On my van build, I have a Grape 190 W solar panel connected to a 30 A fuse, a battery switch, a Victron Smartsolar MPPT 100v/30A, a 40 A fuse, a Victron 500A Smart Shunt, and finally to a SOK LiFePO4 100 Ah battery.
This system worked well for almost 2 years. Several weeks ago the MPPT started only reading ~ 8 V, which isn't enough to charge the battery. The MPPT bulk light also flashes, which the manual says indicates insufficient power to start charging. However, when I measure the VOC of the panel by disconnecting it from the MPPT, I typically get ~ 18 V. The specifications for the VOC of the panel is 24 V, but this is cloudy Oregon in the winter with a low sun angle, so that may explain the difference. I've attached a history graph from the VictronConnect app that shows everything was working fine with a peak voltage of ~ 18 V for multiple days and then the drop of the peak voltage to around 8 V. The battery was very low because it wasn't charging, and after fully charging it with an AC-to-DC charger, the MPPT spiked to 21 V for a few minutes and then returned to its low voltage. I get the same problem with or without loads attached to the system. Everything works fine with a battery-to-battery charger and loads hooked to the battery, so the problem is the panel or the MPPT.
Several posts on this forum discuss a similar problem, and it is ascribed to faulty wiring from the panel or a bad panel (but never the MPPT). Here is an example (old post). However, the VOC going into the MPPT seems reasonable to me. To test all of the wires from the panel would require me to remove the wooden ceiling which they are buried behind, so I want to make sure that this is likely problem before going to so much effort. The panel is clean, and my VictronConnect app is up-to-date.
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