Almost all modern charge controllers and inverters etc have a low voltage threshold at about 9-10VDC.....below that they simply won't turn on, so even if the sun is out the MPPT controller won't charge, for example. There are different field-expedient solutions; but here's me jump-starting a 100-meter MET tower / 24vdc offgrid system with my truck, after lightning tripped the main PV breaker 2 weeks before. About 5 minutes on one 12vdc battery string, and the PV controller woke up to see 750 watts of sun and all was well. The client was skeptical as I explained over the phone what I was doing, but quite happy when all the expensive anemometers and web data logger magically came back online.
Dan Fink Buckville Energy IREC Certified Instructor™ for: ~ PV Installation Professional ~ Small Wind Installer NABCEP / IREC / ISPQ Accredited Continuing Education Providers™ 970.672.4342 On Wed, Dec 17, 2014 at 10:36 AM, Corey Shalanski < [email protected]> wrote: > > Clarification and Update: > - I believe I may have inadvertently thrown Magnum under the bus in in my > initial post. > ᐧ > While on site yesterday I did speak with Magnum's customer support about > my findings and they advised to try to trickle charge the batteries up to > the minimum threshold at which the Magnum inverters would turn back on. > From there we will hopefully be able to run some more determinate tests. My > question about the low-battery-cutout was more intended to explore whether > others have ever experienced any similar issues with this protection > feature. I am finding out that the feature is only relevant during > inverting (not charging) mode and so would imply that the utility feed had > been cut, which does not appear to be the case. > - Our battery distributor has lent us a 12-circuit trickle charger - one > set of alligator clips per battery. I am planning to re-visit the jobsite > later today to put each battery on a trickle charge, which I am told will > take 1-2 weeks for any lasting change to take effect. The distributor > advised to reverse the leads on the batteries with negative voltage, hoping > that they may be recoverable as "reversed pole" batteries thenceforth. > > -- > Corey > > > > On Tue, Dec 16, 2014 at 8:27 PM, <[email protected]> wrote: >> >> >> Wrenches, >> >> I visited a customer today whose grid-tied battery backup system suffered >> some sort of catastrophic failure, and now I'm trying to play detective to >> figure out what happened and whose equipment/design is to blame. >> >> Here is what I know so far: >> - System is ac-coupled with a Sunny Boy 7000 (7.85kW array), Magnum >> MS4448PAE (x2), 3 strings of 4 12v batts (705Ah total) >> - Site visit was triggered by the Sunny Boy registering zero output via >> online monitoring. >> - SPST Solid state relay installed on Sunny Boy output, controlled via >> Magnum router, serves as secondary overcharge protection to Magnum's >> frequency shift feature. Technician who initially responded claims he >> measured 240v across the relay's terminals - relay manufacturer claims >> this >> is "100% impossible". We removed the relay from the circuit, and the Sunny >> Boy is again operational. >> - On arrival I found the Magnum display showing a "Low Battery Charge" >> message with the bank measuring ~4Vdc. The individual batteries were in >> various states of charge, ranging from high of 6.3v to low of -2.6v. These >> measurements were taken at rest, all battery cables disconnected, and yes >> three of the batts were registering a negative voltage. >> - Customer reports that he was not aware of any recent prolonged power >> outages. >> >> The three potential suspects would seem to be: >> - SS relay: The customer is convinced that this is the weak link in the >> system and somehow triggered this failure. I am not so convinced but would >> be interested to hear recommendations for properly testing its >> functionality. >> - Magnum equipment: Since there is low-battery-cutout protection, why >> would >> this feature not have activated and prevented the batteries from draining >> so low? >> - Batteries: I am not very familiar with modes of failure, but our >> distributor suggested that an internal short could be a possibility - what >> might have triggered this? >> >> Clearly I am fishing for potential leads here, so any suggestions are >> welcome. >> >> Thanks! >> -- >> Corey Shalanski >> Joule Energy >> New Orleans, LA >> > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/[email protected]/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > >
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