Lifepo4 voltage drop recently

[wattmatters]

Then my BMS is lying to me

Probably.

State of charge (SOC) indicators of BMSs will drift away from the actual SOC over time, especially if the battery is never really fully charged for a long time.

Many of them rely on a low or high cell or pack voltage warning state occurring before they reset the SOC to 0% or 100%.

If you want to track SOC with better accuracy then a quality shunt will help (but even they are not perfect). Else just make sure the battery gets a decent full charge occasionally so that the BMS is reset to 100%.

14.0 V is likely not high enough to reset the BMS SOC indicator but from a battery charge perspective, provided the battery charge current has tailed off then 14.0 V is plenty high enough and the battery will be 99.x% full.

LiFePO₄ is tricky chemistry to track SOC using voltage due to the voltage barely changing over a wide range of SOC (between 20-80% SOC there is not much change in voltage). As a result voltage is not a good indicator of LiFePO₄ SOC except when the battery is at a very high or very low state of charge - at the SOC extremes the voltage does change a lot more. With other chemistries such as lead acid, sodium and NMC then (no load) voltage more or less tracks pretty well with SOC.

This is why SOC sensors needs the battery to have achieved a full state of charge at the recommended max charge voltage with charge current having tailed off to a very low level.

 

[sunshine_eggo]

Repeating what has already been said in a slightly different way... For a BMS to maintain accuracy, it needs to attain true 100% SoC about twice a month.

Additionally, you need to provide sufficient time above the balancing voltage to ensure the cells stay in balance.

Please post your BMS settings screens.

Please post your PV charger settings.

• Your daily use is limited by your PV and available solar. If you use more than this, you will eat into your battery capacity, and you will eventually consume all your battery.
• Your battery capacity determines how long you can go between charges.

It's important to know how many kWh/day you can collect via solar on good days and to understand how the seasons impact your available solar.

The PVWatts link in line #1 of my signature will allow you to compute your average daily solar hours by month based on your exact location, average weather and array orientation. If you have any shading or partial shading, it all goes to heck.

 

[Echo Dawn]

Thank you so much

 

[Echo Dawn]

These are two apps I use I go back-and-forth cause I like to look at the gorilla one, but I don’t like looking at the blue one lol

 

[PotusGobbleBottom]

Thank you so much

Here is a nice chart for reference. Keep in mind if you are charging or discharging the chart is lass accurate the more you are charging or discharging.

Also, I dont believe anyone has mentioned voltage settling.
You would charge to 14.4 until the current drops to basically nothing. Your charger may do this. (I hope you are not using a lead acid charger!!)
If you disconnected the charger and loads at this point., Do not be concerned if your voltage goes down to 13.8-14v. This is normal. This is called resting voltage and needs to be considered.

 

[Echo Dawn]

Now I know why they show two 100% on the voltage chart just baffled me before lol

 

[Echo Dawn]

My world 100% was fully completely as in the tragically hip.

 

[PotusGobbleBottom]

These are two apps I use I go back-and-forth cause I like to look at the gorilla one, but I don’t like looking at the blue one lol

Cell over voltage in your BMS is set to 3.75. This is a bad practice. I would change that to 3.66
Cell under voltage i would set at 2.8

 

[Echo Dawn]

No, I have a battery charger from the lithium company that sold me the battery

 

[Echo Dawn]

How do I change it?

 

[PotusGobbleBottom]

How do I change it?

No clue. That is between you and the BMS. from the screen shots I do not see any obvious way. Perhaps that pencil edit button does more than change the name of the battery?

 

[sunshine_eggo]

My world 100% was fully completely as in the tragically hip.

A good confirmation of 100% or damn close is if all cell voltages are 3.45V or higher with little or no current charging them.

Cell over voltage in your BMS is set to 3.75. This is a bad practice. I would change that to 3.66
Cell under voltage i would set at 2.8

LFP can technically take 4.20V (very little gain and reduced cycle life vs 3.65V) AND the vast majority of "dumb" BMS trigger off at 3.75V. Initially, all the server rack batteries ran up to 3.9V.

While it may not be best practice, it is a very common practice, and it's not likely to influence cycle life on a low C rate application.

 

[Echo Dawn]

Oh geez I can’t figure out how to change that setting

 

[Echo Dawn]

Will it work if I just watch it manually and then turn off the charger will things be able to balance out or is that even a thing?

 

[sunshine_eggo]

Oh geez I can’t figure out how to change that setting

It's really not that important. I wouldn't' be surprised if the app you are using is either locked down or limited since you bought the battery assembled from a supplier.

 

[Echo Dawn]

I’m at 3402 right now

 

[sunshine_eggo]

Will it work if I just watch it manually and then turn off the charger will things be able to balance out or is that even a thing?

I wouldn't stress about it.

You might want to try the Overkillsolar app for the JBD BMS.

 

[Echo Dawn]

Here is soc atm

 

[sunshine_eggo]

Here is soc atm

with 60A still flowing in, you're still not quite there, but you're getting close.

 

[PotusGobbleBottom]

I’m at 3402 right now

You got a bit to go for sure.