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Thanks William,<br><br>
I just bought some fuses. <br><br>
At 10:00 AM 4/9/2013, you wrote:<br>
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This topic comes up often enough that we ought to mention a yellowed
article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas wrote
<i>Overcurrent Protection for Battery-Powered Systems </i>where he
describes experiments he did back when he was with Ananda. He put a 2000
A Big Switch to initiate a short (4/0 cable) between the terminals on a
set of four golf cart batteries (2 strings @ 12V). In series, he put in a
500A Shunt so he could measure current passing and various fuses and
breakers. “For comparison, we decided to directly short the battery…the
meter read 6960 amps peak current (three seconds) …during each test the
4/0 cable lifted off the ground 4 inches into the air by the forces
generated by the extremely high current..” They videoed the 250 A ANN
buss fuses arc and smoke; the 200A Heinemann Series AM breakers
(paralleled ones that maybe Roy mentioned) went 3 seconds without
breaking and the video showed a flash and blue smoke. <br>
175A ITE breaker with 42,000 AIC “simply tripped…but still allowed a peak
current of 2960 amps<br>
200A Class T Littlefuse “opened promptly with no external signs of
stress…1920 amps peak current”<br>
Christopher’s recommendations: <br>
“Every AE system must have overcurrent protection able to interrupt the
maximum current available from the batteries. For most systems, the main
protection should use current limiting high AIC fuses, such as a Class T
or Class R. A disconnect switch which allows the fuse to be safely
changed should be included. A lower cost alternative is to mount the fuse
in a fuse holder without a disconnect. Although the fuse would always be
electrically hot, it normally would not be changed during the life
of the system. The fuse holder should be mounted outside the battery
enclosure. Fuses should not be bolted directly onto the battery terminal,
as they are not designed to handle the physical stresses that can occur
without the protection of a fuse holder.<br>
<br>
Fuses which have exposed elements, such as ANN fuses, should not be used
because they are not current limiting and have only 2500 amps AIC. They
also may be a significant hazard when installed near batteries. <br>
<br>
High AIC breakers, like the Heinemann Series CF (25,000 Amps AIC @ 65VDC)
can provide overcurrent protection for individual items. They cannot be
used to protect lower AIC breakers. This eliminates their use as a main
disconnect in most systems. <br>
<br>
Low AIC breakers, like the Heinemann Series AM (5000A AIC @65 VDC) or the
Square-D QO (5000A @ 125 VDC) can be used in load distribution centers
and components, but must be protected by a current limiting fuse. Using
low-AIC breakers alone will not provide sufficient protection with a
battery system and may be a significant hazard during short circuit
situations.”<br>
<br>
It won’t pull up anymore on HP’s article search but probably Michael has
a copy he could post for those interested.<i> <br>
</i> <br>
Bill Dorsett<br>
Manhattan, KS<br>
<b>From:</b> re-wrenches-bounces@lists.re-wrenches.org
[<a 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>John Berdner<br>
<b>Sent:</b> Monday, April 08, 2013 7:25 PM<br>
<b>To:</b> Allan@positiveenergysolar.com; RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Fuse sizing in battery circuits<br>
<br>
Allan:<br>
<br>
A pretty accurate retention of the Grass Valley / Nevada County through
2000.<br>
You only missed the Trace to Xantrex “acquisition” that was the start of
the divorce J<br>
<br>
Class T fuses provide better protection for battery based inverters –
always been that way.<br>
The move to breakers was a cost reduction issues when Trace introduced
the DC-250.<br>
I still contend that the way the DC-250 did it was a Code violation when
used with PV in the box (current from all sources issue) but that is
history.<br>
<br>
For high current applications the Boltswitch Pull outs (the ones we used
in the Power Centers) came in 100A, 200A and 400 A sizes and 1, 2, and 3
pole versions. <br>
I think they are still made today.<br>
Still the best way to do currents above 250 Amps.<br>
You can do a Eaton / GJ1P breaker up to 750 Amps but they are Spin
Dee.<br>
<br>
As you noted you can use a single pull out to do up to 3 battery
strings.<br>
You make a copper “comb” to parallel separate fused inputs to a single
inverter. <br>
If you have more than one inverter you can have “back to back” fuse
blocks with an H-H-H shaped bus bar set up.<br>
The biggest one I recall we did was a 12 400 A battery/PV inputs
going to 8 SW inverters.<br>
You size the copper bus bars for 1000 A / square inch of cross section
and you are good to go (this is from the UL 508 design guide).<br>
<br>
Best Regards,<br>
<br>
John Berdner<br>
General Manager, North America<br>
<br>
SolarEdge Technologies, Inc.<br>
3347 Gateway Boulevard, Fremont CA 94538 USA <b><i>(*Please note of
our new address.)</i></b><br>
T: 510.498.3200, X 747<br>
M: 530.277.4894 <br>
<br>
<b>From:</b>
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">
re-wrenches-bounces@lists.re-wrenches.org</a>
[<a 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>Allan Sindelar<br>
<b>Sent:</b> Friday, April 05, 2013 9:00 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Fuse sizing in battery circuits<br>
<br>
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>
<b>Allan Sindelar</b><br>
<a href="mailto:Allan@positiveenergysolar.com">
Allan@positiveenergysolar.com</a><br>
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/">
www.positiveenergysolar.com</a> <br><br>
<img src="cid:7.1.0.9.0.20130409110300.05a8f0a8@redwoodalliance.org.1" width=843 height=912 alt="[]">
<br>
<br>
On 4/5/2013 8:29 PM, William Miller wrote:<br>
<dl>
<dd>Friends:<br><br>
<dd>Good topic. Some questions:<br><br>
<dd>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>
<dd>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>
<dd>Thanks in advance!<br><br>
<dd>William Miller<br><br>
<br><br>
<br><br>
<dd>Troy,<br>
<dd> <br>
<dd>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>
<dd> <br>
<dd>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>
<dd> <br>
<dd>Bill.<br>
<dd> <br>
<dd>From:</b>
<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">
re-wrenches-bounces@lists.re-wrenches.org</a>
[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" eudora="autourl">
mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] On Behalf Of
</b>Troy Harvey<br>
<dd>Sent:</b> Friday, April 05, 2013 3:38 PM<br>
<dd>To:</b> RE-wrenches<br>
<dd>Subject:</b> [RE-wrenches] Fuse sizing in battery circuits<br>
<dd> <br>
<dd>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>
<dd> <br>
<dd>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>
<dd> <br><br>
<br><br>
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