Dead Battery

[Beek's Bluffs]

Hate to admit but I bought a cheap 30 Amp charge controller on Amazon, only to charge 1 200 AMP hour LifePO4 battery to run my 16 cu ft 12 volt frig off grid. It is rated for the LifePO4 and has been working for months. Last weekend it was very cloudy and I noticed my battery voltage on the charge controller read 10% at 11.5 volts, I didn't think LifePO4 did that, they should stay at about 12 then 0 correct? Then the sun came out and by the end of day it ready 80% at 13.3 volts.

The next morning I got up and it read 10% at 11 volts, while still dark out. I took the battery home and charged it with shore power and it holds just fine, I was thinking maybe the BMS was bad. Now I am wondering if the charge controller could give false reading and really was not charging. I have never had this before with any of my systems.

Just want opinions weather I should head of grid with a new charge controller or is this not something that would happen? The frig was running normal cycles and appeared fine.

Thanks for any help.

Rick

 

[LakeHouse]

Your charge controller doesn't know the State of Charge of your battery. At 11.5V it's nearly dead. At 13.3V you (or the charger, or anything else other than a calibrated shunt) have no idea what the SoC is. LFP isn't like Lead-Acid where you can estimate charge by voltage, except at the very top and the very bottom. At 13.3V you could be anywhere from 30% to 80%.

I took the battery home and charged it with shore power and it holds just fine,

What voltage did you charge it to? If it didn't get up to at least 13.8V while charging, you didn't get it fully charged.

 

[Beek's Bluffs]

Your charge controller doesn't know the State of Charge of your battery. At 11.5V it's nearly dead. At 13.3V you (or the charger, or anything else other than a calibrated shunt) have no idea what the SoC is. LFP isn't like Lead-Acid where you can estimate charge by voltage, except at the very top and the very bottom. At 13.3V you could be anywhere from 30% to 80%.

What voltage did you charge it to? If it didn't get up to at least 13.8V while charging, you didn't get it fully charged.

it got up to 13.8 and held. I guess maybe I should have posted in the beginners section because I am new to the LFP batteries and thought that the bars on the charge controller were reflective of SoC

 

[LakeHouse]

it got up to 13.8 and held. I guess maybe I should have posted in the beginners section because I am new to the LFP batteries and thought that the bars on the charge controller were reflective of SoC

No worries. Sounds like the battery just slowly drained over the course of those few cloudy days.
Does your BMS have a bluetooth app? They're not great at tracking SoC, but better than nothing.

 

[Beek's Bluffs]

No it does not, learning as we go. Thanks

 

[Supervstech]

LiFePO4 has a voltage range from 14.4v to 10.0v
VERY little energy between 12.0 ans 10.0, but the bms wont shut you to 0 until it hits 10.0, or one of the cells hits 2.5V