Today's Message Index:
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1. 08:42 AM - Re: Internal Shorting of Batteries (Robert L. Nuckolls, III)
2. 09:58 AM - Re: Internal Shorting of Batteries (user9253)
3. 02:47 PM - Re: Re: Internal Shorting of Batteries (Robert L. Nuckolls, III)
4. 03:49 PM - Re: Internal Shorting of Batteries (user9253)
5. 08:38 PM - Z19RB question about wire length (haribole)
Message 1
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| Subject: | Re: Internal Shorting of Batteries |
At 01:00 PM 6/8/2015, you wrote:
Hi,
I see internal shorting of batteries mentioned often here. I have to
assume that the batteries in question are multi-cell lead acid
batteries. I am puzzled about how such a battery can and will short
internally to the extent that it disables the entire charging system.
Does it start with the melt down of one cell that leads to a high
current in other cells that subsequently melt down and the end result
is that the entire battery becomes one mass of lead?
Inquiring minds want to know,
On several occasions, I've asked comrades-in-slide-rules,
"If you wanted to at least encourage . . . if not FORCE
an SVLA battery cell to short, how would you do it?"
The question nearly always raises eyebrows . . . most
users of these devices and especially purveyors of
SVLA products have never considered the 'task' . . .
I can assert with a high degree of certainty that
the shorted-cell scenario begins with a combination of
depleted chemistry (would have failed cap-check a long
time ago) and/or abuse (extended periods of storage in
deep discharge or perhaps other abuses that cause vents
to open and moisture to be lost. This raises internal
resistance and exacerbates swelling of the active
material that puts insulators between plates at risk.
A shorted cell simply converts a battery from 12v to 10v . . .
and won't 'shut down an entire electrical system'.
As I've suggested for years and demonstrated numerous
times here on the List . . . tale-from-the-wild on
electrical systems failures are seldom, if ever,
teaching moments. MOST of the time there are correlations:
(shorted battery + stopped engine) that are
assumed to be cause and effect . . . assumptions
completely devoid of good analysis which digs to the
bottom of the pile where the simple-ideas are buried.
A battery artfully maintained to be (1) a good
cranking source, (2) a predictable energy source to
electro-whizzies useful for comfortable termination
of flight, (3) charged within pretty broad limits
and (4) never allowed to remain in a discharged state
for extended periods of time is NOT going to suffer
a shorted cell.
Batteries are like house plants. You have to take care
of them but for conditions not physically observable.
Leaves don't change colors, they don't droop
or fall off. This requires the user/maintainer to become
'intellectually one' with his/her battery.
Bob . . .
Message 2
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| Subject: | Re: Internal Shorting of Batteries |
Suppose that the attitude of an aircraft owner towards safety is somewhat lax.
He knows that one of his two batteries is weak, but does not replace it because
he still has one good one, connected in parallel per Z-19. He goes flying
and the weak battery develops a shorted cell. What symptoms would the pilot
observe? Low voltage? High alternator output current? Both? None?
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=443293#443293
Message 3
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| Subject: | Re: Internal Shorting of Batteries |
At 11:56 AM 6/9/2015, you wrote:
>
>Suppose that the attitude of an aircraft owner towards safety is
>somewhat lax. He knows that one of his two batteries is weak,
Non-quantified . . . . weak by how much? One passes cap-check
at 80% and the other doesn't? One is new and the other doesn't
pass cap-check. Has the 'weak' battery become compromised due
to service extended beyond practical utilization? I understand
the hypothetical . . . but anyone conducting such experiments
in with daylight under the wheels is . . . well . . .
> but does not replace it because he still has one good one,
> connected in parallel per Z-19. He goes flying and the weak
> battery develops a shorted cell. What symptoms would the pilot
> observe? Low voltage? High alternator output current? Both? None?
Assuming a relatively robust alternator, 40+ amps, probably
just a rise in alternator output. The remaining 'good' cells
would be receiving an over-charge voltage . . . something
akin to charging a perfectly good battery at 17 volts or about
2.88 volts per cell. Nothing earth shaking. Remaining cells are
at risk of venting and loosing water whereupon they stop
accepting a charge . . . and nothing happens.
Shorted cell will dump all it's remaining energy into
the short. The rate of energy conversion to heat sets
the tone of the symptoms . . . but if the cell is so
badly damaged that it's chemistry has swelled and
produces a short, then there might not be much energy
available to produce spectacular symptoms.
The fact that the accident airplane DID present with
a shorted cell raises lots of questions about that
battery's history and the quality of preventative
maintenance designed to prevent such occurances in
the first place. And what was the condition of the
'good' battery. Certainly no shorted cell but was
it flight worthy? And what was the alternator
doing all this time?
If he was flying without alternator and a single
battery that suffered a shorted cell, then yeah . . .
things could degrade in a hurry. Not necessarily
because of the shorted cell but because the battery
was so badly maintained that it suffered the short
with the remaining cells incapable of serviceable
performance. But a shorted cell battery paralleled with a
truly flight worthy battery and a working alternator
should not be an airplane crippling event.
Bob . . .
Message 4
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| Subject: | Re: Internal Shorting of Batteries |
Bob, Thanks for the response. Good information.
Joe
Do not archive
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=443316#443316
Message 5
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| Subject: | Z19RB question about wire length |
Hi Bob
The Z19RB shows a 2AWG cable from the main battery contactor to the starter contactor
and a seperate 6AWG wire from the starter contactor to the primary bus.
Can the primary bus not be connected directly to the main battery contator?
Thanks
Hari
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=443324#443324
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