I've just come off a passage, and am sitting here in harbor repairing
stuff (that's what happens when you let things get away from you...
[sigh] In process of catching up now.) Interestingly, all the failures
are "good" ones, in the sense that I'm actually happy about them. Why?
Because every one of them, except for a stupid mistake that I made
(don't ask), is a _diagnostic_ failure: it finally and unmistakeably
tells me the answer to a problem that I've been chasing and couldn't
quite solve.
One of them, however, troubles me in its implications, so I'd like to
throw it to you folks on the list (perhaps I'm spurred by Norm's great
example of diesel troubleshootery... thank you, Norm! All the years I've
been working on diesels, and still learned something new.)
PROBLEMS (some seemingly unrelated until now):
1) The engine used to rev up and down, about 750RPM, on a ~10 minute
cycle while charging batteries. The start of this coincided with my
installing a new alternator, however, so after making some measurements
here and there, I gave up, thinking that perhaps it was normal. On the
ammeter, it would go to -12A or so, depending on what I had running at
the time, stay there for about 30 seconds to a minute, and then jump up
to over 100A and slowly taper off to about 60A - then repeat a few
minutes later.
2) The battery capacity had, in my perception, decreased significantly -
but hydrometer testing showed the batteries to be fine (I'll return to
this later), and even a 100A load tester, which I bought for this exact
purpose, showed all the batteries - tested individually - to be fine. I
even doubled the test period; yep, batteries still held up. However, two
things still bothered me: the time between full charge and the 50% point
had gone way down, to roughly half, although my usage patterns hadn't
changed - and firing up my little generator + charger (max 35A, 18-20A
nominal) when the batteries were low immediately made the system voltage
go above 13V. In my experience, that voltage should come up relatively
slowly, then essentially stop at 12-some volts, then follow the charge
curve up to 14.4V. A poor connection to the battery might have accounted
for that, but I tightened the heck out of it and checked for voltage
drops across the cables when charging at 100A or so - and they were all
low and reasonable.
3) Starting the engine, for the past year, has been the bane of my life.
OK, so I didn't have a starting battery (that's one of the changes I'm
making while I'm here), but - cripes, 4 Trojan T-125s have always been
more than enough to spin that starter like a mad spinning thing! I was
almost down to pulling the starter (a big job on this boat) and taking
it to a shop to be tested - but then, firing the engine up right after
the batteries had been charged worked just fine. 10% below top, and,
well, out came the can of ether. Grrrr...
SOLUTION (a.k.a. "diagnostic failure"):
At about 4 a.m., while in the middle of an offshore passage, I heard the
engine note change - maybe a 1500RPM drop - and a slight screeching
noise. This stopped after about 10 seconds. By that time, I had the
engine hatch open and was looking around... and it suddenly happened
again, at which point I saw a couple of sparks (!) shoot out of the
alternator. At the same moment, I noticed that the two starboard
batteries were somewhat swollen and their plasic cases had turned dull;
one of them actually looked like it had started to melt near one of the
terminals. I also noticed that the ammeter shot up to 100A+ during that
time, and back to -18A when it wound down. I immediately put the
throttle to idle (didn't quite want to leave the boat without way on -
there was no wind) dove down into the compartment and disconnected the
negative terminal to that battery pair. Then, I tried upping the engine
speed again.
"And suddenly, there was peace."
All of a sudden, the entire system was working just as it should have
been all along. The engine no longer cycled; the ammetter showed a
steady 6.7A (the batteries were charged to the max, so it was just float
current.) I was actually annoyed/bothered enough by this unexpected
change that I turned off the engine and immediately restarted it - and
it cranked right up, just as it always did on a full charge (but now it
was with only two of the Trojans in the circuit.) That is, taking those
two batteries out did not seem to reduce the system capacity.
And *that* is what I mean by a diagnostic failure. Overall, quite the
learning experience.
At this point, I've been sitting in this harbor for a day, working on
repairing things, making lists to make sure I don't miss anything, and
so on. Seems that the use capacity of the system has indeed been
reduced - I've left the computer on all day while going about my tasks,
and the system voltage is lower than it would have been when all four
batteries were in the circuit.
While I'm here, I'm going to replace all four batteries and add a
starting battery (and weld up some new battery boxes while I'm at it),
which should take care of all that. The frustrating, unanswered part of
this that remains is, why didn't any of the tests - either the regular
equalization and hydrometer testing or load testing - reveal a problem?
What was happening with that set of batteries that caused the engine to
cycle? Was there a cell or two that shorted as it warmed up, and
"unshorted" as it cooled off? Hard to believe - a hydro test would have
revealed that, I'd think.
Any suggestions, comments, or even pertinent thoughts to toss into the
pile would be highly welcome.
--
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