[RE-wrenches] Strings and series of batteries with reverse return linkup

[William Miller]

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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