I have a system with:
1 x MultiPlus 24/3000/70-50 firmware 476 (but problem predates this firmware too)
4 x Trojan SAGM 06 375
for mains backup.
Having clarified a few things since first opening this post I'm listing here the key points as I see them:
The system is not triggering a bulk/abs cycle after anything except a very deep discharge. I.e. it returns straight to float after small to medium discharges.
This means that over time, with several small/medium discharges the SoC indication gradually drops off, when really it should return to 100% once mains returns after such discharges.
I have been told that, by design, the bulk/abs cycle is triggered when the battery voltage drops below 26.2V (2.6V, for 24V systems, below the set absorption voltage of 28.8V). This is happening here, yet the bulk/abs cycle is not activating.
The SoC indicated by the system will not sync to full for long periods of time, which results in the system always showing well less than 100% even when in float. Please see the VRM screenshot below.
I raised this issue somewhere on Victron community/disqus a good while back, but can't find it anymore! We never got a resolution, but I recall it was discussed that the reason was:
i) the battery voltage doesn't drop low enough under the brief discharges/small loads to trigger a full bulk/abs cycle (the SoC does reset to 100% on the rare occasions this does happen).
ii) the repeated absorption feature (which is set at every 7 days on this system) does not trigger a SoC reset on completion
I'd be very grateful for any ideas on how to resolve this, especially now as the system is using the new "shut-down on SOC" feature, which means the batteries will be cut off sooner than necessary due to starting with an already low SoC.
I've added vrm screenshot to compare charts for the same mains failure event for this system and another very similar system (only differences I can think of are 48Vnom/375Ah vs 24Vnom/375Ah and CCGX vs venus GX). This system goes straight back to float, other system goes through bulk/abs cycle.
Just adding another screenshot here as we've had some interesting events over the last three days. Of note is how a bulk/abs cycle was triggered by the full discharge to 40%. However, the most recent discharge to 80% didn't trigger a bulk/abs cycle. I'm wondering if perhaps somehow this system has the bulk/abs cycle voltage level trigger of a 48V system even though it is a 24V system?