I have a MPPT 150/45 battery charger installed with 24VDC 340Ah battery system and a PV array of 3 parallel panels (Voc- 33.7A, Isc 8.92A). I have noticed the SOC% drops down to 0% at the start of the charging cycle around 20 times last year and now, battery is not fully charging to 100% and max SOC remains around 50%. Presumably the battery health was reduced during the period and I'm unable to figure out the reason. This is the only abnormality I found and any advise is highly appreciated
Hi @coshada
There's something wrong with that SOC reading, and I don't just mean the downward spikes. You don't say where it's derived from, but it behaves like nothing Victron. Appears to be Voltage related when it moves, and that alone makes me suspicious. I wouldn't trust it myself, and I surely wouldn't be relying on it to assess battery health.
Maybe you'd like to tell us more?
Hi JohnC, Thanks for your response, These data were exported from the remote SCADA. However, SOC is received via Victron Battery Monitor (BAM010702000). Please see the attached photos with the configuration. I have no experience with Victron and really appreciate if you can guide me where to look. 
"24VDC 340Ah battery system and a PV array of 3 parallel panels (Voc- 33.7A, Isc 8.92A). "
Please confirm array details. 3 series, or 3 parallel panels.
This is an unusual system with the PLC n'all, so a little hard for us to know what's happening.
That part no. suggests a BMV-702, so we have something to work on.
The 0% dips may be being caused by loss of power to it's supply cable. Wiring, fuse, PLC? The dips seem to coincide with a drop in charge current on the graph, so maybe you have something causing that? Switchgear? Bad fuse? There's something.
What happens with the BMV is that when power is restored it will likely reset itself to 100%, regardless of true SOC. Then you need to see the batteries actually get fully charged (when they can't accept more than a minimal tail current), and only then will the indicated and true SOC's coincide. The Victron shunts need tuning anyway for best results, but this happening frequently makes it useless. This particular functionality can be turned off, or you can adjust SOC yourself. If unsure where to set it, just guess, and it should sort itself if set up correctly.
Priority for me would be to find what's causing that power loss. It's possible to get false syncs with poor tuning, but that isn't accompanied by dips to 0%.
Hi JohnC,
Thanks for the update. The 0% drop of SOC is not instantaneous, there are couple of data points logged between 90% to 0% , around 30%. If this is caused by loss of power, I believe the drop of SOC should be instantaneous. I will look into sync settings as you suggested, Feedback I got from the site was system is unreliable and the PLC program stops all the processes if the SOC% is below 50%.
Agreed that an instantaneous drop to 0% would be expected. But the graphs seem to report as 'Average of', so the question then is how many instantaneous data points is it averaging? This would explain the tapering.
Most Victron systems will warn, but carry on reporting the last value when signal is lost. The plc doesn't seem to do that. IMO.
PLC sends instantaneous data every 5mins and it receives the value from Venus GX via Modbus. Apologies, Graph legend is misleading and there is no averaging in the graph. Your explanation makes sense. I found the victron config file and I cannot open it using the latest software as it seems to be not backward compatible. I will check the SOC settings as requested. Thanks for your valuable contribution.
