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Hi I have a victron color, controlling 24kw lithium battery. The max battery voltage is 58.8, this gives a cell voltage of 4.2 volts. The battery currently shuts off at 50v. The percentage figure shown in the display does not make sense as it tell me the battery is at 74% when it reaches 50v. I have not yet charged the battery upto 58.8v but currently the battery is at 88% 53.29v. i just cant get the maths to add up. what is wrong?
Battery Voltage is a very loose method of estimating SOC. The battery Voltage then also depends upon the load or charge current flowing through it. A full battery with a heavy load on it will have a much lower Voltage at the terminals than with a light load, for example.
So, you have a Colour Control, but you did not say what you are using as the battery monitor. Are you using a BMV or are you using a MultiPlus or Quattro as the battery monitor? Perhaps the battery is a smart type which is supposed to be providing the SOC values?
Please let us know the makeup of your system.
I am using the Multiplus, I have a batrium battery management system but this is working to keep the battery balanced and act as a last resort should operating parameters be exceeded.
The battery is a 24kw nissan leaf battery reconfigured to the voltages previously stated.
I understand what you are saying about battery voltage but whether there is a light load or heavy load the battery percentage figure is so far out its not in the ball park.
If I tell the battery that it cant go below 50v then surely the % at this point should be 0, if the battery is full at 58.8 then this should be 100%. I can accept that the terminal voltage could be different depending on the load, so say for instance there was a heavy load that reduced the the terminal voltage and the system shut down still saying it had 5% in, this would be acceptable tolerance, but to shut down saying 70% is way off.
I have attached photos of both my battery and the Multiplus
24KWh is a nice size to have!
So, I'm pretty sure that you are using the MultiPlus as the battery monitor.
It's kind of important to discount the battery Voltage being related to SOC because the battery monitor does take the Voltage into account for the SOC calculations. This is why your maths don't add up. You can set minimum Voltage levels for cutoff points, but these don't relate to the battery monitor or SOC% calculations.
Energy in and energy out is how SOC is calculated, more precisely, Ah in and Ah out. You need to specify the size of the battery so that the battery monitor can make % calculations.
So, it you tell the battery monitor that you have a 24KWh 48V battery, this makes it about 500Ah. If 2.4KWh or 50Ah discharged from the battery then it will calculate the SOC to be 90%.
If, as I suspect, you are using the MultiPlus as the battery monitor, then you need to setup the battery monitor in VE.Configure. Tell it what the capacity of your battery is in Ah and then your SOC calculations should be much more realistic.
The MultiPlus is unable to measure any other DC loads that you may have so you have to bear this in mind. If you really want accurate measurements and include all loads then a BMV is the way to go.
Now, your minimum battery Voltage is still important of course, so you can also set the DC input low shut-down point in VE.Configure to prevent discharge below this Voltage.
I hope this make more sense.
