KC-120 Output ?s [RE-wrenches]

[Wallace Stahle, Future Elec. Energy Co.]

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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