[RE-wrenches] FW: Strings and series of batteries

[Dana]

I sent this thread to Rob Shappell of NWES Battery. Here is his .02.

Dana Orzel

Great Solar Works, Inc
www.solarwork.com
E - dana at solarwork.com
V - 970.626.5253
F - 970.626.4140
C - 970.209.4076

I will be the shift in how the world uses power! - Dana Orzel


-----Original Message-----
From: Rob Shappell [mailto:rob at nwes.com] 
Sent: Thursday, December 03, 2009 8:15 AM
To: 'Dana'
Subject: RE: [RE-wrenches] Strings and series of batteries

Hi Dana,

It's all about even distribution of the energy whether the battery is being
discharged or recharged or no load at all. 2 parallel strings are do-able an
usually don't cause any problems, 3 strings or more however, is where the
problem of un even charging and discharging starts to show up, and aging
batteries amplify the problem. With 3 or more parallel strings we recommend
both, the buss bar and paralleling at the battery. 

Remember that 5 Parallel battery we worked on for the owners of gas wells?
The cabling was very extensive, but I still expected problems down the road.
Nothing that would void the warranty, but problems none the less. 

In any parallel setup, voltage will seek the lowest voltage bank and current
is always flowing until all banks are equal or drained. You only have the
capacity of the weakest cell/bank. Batteries are man made and are not as
consistent as the timeless laws of energy.

-----Original Message-----
From: Dana [mailto:dana at solarwork.com] 
Sent: Wednesday, December 02, 2009 7:40 PM
To: Rob Shappell
Subject: FW: [RE-wrenches] Strings and series of batteries

What's your opinion on this Rob?

Dana Orzel

Great Solar Works, Inc
www.solarwork.com
E - dana at solarwork.com
V - 970.626.5253
F - 970.626.4140
C - 970.209.4076

I will be the shift in how the world uses power! - Dana Orzel


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Michael
Welch
Sent: Wednesday, December 02, 2009 5:00 PM
To: RE-wrenches
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:
What's up with that? If it helps make charging equal, is it worth the extra
expenses and connections involved?
http://www.green-trust.org/wordpress/wp-content/uploads/2008/09/cross-tied-b
attery-bank-300x187.jpg


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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