An incorrect state of charge can be caused by a variety of reasons.
Incorrect battery settings
The following parameter(s) will have an effect on the state of charge calculations if they have been set up incorrectly:
Battery capacity.
Peukert exponent.
Charge efficiency factor.
Incorrect state of charge due to a synchronisation issue:
The state of charge is a calculated value and will need to be reset (synchronised) every now and then.
The synchronisation process is automatic and is performed each time the battery is fully charged. The battery monitor determines that the battery is fully charged when all 3 “charged” conditions have been met. The “charged” conditions are:
Charged voltage (Voltage).
Tail current (% of battery capacity).
Charge detection time (minutes).
A practical example of the conditions that need to be met before a synchronisation will take place:
The battery voltage has to be above 13.8V.
The charge current has to be less than 0.04 x battery capacity (Ah). For a 200Ah battery, this is 0.04 x 200 = 8A.
Both above conditions have to be stable for 3 minutes.
If the battery is not fully charged or if the automatic synchronisation does not happen, the state of charge value will start to drift and will eventually not represent the actual state of charge of the battery.
The following parameter(s) will have an effect on automatic synchronisation if they have been set incorrectly:
Charged voltage.
Tail current.
Charged detection time.
Not occasionally fully charging the battery.
For more information on these parameters see the chapter: “Battery settings”.
It looks like to me that somewhere there is a battery setting where the wrong ah is set.
But I can’t find where.
Battery is 105ah, used around 80+ ah(according to the smartshunt), soc can’t be much higher than 25% if i calculate it right.
In the smartshunt settings i have only one setting for battery capacity right?
To be clear, the soc did reset to 100% at the right time a couple of days ago.
It can drift with time and can also sink to 100% (when really at say 85%) when certain conditions prevail, all have to be monitored and adjusted as required, all part of Getting to Know your System.
My peukert exponent is set to 1.25.
I did read that for lifepo4 it could be closer to 1, but that can’t really be the problem of the wrong soc as i read it right?
The higher that number, the faster soc goes down, and my problem is soc going down too slow. And i have only a small load, around 2a.
I know soc can drift over time, but it drifts from day one, so something must be set wrong somewhere.
And the difference is around 15%, that is just way too much off.
You must change this setting to something like 1.05 because a setting of 1.25 is the exact cause of your problem.
Your understanding of Peukert is only half correct. For a Peukert of 1.25 at high discharge rates the SOC drops faster than the Ah as you note. However, for low discharge rates, the SOC drops more slowly than the Ah which is your exact problem. Peukert works both ways.
@matthijsb
1.25 Peukert is way too high. It will overestimate SOC if your loads are low. Victron normally recommends 1.05 for LFP’s as a start point. (and 99% Charge Efficiency).
