First overnight trip on the boat since all the troubleshooting, and it was super frustrating. When I left troubleshooting the WS500 as communicating with the alternator and the batteries were charging with 100-150 Amps from the Balmar XT250 which is what I would expect.
Outbound - No Charge
However, on the outbound leg of our trip which included about 2 hours of motoring we didn't get more than 15 minutes of charge from the alternator. It initially sensed engine/alternator speed and then it dropped out and didn't return. I confirmed during this time with a direct connection to the field drive (blue wire) from a different battery (starter) providing 13.2v the alternator would immediately start charging again. However when disconnected the external source, the alternator would return to no charge. I reviewed all wiring connections and they looked secure, and moving them had no effect on the performance of the system.
Updates
Early the next morning, I made the suggested changes from the above post... removing the less than ideal wiring management and reterminating the kinked ground connection (engine room fan). I also replaced the wiring connections for the field (blue to blue) and stator (white to yellow) figuring there may flaws in the connections (though I was skeptical of this because the systems worked well for 18 months prior with these connections).
I also updated the Victron Multiplus/Bus firmware to the latest edition during my morning work.
Return Trip
The return trip started well, though confusing. Our SOC was down to about 70% and when we started motoring I saw the system ramp up charge however it started at 20 amps and only ramped up to about 50 amps... which is a small fraction of the capacity of the alternator, and a surprisingly low level given the SOC and the low temp of the alternator. You can see in the graph the field drive percentage dropped down to the 20% range.
The good news was the WS500 was seeing the alternator/engine speeds and seeminly controlling the alternator output - so I figured this was just a settings/configuration issue.
However, after about 20 minutes the alternator/engine speeds dropped out for about 15 minutes... returned for about 5 minutes... then dropped out for 25 minutes... returned for 20 minutes and then did not return for the rest of the return trip.
During this time, I did the lamp test to confirm the field was delivering voltage and it was though at a lower level than I saw previously when I performed the test.
*** Not sure if this is notable, but the engine tach was reporting 2550 RPM, my normal cruising throttle, and the WS500/Cerbo was reflecting 2850 RPM (when it was showing data). ***
Conclusion
At this point, I'm supremely confused by the data drop outs... I've checked all the WS500 connections and alternator connections. All device firmware (Victron, WS500 & REC BMS) is up to date. The lamp and direct connection tests return positive results... so I'm wondering it there is something going on with the WS500, and if I should look at swapping it out to see if its the weak link here.