Ground fault [RE-wrenches]

[Allan Sindelar]

----- Original Message -----
From: "William Miller" <wrmiller at slonet.org>

> The PV modules are old Cariso modules mounted in racks of 8.  Each 8 are
> wired in series for and OC voltage of about 50.  SC amperage was measured
> and averages between 2 and 2.6 amps per rack.  There are 12 racks
connected
> to the charge controller for a maximum total short circuit amps of about
> 30.   This should be well under the approved rating for this unit.

William,
Your numbers don't look right to me. Each -Lam (Arco M52L) is made up of
three paralleled rows of (I think) 10 or 11 cells each. The modules are
around 4V nominal, but about 3 times the current of a 12V module of the same
physical size. So each module will normally put out about 7-8 amps at 4-5V.
Each series of 8 will put out about 7-8 amps at around 36V. Now many of the
Quad-Lams were burned from reflectors on the arrays and were sold at lower
ratings: Super-Golds (no reflectors), Golds, Bronzes, and Muds, as I recall.
But I have seldom seen less than 5A output on a string, even after all these
years. Maybe these were "SuperMuds".  ;-)

I may be wrong, but it sounds like your client has 96 modules total, in 12
racks of 8. If they are putting out anything over 3A per string, the MPPT is
being occasionally maxed out and internally limited (@30% boost, which can
happen with the higher voltages). While I don't dispute the ground fault
issue as the suspected cause, I could also believe that simple
overvoltage/overcurrent (perhaps coupled with edge-of-cloud effect) could
have also contributed. Are you really sure about that 2-2.6A per rack?

Respectfully, Allan @+E

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