Today's Message Index:
----------------------
1. 07:58 AM - Re: Stuck starter contactor . . . (Robert L. Nuckolls, III)
2. 10:42 AM - Question on switch wiring ()
3. 12:09 PM - Re: Re: Starter engaged light, was Starter and contactor (John Burnaby)
4. 12:09 PM - Re: Question on switch wiring (Robert L. Nuckolls, III)
5. 01:51 PM - Re: Re: Starter engaged light, was Starter and contactor (BobsV35B@aol.com)
6. 02:47 PM - Re: Question on switch wiring ()
7. 03:31 PM - Re: Question on switch wiring (Robert L. Nuckolls, III)
8. 08:28 PM - GNS 430 no comm (Brooks Wolfe)
9. 09:02 PM - Re: Starter engaged light (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Stuck starter contactor . . . |
At 02:00 PM 2/7/2010, you wrote:
><aerobubba@earthlink.net>
>
>Hi Bob-
>
>I was able to find this:
>
>http://www.ntsb.gov/ntsb/GenPDF.asp?id=FTW90DRA10&rpt=fi
>
>Some of the physical description of the airframe may be a bit misleading,
>but teh fundamental process seems to be accurate.
Hmmmm . . . interesting. I'm wondering how the operator 'knew'
that the starter contactor had stuck when the FAA inspection
could not identify a source of the fire.
If somebody 'knew' the starter contactor was stuck or
still energized, I'm mystified as to why the aircraft
ever left the parking place.
A starter feeder should have been protected from destructive
overload by some means . . . c/b, current limiter, etc.
Since the fire apparently didn't originate under the cowl
(from a self-destructing starter) then components that failed
to the point of starting a fire had to be things like
unprotected wires, failed insulation, failed contactor, etc.
It's quite possible that the starter contactor on this
airplane looked something like this when new . . .
http://www.aeroelectric.com/Pictures/Contactors/6041_Contactor.jpg
and may well have degenerated to something like this
when failed . . .
http://aeroelectric.com/Pictures/Failures/6041_Contactor_Failure.jpg
A contactor that is "stuck" is generally turned on 'hard'
and is not generating a lot of heat. On the other hand,
this style of contactor (mounted in the wheel-well j-box?)
needs to be inspected (note removable cover) periodically
for degraded contacts or signs of heating off the moving
contact carrier. When these contactors experience a high-
resistance overheat, they can fail rather spectacularly.
The failed contactor I showed came out of a j-box that
routes power to a 130A a/c compressor motor. These contactors
have a relatively high failure rate . . . but being
inside a metal enclosure keeps things from getting
out of hand.
It's also interesting that re-ignition was attributed to
"hot" metal. Things that ignite from hot metal are liquids
with easily ignited vapors . . . it doesn't sound like this
fire went on long enough and with sufficient fuel to heat
aluminum structure or steel landing gear parts to the point
where they become re-ignition hazards. On the other hand,
things that are combustible within the j-box may have
been supporting some glowing coals and been shielded from
the extinguisher. . . or it may be that power was still
present in the j-box.
In any case, it seems unlikely that the real chain of
events for this unfortunate demise of an otherwise
perfectly good airplane are known. Given its age,
it was certainly subject to the effects of time on
electrical system materials that were the best-we-knew-
how-to-do in 1940. One needs to spend an extra effort
to track these materials for continued airworthiness.
Calling this one a "stuck starter contactor" incident
is a WAG.
Bob . . .
Message 2
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| Subject: | Question on switch wiring |
I bought a SPST 12 volt lighted switch from digi-key which I would like
to use as a fuel pump indicator switch.
SWITCH TOGGLE ILLUM SPST 20A GRN
SCHED B: 853650
ECCN: EAR99
LEAD: LEAD ALL
ROHS:
ROHS NONC
CH652-ND
Assumptions: My fuel pump runs via a relay switch (20 amp B & C S704-1
job).
Question: The switch is provided with a third 1/4" tab on the top (on
position) of the switch. Normal use is to add a jumper from the on
position to the top tab to illuminate light when turned on.
The switch works great when used with standard power/ground connection,
e.g. landing light. When I use it in conjunction with the relay switch,
the light comes on when the switch is in the off position.
Ideas appreciated.
Glenn
Message 3
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| Subject: | Re: RE: Starter engaged light, was Starter and contactor |
Hello Old Bob,
Thanks for giving this some thought.
The purpose of the lamp going on when I depress the starter is as a test
of the lamp.
John
Message 4
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| Subject: | Re: Question on switch wiring |
At 12:33 PM 2/8/2010, you wrote:
>I bought a SPST 12 volt lighted switch from digi-key which I would
>like to use as a fuel pump indicator switch.
>
>SWITCH TOGGLE ILLUM SPST 20A GRN
>SCHED B: 853650
>ECCN: EAR99
>LEAD: LEAD ALL
>ROHS:
>ROHS NONC
>CH652-ND
>
>Assumptions: My fuel pump runs via a relay switch (20 amp B & C S704-1 job).
>
>
>Question: The switch is provided with a third 1/4" tab on the top
>(on position) of the switch. Normal use is to add a jumper from the
>on position to the top tab to illuminate light when turned on.
>
>The switch works great when used with standard power/ground
>connection, e.g. landing light. When I use it in conjunction with
>the relay switch, the light comes on when the switch is in the off position.
First, why the relay? The switch is rated for 20A . . .
probably enough to control the pump directly.
The third terminal is for grounding the internal LED/Resistor
combination so that the lamp lights when the switch is closed.
For this switch to be "relay augmented" you'll have to wire
the pump as shown here:
Emacs!
. . . and this is not a very elegant approach. Unfortunately
the switch you have (like most of it's cousins) doesn't bring
BOTH lamp leads out for independent excitation of the lamp.
One end of the lamp is tied to the "power output" terminal
in the assumption that one ALWAYS uses the switch barefoot
to control power in the +supply lead.
Bob . . .
Message 5
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| Subject: | Re: RE: Starter engaged light, was Starter and contactor |
Good Afternoon John,
That sounds good, but if the starter works, won't that give you a check of
the lamp?
The way Beech handled the test function was to present a current from a
dedicated lamp test switch to the starter warning lamp. To keep the lamp
current from trying to drive the starter, they added a diode that only allows
current from the starter to the light and blocks the flow from the lamp to
the starter.
That way we can check the light without closing the starter relay
I did the same thing when I wired my warning lights. Since my factory
warning lights were wired a bit differently, I used a double pole, single throw,
switch to isolate the starter warning light circuit from the other warning
circuits. Works great!
Happy Skies,
Old Bob
In a message dated 2/8/2010 2:11:39 P.M. Central Standard Time,
jonlaury@impulse.net writes:
Hello Old Bob,
Thanks for giving this some thought.
The purpose of the lamp going on when I depress the starter is as a test
of the lamp.
John
Message 6
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| Subject: | Question on switch wiring |
Thanks Bob,
Yes, the switch is overkill (or in reality, perhaps the relay is), but
the switch matches the others if underutilized. I did not look hard and
long enough for a 1 amp or lower with the same size/style. The pump
shipped with 12 ga. wire leads and I really did not want to run a 12 ga.
wire to the switch, thus the relay. The FP is rated for 7-10 amps.
The FP is on the checklist but it's one of the easy to forget items that
sometimes gets left on or off. Therefore an pilot light of some kind is
a nice feature.
Glenn E. Long
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Robert L. Nuckolls, III
Sent: Monday, February 08, 2010 3:02 PM
Subject: Re: AeroElectric-List: Question on switch wiring
At 12:33 PM 2/8/2010, you wrote:
I bought a SPST 12 volt lighted switch from digi-key which I would like
to use as a fuel pump indicator switch.
SWITCH TOGGLE ILLUM SPST 20A GRN
SCHED B: 853650
ECCN: EAR99
LEAD: LEAD ALL
ROHS:
ROHS NONC
CH652-ND
Assumptions: My fuel pump runs via a relay switch (20 amp B & C S704-1
job).
Question: The switch is provided with a third 1/4" tab on the top (on
position) of the switch. Normal use is to add a jumper from the on
position to the top tab to illuminate light when turned on.
The switch works great when used with standard power/ground connection,
e.g. landing light. When I use it in conjunction with the relay switch,
the light comes on when the switch is in the off position.
First, why the relay? The switch is rated for 20A . . .
probably enough to control the pump directly.
The third terminal is for grounding the internal LED/Resistor
combination so that the lamp lights when the switch is closed.
For this switch to be "relay augmented" you'll have to wire
the pump as shown here:
. . . and this is not a very elegant approach. Unfortunately
the switch you have (like most of it's cousins) doesn't bring
BOTH lamp leads out for independent excitation of the lamp.
One end of the lamp is tied to the "power output" terminal
in the assumption that one ALWAYS uses the switch barefoot
to control power in the +supply lead.
Bob . . .
Message 7
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| Subject: | Question on switch wiring |
At 04:44 PM 2/8/2010, you wrote:
>Thanks Bob,
>
>Yes, the switch is overkill (or in reality, perhaps the relay is),
>but the switch matches the others if underutilized. I did not look
>hard and long enough for a 1 amp or lower with the same size/style.
>The pump shipped with 12 ga. wire leads and I really did not want to
>run a 12 ga. wire to the switch, thus the relay. The FP is rated for 7-10 amps.
Do you have real world current values for what
the pump needs in normal operations? Is this a
flight pump or an aux/boost pump that is seldom
used/needed? 7A (100 watts) is a LOT of power
for the pumping of fuel. While your pump may be
capable of drawing that much current at rated
maximum volume and pressure, I've found that
most real-world installations are much less
demanding.
I think it likely that you can simply wire
the pump system with 16 awg wires through
the un-aided switch protected by a 10A
fuse/breaker. But you need to get some
real numbers from somebody who's flying
the system or the folks who engineered
the system and have numbers.
Alternatively, wire it all with 14AWG,
15A breaker and leave the relay out. MUCH
simpler and more reliable. The built in
lamp can be used as defined in original
design goals.
Bob. . .
Message 8
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I'm just wrapping up my 430 installation, and was hoping to hear somethin
g
(anything) through my headphones.. Nada.
I have a used GNS 430 from Wentworth installed. New Sigtronics intercom
(at
least *this* works). The Garmin is plugged into the intercom with the 50
0
Ohm Audio Hi output. The 500 Ohm Audio Lo is grounded. The Garmin insta
ll
manual shows a paired "Audio 1" Hi and Low on P4001, but I can't find any
other use for it mentioned anywhere, so it's not connected.
Pressing the squelch button also makes no noise, as I would have expected
=2E
One issue that has me concerned is an incident in my hangar a few weeks a
go
-- A particularly long and bizarre chain of events led to the GNS430
dropping from table to concrete floor. Not far, but enough to give the c
ase
a tiny bit of wrinkle at the back end. While the unit seems to power up
just fine, I can't help but wonder if there might have been some physical
damage, causing this inability to get audio.
Brooks
Message 9
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| Subject: | Re: Starter engaged light |
At 02:01 PM 2/8/2010, you wrote:
>Hello Old Bob,
>
>Thanks for giving this some thought.
>
>The purpose of the lamp going on when I depress the starter is as a
>test of the lamp.
The rule of thumb for lights that routinely illuminate
during the process of getting ready for flight don't need
press-to-test features. For example, the low volts warning
light should be flashing at you before the engine starts
and go out when the alternator comes on line. The starter
engaged light should be illuminated while you're cranking
and go out when you release the button. The criteria for
"pre-flight-detectable" are satisfied.
Bob . . .
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