I'm not sure too many people are using this feature but after some back and forth with MPP Solar about odd behavior with the timer, I finally understand a little more about how it works and wanted to share it in case it helps anyone else. I am making some assumptions based on my observations - feel free to let me know if they're incorrect and I'll update the post accordingly.
tl;dr if using the output source/charger source priority timers in the LV6548 (and probably any other Voltronic-based inverter that has this feature), please treat the starting time as the top of the hour and the ending time as the end of the hour. Example: if you'd like USB priority from 7am to 3pm and SBU priority from 3pm to 7am, you should set USB priority start at 07 and end at 14, and SBU priority start at 15 and ending at 06. Do not edit/change setting 01 (global output source priority) after you've set a timer. If you have multiple inverters in parallel, for output source priority timers, you only need to configure the timer on the primary inverter. All of the secondary inverters sync the output source priority automatically. If you're using charger source priority timers, you must configure them on all inverters (thanks
@DanielS for confirming this).
If you incorrectly use USB 07-15 and SBU 15-07, what you're actually saying is you want USB from 0700-1559 and SBU from 1500-0759, which as you can see overlaps. So what happens when you do this? The inverter accepts these values and does not perform any overlap detection. The last setting that is saved will be the active setting. If I set USB 07-15 first, then set SBU from 15-07, what I actually get is USB from 0800-1459 and SBU from 1500-0759. This is of course not exactly what I wanted as the transition from SBU to USB will now occur at 8am rather than 7am.
The way this works is that there is a 24 hour (from 0-23) table and in it, each hour is assigned an output source priority setting (USB is assigned the code 0, SUB code 1, and SBU code 2). When the clock ticks over to the next hour, the inverter checks this table and switches (if necessary) to the new output source priority. If my table looks like this:
2 2 2 2 2 2 2 2 0 0 0 0 0 0 0 2 2 2 2 2 2 2 2 2
it basically indicates SBU priority from midnight through 7:59, USB from 8:00-14:59, and SBU from 15:00-23:59.
When you update setting 01 (global output source priority), I believe that it essentially writes the selected value over all 24 slots in that table. For example, if I go to setting 01 and set it to USB, my table would look like:
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
When you update one of the output source priority timers, it takes the start time and iterates through the end time (inclusive) and sets the corresponding output source priority into the output source priority timer table. If I start with the above example (setting 01 set to USB), and then set an output source priority timer for SBU with start 07 and end 14, the firmware will overwrite those slots in the timer table and we'd have:
0 0 0 0 0 0 0 2 2 2 2 2 2 2 2 0 0 0 0 0 0 0 0 0
Each successive change simply overwrites the corresponding slots in this timer table. This is why you cannot edit/change setting 01 after setting timers.
When the start time and the end time are both set to 00, this seems to be a special case and is ignored. I think this means you can't set a timer to begin at midnight and end at 00:59, but if you've gotten this to work, let me know!
I believe the same applies to the charger source priority timer, if you're using that. There is also a way to view this table over the RS232 port (you'll need a USB to DB9 RS232 adapter). Please see the attached PDF for more instructions.
