Maybe I was expecting too much cleverness from the charged detection. I thought if I set the tail current to 4% (=24A) then if the battery is approaching absorption but the sun goes in it would erroneously set SoC to 100%. As you say pwfarnell, if this makes very little difference to the actual charge state near absorption then I don’t need to worry about it. I do need to set it below 4% though because I have a 25A charger to top up from the grid when needed and 4% seems too close to this. So I’ll go with 2% and 3 minutes and see what happens.
If the sun goes in and the charge current drops, the voltage drops because it is the charge current that holds the voltage up, so it will not synchronise under these circumstances.
Attached is my charge curve for 600Ah of Victron NG batteries albeit at 12V. The current hit 24A = 4% tail current at 14:12 and reached 1% = 6A at 14:20 ignoring the dip, so 8 minutes at an average current of 12A doing the maths at each minute reading. 12A for 8 minutes = 12 x 8 ÷ 60 = 1.6Ah, which for a 600Ah battery is 0.26% of SOC, pretty inconsequential.
Thanks that’s really helpful. I have learned not to be so worried about the last half percent!
I am having the same problem with a Victron MultiPlus-II 48/3000 with a Fogstar 16.2kWh battery.
I have tried manually setting the SOC and, while it clearly updates the SOC values, it does not track after that.
I have now revised the Smartshunt values and the plan is to use the Charge Only (I) option on the inverter and, when the battery approaches 100%, try the synchronise function.
It’s a pity that the synchronise will not take the manually entered value and recalculate from there. Once the system has reached 100% the system could then automatically re-synch. Tracking from the manually entered value, albeit temporarily, until a 100% sync would be better than nothing.
I set my shunt to 2% and 3 minutes and it seems to be working fine syncing when charging from the Solar MPPT charger over the last few days. I haven’t tried the top up charger from the grid but I see no reason why it shouldn’t work then too. Thanks all.