Does it make any difference to do as boB recently suggested
and inter-connect the strings? So in other words, if you have
two parallel strings, what happens if you parallel each
battery in one string with the battery in the other string?
Has anyone tried this? It might help insure more balance
between each series string.
Hi boB,
I would say
maintenance is a large issue - especially when dealing
with L-16's or the like, as the number of cells &
connections gets large, i.e. 1000-1200AH @ 48VDC is three
(3) strings, 24 batteries and 72 cells. Will a client
water 24 cells...maybe - 72??
However, from
Tech Support days, imbalance is the larger problem. It
seems to take 18 months - 3 years and then you would get
SG readings where one (1) bank was perfect and the
other(s) is significantly lower......which is hard to
overcome without effort (either break the banks &
charge independently or hammer the banks and allow the
high string to get even higher).
One of the
key take aways that often gets overlooked is the proper
initial activation of the strings. It is impossible for
all cells to have identical resting voltage. During
commissioning, each string should be charged to
2.45-2.5VPC and held until all cells read the same
voltage. If running multiple strings, then connect the
strings and run the entire bank at 2.45-2.5VPC until all
cells measure the same voltage. Now the bank is well
balanced and the chances of a major imbalance are greatly
reduced. However, even after this effort, if you use an
amp clamp, you will notice slight differences in the
amount of current being accepted by each bank.
Best,
Jamie
>>> boB Gudgel <b...@midnitesolar.com>
6/1/2011 5:00 AM >>>
On 5/31/2011 11:25 PM, Tom Elliot wrote:
I
totally understand the concern about multiple
strings *if the strings are connected across the
battery bank* as had always been the tradition in
off-grid installations. My own experience with such
a bank in my system showed why when I had a single
cell get to near meltdown. I was lucky to find it.
This might be a good reason for an installer to have one of
those FLIR (or similar) thermal imager cameras. They're a
bit on the expensive side, but could
really be helpful for so many things. Even just to know if
you have left a nut loose (under load of course)
boB
Maintenance
is another reason, such banks are far more difficult
to maintain. But I think those concerns are
ameliorated a great deal with a buss bar
installation and once I did that I never had another
problem and found the battery bank much easier to
maintain because the strings no longer had to be
right next to each other. Heck, it would be
possible to put each series string in its own box
for that matter. And with the inclusion of string
fuses that reduces problems even further.
When
living with an off-grid system my biggest concern
was system reliability and redundancy and the idea
of a single string failure was a big worry which is
why I never would consider it.
Sent:
Tuesday, May 31, 2011 8:16 PM
Subject:
Re: [RE-wrenches] 24 volt Battery Bank
comparison
OK, I've been hearing for years now that one battery
string is best and maybe two but no more should be
used.
What is the reason for this fear ??? What is the
experience with multiple strings in parallel ??
If it is because of current sharing of the strings,
that shouldn't be an insurmountable problem if the
wiring is done right.
If it has to do with the possibility of fire, which
Darryl mentioned, seems that series string fuses
could mitigate the possibility of that issue, if
because of shorted cells, just like PV combiners.
Or maybe it has to do with the trouble of getting
into the middle of a pile of batteries ? Use
battery boxes ?
The strings are in parallel and so they all get the
same voltage, theoretically anyway if the
connections are good.
I would think that the more strings, the LESS stress
on individual batteries, not more. The current in
each battery should be less than it would be I would
think.
So what is the real experience ??
Is a battery balancer the answer ??
Thanks,
boB
I
think the verdict is 12 -
Rolls 2-YS-31 2430 AH @ 20 HR (one string) and
one dry spare in storage is the best case
scenario!
Wayne
Irwin, EE
Director of Engineering
Pure Energy Solar International Inc.
State Licensed Solar Contractor
License # CVC56695
wa...@pureenergysolar.com
http://pureenergysolar.com
352
377-6527 Office
352 336-3299 Fax
352 316-1637 Cell
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