[RE-wrenches] Strings and series of batteries

[Mick Abraham]

I also have been following this thread and wondering "whazzup" about
buss bars being better than just parallel cables from one battery
string to the next.

Agreed that the parallel cable method "is merely using the terminal of
the battery as a connector between two cables." Maybe if there's big
amperage involved on that battery post and that post warms up then
conducts heat to the inner structure of that battery...maybe...but
those lead posts are massive enough that it would take a lot of
amperage...plus maybe a deteriorating connection to generate much
heat.

I advocate "cross-tying" the pack as a way to average out strong/weak
monoblocs. This is electrically much the same as if the monoblocs were
bigger ampacity because the cross-ties mimic what occurs inside each
plastic case with plates in parallel.

Steve at Green Trust had posted the cross-tie diagram as referenced by
Michael and asked my opinion. I opined that using two cross ties at
each "voltage node" in the series string is redundant and cannot
improve upon what occurs when using only one cross tie at each voltage
node. Unfortunately I cannot now find my explanation of that on
Steve's website.

Jolliness,

Mick Abraham, Proprietor
www.abrahamsolar.com

Voice: 970-731-4675



On Wed, Dec 2, 2009 at 5:00 PM, Michael Welch
<michael.welch at re-wrenches.org> wrote:
>
> 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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