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<div class="moz-cite-prefix">William,<br>
For this I went deep into the catacombs of our hardware file
cabinet, and quickly found a 1996 spec sheet from an Ananda Power
Technologies SafeT-Block. For the young'uns, Ananda was a quality
company, the originator of the listed Powercenter - the breaker
and terminal block hardware that is part of every batttery-based
system nowadays. Ananda became APT, then Pulse, then part of Trace
(the PC250 and PC500) as part of a short-lived marriage followed
by a messy divorce, the results of which led, as an act of revenge
insurrection, to the introduction into the U.S. market of the
Sunny Boy and AC-coupled systems, and the rest is even more wacky
history. But I digress, after a run-on sentence bad enough that my
high school English teacher is rolling over in her grave...<br>
<br>
I have attached a scan of page two of the spec sheet. In the upper
left corner is a chart of current vs. time for a Class T fuse.
Once I understood this chart I never again worried about nuisance
tripping, as whether described as fast-acting or not, Class T
fuses have an inherent surge capacity of about 2 1/2 times their
rating, and thus can handle surges.<br>
<br>
If you put them on individual battery strings, the point is to
prevent overcurrent on one string, which is only likely to occur
when either 1) a terminal is corroded sufficiently that one string
fails to carry its share of the load or charge (we have seen this)
or 2) one string fails when the batteries reach end-of-life. When
the Class T fuses blows in that situation it has done its job.<br>
Allan<br>
<br>
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<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a href="mailto:Allan@positiveenergysolar.com"><font
face="Times New Roman, Times, serif" color="#000099"><u>Allan@positiveenergysolar.com</u></font></a></small><font
face="Times New Roman, Times, serif"><br>
<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder and Chief Technology Officer<br>
<b>Positive Energy, Inc.</b><br>
3209 Richards Lane (note new address)<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/"
target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></font>
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On 4/5/2013 8:29 PM, William Miller wrote:<br>
</div>
<blockquote
cite="mid:6.0.1.1.2.20130405192312.03083f90@millersolar.com"
type="cite">
Friends:<br>
<br>
Good topic. Some questions:<br>
<br>
1. Most manufacturer's present an installation guide that shows
one OCPD
in the battery circuit and that is in the BOS cabinet. This means
the battery leads are unprotected. Do we need an OPCD at the
battery terminals?<br>
<br>
2. Class T fuses are generally recommended for this application.
The data shows them as "fast acting." Is this a
problem? Will they act too fast and open during normal surge
loads?<br>
<br>
Thanks in advance!<br>
<br>
William Miller<br>
<br>
<br>
<br>
<br>
<br>
<blockquote type="cite" class="cite" cite="">Troy,<br>
<br>
Overcurrent device size is matched to the conductor size. The
inverse
time constant nature of an overcurrent device can typically
handle the
surge currents as long as conductor sizing has truly been done
correctly
for the conductor. Circuit breakers are preferred to fuses
because they
can be reset. <br>
<br>
There has been volumes written on this issue. The constant
current at
lowest battery voltage should be used, plus the ac ripple
content on the
battery circuit. This is usually a much larger conductor than
your
average designer will plan for. The best thing is to look at
Midnight,
Outback, and Schneider and see what size overcurrent devices
they require
for their products. That will give you a good clue as to how to
size the
conductor and overcurrent device.<br>
<br>
Bill.<br>
<br>
<b>From:</b> <a class="moz-txt-link-abbreviated" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a moz-do-not-send="true"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
eudora="autourl">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Troy Harvey<br>
<b>Sent:</b> Friday, April 05, 2013 3:38 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Fuse sizing in battery circuits<br>
<br>
I've got a question about battery string fusing. Typically we
size the
wire from the batteries to the inverter based on continuous
rating
procedures (max power/efficiency)*125%. <br>
<br>
However a 6kW inverter, can peak at 12kW for 5-10 seconds,
doubling the
source current. That is no big deal for the wire, because it is
a short
time frame... little heat will be generated. However, in fusing
the
sub-strings, you need to account for that peak surge current so
you don't
blow fuses all the time. But if you put a 500-1000 amp fuse on a
4/0
wire, above the max surge draw of the inverter, the wire will be
under-protected for its ampacity rating. Any thoughts on the
catch-22?<br>
</blockquote>
<br>
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