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Wrenches, A longtime off grid customer with a 1997-era Trace SW4024 and a Kohler 8.5RMY backup generator (with 1,800 hours over 16 years) has never had an inverter failure, but requested my assistance with a recent development. His generator has been set up on automatic operation using standard Trace voltage, quiet time and load-start program parameters. When it was called to run, it would charge to 29.6 V with a one-hour absorption, then shut off. This has worked well until recently. The automatic operation includes a cool-down and the modest absorption means that the AC input current at shutdown is going to be pretty low. Recently he called me because his generator was starting more frequently and running for longer duration. Of course, I immediately suspected the batteries, which are ten-year old 5000 series Surrette 4KS-25PS cells. Upon checking I found two weak cells, which would explain the inability of the batteries to reach full voltage and shut off after absorption. I will be replacing these two cells, which fortunately are both within the same red polypropylene case, as our only option, as the homeowner's budget won't allow replacement of the whole set. As a single string, the two new cells should play reasonably well with the old cells for a few more years. Because of this, the homeowner had recently shut off the generator at night using the buttons on the inverter, and when he did this he saw a spark flash from inside the inverter on the AC end. I was able to duplicate the flash, which I assume to be the AC2 input relay. The AC2 In setpoint is set to maximum 35A AC. Until the failed cells are replaced, I have advised the homeowner to manually control the generator at the generator, using its AC output breaker to disconnect the current to the inverter before the 108V AC default input voltage threshold causes the inverter AC input relay to unlatch under load. While the SW latches while unloaded and then ramps up input current, I don't believe that it can reduce input current to zero before unlatching when shutting down. My guess is that after 15 years of flawless performance, the relay contacts have pitted enough to cause arcing at disconnect, and if not addressed, the relay on the AC board will eventually fail. As AC relay boards these days are likely made out of unobtanium, I'd rather avoid this failure. So my questions, please: 1. Have I likely correctly identified the AC input relay as the most likely cause of the visible arcing when the generator is turned off at the inverter? 2. Should manual control be a permanent solution? 3. Any other suggestions for this customer? Thank you, Allan --
Allan Sindelar A
Certified B CorporationTM
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