[RE-wrenches] Strings and series of batteries

[Tom Elliot]

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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