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, <cshalan...@joule-energy.com
<mailto:cshalan...@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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