[RE-wrenches] Magnum System - Discharged Battery Bank

[Dan Fink]

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 <
cshalanski at joule-energy.com> 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, <cshalanski at joule-energy.com> 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
>>
>
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