Fw: Battery Bussing [RE-wrenches]

jay peltz jay at asis.com
Mon Sep 10 10:32:15 PDT 2001


Hi Joel, and Tom,

My question is about wire lengths.  In the plumbing world, to truly parallel
something, the lengths of pipe,fittings etc must be the same length.  Seems to me
that the shorter wires will pull more power.  Yes I realize that we are talking
really small differences here, but it is going to take the path of least resistance.

What say you?

jay

peltz power

Joel Davidson wrote:

> Tom,
> Thank you very much for the pictures and story on your web page. Using a common
> bus makes a lot of sense. I wish I had more time and money to do research and
> testing. It would be good to put ammeters on the series and parallel  cables to
> confirm lower current coming from inner batteries. Perhaps your battery supplier
> has some test data.
> Best regards,
> Joel Davidson
>
> Tom Elliot wrote:
>
> > Allan,
> >
> > I've been following this thread with some interest as I've just gone through
> > my own changeover due to (what I consider) premature cell failure in an L-16
> > in my original bank.  I've done a write-up on my web page (the write-up is
> > at http://www.wagonmaker.com/newbatt.html ).
> >
> > As I say on the webpage, the battery people I deal with who do large telco
> > installation literally cringed when I said I had a series/parallel
> > installation.  The cell in my system that failed first was the one closest
> > to the positive inverter takeoff.  I didn't have cross-connection on the
> > bank, I took the power from one end (I know not the best) but they told me
> > it only made a little difference to take power from opposite ends of the
> > bank.
> >
> > According to what I was told, virtually *any* paralleling of batteries is a
> > bad idea.  The center strings add voltage but not much current to the
> > inverter draw which means that the outside series strings take more of a hit
> > than the center strings.  (I'm getting clarification and more technical
> > explanation of this from them but it may take time).
> >
> > Anyway, when I saw the "battery bussing" subject line I thought folks would
> > be talking about the way I've installed my "new" (to me) bank of AGMs.  All
> > my series strings (pairs, each is 12 volt) have their own connection to a
> > main set of buss bars so that each series strings contributes equally and is
> > charged equally.  This makes for more cable but an ultimately easier to
> > maintain installation.  It also means none of that rotating batteries in a
> > bank stuff.  I have a friend who does that also and it seems like a
> > hellacious waste of time.
> >
> > Another great thing about using a main buss bar setup is that you have no
> > limits on the number of series strings you can use and it makes it easier to
> > use more, smaller, batteries in large systems.  If you get a chance check
> > out a large telco installation and see how they do it.  They are often
> > connecting over 100 batteries to main busses.
> >
> > My original set of L-16s failed (at least one cell did) after only 7 years
> > of use and an excellent maintenance and charge regime.  I expected a lot
> > more out of them and if I had done it this way originally they'd still be
> > chugging along just fine.
> >
> > Telco installations change out their banks much more frequently than we in
> > the industry do and they were surprised at my 7 year battery life but in our
> > kind of installations and usage patterns longer life should be a bit issue
> > and I think eliminating parallel strings would extend battery bank life.
> >
> > Tom Elliot
> > Guffey Energy Works
> > http://www.wagonmaker.com
> >
> > ----- Original Message -----
> > From: "Allan Sindelar" <allan at positiveenergysolar.com>
> > To: <RE-wrenches at topica.com>
> > Sent: Thursday, September 06, 2001 2:22 PM
> > Subject: Re: Fw: Battery Bussing [RE-wrenches]
> >
> > >
> > > Re this part of my earlier post on battery interconnects:
> > > > The point of diagonal tapping is to minimize
> > > > the effect of cumulative interconnect and terminal resistance from
> > causing
> > > > one string to charge and discharge "sooner" than the others; you could
> > > also
> > > > say "more" or "less" than the other strings. The additional resistance
> > is
> > > > very slight with clean connections, but as the amperage can be very
> > high,
> > > > the resultant voltage drop from parallel string to parallel string can
> > be
> > > > significant. A consistent variation in voltage over time leads to
> > > > incremental premature failure of some strings--and I admit I'm not sure
> > if
> > > > it's the harder-working strings or the less-cycled strings that would
> > fail
> > > > first.
> > > Can anyone answer my question? How will an unevenly-matched battery bank
> > > deteriorate? Which cells will fail first, and why?
> > > Thank you...
> > > Allan at Pos E
> > >
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