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<div class="moz-cite-prefix">HI Kent;<br>
<br>
I actually used to have info from Trojan on the short circuit
current available from the T105 and L16. I just don't remember it
exactly, but I recall it was around 2000 amps for the T105. I
agree its really shameful how lame most battery manus are at
providing info anymore. Its hard to even get good cycle life
tables.<br>
HUP does show their short circuit #s. The 845 AH battery is 9600
amps and for comparison, the 2490 AH is 29,100 amps.<br>
So yes, we could have trouble.<br>
B&B a manufacturer of sealed deep cycle batteries shows their
12 v 90 AH battery with a whopping short circuit current of 2300
amps but only for 100 milliseconds.<br>
Midnite shows their breaker AIC ratings and its 10,000 amps for
the PV breakers up to 50,000 amps for the 175 and 250 amp
breakers. The class T fuses I checked are 20,000 amps AIC.
Remember that this is all rated at 125 to 150 vdc, so all of these
OCPDs will have even better AIC at lower voltages. (I wish we
could get a chart that showed AIC relative to voltage.) The other
factor in our favor is that the batteries might be able to exceed
the AIC for tenths of seconds, but it can't sustain it like the
grid can.<br>
Sorry that this is not enough info to do a definitive design, but
at least it can get us all thinking about AIC ratings relative to
bigger battery banks.<br>
<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 4/6/2013 1:21 PM, Kent Osterberg wrote:<br>
</div>
<blockquote cite="mid:516075A4.4030703@coveoregon.com" type="cite">
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<div class="moz-cite-prefix">Phil,<br>
<br>
Thanks for the code references, they are very useful and point
out an area where I fear many installations of battery based
inverters are deficient. You are right the manufacturers have
not made this easy!<br>
<br>
First, data on the short circuit current available from most
batteries isn't easily available, if available at all. Concorde
publishes short circuit current numbers for the SunExtender
batteries. Neither Trojan, Rolls/Surrette, nor Outback publishes
short circuit current data for their batteries. Full River
publishes an internal resistance number that can be used to
estimate the short circuit current. Taken as a whole, battery
manufacturer's certainly haven't made it easy to comply with
690.71<br>
<br>
Second, sometimes interrupting capacity data on the breakers
being used in BOS equipment is also missing. Take a look at
Outback's catalog and try to find the AIC for the breakers used
to protect the inverter wiring. Is it published anywhere else?
Should a system designer have to buy the Outback breaker, find
out who manufactured it, and then search for the correct ratings
in the in the breaker manufacturer's catalog? Obviously not. <br>
<br>
Third, BOS manufacturers often connect circuit breakers for
charge controllers or dc utilization circuits that have AIC
ratings of only 5000 amps directly to the battery. So while the
inverter may be protected with a breaker having an AIC rating
25,000 or 50,000, other devices don't. BOS manufacturer's should
include on the dc breaker panel data showing the <big>lowest</big>
AIC breaker that is connected directly to the battery. Then
installers would have at least half of the information needed to
decide when a fuse is needed to backup the dc breakers. And
shouldn't the instructions for BOS equipment point out that a
fuse may be necessary at the battery.<br>
<br>
The short circuit current from a single string of golf cart
batteries or L16 batteries is probably less than 5000 amps.
Fuse(s) are probably needed in most installations with larger
batteries or battery systems with multiple strings of batteries.
2011 NEC 240.21(H) allows overcurrent protection to be installed
as close as practical to battery terminals - even in classified
locations. <br>
<br>
<pre class="moz-signature" cols="72">Kent Osterberg
Blue Mountain Solar, Inc.
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="http://www.bluemountainsolar.com">www.bluemountainsolar.com</a>
</pre>
<br>
On 4/6/2013 7:29 AM, Phil Undercuffler wrote:<br>
</div>
<blockquote
cite="mid:CAPLQxEL9K1yPVccqJ0J671gy+JLZDGUvzhvupL_s9e3ymAf55Q@mail.gmail.com"
type="cite">Ray,
<div><br>
</div>
<div>690 does offer the protection, it's just that most
maufacturers haven't made it easy.</div>
<div><br>
</div>
<div>690.71 Installation</div>
<div class="pa-70-2011-58-para"
style="margin-top:3.6pt;margin-bottom:3.6pt">
<p class="pa-70-2011-58-para"
style="margin-left:7.2pt;margin-top:1pt;margin-bottom:1pt"><font><span
style="line-height:normal;background-color:rgba(255,255,255,0)"><span
style="font-weight:bold">(C)</span> <span
style="font-weight:bold">Current Limiting.</span> A
listed, current-limiting, overcurrent device shall be
installed in each circuit adjacent to the batteries
where the available short-circuit current from a battery
or battery bank exceeds the interrupting or withstand
ratings of other equipment in that circuit. The
installation of current-limiting fuses shall comply with
690.16.<span></span></span></font></p>
</div>
<div><br>
</div>
<div>
<div style="">The telcom industry has been doing this for
years. Their norm is to have each string of batteries on a
shelf, and terminate at a breaker. Each string then is
combined at a bus bar or plate, to help ensure equal current
on each string. The loads and charging sources all come to
that same bus bar. It has some advantages, as individual
strings can be monitored and serviced without taking the
entire system down.</div>
</div>
<div style=""><br>
</div>
<div style="">
<div>FWIW, OutBack makes a battery rack for AGM batteries with
series string overcurrent and disconnects on every string.
It's also to my knowledge the first UL1741 Listed device
available -- the other stuff I've seen is either not listed,
or is trading on old 508a standards. AGMs might not be for
every installation, but for jobs where they are appropriate
this could be a good, code-compliant solution.</div>
</div>
<div style=""><br>
</div>
<div style=""><br>
</div>
<div style="">Phil Undercuffler</div>
<div style="">OutBack Power</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
<br>
On Friday, April 5, 2013, Ray Walters wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>I just finished a rewire and we kept the Ananda power
center, Allan <span><span> :-) </span></span><br>
Back when we used class T fuses more they were always
over sized relative to Heinemann breakers.<br>
400 amp class T fuse = 250 amp breaker= 4/0 cable<br>
200 amp class T fuse = 175 amp breaker= 2/0 cable<br>
<br>
I still think class T fuses are superior in some ways to
breakers: they have better interrupt capacity and trip
faster in a short circuit condition.<br>
<br>
However, If you spend too much time thinking about and
looking at the trip curves, you'll break your brain and
special order some weird fuses and breakers. (anybody
need a 350 amp class T fuse?)<br>
Just follow the inverter manufacturer's recommendations
and all will be well.<br>
On the other hand, William has brought up a topic I have
harped on for years: Having the OCPD in the cabinet
doesn't protect the majority of the circuit. Class T
fuses at the battery terminals do, but they're not rated
for the corrosive environment. I have thrown a few
class T fuses away that had acid eating away at the
ends.<br>
I don't have the solution, but I will continue to point
out that this is a real problem. Dropping a wrench
across the battery terminals can lead to a spectacular
failure that not only can cause a fire, but might even
cause a battery explosion, yet NEC offers no
protection. <br>
We use insulated wrenches from experience, and hope for
the best. <br>
<pre cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 4/5/2013 8:29 PM, William Miller wrote:<br>
</div>
<blockquote 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">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 moz-do-not-send="true"
href="javascript:_e({}, 'cvml',
're-wrenches-bounces@lists.re-wrenches.org');"
target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a moz-do-not-send="true" href="javascript:_e({},
'cvml',
're-wrenches-bounces@lists.re-wrenches.org');"
target="_blank">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>
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