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

Thu Sep 8 10:13:38 PDT 2016

Certainly seems like a stumper so far! I'd still check voltage and
polarity with the strings through the conduit but not landed in the
inverter. We've seen all kinds of mistakes where the negatives were
mixed-up between strings, etc, causing strange behavior. Voltages can test
fine when landed in inverters (even with fuses pulled) but exhibit
different behavior when completely isolated. The fact that the system ran
at first would lead us to believe that the wiring was done properly,
however. It seems like the other suggestion of some sort of mild ground
fault is a good path to follow. I also would highly question how those
Tigo optimizers might be adding to the equation. You could also run the
inverter with everything wired up and your volt meter on the DC inputs to
see what is happening. The conduit factor here can only be causing ground
issues or possibly some kind of inductance hokey pokey, but that seems
unlikely.

August

-----Original Message-----
From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Matt Partymiller
Sent: Wednesday, September 07, 2016 6:55 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Troubleshooting Stumper - Homerun Interference
in Conduit/Inverter Turning Off/On Rapidly

Thanks for all the questions and interest in my troubleshooting.

The polarities are definitely correct.  When testing wires at the inverter
with the DC disco off and fuses pulled, we see correct voltage on each
string.

We have tried using two clamp meters to measure current on each string
while operating the inverter with our homeruns in the conduit.  Using the
max function we never saw a meter get above about 1.5A (even less earlier
in the day).  String two seemed to be consistently lower but I really
wasn't sure if that was an inverter function or not as it ramps up towards
max power.  With the homeruns outside of conduit the inverter operates
fine and both strings show similar, but not identical, current.  Doing the
math it appeared each string was producing roughly half of inverter output
at that time.

To Jerry's question, the system did operate fine for about a week and 65
kWh.  The inverter then failed.  Our technician replaced that inverter
with a new Solectria 3.8 kW unit, restarted the unit, and noted the
problem.  With Solectria's help he arrived at the idea that we had a
faulty inverter, got a new one in, and noted the exact same error codes
and began trying to troubleshoot.  He left the third inverter installed
and also installed a new Tigo Cloud Connect and Gateway for the Trinasmart
system.

The modules are 255 Trinasmarts with the integral Tigos.  The folks at
Tigo insist the issue is not theirs and, given that either string works
fine by itself and both strings work fine when not in conduit, I tend to
believe them.  I just don't appreciate how having 20' of undamaged homerun
wire in conduit as opposed to free air can make an inverter stop
operating.

Thanks,

Matt

On Wed, September 7, 2016 8:58 pm, jay wrote:
> hate to ask the obvious here, but you mean to say that volts and
> polarity are correct on both sets of wires at the inverter when not
connected?
>
> and
>
> 2. what wattage modules are you using?
>
>
> jay peltz power
>
>
>
>
>
>
>
>
>> On Sep 7, 2016, at 2:45 PM, Matt Partymiller
>> <matt at solar-energy-solutions.com> wrote:
>>
>>
>> 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
>> matt at solar-energy-solutions.com
>>
>>
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Matthew Partymiller
Solar Energy Solutions LLC
(877) 312-7456
matt at solar-energy-solutions.com

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