question

I agree with you - that if the charge cycle does NOT include an absorption period at all OR if the absorption period is very short (ie. for lithium batteries) then this will work & should work well (with only the simple calculation).

But when you have up to ~6h of absorption to finish off the last ~15% (such as for an AGM, Gel, etc) then it would NOT be accurate or useful at all.

So how to best handle this (to avoid confusion) would be difficult.

Hi technomadia,

Yes, as per my reply to Geomz above - I agree that this will work well if 100% SOC is achieved at the end of bulk (with no absorption phase at all or if its very short/negligible). So for lithium batteries I agree & support.

But if the same logic is used with lead acid based based batteries (or any battery type where a lengthy absorption period is included to achieve 100% SOC), then it would be highly inaccurate for 2 reasons;

1- The 'basic' time calculation would work out time to achieve 100% SOC based on the Ah drawn & current charge current, but the bulk phase would only replenish the Ah lost up until ~85% SOC

2- The 'basic' time calculation assumes that there will be full/constant charge current that continues up until 100% SOC, but once in absorption phase the charge current gradually reduces with time

Accordingly, in THIS case (which would represent a large proportion of users) the initial time calculation provided during the bulk phase would be highly inaccurate.

This does not mean that such a change should not be implemented, but if it was then it would need to be structured in such a way that Victron would not receive a bombardment of complaints about 'inaccurate time to full charge calculation'.

Maybe the solution could be a logic change triggered by a simple YES/NO answer to the question of 'is an absorption period used for charging?'...

Now even if an absorption period is used, it would not be impossible to make a similar/useful calculation for time to reach 100% SOC. However, the calculation would be a bit more involved, there would need to be some assumptions made & it would probably need to be handled by a Venus device with inputs from BMV & MPPT or Multi (since even absorption duration is a calculated duration & it can be different for each individual charge cycle).

One solution could be, just like time remaining has a floor to calculate down to, time-to-full could have a ceiling to "desired" charge. (Heck, it's practically already there since the Low SOC relay is the current floor trigger for time to go. The top number could be used for that purpose in the other direction. Although, I think there's probably a better way to do that).

I rarely charge my batteries to 100% (I actively avoid it, whenever possible).

That way, lithium users can set a desired time-to-charged of say 80-90% and lead users can put in a number that matches the end of bulk.

The issue would arise again if users elect 100%, but I still don't think that'll be an issue.

The time remaining calculation is still based on a sample of time (time to go averaging period) and it is not as an absolute number. Meaning, it's constantly changing anyway, all the time, based on load. It could easily be doing the exact same thing, the other direction, and nothing would have to change other than math and a + or - sign on the same display.

Lead users would see the number continue to climb as absorb hits (as they should, as charge rate decreases) and lithium users can see the same numbers, based on their charge rate, to their desired fill level.

Everyone's happy :)