[RE-wrenches] 24 volt Battery Bank comparison

Thu Jun 2 09:03:08 PDT 2011

Excellent comment tom, so true.  I get concerned that some of my experiences are a collection of exceptions.  I like Larry's comments because he has worked so many systems.  I have seen fires, but  mostly because I have a reputation and people wnat me to come and see what happened.  

Darryl

________________________________
From: The Solar Powered Office of Tom Duffy <tom at thesolar.biz>
To: Allan at positiveenergysolar.com; 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, June 2, 2011 9:34 AM
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison

Wrenches:

This
is a really great thread. Here’s my two cents…
I
started selling and configuring battery systems when I got out of the Army back
in 1967 I’m a marine electrician. In the boat environment everybody tries to
make a big battery out of a bunch of small batteries, Over the years this is
what I’ve witnessed; All else being equal.
3
parallel strings = 4 ½  to 5 ½ years Max
2
parallel strings = 5 ½ to 6 ½ years Max
1
series string = 8 to 12 years Max
The
above seems to hold true if the charge settings, Bulk, Absorb time and Voltage
are correctly set. But as we all know 85% of the time this is not the case.
So my
conclusion is that parallel configured banks just about cut the life in half. 
And
there is always the stories about the guy that drank a quart of Bourbon a day
and smoked cigars chasing women until he was 102 years old. The same is true
with batteries… the exception but not the rule.

  Tom Duffy
  Systems Design Engineer

     tom at thesolar.biz
       575-539-2111 X 122
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no trees were killed in the sending of this message, a large number of
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From:re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
Sent: Wednesday, June 01, 2011
11:07 PM
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] 24 volt
Battery Bank comparison

I had done this a few times in the distant past, and
also had done it in recent years on my own previous battery bank (four strings
of S-530s - yes, I know; it was in anticipation of future plans to upgrade to
48V, and two strings wouldn't have been enough).

It worked fine - and that turned out to be a problem. I had noticed reduced
capacity, but assumed foolishly that it was simply to age and cycle life (going
on six years and three teenagers). Found out I had two failed cells in two
different strings. The parallel connections probably - I'm not sure here -
allowed the bank to perform more robustly and less obviously weakened. It might
have even allowed the bank to perform as if both failed cells had been in the
same string. But it also allowed me to not pay enough attention to a
potentially serious problem by disguising it.

I blame myself more than the parallel connectors (just some #2 interconnects I
had lying around). I'm just not sure I would use it on a customer's system.

Allan Sindelar
Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic
Installer
NABCEP Certified Technical Sales Professional
New Mexico 
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe , New
  Mexico 87507
505 424-1112
www.positiveenergysolar.com 

On 6/1/2011 9:20 AM, toddcory at finestplanet.com wrote: 
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.

Todd

On Wednesday, June 1, 2011 3:06am,
"James Surrette" <james at surrette.com> said:
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 <boB at midnitesolar.com> 6/1/2011 5:00 AM >>>
On 5/31/2011 11:25 PM, Tom Elliot wrote:
Bob,
> 
>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.
> 
>Tom
> 
> 
> 
>From:boB Gudgel
>Sent:Tuesday,
May 31, 2011 8:16 PM
>To:RE-wrenches
>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
>
>
>
>
>
>
>>On May 31, 2011, at 8:23 PM, "Wayne Irwin" <wayne at pureenergysolar.com>
wrote:
>>I think the
verdict is12 - 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 
>>>Wayne at PureEnergySolar.com
>>>http://pureenergysolar.com
>>>352 377-6527 Office
>>>352 336-3299 Fax
>>>352 316-1637 Cell
> 
> 
> 
>
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