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

Joel Davidson joel.davidson at sbcglobal.net
Fri Dec 4 18:52:43 PST 2009


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" <telliot at wagonmaker.com>
To: "RE-wrenches" <re-wrenches at 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.welch at re-wrenches.org>
> Sent: Friday, December 04, 2009 11:55 AM
> To: "RE-wrenches" <re-wrenches at 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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