[RE-wrenches] Fuse sizing in battery circuits
Drake
drake.chamberlin at redwoodalliance.org
Tue Apr 9 08:03:54 PDT 2013
Thanks William,
I just bought some fuses.
At 10:00 AM 4/9/2013, you wrote:
>Content-Type: multipart/related;
> boundary="----=_NextPart_000_0046_01CE3500.A0F44C00"
>Content-Language: en-us
>
>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 Overcurrent Protection for Battery-Powered
>Systems 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.
>175A ITE breaker with 42,000 AIC “simply
>tripped
but still allowed a peak current of 2960 amps
>200A Class T Littlefuse “opened promptly with no
>external signs of stress
1920 amps peak current”
>Christopher’s recommendations:
>“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.
>
>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.
>
>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.
>
>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.”
>
>It won’t pull up anymore on HP’s article search
>but probably Michael has a copy he could post for those interested.
>
>Bill Dorsett
>Manhattan, KS
>From: re-wrenches-bounces at lists.re-wrenches.org
>[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of John Berdner
>Sent: Monday, April 08, 2013 7:25 PM
>To: Allan at positiveenergysolar.com; RE-wrenches
>Subject: Re: [RE-wrenches] Fuse sizing in battery circuits
>
>Allan:
>
>A pretty accurate retention of the Grass Valley / Nevada County through 2000.
>You only missed the Trace to Xantrex
>“acquisition” that was the start of the divorce J
>
>Class T fuses provide better protection for
>battery based inverters – always been that way.
>The move to breakers was a cost reduction issues
>when Trace introduced the DC-250.
>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.
>
>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.
>I think they are still made today.
>Still the best way to do currents above 250 Amps.
>You can do a Eaton / GJ1P breaker up to 750 Amps but they are Spin Dee.
>
>As you noted you can use a single pull out to do up to 3 battery strings.
>You make a copper “comb” to parallel separate
>fused inputs to a single inverter.
>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.
>The biggest one I recall we did was a 12 400 A
>battery/PV inputs going to 8 SW inverters.
>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).
>
>Best Regards,
>
>John Berdner
>General Manager, North America
>
>SolarEdge Technologies, Inc.
>3347 Gateway Boulevard, Fremont CA 94538
>USA (*Please note of our new address.)
>T: 510.498.3200, X 747
>M: 530.277.4894
>
>From:
><mailto:re-wrenches-bounces at lists.re-wrenches.org>re-wrenches-bounces at lists.re-wrenches.org
>[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
>Sent: Friday, April 05, 2013 9:00 PM
>To: RE-wrenches
>Subject: Re: [RE-wrenches] Fuse sizing in battery circuits
>
>William,
>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...
>
>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.
>
>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.
>Allan
>Allan Sindelar
><mailto:Allan at positiveenergysolar.com>Allan at positiveenergysolar.com
>NABCEP Certified Photovoltaic Installer
>NABCEP Certified Technical Sales Professional
>New Mexico EE98J Journeyman Electrician
>Founder and Chief Technology Officer
>Positive Energy, Inc.
>3209 Richards Lane (note new address)
>Santa Fe, New Mexico 87507
>505 424-1112
><http://www.positiveenergysolar.com/>www.positiveenergysolar.com
>
>[]
>
>
>On 4/5/2013 8:29 PM, William Miller wrote:
>Friends:
>
>Good topic. Some questions:
>
>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?
>
>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?
>
>Thanks in advance!
>
>William Miller
>
>
>
>
>
>Troy,
>
>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.
>
>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.
>
>Bill.
>
>From:
><mailto:re-wrenches-bounces at lists.re-wrenches.org>re-wrenches-bounces at lists.re-wrenches.org
>[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Troy Harvey
>Sent: Friday, April 05, 2013 3:38 PM
>To: RE-wrenches
>Subject: [RE-wrenches] Fuse sizing in battery circuits
>
>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%.
>
>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?
>
>
>
>
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