Ground fault [RE-wrenches]

[William Miller]

Allan:

The client did all of the module installation and measured and logged the
SC current and OC voltage on all of the racks.  Having said that, I think
I'll measure them myself next time I'm up there!

William




At 06:20 PM 11/18/02 -0700, you wrote:
>
>----- 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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