Here's some good info:
http://photovoltaics.sandia.gov/docs/battery1.htm
or
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=CC366D87BBE1C7C3BCBEEAFD87A3D0D7?purl=/402426-htwdT8/webviewable/
or
http://www.osti.gov/bridge/purl.cover.jsp?purl=/125071-E7W1qQ/webviewable/
Joel Davidson
----- Original Message -----
From: "Tom Elliot" <tell...@wagonmaker.com>
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Sent: Friday, December 04, 2009 3:01 PM
Subject: Re: [RE-wrenches] Strings and series of batteries with
reversereturn linkup
I would love to see some studies on that Michael. I do know that I saw
none of the supposed problems of paralleling more than just 2 or 3 series
strings and the batteries have lasted far longer than the original L-16s
did in a "traditional" bank even though there are 12 strings paralleled
together.
I do know that the engineer I spoke with at length so many years ago was
quite specific about there being a significant difference in how such a
system functioned using bus bars over interconnected terminals but I
cannot remember the specifics of his reasoning.
I do recall quite clearly the telco installers saying, more than once,
that paralleling strings the way we always did was "nuts" and they
couldn't understand why we did it that way.
Maybe Jamie has more specifics.
Tom
--------------------------------------------------
From: "Michael Welch" <michael.we...@re-wrenches.org>
Sent: Friday, December 04, 2009 11:55 AM
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Strings and series of batteries with reverse
return linkup
Yes, the bus bar technique will always add 1 cable and 2 connection
points. And extra cost.
As far as I can see and from what I have read in this thread, the only
advantage to the bus bar method is absolutely equal interconnection
resistances for all the strings. Maybe this advantage is only be useful
for those that put many strings of batteries in parallel. Not so
important when one has only 2-3 strings, the max that most folks
recommend.
But if appropriately large enough cable is used in a conventional cabling
method for 2-3 strings, my gut says the resistance differences should be
marginalized to the point of irrelevance.
As Kent points out, internal resistance is a differentiating factor which
cannot be fully controlled, a factor of greater concern that seems to
further marginalize the value of bus bars and equal cable lengths.
To me, this discussion seems really important. The opinions here are
varied, but if the results are real, significant, and verifiable, we will
all want to become proponents of this method.
Jamie, Rob, & Tom: Have there been any studies done comparing those two
techniques, or is this something that has been passed down over
generations in the battery industry?
(BTW, my very first bank of batteries was situated such that I bolted the
string ends directly to pieces of copper flat stock, 1 for each string
polarity -- no cables, except to the load. The best of all worlds, I
suppose.)
William Miller wrote at 10:53 AM 12/4/2009:
Colleagues:
I found Tom Elliot's buss bar solution intriguing, but instinctively
something bothered me about it. Although I like fondling wiring hardware
as much as any of us, this procedure seemed to unnecessarily complicate
the battery cabling system. Each added cable and each added connection
point contributes actual resistance and potential problems.
I undertook to simplify this into an electronic circuit with each cable
represented by a resistor (which it is) and at the same time providing a
clear depiction in which one can count the cables and connection points
for each of a number of battery strings. The result is a simple PDF
drawing on our web site: http://millersolar.com Go to "Case Studies"
and find Battery Wiring Options as the last entry. I welcome each of you
to poke holes in my analysis, graphics and/or analysis.
Please note the balance achieved in both systems. The merits then lie in
the actual number of cables and connection points, IMHO. Lastly,
consider the labor and materials required in a either installation.
Sincerely,
William Miller
PS: I have a pathological dislike of splices or connections that are not
mounted to a surface -- when secured you always know where they are and
they are easy to get a probe on. This is why we use power distribution
blocks whenever possible. Polaris connectors in a battery compartment
don't seem right -- they could easily trap corrosive fumes and hide
corrosion problems from view.
Wm
At 09:59 AM 12/4/2009, you wrote:
Hi Kent,
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.
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.
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).
Hugh
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