I have a MPPT Smart Solar 75/10 connected to a 100W panel and a bank of 3 batteries 12 Volt 90 Ah each, on a sailboat.
Whenever I go for a sail and the batteries stop being charged by the land connection or the engine, I need to execute the following procedure for the MPPT to start charging:
disconnect all loads
main switch off
disconnect the panel
wait 10 seconds or so
connect the panel (yellow LED gets active only now)
main switch on
reconnect needed loads
Without this procedure, the charging via MPPT never starts.
With this procedure, the charging starts 90% of the time.
Yes I have checked the connections. Polarity is OK as I get to charge the batteries in some cases. No, there are no wobble contacts.
Yes I have washed the panels.
Yes the sun is shining high in the sky.
The panel reads 22-24 Volts when disconnected. I have no way of measuring the voltage when the panel is connected.
Yes these 22-24 V read even on the cables at the MPPT so cables between the panel and the device are OK.
Do you have a Cerbo and have the solar connected via VE Direct cable AND a VE Smart Network set up. If so, then switch off the VE Smart Network as this can stop the charger starting.
How long do you wait between stopping the shorepower or alternator and seeing the MPPT start charging, if you are only waiting a short period then this applies. If the batteries are completely full and the MPPT has been forced into float because of the other chargers then it will not restart charging until the battery voltage falls below the float voltage and it can take some time after alternator charging at say 14.4V for the battery to fall to 13.5V, especially lithium if the usage is quite low. There is also a setting called “rebulk voltage offset”. If the float is say 13.5V and the “rebulk voltage offset” is 0.4V then the solar charger will not restart a full charge cycle at 14.4V until the battery voltage is below 13.5 - 0.4 = 13.1V. Watch how the voltage responds after you stop shorepower or alternator charging and wait until it goes below float voltage before seeing if there is an issue.
If Nos 1 and 2 do not help then I am not sure what the issue is., but if you come back with some battery history screenshots we may be able to help more.
I have no smart network. The setup is precisely as I described above - MPPT connected to PV and to the battery, but not to load.
Right now the battery is at 12,6 V and still no charging (this is one of the 10% cases when resetting does not help).
Battery history screenshots? What do you mean? And yes I think the batteries approach the end of their lives (10 yrs old with two cases of deep discharge) - but why does it prevent the MPPT from detecting the panel?
You have answered the common causes are not applicable. The other common one is poor connection on the solar supply but you have confirmed voltages rise to battery voltage +5V.
Even with aged batteries it should restart. No idea why it is not restarting.