<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Hi Allan,</div><div><br></div><div>I would try turning off string #3 and see what happens to the vmp. </div><div>I'm guessing it'll go up to a more normal voltage. </div><div><br></div><div>I just had a very similar experience, also BP modules, very brown. </div><div>2 sets of 4 billion n series to a 12v system. One set was totally dragging down the VMP, I disconnected it, all normal. I tested voc of all modules after they were replaced,(190 watt 72 cell) customer wanted more watts, and all were normal and the same. I didn't spent the time to do a ISC. </div><div><br></div><div>Replacement is my thought. </div><div><br></div><div>Jay</div><div>Peltz power. </div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br>On Aug 25, 2016, at 7:04 AM, Allan Sindelar <<a href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a>> wrote:<br><br></div><blockquote type="cite"><div>
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Wrenches,<br>
Here's one I haven't seen before. 1997 grid-tie battery backup
system that was one of my first, although actual installation was by
another before I was licensed. 16 BP 275, 36-cell 12V modules, the
standard of that time. Early Outback MX60 replaced C40 around 2005;
array rewired to four 48V strings of four modules at that time,
serving a 24V battery bank. Tested with an end-of-life 9-year-old
AGM battery bank in the system, but in Sell mode with a 26.4V Sell
voltage setpoint.<br>
<br>
At 11 am, 68ºF, 900W/m<sup>2</sup> on the Daystar, with the array
under charge, I measured 3.5A, 3.4A, 2.4A, and 3.6A.
Short-circuiting each string, I measured 4.0A, 3.7A, 3.8A, and 3.7A.
Original rating was 4.45A, so except for the third string, current
is what I'd reasonably expect from 20-year-old module degradation.
However, watching the periodic MPPT sweep from the MX60 at the
array, the maximum power point voltage for the entire 48V array
settled at 14.6A at 37.2V, or about 540 watts from a 1,200W
(originally rated) array.<br>
<br>
I have commonly seen the current reduce substantially with
age-related degradation, while the MPP voltage remains fairly close
to original. I have never seen the voltage drop this far - an
average of 9.3V MPP per each 12V module. All of the cells are
seriously browned. I have other systems out there with the same
modules of similar age that don't exhibit this weird behavior. Can
anyone help me understand why the MPP voltage would drop so far
below what is typical?<br>
<br>
There is a slight possibility of corroded buried input conductors,
because of a serious but corrected issue of galvanic corrosion from
a ground fault (a Romex connector pinching a conductor and allowing
seepage to ground). This was corrected years ago, but the input
conductors were direct burial for ~100' and there was never a
bonding conductor between the array and the house, so there is a
potential for corrosion damage. However, the voltage measured at
both ends while charging was identical, so I think that would
indicate that high conductor resistance isn't the issue.<br>
<br>
As usual, thank you for the collective and individual wisdom shared
here.<br>
Allan<br>
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<p class="MsoNormal"><b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span style="mso-bidi-font-weight:bold">Positive
Energy,
Inc.</span><br>
<b>505 780-2738 cell</b><br style="mso-special-character:line-break">
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