I look at batteries the same way as modules each string gets it own protection, its good for trouble shootings and for safety. we use the magnum Energy Class T fuse and holder, its cheap and works very well. If you have ever seen a short of a battery bank you would always install fuses right there at the bank and even just one bank Jerry
On Thu, Feb 6, 2014 at 3:20 PM, Jason Szumlanski <ja...@fafcosolar.com>wrote: > Allan's assessment matches my experience. > > Interesting note: Outback's IBR enclosures include string-level > overcurrent protection "for added safety" according to their data sheet. > > > http://www.outbackpower.com/downloads/documents/integrated_battery_rack/spec_sheet.pdf > > > http://www.outbackpower.com/downloads/documents/integrated_battery_rack/integrated_battery_rack_installation_manual.pdf > > > Jason Szumlanski > > > > On Thu, Feb 6, 2014 at 6:06 PM, Allan Sindelar < > al...@positiveenergysolar.com> wrote: > >> Dave, >> I'm not really clear what your question is, but let me take a stab at it >> anyway. >> >> Parallel strings of batteries are routine in PV systems; indeed, far more >> common than single strings of large cells. Seldom are the individual >> strings separately fused, and I have never seen it required as a Code >> issue. The entire battery bank as a single entity is considered a single >> current source. Overcurrent protection is sized in accordance with the >> battery cable size - or rather vice versa: the overcurrent protection is >> sized to the requirements of the inverter(s) and the cables are sized to >> the overcurrent protection. >> >> Having said that, there are at least two cases where it's a good idea to >> account for it, whether or not addressed in the Code: >> 1) In smaller systems, such as with two or three strings of common >> batteries, you will eventually have a cell failure. When that happens, the >> amps increase on the other remaining strings. So it is good practice to >> oversize series and parallel interconnects for that eventuality. >> 2) For similar reasons, in large battery banks we have sometimes added >> Class T fuses, appropriately sized to the application, to the B+ output of >> each string before combining them on a bussbar. These fuses serve only as >> catastrophic protection in case the entire load tries to exceed the >> ampacity of one set of cells and thus one set of cables. >> >> When we have done what I think you have described - two parallel 48V >> strings of 4 12V batteries each - we combine them with cables, without >> additional string-level protection. That is in accordance with >> manufacturers' instructions. >> >> Allan >> >> *Allan Sindelar* >> *al...@positiveenergysolar.com* <al...@positiveenergysolar.com> >> NABCEP Certified PV Installation Professional >> NABCEP Certified Technical Sales Professional >> New Mexico EE98J Journeyman Electrician >> Founder, *Positive Energy, Inc.* >> >> A Certified B CorporationTM >> 3209 Richards Lane >> Santa Fe, New Mexico 87507 >> *505 424-1112 <505%20424-1112> office 780-2738 cell* >> *www.positiveenergysolar.com* <http://www.positiveenergysolar.com/> >> >> >> On 2/6/2014 3:23 PM, Dave Click wrote: >> >> All, >> >> I think that in the past, list discussions have talked about fusing of >> parallel battery circuits as a best practice, but it's required per 690.9 >> right? (text below from 2008 NEC) >> >> Also, if someone (don't look at me) really wants to use 2 parallel >> circuits of 12V batteries, what equipment is recommended to provide >> overcurrent protection? The installer is using Outback hardware (FW500?) >> and has two battery circuits combined in the battery enclosure and run to a >> Big Bus feeding the two 125A dc disconnects for two GVFX3648s. If you've >> read this far, this area is more your wheelhouse than mine. Thanks in >> advance! >> >> >> 690.9 Overcurrent Protection >> (A) Circuits and Equipment. Photovoltaic source circuit, photovoltaic >> output circuit, inverter output circuit, and storage battery circuit >> conductors and equipment shall be protected in accordance with the >> requirements of Article 240. Circuits connected to more than one electrical >> source shall have overcurrent devices located so as to provide overcurrent >> protection from all sources. >> >> Exception: An overcurrent device shall not be required for circuit >> conductors sized in accordance with 690.8(B) and located where one of the >> following apply: >> (a) There are no external sources such as parallel-connected source >> circuits, batteries, or backfeed from inverters. >> (b) The short-circuit currents from all sources do not exceed the >> ampacity of the conductors. >> >> > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Change email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > >
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