Battery Bussing [RE-wrenches]

[Joel Davidson]

Now, if inverter manufacturers were only as smart as Windy...
(but then I would be asking for too much)

"Windy Dankoff, Dankoff Solar" wrote:

> >Consider this. A battery bank has 8 each T-105 batteries from the same
> >production batch with the same specific gravity .....      .........
> >......   under what conditions will interconnect current flow differ?
>
> This is an aside, related to the discussion.
>
> Many of us have pondered over the years of observing premature cell
> failures in multi-string battery banks. No matter how well you
> attempt to establish symmetry between two or more parallal strings,
> you should expect a greater chance of premature cell failure than a
> single-string battery bank.
>
> One of my old customers has batteries in an insulated box outdoors.
> They were a 5-parallel string at 24V. Three times in 14 years, the
> batteries located on the outside of the pack failed first. I had to
> conclude that it was temperature differences that were the culprit.
> The outer units were less temp-stable than the inner ones. I've heard
> of other cases where inner cells fail first because they run hotter.
> (One lesson is to leave space between batteries for air circulation.)
>
> A more common culprit is terminal corrosion. A slight added
> resistance in one string, from one or more slightly corroded
> contacts, will cause less current to flow through that entire string
> and thus more to flow in the other(s). Yet, the charge controller
> responds to only one voltage reading, being the net of the parallel
> bank. This can result in uneven states of charge and failure of one
> string to finish-charge, especially with an RE charging source.
>
> Big cells/single strings are the only battery banks that I believe
> are likely to live to their full potential, but we have to do what we
> can with customers and their budgets.  Use your favorite goop
> (vaseline or whatever) on terminal parts BEFORE assembly. An annual
> maintenance check should include comparing current between battery
> strings under a high-current charge or discharge condition, using a
> clamp-on ammeter.
>
> Windy
>
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