[RE-wrenches] Testing strings with Tigo

[Nick A Lucchese]

Good morning William,

Yes there are a couple new things to learn when working with these RS units. I’ve done a few now, the most recent three with the same controllers as you and Dave.

I am assuming the wording about being terminated at the inverter can also be understood as having landed the conductors inside the GSLC on the appropriate bus bars and 300v breakers. If you’re using Tigo’s AC to 12vdc converter then of course the inverter must be operational to produce the AC source to energize the converter so perhaps that’s why they want it landed at the inverter since they don’t really promote the use of a DC to DC converter. I use a 48 VDC to 12VDC converter so the keep alive signal doesn’t rely on the inverter being on so as long as I’ve got the battery bank assembled it allows me to do all the appropriate testing at the array.

One major thing to know is that you don’t want to operate with a partial amount of your strings energized while you work on the others. I (used to in the past) often do this at off grid sites so their continuity of power service is least interrupted and to negate the need to use a fossil fuel based power source. Apparently the TS4 units “learn” the sum of all the paralleled string resistances together so if trying to add additional strings later you may have individual units lock up and not push any power. I’ve had this happen twice where the .6vdc unit expected sums added up but don’t actually pass the array voltage from the two modules out of the affected TS4-2. For example, 3 x TS4-2 units with six modules yet only seeing the expected VOC out of four modules. Each time this occurred it was with the TS4-2 varieties and would happen on the first strings commissioned whereas the newest strings would pass the expected string voltage. Their helpful tech’s suggested power cycling the converter along with transmitter however after multiple attempts I’ve still had this not remedy the situation on one of the projects and required me to swap out the TS4-2 in question. 

Quite a drag when you’ve already got your cable management all wrapped up and thinking you’re done on a 12/12 roof. Since they’re so inexpensive I held on to affected unit so I can try to recreate this issue on a mock up system. Perhaps they can be “unbricked” if they are the single recipient of the transmitter's output, we’ll see. Looks like we’re going to be stuck with this equipment for awhile so I figure it’s worth playing with at home.

The other thing I observed is that when you initiate a rapid shutdown command the FM100’s see it as an arc fault. Again, have had this happen twice however each time a complete power down on the FM100’s cleared it. Earlier FM100’s failed for me frequently so now anytime I need to power down an FM100 anymore I cross my fingers it will come back. So far so good with this particular arc fault scenario and seems like the FM100’s are generally quite more reliable than they were during that painfully long period of Outback woes.

As Jerry always says “fun times”. Stay cool up on that roof, Nick




> On Jul 5, 2023, at 10:04 PM, William Miller via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
> 
> Friends:
>  
> We are in the midst of our first off-grid, DC coupled project using Tigo TS4-A-F RSS switches.
>  
> In my few years installing solar I am accustomed to testing PV strings with a Fluke 87 for Voc, Isc, Vmp and Imp, or some combination.  I do this regularly in the midst of installing PV so I can be confident once we are finished there will be no issues with the panels or the wiring.
>  
> I understand these tests are not possible with the Tigo units.  With the circuits unterminated, I can see the 0.6 VDC/Tigo with no keep-alive signal transmitted.  With the signal being transmitted, I do not see the expected readings for Voc.  I get only the 0.6/Tigo.  When shorted into the Fluke DC input the Isc jumps around between 0 and about 2 amps.
>  
> I was told by tech support the PV circuits need to be “terminated” at an inverter before any voltage or current can be measured.  The circuits do not terminate in an inverter; they will connect to a charge controller (FM100, in this case).
>  
> We have not pulled the PV feeders so connecting to the charge controllers is not yet possible.  I am nervous about installing the remainder of the modules without knowing for certain they will produce as they should.
>  
> What would you all do to assure yourselves the PV will produce once connected?
>  
> TIA.
>  
> William
>  
> Miller Solar
> 17395 Oak Road, Atascadero, CA 93422
> 805-438-5600
> www.millersolar.com <http://www.millersolar.com/>
> CA Lic. 773985

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20230706/439b8a8f/attachment.htm>