Victron recommended settings for LFP 10-90% SoC

[John Frum]

For the SCC's, I would think re-bulk voltage offset might help trigger the SCC to kick back into bulk mode if you're significantly undercharged, though there'd still be a delay for the battery to settle, as well as the risk of microcycling under normal usage since you have to go into bulk mode before you can drop back into absorption.

You talk about discharging to 10% but I think what you want is to rebulk when the sun starts shining in the morning.
The part we haven't really talked about is low voltage disconnect.
Lets leave that for a later message if you are really interested.

The problem with re-bulk in the context of a solar charge controller is that you want to use solar power when the sun shines.
If you use a re-bulk voltage that corresponds with 10% SOC the SCC will not charge until the voltage dips to the re-bulk point.
You also want to power your loads directly off of the SCC while the sun shines.
In order to do that your SCC voltage must be higher than that of the battery.
You could set a float voltage higher than full resting voltage to achieve that goal.
Its a bit more stress on the batteries but most everything in life is a trade-off.
Shooting for 10-90% is aspirational ideal but the sun rises when it rises and sets when it sets.
You want to make use of that power when it is available.

 

[thegoogler]

Right now my float is 13.2V, which is below the battery. During the day once the SCC goes into float mode that powers the parasitic loads for hours but it's below the ~13.3V the battery rests at so the battery doesn't receive a charge (and the BMS seems to confirm that). I actually feel pretty good about that setting and I think it's working as expected. Granted I don't think my setup would ever re-bulk unless I drain the battery considerably since the battery needs to hit 13.1V for re-bulk to kick in... however at least during quiet periods my basic devices seem to run off the SCC float.

That said if I put a big load on the battery during the day when the SCC is in float then yeah you're absolutely right I'm not taking advantage of the sun to recharge it.

I'm not too concerned about LVD... it's rare I'll get down that low (if ever) and it's pretty easy to adjust the BMS to handle that if required. Over the 5 week trip I did this summer I never got below ~68%, even when buried in heavy trees for days.

And yeah everything is a trade-off, I know. In my experience I get 2 or *maybe* 3 years out of a lead acid battery, so my hope is to do better and ultimately to be able to run this setup for ~10 years

 

[John Frum]

Right now my float is 13.2V, which is below the battery. During the day once the SCC goes into float mode that powers the parasitic loads for hours but it's below the ~13.3V the battery rests at so the battery doesn't receive a charge (and the BMS seems to confirm that).

If the battery voltage > float voltage the battery services the load.
If the battery voltage < float voltage the scc services the load and charges the battery.
When the battery voltage has reached homeostasis with the float charge then the solar charge controller services the load and very little current flows into or out of the battery.