I have a lifepo4 battery system which is only charged via Victron mppt controllers.
Can I, using a Cerbo GX or similar, set a SOC limit - so that solar charging stops once the battery reaches the desired SOC (say 80%).
I’m assuming (if possible) the Cerbo is able to control the MPPT controllers? Is this possible even on thecheaper Smartsolar MPPT 100 | 20 controllers?
I think you could enable ESS assistant and set limits there:
Best way is to enable DVCC and set a lower charge-voltage-limit that equals about 80% Soc.
But mind, that over time - if you not charge to 100% - you will be facing soc-drift issues of the BMS, cell imbalance and the like.
Getting (heavily) imbalanced cells back on track can be a very time consuming task especially on passive balancing BMS.
I would recommend to stick with 100%, mind it’s not like the battery would sit at 100% for “days”.
Just to explain this is a system where for long periods of time it’s relatively dormant… a low load which the solar can basically offset. However if I don’t limit the charge to say 80% then it’ll end up resting for months on end at 100%. It does have a 2A active balancer so hopefully if it drifts then the occasional charge to 100% would allow it to reset.
However when you said that you set a charge voltage - I thought, with the lifepo4 voltage curve being so flat, then it’s pretty hard to get the SOC just knowing the battery voltage… is that wrong?
Also I’m taking from this that the Victron system is not able to stop charging based on the state of charge of the battery (as reported by the battery BMS)?
Reading that link, unless I’m wrong, it does not look like ESS is able to affect charging from the MPPT controllers. (I think it can only influence charging from the grid).
If your battery sends the SOC to the GX and the MPPTs are connected to the GX then you can write a Node-RED flow on the GX to do this. However, as said above, without regular charging to 14+ Volts the SOC will drift and the cells may go out of balance.
The other thing you could do which may be more preferable is to allow charging to 14+V and then shut the MPPTs down until the SOC reaches 80%, at which point a recharge is initiated.
Correct.
Out of the box, you can set minimum SOC only and no max SOC.
With “battery life” you can push charges but not limit.
But with DVCC - as DogNose wrote - you can limit the charge voltage.
With NodeRed you can do literally any stuff.
Just saw the Battery Safety Controller BSC can change CCL and CVL depending on SOC. The BSC connects in between your battery’s BMS and the GX.
Lot’s of assumptions here. I think it’s not a bad idea to go to 80%. It differs a little from cell supplier, but that would be around 3.35-3.38V per cell/13.4-13.6V I think (when charging, when discharging the Voltage will be different at 80%). And you can program that voltage as the absorption voltage in the MPPT. Yes, voltage curve is flat, but not that flat that you can’t measure this. Look at the charge diagram. So, for the love of the cells, it’s a good idea. However, once in a while (and when that is is really depending on your usage of the system) you should go to 100% because of syncing the SOC and having the cells balanced again. But, with a good BMS you know if cells are getting out of balance, so that can never be a reason to go to 100% every time, imho. Cells will love you!
