[RE-wrenches] Magnum System - Discharged Battery Bank

[Ray Walters]

I've never seen an inverter not disconnect on low voltage.  My 
understanding is that they just can't operate below a certain threshold.
However, I have seen behavior as described caused by DC loads that did 
not have a LVD in place.  Were there any other DC connections to the 
battery bank besides the inverter?
Once the whole bank gets low enough, even the charge controllers will 
not reconnect, and the entire bank is quickly ruined.
This is why I rarely use DC direct loads anymore, and If I do, I always 
recommend a LVD.
Any chance of a short circuit in the cabling before the inverter?
The only other thing I could think of is a shorted cell in one of the 
batteries, that then drained the rest of the batteries.


R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 12/17/2014 10:36 AM, Corey Shalanski wrote:
> Clarification and Update:
> - I believe I may have inadvertently thrown Magnum under the bus in in 
> my initial post.
> ?
> 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 
> <mailto: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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