question

Sounds as if your solar installation is not keeping up with demand.

The mat PWM might help if connected to the batteries.

When I am at anchor the solar will keep up with demand. Two days ago I generated 1.6kw and consumed 1.2kw. However when I sail I use more power (instruments and autopilot) plus the sails often block the sun from my panel so yesterday the situation was reversed with 1.7kw consumed and only 1.2kw generated.

Having said this, although my batteries get to 13.8V and the SmartShunt calculates 100% SOC, the solar panel MPPTs very rarely get into absorption mode, let alone float. This usually only occurs if I use the engine a fair bit, or get shore power. Is this going to cause battery degradation in the long term?

My question is really about the charging algorithm that the Victron MPPT use and if this will be messed up by adding the PMW to the battery given that the PMW is supplying a higher current (13.8A) than the MPPT when in bulk mode. I find that in bulk mode the MPPT supply lots of amps but the voltage is at or very slightly above the battery voltage. Is this expected?

I have only just got my Raspberry Pi Cerbo installed (after it sitting in my project box for over a year) and I'm beginning to get a clearer picture of both demand and solar supply.

Update: I was reading the details from the PMW incorrectly. 13.8V is the float voltage and not the supply voltage.
I have added the PMW to the batteries and it appears to be reducing the load / increasing the charge on the system.

I'd still appreciate comments on my questions relating to the MPPT not going into absorption mode.

In general undercharging LiFePO4 will do no damage. However they need to be fully charged at regular intervals so that the BMS can equalise/balance the cells in the battery. This frequency you should check with the battery maker specs. AGM, which I think your house bank is, will be damaged very quickly by undercharging.

You should be reaching over 14 Volts, battery dependant, probably between 14.2 and 14.6V, again dependant on makers specs.

MPPT not going into absorption is because your panels are too small. So battery voltage is not rising high enough as it charges to kick the MPPT into absorption.

Smart shunt SOC can be very accurate, if parameters set correctly. I suspect this isn't the case. If incorrect, or not suitable for local conditions, it can synch to 100% wrongly. There's a good video on the Victron YouTube channel about tweaking these settings. In essence the SOC synchronises to 100% when charged voltage is reached and current drops to the tail current setting for the detection period. Clouds/shading can trick the shunt. Suggest you check and set charged voltage to absorption, or very slightly below, tail current down from 4% to 2% or less and increase detection time to 10 minutes or more.

Normal values for AGM are approx 14.4V absorption, 13.7 float and off charge will drop to and maintain about 12.6V fully charged. Will drop due to self discharge over following days, but overnight with no load, you should stay at or over 12.6V. these voltages are for 25C, will reduce as temperature rises.

Maybe this helps, it's a whole day, yesterday, from my camper. System is 24V, so I've adjusted volts accordingly. Solar only at present.

There's a fridge and fan running continuously, but overnight voltage dropped to about 12.5 due to load/heat. As soon as solar kicked in battery voltage went up to about 14.3. this was maintained as the batteries charged, you can see current dropping quickly, then there's a second voltage drop as the MPPT switched to float. Once sun disappeared, voltage dropped as expected, but was maintained by the batteries despite the load.

Another thought. What are the battery settings in the MPPTs?