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So would you agree that battery inequalities show up more at:<br>
a) high discharge/charge rates (greater than C5) <br>
b) higher battery voltages (more cells in series, over 48v)<br>
c) more parallel strings<br>
d) bad/ corroded/ loose connections<br>
e)lack of initial EQ/ activation charge and periodic EQ after long
or heavy discharges<br>
f) main cables not at least wired to opposite sides of battery bank
or better: separate parallel cables to buss bar <br>
h) lack of maintenance (watering, uneven cell temperatures)<br>
Did I miss anything?<br>
<br>
Ray<br>
<br>
<br>
On 6/3/2011 12:10 PM, James Surrette wrote:
<blockquote
cite="mid:4DE8F9770200007700087A49@mail.corp.surrette.ca"
type="cite">
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <font
face="Arial" size="3">Hi Ray,</font> </p>
<br>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <font
face="Arial" size="3">Just a quick chime in on your series
string comment.</font> </p>
<br>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <font
face="Arial" size="3">If you hook up 4 x 12V monoblocks for a
small 48VDC system and begin charging at 58.8V, total voltage
will be 58.8V very quickly but individual battery voltage will
not be 14.7V. Battery voltage will have a large range from 14
to almost 17V. This problem is only exacerbated in higher
voltage systems, ie, Australian 120VDC. Stealing from the
Telcos, the best solution is an initial activation to balance
all cells. When this is completed and assuming all leads stay
tight, no bad cells, etc the bank will charge and discharge in
relative harmony. However, if the cells / batteries are
bolted together and discharged right out of the gate, there's
a good chance SG & Voltages will be all over the map in
short order.</font><br>
</p>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <font
face="Arial" size="3">Jamie</font><br>
>>> Ray Walters <a class="moz-txt-link-rfc2396E" href="mailto:ray@solarray.com"><ray@solarray.com></a> 6/3/2011 2:53
PM >>><br>
I've set electric vehicle parallel strings up like this too.
Once a month I charge each string separately. At higher charge/
discharge rates, the problems of unequal batteries increases
dramatically. BTW, single strings are not the magic bullet
either; I've had single strings with equal current through each
battery, but some batteries would be at 15.5 volts, while others
next to it would be at 13. The charge controller shuts off when
the sum of the voltages hits the bulk charge V, but meanwhile
some cells are chronically overcharged or undercharged.
(parallel strings no where to be seen)<br>
Manzanita Micro makes a device that shunts current past
batteries that hit full charge in a string. This monitoring of
each individual battery is the state of the art right now for
Li+ batteries in EVs.<br>
I agree, we need much better battery management and safety
devices for solar. Its ridiculous some of the mundane issues we
discuss here sometimes, while hundreds of huge battery packs are
just waiting for one of us to drop a wrench across the
terminals, with zero safety to interrupt it, and its all NEC
compliant.<br>
Batteries themselves need to have a current limiting device
built into the positive terminal. Possibly the same device that
controls charge current to it too?<br>
<br>
Dreaming up future BOS equipment,<br>
<br>
Ray Walters<br>
<br>
On 6/2/2011 7:44 PM, <a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:dan@foxfire-energy.com">dan@foxfire-energy.com</a> wrote:
</p>
<blockquote type="cite"
cite="mid:20110602184417.720a661d8db719b1f2ad39509c9edaa3.5de8cf490d.wbe@email14.secureserver.net">
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> What I like
best about Mark's set up (the retired phone co. dude w/ half
a hand), is that he can select individual strings at random.
he can eq an individual string, or top off a few strings and
park them. he can even run strings of T 105s, or even nicad
(individually of course) in the same system as L-16s and the
like.. he just reprograms the chargers (and logs it). I
think he got the design from his days in the Navy. </p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <br>
</p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> So boB, how
about a controller that can be user programed to charge
multiple battery configurations with a soft switch? i.e.
Bank A, Bank B...? and while you're at it, maybe a multiple
string DC box? Something with a shunt and a breaker for each
string? A four string set up would be nice.<br>
</p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <br>
</p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> I could use
2% of your first million. </p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <br>
</p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> db<br>
</p>
</div>
<div>
<p style="margin-bottom: 0pt; margin-top: 0pt;"> <br>
Dan Brown </p>
</div>
</blockquote>
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