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<br>
Nobody mentioned this in this thread, but it occurs to me that the
answer may be made clearer<br>
by looking at the Voc of each battery string after so many Amp-Hours
(years) of service.<br>
<br>
i.e., disconnect the strings' parallel connection and measure the
individual string voltage after charging them all the best that can
be done.<br>
<br>
This would be making the assumption that the batteries themselves
were fairly equal capacity and voltage at installation time. <br>
<br>
And for whatever reasons, connections, temperatures and everything
else discussed here, the strings degrade differently.<br>
<br>
The older and more worn out batteries should have a lower voltage
(Voc) than the less worn out strings. Thus, the better strings<br>
may be tending to hold up the worse strings by dumping charge into
them when the whole bank is discharging,<br>
and wasting energy and battery efficiency.<br>
<br>
I guess that just large 2V cells are the answer in this case, if at
all possible.<br>
<br>
Thanks for the help on this question !<br>
<br>
boB<br>
<br>
<br>
<br>
On 6/2/2011 10:42 AM, Tom Elliot wrote:
<blockquote cite="mid:A4EB2F42564C42A996084E6F44A4610E@Haikulaptop"
type="cite">
<div dir="ltr">
<div style="font-family: 'Arial'; color: rgb(0, 0, 0);
font-size: 10pt;">
<div>Not surprised at all about the phone company guy. It was
a phone company guy who read me the riot act that no one in
their right minds would ever parallel battery banks the way
PV off-grid systems did and got me to set up my system with
separate strings connected independently to buss bars. The
battery engineer I talked to years ago at Dynasty not only
said the same thing but also said keeping strings separate
meant individual string distance from the bars became
irrelevant (given correctly sized wire for each string’s
parallel connectors). I had a system with 12 100 amphour
strings of paired 12v Dynasty AGMs which was rock solid
until the day I sold the house. The last time I checked
the system before the sale no single battery varied from any
other in the system by more than 1/10 volt and the majority
were still holding identical voltages.</div>
<div style="font-style: normal; display: inline; font-family:
'Calibri'; color: rgb(0, 0, 0); font-size: small;
font-weight: normal; text-decoration: none;">
<div style="font: 10pt tahoma;">
<div> </div>
<div style="background: none repeat scroll 0% 0% rgb(245,
245, 245);">
<div style=""><b>From:</b> <a moz-do-not-send="true"
title="dan@foxfire-energy.com"
href="mailto:dan@foxfire-energy.com">dan@foxfire-energy.com</a>
</div>
<div><b>Sent:</b> Wednesday, June 01, 2011 4:14 PM</div>
<div><b>To:</b> <a moz-do-not-send="true"
title="re-wrenches@lists.re-wrenches.org"
href="mailto:re-wrenches@lists.re-wrenches.org">RE-wrenches</a>
</div>
<div><b>Subject:</b> Re: [RE-wrenches] 24 volt Battery
Bank comparison</div>
</div>
</div>
<div> </div>
</div>
<div style="font-style: normal; display: inline; font-family:
'Calibri'; color: rgb(0, 0, 0); font-size: small;
font-weight: normal; text-decoration: none;"><span
style="font-family: verdana; color: rgb(0, 0, 0);
font-size: 10pt;">
<div>Good thread. Thanks. </div>
<div>In my experience, it all boils down to the customer.
I've seen one temp. set up with like 12 strings (for a
concert). but they were recharged and sold individually
within a few weeks.. I've also seen a single string
(Teledyne aircraft batteries) fail in less than a year..
they were in a brand new airplane tug that was never
charged -- ever. (the guy said "I dunno, it just stopped
working").</div>
<div> </div>
<div>I have one customer who (last I knew) was running 6
strings of mixed aged L-16s going on 8 years. Thing is,
he's a retired phone company dude (Who's missing half of
his right hand from using one of those pocket pal
screwdriver thingys on a key chain in a hot DC rack..
like he'd done hundreds of times before.. but that's
another tale). But I do like his set up.. he has each
string set up with it's own fused Disco and Trimetric..
Gives him random control over each string. And yes, he
keeps a very detailed log, and you can bet that when he
takes a battery out of service, it's done.<br>
</div>
<div> </div>
<div>Me? for an average bullet proof off grid system, I
shoot for a max of two strings for 24V systems (for the
redundancy), and manually reconfigure them every few
years. for 48V systems, I shoot for <span>one string of
two Volt cells<span id="GD__CURSOR"></span></span>..
thinking that if I loose a cell I can still operate a
46V system until I get a replacement.</div>
<div> </div>
<div>And Yes, as we all know, there are folks out there
that really shouldn't be allowed to operate a popsicle
stick. </div>
<div> </div>
<div>db<br>
</div>
<div> </div>
<div><br>
Dan Brown<br>
Foxfire Energy Corp.<br>
Renewable Energy Systems<br>
(802)-483-2564<br>
<a moz-do-not-send="true"
href="http://www.Foxfire-Energy.com">www.Foxfire-Energy.com</a><br>
NABCEP #092907-44</div>
<div><br>
<br>
</div>
<blockquote style="border-left: 2px solid blue;
padding-left: 8px; font-family: verdana; color: black;
margin-left: 8px; font-size: 10pt;" id="replyBlockquote"
webmail="1">
<div id="wmQuoteWrapper">-------- Original Message
--------<br>
Subject: Re: [RE-wrenches] 24 volt Battery Bank
comparison<br>
From: Michael Welch <<a moz-do-not-send="true"
href="mailto:michael.welch@re-wrenches.org">michael.welch@re-wrenches.org</a>><br>
Date: Wed, June 01, 2011 1:43 pm<br>
To: RE-wrenches <<a moz-do-not-send="true"
href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>><br>
<br>
Every now and then I see reference on this list to the
need for thermal detection. Here is an interesting,
inexpensive piece of equipment that could be used for
finding hot (loose or corroded) connections, hot
batteries, hot PV cells in modules, and even poorly
insulated spots, its original intended purpose:<br>
<br>
<a moz-do-not-send="true"
href="http://www.blackanddecker.com/power-tools/TLD100.aspx">http://www.blackanddecker.com/power-tools/TLD100.aspx</a><br>
<br>
I have one and used it for finding uninsulated spaces,
but cannot attest to its durability or suitability for
the other uses mentioned above.<br>
<br>
<br>
boB Gudgel wrote at 01:00 AM 6/1/2011:<br>
<br>
>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<br>
>really be helpful for so many things.  Even just
to know if you have left a nut loose (under load of
course)<br>
><br>
>boB<br>
<br>
<br>
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