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Xantrex: Migrating from STXR2500 To GT2.5 - Wiring Question
http://solar-guppy.com/forum/viewtopic.php?f=19&t=628		 Page 1 of 2
Author:  Kenji [ Mon Apr 28, 2008 3:05 pm GMT EthGMT ]
Post subject:  Xantrex: Migrating from STXR2500 To GT2.5 - Wiring Question
My STXR2500 inverter started having the Thermal Derating issue, and after a call to Xantrex, I decided to take advantage of their $999 "customer loyalty" deal and upgrade to a GT2.5 inverter with its 10-year warranty.

My current system consists of 6 arrays of PV modules with the power and ground outputs of each array connected to the STXR2500's built-in combiner. However, the GT2.5 seems to have connections for only two arrays, so I obviously need to somehow combine my 6 pairs of array wires down to 2 pairs.

My question is: how exactly should I combine the array outputs? Should I wire triplets of arrays in series to keep the amperage down, or should I connect the array outputs in parallel using a separate combiner box, or what?

Thanks for any input.
Author:  Solar Guppy [ Mon Apr 28, 2008 4:16 pm GMT EthGMT ]
Post subject: 
The GT is a high Voltage String Inverter ( 190-600V ), the Suntie is low voltage ( 48V - 100V )

Assuming that the 6 strings are 48 volt nominal and all the same panel type you should be able to wire the strings in series so you have a 24 panel single string for the GT.

You should use the Xantrex String Sizing tool to verify your setup

http://www.xantrex.com/support/gtsizing ... p?lang=eng
Author:  Kenji [ Mon Apr 28, 2008 4:58 pm GMT EthGMT ]
Post subject: 
I have 6 arrays of 4 Kyocera KC120s each, so (according to the Xantrex sizing tool) I should be able to do what you suggest.

There's a junction box up on my roof where all of the array's outputs collect before they all head down to the inverter via two huge runs of conduit. Conceptually, it would be nice if I could wire all of the array outputs in series in the junction box and feed only a single pair of outputs down to the inverter, since that would eliminate 10 long runs of 6 gauge wire. Do you know whether I could still use 6 gauge wire for the single pair of runs from the junction box to the the inverter? It seems to me that I could, but I'd like to know for sure.

Thanks for your help.
Author:  Solar Guppy [ Mon Apr 28, 2008 5:45 pm GMT EthGMT ]
Post subject: 
That would be Ideal, rewire to series in the junction boxes, then a single pair down to the inverter. 6AWG is fine for the run, but you will need to reduce the wire at the inverter terminals, easy way is to just cut off a few strands right at the terminal

You could also just pull the inverter, and series everything inside the GT's BOS box, only downside is you will have much longer runs of wire, but with 6AWG, it won't be much of a loss.

I have done both ways with the same panels you have swapping out a UPG to a GT2.5
Author:  Kenji [ Mon Apr 28, 2008 5:49 pm GMT EthGMT ]
Post subject: 
Cool. The GT documentation claims that its terminals can accept up to 4 gauge wire, so hopefully I won't have to do the "custom wire reduction" you describe. Thanks again for your help.
Author:  mike90045 [ Tue Apr 29, 2008 9:41 am GMT EthGMT ]
Post subject:  Re: Migrating from STXR2500 To GT2.5 - Wiring Question
Kenji wrote:
My question is: how exactly should I combine the array outputs? Should I wire triplets of arrays in series to keep the amperage down, or should I connect the array outputs in parallel using a separate combiner box, or what?

Thanks for any input.


Wire them all in series, you need the high voltage, and can remove some of the redundant wires out of the conduit (unless you wan to to keep them for future expansion)
SG has already covered this, so I'm being redundant.
Author:  DFriedeck [ Thu May 01, 2008 12:56 am GMT EstGMT ]
Post subject: 
Hello all,

Do the two strings on the GT2.8 act as two independent strings? I am having to replace my old SunTie with the GT2.8 and I am working on how to best re-wire my panels.

I have the old Photowatt PW1000 panels that can run in 12 VDC mode or 24 VDC mode. With 26 panels I have some options.

Can someone here confirm if the two strings can have different characteristics?

Thanks in advance,

Dave
Author:  Solar Guppy [ Thu May 01, 2008 7:51 am GMT EstGMT ]
Post subject: 
No, on the GT is a common input no independant strings like the Suntie.

Sounds like you should be OK with all 26 in series if your not in a cold climate ...

I have rewired a pair of 24 panel KC120/Suntie systems to be in series with great results

If its regulary mild or cold climate, then look at two strings of 13 ... it would be near the minimum input ( 195V ) when hot but in mild weather should be OK
Author:  DFriedeck [ Thu May 01, 2008 10:15 am GMT EstGMT ]
Post subject: 
Guppy,

I assume you mean with the panels in 12 VDC configuration, max output at about 17 volts. So 17 * 26 = 442 VDC. This does mean I will have to touch most of my panels to re-wire as 18 are configured for 24 VDC opperation. I will use the time to put a little high end polish on all the panels.

I assume in this configuration any shade is an issue. Then again with only a single true string then any shade period will be an issue.

Thanks again for all your help.

PFM
Author:  Solar Guppy [ Thu May 01, 2008 10:25 am GMT EstGMT ]
Post subject: 
No, single string with shade, only the shaded panels drop offline as the bypass diode kicks in.

on the configuration, you really need to look at the Xantrex configuration tool and adjust for your location.

24 panels ( 12 volt ) really is the limit in a string if you get down to 32F ... here in Florida, with the warm tempatures and roof mounted array I have run the equavilant of 30 panels in a string for 3 years without issue, because the tempature is alway hot

You can run two strings of 13 ( configured for 24V on the panels ) the concern would be hot weather the vmp might be below the the units minimum of 195V
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