KC-120 Output ?s [RE-wrenches]

[Joel Davidson]

One quick way to test PV modules for possible cracked cells and bad cell
interconnects is hook up a current meter, hold the module in sunlight and rack
(twist) the module to open the bad connection. Modules can twist quite a bit,
but will break so only rack the module slightly. Sometimes problems only show up
when the module is hot from being in the sun for a while.

"Wallace Stahle, Future Elec. Energy Co." wrote:

> Greetings Wrenches and interested others,
>
> I have a bit of a mystery unfolding on a two Zome tracker installation with
> twelve
> KC-120 modules on each tracker. Each tracker has three strings of four
> modules wired in series for the 48 volt nominal system. The system became
> operational in
> March, 2001 and performed as expected then.
>
> A quick check of the system two weeks ago showed that there was no output on
> one of three strings on each tracker. Reduced output on the other strings
> was apparent also.  A quick check of the suspect string showed no output on
> one of the modules. Due to travel and work schedule, yesterday was my first
> chance to investigate since then.
>
> The previously nonworking module was now working, which means either an
> intermittent failure or a misapplied test procedure.
> I discovered short circut current flows for all modules in the 6.22 - 6.50
> range with 7.45 being rated peak Isc.
> The voltage under load however ranged from a low of 10.9 -16.4 volts.
> The rated peak voltage is 16.9.  Twelve of the modules are less than 14
> volts,
> five are14 - 15.0 volts, and seven are above 16 volts.
>
> These were tested with a Fluke 36 and at the +/- terminals of each module
> while connected to the Pulse 60 amp charge controller. Isc was tested with a
> DMM. Series wiring is #12 THHN in FNMT pvc conduit to a fused combiner box
> on the tracker post.
> Wide voltage variation from module to module is seen on five of the strings.
>
> What  factors other than internal failures would give this result, and how
> so?
>
> Thanks for your shared knoweledge in advance.
> Wally Stahle
>
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