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Steve,<br>
Yes, in the same sequence: 75.5V, 73.8V, 73.9V, 74.0V. All just
about what I'd expect.<br>
<br>
Brian,<br>
I have seen that with KC120s over the years - good Voc and Isc but
no MPP. That's a known failure that Kyocera (to their credit)
continues to warrant 15 years out. But I haven't seen it with the
many 75W BPs we installed in that same time period. So it's
possible, but unlikely, especially with all four strings behaving in
a similar manner.<br>
Thank you. I'm off on field work now, will respond to any more
replies tomorrow.<br>
<br>
Allan<span style="font-size:10.0pt"></span><o:p><br>
<br>
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<div class="moz-cite-prefix">On 8/25/2016 8:24 AM, Steve Bell wrote:<br>
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<blockquote
cite="mid:CAOfTF50gpzMtRSLtPgzuoZh+QzvSq9mMZrkZV7zdqJ3PYLuDvg@mail.gmail.com"
type="cite">
<div dir="ltr">Hello Allan,
<div><br>
</div>
<div>Did you check the Voc of each string? Is it possible that
there could one or more shorted bypass diodes in the modules?</div>
<div><br>
</div>
<div>Just a thought.</div>
<div><br>
</div>
<div>Steve Bell</div>
<div>Morningstar tech support</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Aug 25, 2016 at 8:04 AM, Allan
Sindelar <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:allan@sindelarsolar.com" target="_blank">allan@sindelarsolar.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div
style="background-color:rgb(255,255,255);color:rgb(0,0,0)"
bgcolor="#FFFFFF" text="#000000"> 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.<span class="HOEnZb"><font
color="#888888"><br>
Allan<br>
<div>-- <br>
<div>
<p class="MsoNormal"><b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a
moz-do-not-send="true"
href="mailto:allan@sindelarsolar.com"
target="_blank">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>Positive Energy,
Inc.</span><br>
<b><a moz-do-not-send="true"
href="tel:505%20780-2738"
value="+15057802738" target="_blank">505
780-2738</a> cell</b><br>
<br>
</span></p>
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