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with rev</title></head><body>
<div>Hi Kent,</div>
<div><br></div>
<div>I am sorry but I disagree with your conclusion that it only keeps
the wire resistances the same for 2 strings. This diagonal
system, which I believe many people would call 'reverse return' in the
states, actually provides for exactly equal resistance on all paths to
all strings. Each time you add a link in the positive path you
remove one in the negative path. I admit that the voltage drops
will be very slightly different due to different currents in the
various links but the differences now are so tiny that I would not
worry about them.</div>
<div><br></div>
<div>I agree that you will get imbalances in multiple battery strings
at times - usually during periods of prolonged low winds. But
you cannot persuade me that multiple strings 'don't work right'
because they are used in most of the systems I work with since the
1970s. I see just as much sulphation in large capacity cells as
I do in small capacity cells (in multiple parallel strings). I
would say that going from 12-volts on up to 48-volt systems has caused
me a lot more headaches with unequal battery states than paralleling a
lot of batteries has. Batteries connected in parallel will tend
to take what they need. Connected in series they take what they
are given. Also, a cell failure in a 12-volt system attracts
attention at once, whereas a cell failure in a 48-volt system can be
overlooked for much longer.</div>
<div><br></div>
<div>There are plenty of points of view about batteries :-) Part
of it is the difference in mentality between solar users (who count
out the amp hours and know exactly what they have to work with each
day) and wind users (who can party like mad sometimes and then have
nothing at other times).</div>
<div><br></div>
<div>Hugh</div>
<div><br></div>
<blockquote type="cite" cite>Hugh,<br>
<br>
Feeding off diagonal corners, as you are describing, only keeps the
wire resistance of the parallel paths balanced when there are two
parallel strings of batteries and the connections between the
batteries are all the same length (or at least they add up to the same
total length). With three or more parallel paths, the resistance
of the wire is going to cause imbalanced current between the parallel
paths. <br>
<br>
But the internal resistance of the batteries is important too.
Unfortunately even with bus bars and equal length wires, imbalances
between the parallel paths will develop because of the batteries'
internal resistance. Consider what happens when a battery gets
sulfated: its voltage goes up quickly while charging and it goes down
quickly while discharging -- in other words: its internal resistance
goes up. Despite our best attempts to keep the wire resistance
balanced, some cell will sulfate more quickly than the others, then it
is a down hill spiral with the current balance getting worse and
worse. <br>
<br>
With paralleled batteries keeping them equalized becomes critical and
the more parallel paths there are - the harder it is to get them all
equalized.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar<br>
<a
href="http://www.bluemountainsolar.com/">www.bluemountainsolar.com</a><br
>
<br>
<br>
<br>
Hugh wrote:<br>
<blockquote type="cite" cite>Tom,<br>
<br>
Sorry, I failed to write clearly. I was not talking about bus bars in
this sentence. I meant to say that I 'daisy chain' links from
one string to the next. I parallel them by connecting A to B, B
to C, C to D. Then I connect positive of A to the inverter, and
negative of D to the inverter. In this way the connections are
all balanced without the use of a bus bar. You can connect the
positive of D to the wind turbine (and the negative of A) to reduce
the danger of a direct connection without batteries.<br>
<br>
If a battery is well charged I see no problem with parallel strings.
As it gets older then you do need to monitor the individual
cells/units for failures and take action. Standard smaller sized
units are easier to re-group, and if desired to replace.<br>
<br>
Tom wrote:<br>
<blockquote type="cite" cite>"If you connect links between
all of the positives, and links between all of the negatives,<br>
to parallel the battery, then the only issue is where you connect the
charge source and/or inverter."</blockquote>
<blockquote type="cite" cite><br>
Hugh,<br>
<br>
The connection is very easy, if you look at the photos on the page I
linked to the connections to the inverter breaker (which is where I
also connected the charge source) come off the bus bars. It's
actually a very simple installation and I found it much easier and
safer to work on that a large series/parallel bank of L-16s, which was
what my first bank in that system consisted off and it turned out to
be a mess (designed and the components built by Jade Mountain...)<br>
<br>
Tom<br>
<br>
<br>
<br>
--------------------------------------------------<br>
From: "Hugh" <a
href="mailto:hugh@scoraigwind.co.uk"><hugh@scoraigwind.co.uk></a
><br>
Sent: Thursday, December 03, 2009 8:30 AM<br>
To: "RE-wrenches" <a
href="mailto:re-wrenches@lists.re-wrenches.org"
><re-wrenches@lists.re-wrenches.org></a><br>
Subject: Re: [RE-wrenches] Strings and series of batteries<br>
<blockquote type="cite" cite>Just for a contrasting opinion:<br>
<br>
I rarely use grease or vaseline unless it proves necessary. I
have<br>
changed out battery banks after seven years and the connectors are<br>
still pristine whilst dry. I agree that sometimes there will
be<br>
localised corrosion on battery terminals. I find it rarely, and
I<br>
deal with it as and when. I might use vaseline then. Or
spray on<br>
some oil. Not a big deal to be honest. The contact
resistance is<br>
not affected by corrosion on the outside. Probably due to
some<br>
moisture arriving on the terminal? But vaseline/grease
attracts<br>
dust, makes a big mess and mess is not nice around batteries.<br>
<br>
Bus bars sound great, but what a hassle. If you connect
links<br>
between all of the positives, and links between all of the
negatives,<br>
to parallel the battery, then the only issue is where you connect
the<br>
charge source and/or inverter. I have learned to connect them
at<br>
opposite ends of the parallel links. 'Diagonally opposite' you
could<br>
call it. In this way the resistance is identical to each
string.<br>
One string has a direct connection to plus. One has a direct<br>
connection to minus. All have equal number of links between them
and<br>
the inverter. If there is a wind turbine then I will often
connect<br>
this to two corners and the inverter to the opposite two corners,<br>
making it very difficult to (both) disconnect the battery and
(also)<br>
leave the wind turbine connected to the inverter. This probably
has<br>
saved a few inverters from instant death due to carelessness.<br>
--<br>
Hugh Piggott<br>
<br>
Scoraig Wind Electric<br>
Scotland<br>
<a
href="http://www.scoraigwind.co.uk">http://www.scoraigwind.co.uk</a><br
>
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<div><br></div>
<div><br></div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div>Hugh Piggott<br>
<br>
Scoraig Wind Electric<br>
Scotland<br>
http://www.scoraigwind.co.uk</div>
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