Lifepo4 battery dropping voltage suddenly after taking off float

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spelunkerza asked Feb 12, '22

Lifepo4 battery dropping voltage suddenly after taking off float

Hi

I have a Victron smartsolar mppt 100|20 connected to a brand new 100ah lifepo4 battery (12.8v nominal, make is cfe 1280S). I have set the preset to lithium lifepo4 and have a 200w solar panel connected to it. I started at 13.3v and I ran it down to 13.1v (it said 88% on its voltage panel) and then charged it back up.

The charge controller completed charging, having completed bulk, then absorption at default 14.2v and went onto float at 13.5v which is default too.

I then shortly disconnected the battery from the solar charger and the weird thing is the voltage instantly dropped from 13.5v to 12.8v. No loads connected during charging or afterwards. Now the battery says it is at 72%. The controller said it put in 260w in total, so how is it possible it is lower now than when I started? Is the battery faulty? Do I need to change a setting?

Would greatly appreciate any help.

Thanks!

Lithium Battery

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Answer 1 · 2022-02-13T10:11:33Z

VK2EVA answered · Feb 13, 2022 at 10:11 AM

LiFePo4 has a nominal voltage of 12.8v

The battery will be at around 13.5-14.6v when "charging" and will usually drop to around 13.0-13.2v for most of its SoC.

So its entirely possible that its fine, and just needs to be charged more. You cant go off the voltage to determine SoC with LiFePo4 as its got an extremely flat voltage curve on discharge.

I suggest charge it up to a known full state (like hook up to a bench PSU at 14.6v for a day or two until current drops to <1A) and then you know when its full, you could then calibrate your SoC to 100% if you have a smartshunt or similar.

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