Michael,
There are 12 1/0 cables running from the batteries for each side of the
buss, pos and neg plus the two 4/0 cables. There are 12 series strings in
that 24v system wXH consisting of two 12 volt 100-amphour DCS-100L Dynasty
deep cycle AGM batteries. That system has so far been in place for 6 years
and is rock solid. We've since sold the house but my last two annual
checkups (which I don't do anymore) showed nothing great than a 1/10 volt
difference between the individual 12-volt batteries throughout the bank.
I've replaced one cable which is incredibly easy (as easy as working with
batteries ever gets anyway) and required no shutting down of the system.
It's been a while since I had the engineering discussion with the Dynasty
engineer who spec'ed these batteries for me and reiterated what I'd already
been told about using buss bars by the wholesaler I used to deal with. I
suspect Jamie can give a better technical explanation but I do recall he
said that while the virtual circuit looks the same in a diagram the behavior
of the system is different using the buss.
Tom
--------------------------------------------------
From: "Michael Welch" <[email protected]>
Sent: Wednesday, December 02, 2009 5:05 PM
To: "RE-wrenches" <[email protected]>
Subject: Re: [RE-wrenches] Strings and series of batteries
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" <[email protected]>
Sent: Wednesday, December 02, 2009 2:00 PM
To: "RE-wrenches" <[email protected]>
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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