[RE-wrenches] Troubleshooting Stumper - Homerun Interference in Conduit/Inverter Turning Off/On Rapidly

[Drake]

The maximizers sound like the most likely explanation to me.

That being said, one point in the diagnosis that I would still do is 
to Megger test the wiring while the wiring is in the conduit. If I 
understood correctly, the wiring was tested while out of the conduit. 
This can miss the problem since a wire can fault against the wall of 
a conduit and find nothing to fault to when out of the pipe.

At this point, I'd bet on the Tigo Maximizers being the most likely culprit.

At 12:38 PM 9/10/2016, you wrote:
>Yes this is an interesting case, as are the debug suggestions given. 
>The wire pairs working out of metal conduit point strongly at either 
>ground faulting or inductive coupling. You seem to have eliminated 
>the obvious wiring issues like polarity and grounding. Since you 
>have a working system next door and you are already putting in the 
>hard work of swapping inverters and wires, it is worth trying to 
>swap the inverter from that working system with the non-working one. 
>This would either indict or eliminate the inverter as the culprit.
>
>It is worth noting that the TrinaSmart modules with Tigo Maximizers 
>are quite capable of being the source of the problem. They attempt 
>to do MPPT at the module level, and can conflict with the inverter's 
>attempts at MPPT. We have had problems with other inverter brands to 
>the extent that power production was impaired, although not as bad 
>as your complete shutdown. It was necessary to use the inverter 
>setup options to shut off MPPT. If Solectria allows this it is worth trying.
>Also I have had problems with Tigo Maximizers on mismatched strings 
>shutting down one string completely to "maximize" others. You may be 
>seeing the effect of communication problems from the maximizer 
>wireless controller. Try disabling them if possible by shutting down 
>their controller with its secret software.
>I'm guessing that plain dumb modules with a plain dumb inverter 
>would not be suffering this shutdown problem. Something in your 
>system is too smart for your own good.
>
>Don Barch
>Energy Solar
>
>-------- Original Message --------
>
>
>-----Original Message-----
>From: RE-wrenches 
>[<mailto:re-wrenches-bounces at lists.re-wrenches.org>mailto:re-wrenches-bounces at lists.re-wrenches.org] 
>On
>Behalf Of Matt Partymiller
>Sent: Wednesday, September 07, 2016 4:46 PM
>To: 
><mailto:re-wrenches at lists.re-wrenches.org>re-wrenches at lists.re-wrenches.org
>Subject: [RE-wrenches] Troubleshooting Stumper - Homerun Interference in
>Conduit/Inverter Turning Off/On Rapidly
>
>Wrenches,
>
>One of our systems is having an issue I have not encountered before where
>the inverter switches between nighttime mode and interconnection every few
>seconds. I am hoping for some technical wisdom from the community.
>
>We have an array of 20 TrinaSmart modules in two strings of 10. The array
>is connected to a Solectria 3.8 kW inverter. The conduit run is simple, all
>four homerun wires (#10 PVwire) in 1" EMT down to the proximity of the
>Solectria inverter where the conduit switches to 1" LFMC before entering the
>inverter. The run is about 20', straight down the side of the wall before
>hitting the inverter. A 600V jacketed communications wire was also in the
>conduit but has since been removed and run separately.
>
>Our inverter is starting up, running for a few seconds, giving a low voltage
>error, briefly showing nighttime mode, then going into startup mode again.
>Solectria was gracious enough to send us a new inverter but we have the
>exact same issue. They tell us their error codes (266, 274) indicate 0
>volts. The transition between low voltage error and startup is almost
>instant. Basically we have 20 seconds of start up, 5 seconds of run, 5
>seconds of error then repeat. This is not a grid problem, the identical
>system next door works fine.
>
>In the process of troubleshooting, our technician pulled all four homerun
>wires out of our conduit and meggered them. They all tested fine so he
>connected to the inverter. The inverter worked fine. The technician
>verified grounding of the array and conduit, pulled new homeruns back
>through the conduit, and reconnected to the inverter. He had the same error
>as before.
>
>He connected each string separately to the inverter by removing the string
>fuses. Either string will operate fine independently. With string one in
>conduit and either homerun of string two in conduit (but not both) the
>inverter operates fine. With string two in conduit but string one outside
>of conduit, the inverter does not operate.
>
>I was certain the error had something to do with homerun roof wiring so I
>went out with the technician and removed and checked pretty much every
>module. Everything appears fine, all connections solid, all homeruns have
>been remade at least once at this point. Now I am stumped and lack the
>technical knowledge to diagnose the problem. I would be extremely grateful
>if an esteemed wrench can provide technical support/advice.
>
>Thanks,
>
>Matt
>
>
>
>
>Matthew Partymiller
>Solar Energy Solutions LLC
>(877) 312-7456
><mailto:matt at solar-energy-solutions.com>matt at solar-energy-solutions.com
>
>
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