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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