]

you need to look at the UPS diagram. But why not just add another Battery to increase the voltage?

[@fernandofrediani9010]

@@Den_Electro_channel adding another battery doesn't make sense as for the 12V level the number of cells are always 3. Adding amother pack in paralel only increases the time, but the fundamental issue of slightly differente voltages the UPS doesn't go away.

[@Den_Electro_channel]

I also assembled it this way but with 4 lithium iron phosphate batteries and everything worked great. 12 volts is the operating voltage, it is made up of four 3 volt batteries. Lithium delose phosphate batteries have an operating voltage of 3.2 volts. And the maximum, without load, is 3.65 volts. kzbin.info/www/bejne/aZXRmKqqiNGriZY

[@fernandofrediani9010]

@@Den_Electro_channel that doesn't make much sense and is not what most people do. The nominal voltage of a fully carged cell is 4.2V

[@dmagill4]

@@fernandofrediani9010 Incorrect in this case -- Li-ion batteries are 3.7 to 4.2V, LiFePo4 batteries max out about 3.65 and are considered 3.4.v batteries -- it takes 4 to make a 12v replacement