We have an off grid system experiencing charge controller issues. 3.24kW PV array (18) Evergreen ES-180's in (6) strings of (3) modules in series. Approximately 77 VDC Vmp, 60 Amps typically highest charging amps into a 33.6kWh (rated storage) 48 volt battery bank. Charge controller originally was an Apollo T-80 that never worked correctly (lots of various issues, we ended up trying three different Apollo's before the homeowner wanted us to try another controller). We went with a tried and true Out Back MX60 as the 80 Amp Flex was not available yet. We knew the MX 60 was outside it's recommended PV array capabilities but we needed to get the client's PV system charging the battery bank ASAP. We planned on upgrading to the FM-80 when available.
The MX-60 worked flawlessly for several months until it failed to control absorption charging. It would allow the batteries to charge at bulk voltage (58.8) for hours with out switching to float (54). Absorption time was set to two hours. Resetting and reprogramming did not resolve this situation and the batteries were being overcharged when a couple of sunny days were strung together. We swapped in a new FM-80 controller on April 2nd and it worked perfectly until today. It was a sunny day and the FM-80 was in absorption mode by noon time. The homeowner noticed at 2:30pm that the FM was not in float as it should have been. It was a typical sunny day with no big loads on. The homeowner reported that the FM-80 was repeatedly going through a 6 minute cycle. Snooze for 5 minutes, wakeup 5 seconds, tracking 10 sec, bulk 30 sec, absorb charge 20 sec, and back to snooze where it began another identical cycle. The batteries were 100% charged by 2:000pm, the battery voltage was at 53.5VDC (two OB VFX3648's ON powering lights and drawing 5 amps DC) when the FM-80 was not in bulk, or absorb charge. When in bulk charge the PV amps (35A mid afternoon, warm day) were connected to the battery bank the battery voltage climbed back up to 58 volts quickly. The "tech" we called at Out Back was not very helpful, "never heard of this situation" and tried to blame it on poor battery connections, he could not understand why the battery voltage would be 53.5V with a 5 Amp load and then 58 volts 30 seconds later when 35 amps were charging into the batteries on a 100% charged battery bank. Anyone else had an issue like this? Any advice? Thanks, Dave David Palumbo, President Independent Power LLC 462 Solar Way Drive Hyde Park, VT 05655 NABCEP Certified www.independentpowerllc.com
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