Today's Message Index:
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1. 08:37 AM - Re: Re: Dual Battery Question (Robert L. Nuckolls, III)
2. 09:49 AM - Re: Re: LiFe Battery (Robert L. Nuckolls, III)
3. 02:37 PM - Re: Thermocouple wire extension (Paul Eckenroth)
4. 02:58 PM - Thermocouples: grounded or ungrounded (Paul Eckenroth)
5. 09:37 PM - insinkerator garbage disposal reviews 2022 (JanomeDC2014)
6. 10:09 PM - Re: Thermocouples: grounded or ungrounded (Robert L. Nuckolls, III)
7. 10:40 PM - Pro Coinbase: A Quick Guide to Get Started (jackbuff)
Message 1
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| Subject: | Re: Dual Battery Question |
At 07:57 AM 7/2/2022, you wrote:
>
>Another way to look at it is that an electrical load will always
>draw current from the source with the highest voltage.
>After the voltage on one battery drops to that of the other battery,
>then current will be drawn from both batteries.
Let me hypothesize a particular condition.
Two batteries of different size are connected
in parallel. One cap-checked at 80%
of as-new capacity. I.e. ready for retirement.
The other is brand new.
Okay, put them into any system that offers
a constant voltage distribution bus set for
say 14.2 Volts (the magic number for regulator
set point for nearly 100 years). Assume independent
battery ammeters are installed.
Operate the system for time sufficient to
fully charge both batteries (recharge current
drops to an Amp or less). Now, shut off the
alternator. Leave normal system operating loads
on. Start your stopwatch. When voltage drops below
11 Volts, hit the stopwatch.
You will discover that battery only operations
track closely with energy measured as (Battery A x 0.8)
+ (Battery B x 1.00) = total stored energy.
The two batteries have no way to know that the
other battery exists. Both will ACCEPT maximum
energy as limited by condition of their chemistry.
Both batteries will DELIVER the same energy
that was confirmed by cap-check. Whether they
'shared' the load in any pre-ordained way is
immaterial. Each will function to limits
defined by its current physical condition.
Because they're connected in parallel, they
will arrive at 11.0 volts at the same time.
This is analogous to having an airplane with
two fuel tanks of unequal size and a fuel
selector valve having a BOTH option. The
engine will run until all fuel is exhausted
irrespective of where it came from.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Re: LiFe Battery |
>Others might say we already have that failure mode
>covered, so it is no big deal. OK for you guys.
How does one arrive at a conclusion of
'no big deal'? There are no suppositions
allowed in the conduct of an FMEA. Some things
are known by simple deduction . . . if that
wire becomes unhooked, some electro-whizzy
ceases to function.
But what about that battery disconnect
thing? There are a number of variables that
drive the system's ability to function.
Regulator design, alternator dynamics,
nature of operating loads. FEMA credit
for any particular failure cannot be
claimed without CONFIRMATION of a
condition for which there is no obvious
or first-hand knowledge.
>I do know of two pilots I have reason to trust who have described
>their own experiences with a total failure of a battery (not wiring,
>but an internal failure that isolated the battery electrically from
>the airplane) while in flight. While anecdotal, I suspect that gives
>us some reason to believe that such a failure has some real
>frequency in our airplanes. I have no idea how small this frequency
>is and admit that I know nothing of the rest of the maintenance
>state of these batteries.
It would have been interesting to do a
failure analysis on the subject batteries.
Exactly. Yes, there are cases where batteries
have gone open-circuit. Skip Koss (Concorde
battery guru) related several events to
me . . . post event teardown revealed
manufacturing defects. In his tenure with
Concorde, he could count those events
the fingers of one hand.
All cases occurred in aircraft that would
function alternator-only. The famous
(or infamous) split-rocker switch was
birthed out of a concern for alternator-
only operations. Generators would run
happily sans-battery but those alternators
were a new thing. I was a lowly tech-writer
back then an not privy to any testing
or perceptions of risk experienced by the
engineers. Nonetheless, whether or not it
was really necessary in all cases, the split
rocker became firmly embedded in aviation
zeitgeist for about 60 years.
A few years later, I was tasked to craft a
new regulator design for the Bonanzas and
Barons. I was astonished to read that Beech
expected an alternator to start up cold and
run sans-battery. Cold start? No battery?
Seems that these airplanes had independent
alternator and battery switches. There was
no prohibition in the POH for alternator-only
operations. Further, the alternators being
used at the time had residual field flux that
would permit start-up sans battery. That's
a long story!
>The two events occurred in flight. One was detected by an
>oscillating ammeter reading then the alternator field breaker
>tripped (or a reset was attempted), resulting in a total electrical
>failure. In the other case the alternator stayed online until shut
>off on the ground, and was found that the battery was off line. In
>both cases the airplanes were simple magneto fired engines being
>flown in VMC, and were flown to airports for safe landings, which
>only reinforces our training here that adequate backup really should
>be present for the failures we think are real.
To be sure, artful FMEA discovers and mitigates
real risks. Suppositions requiring verification
need to be tested. While doing the obligatory
test-area-flyoff with a new or recently modified
airplane, one is well advised to do the good
test pilot things and confirm/refine your
plan-A/plan-B operations.
>Adding failure modes to a system does increase total risk from the
>system (risk = severity * frequency) unless other parts of the
>system have been made more reliable in the same process. I suspect
>that internal battery connections are not much different in SVLA and
>in LiFe batteries, but I could be wrong.
The unfortunate thing about the dark-n-stormy-night
stories is that they very seldom achieve resolution
of root causes. The instances you've cited
cannot rise above anecdotal status without
investigation and discovery of root cause.
But they certainly contribute to builder/pilots
who have 'worries' but lack tools for mitigation.
This is the beauty of FMEA . . . we don't wrestle
with failure rates we only study outcome of flight
assuming that the failure will occur. It matters
not if MTBF on the thing is 1000 or 100 hours.
>As we are trained on AEC, the concerned designer can examine the
>failure modes and see to it that any failure mode does not result in
>a severe outcome nor unnecessarily raise total risk by checking for
>and perhaps adding suitable redundancy. That issue does not change,
>but I do suspect that batteries with added internal gadgets may well
>have higher likelihood of total failure. Be forewarned and design accordingly.
True . . . but artful design is limited by
a lack of information. The 'scientific method'
demands that every supposition be questioned.
The more folks participating in the conversation
the better.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 3
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| Subject: | Re: Thermocouple wire extension |
Thanks for the informative replies concerning the wire extensions. I was able
to locate thermocouples with 6" leads so I don't think that wire extensions will
be an issue.
Paul
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http://forums.matronics.com/viewtopic.php?p=507405#507405
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| Subject: | Thermocouples: grounded or ungrounded |
I would like advice on which thermocouples to use on my Revmaster engine, grounded
or ungrounded. The thermocouples I will buy have a flag surrounding the thermocouple
end with a hole for a bolt . The end will be bolted to the stator
using one of the attachment bolts so the outer surround will be grounded. The
thermocouple reader has continuity between the thermocouple ground and the
power ground. So the concern with using a grounded thermocouple is the potential
for a ground loop. The question is will any resultant ground loop be sufficient
to cause a audio problem. The ungrounded probe has a sheath of brass while
the grounded uses stainless which I think would be more robust. The grounded
also has quicker response to temperature change. So, help me avoid a coin
toss here. Thanks.
Paul
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507406#507406
Message 5
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| Subject: | insinkerator garbage disposal reviews 2022 |
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Message 6
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| Subject: | Re: Thermocouples: grounded or ungrounded |
At 04:58 PM 7/4/2022, you wrote:
>
>I would like advice on which thermocouples to use on my Revmaster
>engine, grounded or ungrounded. The thermocouples I will buy have a
>flag surrounding the thermocouple end with a hole for a bolt . The
>end will be bolted to the stator using one of the attachment bolts
>so the outer surround will be grounded. The thermocouple reader has
>continuity between the thermocouple ground and the power ground. So
>the concern with using a grounded thermocouple is the potential for
>a ground loop. The question is will any resultant ground loop be
>sufficient to cause a audio problem. The ungrounded probe has a
>sheath of brass while the grounded uses stainless which I think
>would be more robust. The grounded also has quicker response to
>temperature change. So, help me avoid a coin toss here.
What's your readout instrument? Does
it's installation manual suggest one
type over the other?
Insulated thermocouples are never 'bad'
but depending on the signal conditioning
circuitry of the display, the common mode
noises endemic to grounded thermocouples
may affect measurement quality.
Speed of response would not be an issue
here. The ground loop would not be a potential
problem with other avionics, just the
temperature display.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 7
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