On Mon, Nov 22, 2010 at 07:18:59PM -0800, Eric T. wrote:
> If a cell becomes 'shorted' when fully charged does the chemical reaction
> that normally produces voltage continue normally?
I'm sorry, but the chemical reaction doesn't produce voltage - it simply
reconverts lead sulfate and water back to lead and sulfuric acid.
Batteries do not "store" voltage as such; they're "factories", not
"warehouses".
However, to answer your question - no, the chemical reaction would not
proceed. In order for it to do so, the plates/solution would have to
have the charging current going across them; if the cell is shorted,
that does not happen, since the current takes the path of least
resistance - i.e., across the short rather than through the plates and
the solution.
> The symptoms you describe sound very much like an intermittently shorting
> cell. Thus the 100+ amps from the alternator and the resultant loading of
> the motor.
Actually, the 100A+ is a reasonable charging current for my setup - at
least initially. That works out to about 50A per pair, or ~20% for a
240A/h battery; not even particularly high, really.
Another thought experiment: assuming that the problem was indeed a cell
that was somehow shorted but could not be detected by measurement, what
would cause it to cycle? Better yet, what would cause it to cycle every
10 minutes, like clockwork? What would cause it to do so reliably, every
time it was charged, over a period of a year and more?
> If the cycle of the period was long enough to allow a near normal state of
> charge to be reached
That's not the case, I'm afraid. As I mentioned, the cycling started
almost immediately after the engine was turned on. This would happen
regardless of the state of charge.
(Incidentally, I've been running the engine since I fired it up to test
the WD-40 idea; more than an hour now. Not a single sign of cycling.
Ahhh... so nice. :)
> and then the motor was shut down the battery might only
> be getting shorted when the boat was underway. Maybe bow up a little moved
> some loose lead in the bottom of the battery.
Again, not the case. For the majority of the time that I had the
problem, the boat's been sitting. Although the reason it finally blew
out - interesting that it was both batteries in the pair at the same
time - may well have been what you say: I was in a rather rolly seaway
at the time, and there may have been enough PbSO[4] in the bottom of the
battery to short it. The other pair seems to be fine, though.
> Any way you look at it, you were suffering from an intermittent cell (or 2)
> shorting condition.
I'm afraid that I can't agree with your logic, but I do appreciate your
input.
> The circuit breaker concept would still have identified the bad battery/
> battery pair.
[smile] I guess we'll never know, at least for this battery pair. I
pulled it out today, demolished what remained of its (partly rotted)
plywood enclosure, cut off the remains of the rusty steel supports, and
started designing the platform for where the new batteries will go,
including the additional starter battery. I still haven't quite decided
whether to just dump and replace the other pair - it's coming up on the
end of its service life, presumably - but it'll get the same treatment
once I've rebuilt the starboard bank.
Doing this while living aboard isn't quite like sawing off the branch
you're sitting on... it's like sawing off and replacing that branch so
skillfully that the leaves on it never notice the loss of nutrients. :)
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