[RE-wrenches] Strings and series of batteries

[Michael Welch]

Thanks, Tom. I think I have seen those photos before.

Am I seeing 16 cables hooked up to each bus bar? Are you using 2 cables for each end of each string? Is that 8 series strings?

I can certainly see the advantage of being able to easily remove a string from the system.

But I still do not see how it will treat the individual batteries much better than using large parallel cable interconnects, which might be cheaper if the runs are not too long.


Tom Elliot wrote at 06:45 PM 12/2/2009:
 
>Michael,
>
>Here are photos of how it's done in a home situation http://www.wagonmaker.com/newbatt2.html
>
>What is handy about the buss bar is the ability to use much smaller cable from each series pair (in this case) to the buss bar, thus less expense in cables than otherwise and additional expense for the smaller cables is far better if it produces extended battery life and ease of service than the alternative.  The buss bars themselves are tinned copper bars mounted on stand-offs.
>
>Thanks to Jamie Surrette for confirming the wisdom of such setups.  I would love to see battery companies beginning to provide hardware for such systems and educating installers on how to use them.
>
>Tom
>
>
>--------------------------------------------------
>From: "Michael Welch" <michael.welch at re-wrenches.org>
>Sent: Wednesday, December 02, 2009 2:00 PM
>To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>Subject: Re: [RE-wrenches] Strings and series of batteries
>
>>
>>I wish I understood this bus bar use better. Electrically, these seem to be the same thing. But by using the bus bar, there has to be more cables, cable ends, and connection points. And cost.
>>
>>I just drew a battery bank (see below link to graphic), three series strings in parallel. On the negative side I drew a bus bar. On the positive side I drew normal parallel cable interconnects.
>>
>>The bus bar side requires 3 cables with 6 cable ends and 6 interconnection points.
>>
>>The cable side requires 2 cables with 4 cable ends and 3 interconnection points.
>>
>>How can a bus bar possibly be better? There will always be one more cable, and 2 more cable ends to connect.
>>
>>I do not see how either way could cause the current for one battery pass through another. It is merely using the terminal of the battery as a connector between two cables. Ditto for any difference in how internal resistance reacts, they both seem the same to me.
>>
>>Related question #2:
>>
>>It also has been noticed that some installers use "cross tie" interconnects for paralleling batteries in the middle of the series strings where the positive of one battery connects to the negative of the other -- not just at the final pos. and neg. outer ends of the strings. In fact, some even recommend two cables between:
>>http://www.green-trust.org/wordpress/wp-content/uploads/2008/09/cross-tied-battery-bank-300x187.jpg
>>
>>What's up with that? If it helps make charging equal, is it worth the extra expenses and connections involved?
>>
>>Here is a little jpg that illustrates both of these questions:
>>ftp://ftp.re-wrenches.org/pub/bbvscablewcrossties.jpg
>>
>>
>>
>>Tom Elliot wrote at 02:19 PM 12/2/2009:
>>
>>>Darryl, The process of paralleling through buss bars means attaching each serial string to a pair of buss bars rather than to neighboring series pairs so batteries aren't passing current through each other and aren't affected by each others internal resistance.  The buss bars then feed the inverter breaker.  It's standard practice in large telco installations which is where I got clued into the process.  I got some batteries from a wholesaler who did those installations and he was aghast at the idea of series/parallel installations the way off-grid systems have been done traditionally.
>>
>>
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