Season's Greetings Wrenches We have been attempting to use MidNite SOB's with Sol-Ark inverters this year. In Canada we only need one SOB per string since our Code requires Rapid Shutdown for PV source or output circuits more than 1 meter from the array.
However, not all the SOB's were closing the circuit when we had two strings on one MPPT - both when we combined two strings on the Sol-Ark PV input terminals or when we used MC4 Y connectors outside the Sol-Ark to combine two strings. MidNite had no solution for this back during the summer and tech support there only suggested that we had configured the system incorrectly or that we shouldn't combine strings that way. This array also had a very long underground run between the array and inverter. So, at that time, not knowing if it was distance, interference from something else or gremlins, we just took out all the MidNite equipment and installed a DC SunVolt Rapid Shutdown box. Diagnosing the problem was a challenge since only one of the parallel strings on each MPPT was not producing power at any given moment. Also, everything worked fine while I made voltage and current measurements but when I pushed the coil and wires into the JB I lost half my solar power. Anyway, today I solved the problem on a new system I was commissioning by wrapping the SOB Transmitter coil, with the positive conductors passing through it, in aluminum foil. I hypothesized that with the coil on the positive conductors, the negative conductors, which were very close to the coil, all of which was inside a metal junction box, were picking up a signal from the coil and this was interfering with the signal on the positive. It's a bit cludgy, but shielding the coil seems to be the solution. I'd love to hear if anyone else has had this problem and/or solution. Eric Smiley, MASc Project Manager, North Island E: e...@vecoop.ca T: 1-888-386-0116 ext 702 (toll free) C: 250-703-6004 W: viridianenergy.ca <http://www.viridianenergy.ca> <http://www.viridianenergy.ca/> RENEWABLE POWER NOW
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