Today's Message Index:
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1. 08:54 AM - Re: Re: B lead circuit breaker (Robert L. Nuckolls, III)
2. 10:20 AM - Re: Re: B lead circuit breaker (FLYaDIVE)
3. 07:15 PM - Re: Re: B lead circuit breaker (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: B lead circuit breaker |
At 09:21 PM 10/9/2018, you wrote:
>
>The vast majority of electrical problems are due to bad
>connections. Check every connection in the charging circuit and in
>the strobe circuit. Take apart connectors, clean them and put them
>back together.
I disagree . . . I can recall only one 'degraded
connection' that was so elusive that it took several
'teams' over a month to chase down . . . but only
because it was so buried in the hardware (pushed
back pin in a pressure bulkhead connector) and
only manifested at low temperatures requiring a
test flight to 41,000 feet to cool the thing
off before we could even begin to look.
All other bad connection manifested with rather
gross symptoms like those we've discussed here
on the List concerning switch failures, burned
terminals, etc.
This problem would be easy to 'divide and
conquer' if you had a data acquisition system
you could clip to the bus and watch for
transients that might be antagonizing the
ov protection system on the alternator.
Assuming that the design dynamics for the ov
sensor are correct, an ov trip can originate
from one source only . . . the alternator.
A too high output from the alternator suggests
that the regulator has lost control due
to failure.
On thing you might try is to replace the 5A
breaker. This will help you decide if
the 5A breaker has (1) degraded with age
(rare but not unheard of) but is indeed being
'crow barred' open by a triggering of the
alternator's ov protection.
Does this alternator have an externally mounted
ov module? Early versions of the PP
machines did. It was a plastic box mounted
to the back of the alternator. A wire ran
into the alternator through a cooling hole.
Bob . . .
Message 2
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Subject: | Re: B lead circuit breaker |
On Wednesday, October 10, 2018, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 09:21 PM 10/9/2018, you wrote:
>
>
> The vast majority of electrical problems are due to bad connections.
> Check every connection in the charging circuit and in the strobe circuit.
> Take apart connectors, clean them and put them back together.
>
>
> I disagree . . .
>
Barry - I have to TOTALLY AGREE!
I do aircraft repairs weekly and the number of non working, lights,
intercoms and antennas that come into the hanger almost weekly is probably
way more than all the fellows here on the list see in a their life time...
Just had one last week Friday. If I had to put a number to it, 90% were
due to bad contacts due to corrosion. You can not visually inspect a
ground connection. It must be undone, wire brushed, NEW star lock washers
replaced and tightened securely... Yes, tightened even beyond specs.
Then, you can spray some chromate paint over the connection for a bit more
corrosion protection.
Wait a second Bob, aren=99t you the one the advocates the use of Diel
ectric
Grease on connections just to prevent corrosion?
I agree with the Dielectric Grease idea. Been doing it for decades.
Talking about tracing CRAZY electrical issues. TWICE, I have come across
bulbs that check good on continuity yet DO NOT LIGHT!
No, it was not corrosion, not this time. Care to take a SWAG at it?
I would bet the airport that no one would guess.
The failed bulbs were Marker Nav Light Bulbs. =94- hint, hint.
On a 12 VDC system the bulbs are really a 24 VDC bulb. And on a 24 VDC
system, yes you guessed it, they are really a 48 VDC BULB. It is done that
way to extend the life of the bulb. Vibration is your enemy as well as
weather.
So, what happens is the filament breaks but stays in contact with the
=98post=99. I have seen the problem happen twice and both time
s it was at the
mounting post of the filament.
The low current of the DMM checks the bulb as good. But when operational
voltage and CURRENT is applied the break heats up and opens.
My Rule: Do not believe the DMM, apply a separate and full voltage &
current to the bulb. If it lights, LQQK elsewhere for the problem.
Good time to Check Grounds.
Barry
--
Barry
"Chop'd Liver"
If you wash your hands before you go to the bathroom you may have the
makings of a Crew Chief.
Message 3
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Subject: | Re: B lead circuit breaker |
>If I had to put a number to it, 90% were due to bad contacts due to
corrosion.
>You can not visually inspect a ground
>connection. It must be undone, wire brushed,
>NEW star lock washers replaced and tightened securely... Yes, tightened
even
>beyond specs. Then, you can spray some chromate paint over the connection
>for a bit more corrosion protection.
I've never seen this kind of effort expended on a ground
to the airframe. A bizjet has HUNDREDS of such grounds.
All are made up with flat and clean faying surfaces assembled
to the proper compression specs (torque). The natural
crush that occurs in the terminal creates the gas-tight
interface that excludes moisture+air; hence corrosion.
A ground connection can look pretty bad on the surface
of components but still maintain electrical integrity
if assemble properly in the first place.
>Wait a second Bob, aren't you the one the advocates the use of
>Dielectric Grease on connections just to prevent corrosion?
>I agree with the Dielectric Grease idea. Been doing it for decades.
It sure doesn't hurt but recall that the purpose of
the grease is to fill voids in the surfaces that did
not get closed when the joint was made up in the
first place. A void full of grease won't admit
moisture+air.
Here's a ground cluster in the nose of a Beechjet
http://aeroelectric.com/Pictures/Grounding/MVC-699X.JPG
Bright? yes. Clean? yes. Grease? No, Overspray? No.
This installation was in s/n RK24, an experimental
flight test aircraft which was 20+ years old at the time.
If the airplane is operated in a particularly
wicked environs, like the sea coast, the surfaces
on and around such joints will enjoy protection
from accelerated corrosion but if the joint was
properly made up in the first place, the service
life of the joint is probably not extended much.
>Talking about tracing CRAZY electrical issues. TWICE, I have come
>across bulbs that check good on continuity yet DO NOT LIGHT!
>No, it was not corrosion, not this time. Care to take a SWAG at it?
>I would bet the airport that no one would guess.
>The failed bulbs were Marker Nav Light Bulbs. hint, hint.
>On a 12 VDC system the bulbs are reaally a 24 VDC bulb.
>And on a 24 VDC system, yes you guessed it, they are really
>a 48 VDC BULB. It is done that way to extend the life of
>the bulb.
Where is this idea published? In chapter 12 of the
'Connection I speak to the relationship between
applied voltage and life/current/intensity of
the typical incandescent bulb.
Emacs!
For every ~5% reduction in voltage from the
bulb's design center, life approximately doubles.
So in your hypothetical 50% drop from design
center, bulb life goes up HUNDREDS of times.
At the same time, light output drops to about
10% of the design center . . . and in fact
is quite redish in color.
Emacs!
An exemplar navigation lamp is in the 21-26watt class
and operates at a color temperature strongly suggesting
a design optimized for light output/color . . . and NOT
de rated for service life.
> Vibration is your enemy as well as weather.
Also discussed in Chapter 12. In fact, we suggested a
keep-warm circuit to hold incandescent lamps at about
10% of nominal operating voltage when turned OFF. This
keeps the tungsten filament ABOVE the brittle/ductile
transition temperature making the bulb more resistant
to both vibration and warm-up shock when turned ON.
Yeah, the air around the airplane can carry a host
of antagonistic stressed into vulnerable locations,
like the metal parts of a lamp socket. Dielectric grease
on the shell and tip of a lamp base is a good thing.
>So, what happens is the filament breaks but stays in contact with
>the =98post=99.=C2 I have seen the problem happen twice and
both
>times it was at the mounting post of the filament.
>The low current of the DMM checks the bulb as good.=C2 But when
>operational voltage and CURRENT is applied the break heats up and opens.
So does the bulb come back on when it cools only to
immediately go dark again?
Bob . . .
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