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We are talking to Kirk offline about this but the main issue here is
that the enclosure<br>
for the 2000A combiner is made out of steel which is ferrous. That
means that when the<br>
120 Hz ripple current induces into the chassis it can vibrate just
like a transformer.<br>
<br>
Low frequency transformer inverters are have higher ripple than the
newer HF transformer units<br>
but they have some AC ripple on the battery cables as well. <br>
<br>
This combiner is evidently been around for about 8 years and we
haven't heard any complaints<br>
but maybe others have been silent on this. I am not surprised at
all that this happens.<br>
<br>
Aluminum chassis has the problem that it is a good conductor so when
the whole enclosure forms<br>
around the cables, the aluminum can act as a shorted turn in a
transformer. It is usually just<br>
lossy but should vibrate much less, if at all. <br>
<br>
There are other issues in switching to aluminum that Robin mentions,
here:<br>
<br>
<i>"One reason is cost, the other is fasteners, We would need to use
press nuts instead of snail shells. </i><i><br>
</i><i>Snail shells and sheet metal screws don’t do well in
aluminum. It is too soft. Aluminum would not </i><i><br>
</i><i>vibrate from magnetic ripple activity though."<br>
<br>
</i>He has some ideas to make aluminum work so we will try those.<i><br>
</i><br>
Now, plastic could work. Just has to be real thick. Darn
physics !<br>
<br>
Damping can help, like Kirk tried (more can be done here too).
Keeping the cables<br>
together best as you can inside the chassis may help as well but
moving and routing <br>
the cables might also reduce the buzzing some more.<br>
<br>
That's the latest buzz from here.<br>
<br>
🌜boB🌛<br>
K7IQ<br>
<pre class="moz-signature" cols="72">
</pre>
<div class="moz-cite-prefix">On 6/30/2023 8:45 AM, david quattro via
RE-wrenches wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAFA1dAnpMgC-JHhMxW_Dep9g+sFHiHJ-cFEwuir113RCbbThCQ@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Ferrite cores can be used for the battery cables to
pass through to reduce common mode current<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Jun 30, 2023 at
3:59 AM Kirk Herander via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true" class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">I have -15- sets of 4/0 cable (1 per 32 kwh
stack) into the combiner. They are paired and within .25 "
of one another in wire cable tray for 80% of their
respective distance.
<div><br>
</div>
<div>The inverter to combiner sets are 2/0 for each
respective inverter. They are paired (not twisted) in
cable tray, anywhere from 10 -20' in length. Maybe I can
send some photos, but can't at present due to computer
issues.</div>
<div><br>
</div>
<div>I used cable tray because the CT-rated cable is in free
air, no derating of current required. But merely pairing
the leads may be the issue.</div>
<div><br>
</div>
<div>I could rearrange the inverter cables and twist the
sets, but doing it from combiner to battery cabinets is
impossible.</div>
<div><br>
</div>
<div>And I'm wondering if this is really necessary if the
customer is willing to live with the issue. What are the
ramifications down the road? Loosening of connections I
suppose would be one.</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Jun 30, 2023 at
12:40 AM Jerry Shafer via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="auto">
<div>Kirk</div>
<div dir="auto">As the batteries come up to charge does
the vibration subside. Are the battery cables spun
together "corkscrew like" l have seen this correct DC
noise. I have an 8 on 8 just like your 10 and l have
no noise at all, mine come in from each side of the
battery combiner, how is your install configured, how
is the cable length same close or very short to very
long some length is better on FLA's due to resistance
under load and charge. More information may help with
a solution.</div>
<div dir="auto">Fun times solar</div>
<div dir="auto">NABCEP PV Inspector <br>
<br>
<div class="gmail_quote" dir="auto">
<div dir="ltr" class="gmail_attr">On Thu, Jun 29,
2023, 8:19 AM Kirk Herander via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px
0px 0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">All,
<div dir="auto"><br>
</div>
<div dir="auto">I am in the middle of
commissioning a 480kwh BP LFP battery bank,
connected to -10- OB Radian 8kw
inverter/chargers.</div>
<div dir="auto"><br>
</div>
<div dir="auto">For the DC combiner I am using
midnite 2000 amp combiner boxes, modified to
mount class T fuses on the positive bus, for
both battery inputs and inverter outputs.</div>
<div dir="auto"><br>
</div>
<div dir="auto">For starters, I set the master
inverter at a max charge rate of 20 AC amps,
which equates to a DC charge of about 74 A. All
the other inverters are automatically set to
this charge rate as well.</div>
<div dir="auto"><br>
</div>
<div dir="auto">Turning the chargers on one by
one, I started to get quite an audible vibration
from the combiner box at a combined charge of
about 400 to 500 A. </div>
<div dir="auto"><br>
</div>
<div dir="auto">So I took the cover off of the
combiner, which was vibrating noticabllly by
feel. Most of the noise was from the cover not
fitting tight. But the The box itself is also
vibrating by feel.</div>
<div dir="auto"><br>
</div>
<div dir="auto">I took the combined charge up to
640A dc. This level of vibration definitely
increases with an increased charge rate. And I
am surprised because after all, we’re not
talking AC here we’re talking DC. It almost
reminds me of a large AC transformer in its
behavior. The vibration did not seem to be
originating at the inverters, then resonating to
the combiner.</div>
<div dir="auto"><br>
</div>
<div dir="auto">I can dampen the vibration by
adding a few things, but I’m surprised that this
is happening. All connections in the combiner
are tightened properly. Ideas?</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
<div dir="auto"><br>
</div>
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