I thought the relays on the SWs were sealed, so visible arcing sounds
bad. Are you sure its not a loose connection?
Also on the batteries, anytime I've ever seen someone replace just a
couple of cells in a bank that old, it never ended well. It was like
that gopher stomping game, and you hit one problem, and then another
pops up right after.....
We need some kind of financing program for battery replacements, so that
people can get what they really need: a whole new set.
That very situation, is why I quit doing as many single series strings:
one or two cells fail, and the whole system goes.
In this same situation with 2 strings, you create a single string of
your strongest cells to limp the customer along, until they can afford
to replace the set. As cells go down, you keep pulling in replacements
from the retired string. This would be a great time to take a few of the
best used cells from another aging set on another system that is
getting replaced.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 11/18/2013 5:01 PM, Allan Sindelar wrote:
Wrenches,
A longtime off grid customer with a 1997-era Trace SW4024 and a Kohler
8.5RMY backup generator (with 1,800 hours over 16 years) has never had
an inverter failure, but requested my assistance with a recent
development. His generator has been set up on automatic operation
using standard Trace voltage, quiet time and load-start program
parameters. When it was called to run, it would charge to 29.6 V with
a one-hour absorption, then shut off. This has worked well until
recently. The automatic operation includes a cool-down and the modest
absorption means that the AC input current at shutdown is going to be
pretty low.
Recently he called me because his generator was starting more
frequently and running for longer duration. Of course, I immediately
suspected the batteries, which are ten-year old 5000 series Surrette
4KS-25PS cells. Upon checking I found two weak cells, which would
explain the inability of the batteries to reach full voltage and shut
off after absorption. I will be replacing these two cells, which
fortunately are both within the same red polypropylene case, as our
only option, as the homeowner's budget won't allow replacement of the
whole set. As a single string, the two new cells should play
reasonably well with the old cells for a few more years.
Because of this, the homeowner had recently shut off the generator at
night using the buttons on the inverter, and when he did this he saw a
spark flash from inside the inverter on the AC end. I was able to
duplicate the flash, which I assume to be the AC2 input relay. The AC2
In setpoint is set to maximum 35A AC. Until the failed cells are
replaced, I have advised the homeowner to manually control the
generator at the generator, using its AC output breaker to disconnect
the current to the inverter before the 108V AC default input voltage
threshold causes the inverter AC input relay to unlatch under load.
While the SW latches while unloaded and then ramps up input current, I
don't believe that it can reduce input current to zero before
unlatching when shutting down.
My guess is that after 15 years of flawless performance, the relay
contacts have pitted enough to cause arcing at disconnect, and if not
addressed, the relay on the AC board will eventually fail. As AC relay
boards these days are likely made out of unobtanium, I'd rather avoid
this failure.
So my questions, please:
1. Have I likely correctly identified the AC input relay as the most
likely cause of the visible arcing when the generator is turned off at
the inverter?
2. Should manual control be a permanent solution?
3. Any other suggestions for this customer?
Thank you,
Allan
--
*Allan Sindelar*
_Allan@positiveenergysolar.com_ <mailto: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 Corporation^TM
3209 Richards Lane
Santa Fe, New Mexico 87507
*505 424-1112 office 780-2738 cell*
_www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
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