So. California SW GTI (grid tie) System with aging AGM batteries--what next

I'm a new member here as of today, but an old solar enthusiast, and I appear to have a multi-faceted problem that started up recently - thought to share it with you folks.


System Specs:

Installed in early 2002: Grid-Tie PV system consisting of (40) 120 watt mono-crystalline panels two Trace/Xantrex SW4048 inverters with GTI (Grid-Tie Interface Units). I only have one inverter active at present. The PV array is arranged into 10 groups of 4 panels each, wired in series for a 48 volt system. The 10 groups run through two Trace TCB-10 combiner boxes (5 circuits on each TCB), run through a GFI unit and then to two C-40 charge controllers. The battery bank consists of (4) Concorde PVX-12255 batteries. Also, a small 400 watt 48 volt wind generator connects directly to the battery bank (no load or diversion controller). BTW, the wind genny doesn't get too much action here.

The system typically pumps good voltages back into the grid during daylight hours and the C-40's consistently read upwards of 52 ~ 53 v DC.


The problem:

Over the passed few months, I started noticing that transmitted RF signals from my Amateur radio equipment was interfering with the solar system, 'tripping' the system, especially at night. This has never been a problem up until now. When the RF signals are transmitted, the load side of the inverter's output would start pulsing, and more recently shut down ('trip') completely after a few minutes. The inverter's outages will last for a minimum of 5 minutes, and as long as up to 15 minutes before restoring full power.

Note, I do not loose AC from the grid, as standard grid connected loads remain energized, but it seems that the transmitted RF signals somehow cause the inverter to either disconnect from the grid and start pulling from the battery bank or from some other condition that I haven't determined yet.

During one of the night time power outages, I checked the voltage readings at the C-40's and on the inverter meter, and noticed low voltage readings (approx 37 v DC). When I checked the individual batteries during normal daylight conditions, I found three of them were reading 14 ~ 15 v DC and one was reading low at 8.7 v DC.


Tracking down the root cause:

I removed a 25 year-old linear power supply that was powering the radio equipment. This power supply unit was powered from the load side the inverter providing emergency back-up capabilities. My thinking was that the linear power supply might be absorbing RFI, so for testing purposes, I replaced it with a different (and newer) switching-type power supply ... this appears to have cured the 'tripping' problem.

I cleaned off a fair amount of semi-conductive dust from the regulator circuit board ans all the components in the linear power supply and found one leg of an MOV had come undone from across the 120 v AC input legs. The MOV was soldered back into place and the power supply's output readjusted to 14 v DC. I will reinstall the power supply in it's original location in the near future to determine if the loose MOV and/or the conductive dust accumulation was the cause for the 'tripping', but regardless, I still have a failing battery in the bank to deal with.

Being that the system's batteries are at least eight years old now, I'm not sure if I should purchase a single new AGM battery to replace the failing battery or to purchase an entire new bank of four. (?)

I have read that some AGM's can remain in service for up to twenty years if they are maintained properly ... has me wondering what the true track record is for AGM's ... what's a good load test for AGM's?


Another option I'm contemplating, is to just Grid-Tie the system and not maintain back-up batteries - and tie in my 6500 watt auto-start generator to the SW4048 for those emergency grid outages (?)


All replies welcome ...


Mark S.
So Cal