New 4 cell build, inverter low voltage cutoff

Joedeath332

New Member
Joined
Oct 13, 2021
Messages
6
Hi I am going to built a 280ah 12v 4 cell lifepo4 battery for the first time, this will be to replace the current lead acic battery bank in place.
Well while reading / researching before the built I came across this in a sticky here on the forums from @Will Prowse :
12V 4S LiFePO4 Battery w/ BMS:
  • Absorption: 14.5V
  • Float: 13.6V
  • Inverter Cut-off: 10.7V-12V (depending on size of load and voltage drop etc
[/QUOTE]


But when I look at the spec sheet for my 1500w pure sine inverter it lists the low voltage cut off as 10.2v
The inverter is mainly used to run the microwave which runs for 3.5 minutes twice a day and when running my draw at the shunt is around 120amps.
As far as I know the low cut of voltage on the inverter is not adjustable, so will this be an issue even before I start to built the lifepo4,
Actually after typing this all out I just realised about the daily bms cell low voltage protect setting, I was gonna set it at 3v, so am I right in thinking this will shut the battery of once it reaches 12v assuming all cells are equal.?
 

mikefitz

Solar Addict
Joined
May 28, 2020
Messages
860
The non adjustable low volt limit on the inverter will not be an issue. Firstly you will have a low voltage limit set in the BMS and secondly you should know the SOC in the battery and will use common sense not to use the inverter when the SOC is low. If the BMS ( or you) were to fail, 10 volts pack voltage will not cause damage, ( provided the battery were not left in this state for a long period).
A low volt pack protect of 12 volts is OK. Cell protect , perhaps allow a little variance in the cells and set to 2.8 volts
I suggest setting the absorption no higher than 14 volts, 13.8 to 14 volts will give a low stress charge. Float is ideally set to the resting voltage or lower of the battery, 13.3 to 13.5 volts.

You will need a BMS suitable for your application regarding load current. I prefer the JBD range over Daly. Make sure you get a smart BMS.

Mike
 

DLTooley

Solar Enthusiast
Joined
Jan 12, 2020
Messages
131
The BMS will do it.

That voltage disconnect on lead acid designed inverters is an important point. I don’t think it will kill a LiFePo4, but I wouldn’t do it every day. I’m sure someone here could speak to this with more authority.

Generally there is a longevity benefit to staying in a narrower range of capacity. I have two charge profiles on my controller that will allow me to max capacity only when needed.

Otherwise the default bm settings are fine.
 

Joedeath332

New Member
Joined
Oct 13, 2021
Messages
6
@mikefitz thanks for the info, I have already purchased a daily 250amp Bluetooth BMS
@DLTooley that is my plan to try to not min / max battery discharging / charging to try to prolong the cells life
 
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