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

[Michael Welch]

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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