Today's Message Index:
----------------------
1. 04:01 AM - Intercom to Radio Wiring (Ron Walker)
2. 04:54 AM - Re: Intercom to Radio Wiring (Jared Yates)
3. 06:42 AM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III)
4. 06:49 AM - Re: Intercom to Radio Wiring (Robert L. Nuckolls, III)
5. 07:18 AM - Re: Intercom to Radio Wiring (Tim Andres)
6. 08:39 AM - Re: Intercom to Radio Wiring (Sprocket)
7. 08:41 AM - Re: Alternative battery technologies . . . (B Tomm)
8. 08:41 AM - Re: Alternative battery technologies . . . (B Tomm)
9. 12:26 PM - Re: Intercom to Radio Wiring (Robert L. Nuckolls, III)
10. 12:34 PM - Re: Alternative battery technologies . . . (Robert L. Nuckolls, III)
11. 03:52 PM - Re: How do I prevent starter engaged LED from failing? (eschlanser)
12. 05:21 PM - Re: trim indicator buffer (D L Josephson)
13. 06:35 PM - Re: Re: How do I prevent starter engaged LED from failing? (Robert L. Nuckolls, III)
Message 1
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Subject: | Intercom to Radio Wiring |
This is a question regarding technique rather than specific equipment.
I'm about to start my third try to wire my 4 place intercom to my radio.
My goal is to get all the wires at the connector to actually look
semi-decent and not the fat-collection-of-rats-nest bundle that has
resulted from my first two attempts. It CAN be done, I've seen it. I
just don't know any of the secrets ... wondering what they are ?
Is there a technique or process/pattern to this ? With all the wires
coming in - 3 from each headset connection, 2 additional pair for ptt,
power and then the connections to the radio - there's gotta be something
I'm missing because I've seen it done nicely ...
I checked the aeroconnections site and used a couple of the tricks
there, but they really didn't get me very far.
Any advice other than hiring the task out ?
Thanks
--Ron
Message 2
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Subject: | Re: Intercom to Radio Wiring |
Hi Ron, I ran into the same problem. This was my solution to combining the
left audio, right audio, and ground signals for the right front and rear
passengers:
http://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg
I brought all of the incoming wires into a regular machined-pin 25-pin
d-sub connector. Then I used an opposite-sex solder d-sub to make the one
shown in the picture. I soldered a little piece of wire across the
appropriate pins. I think in the final configuration I stripped a 5/8" or
so long piece off of the end of a longer wire, soldered the stripped part
across the cups, and then connected the other end of that wire to the
intercom input. This would be an option if you run out of pins. I didn't
take a picture of the final configuration, but I think I did run short of
pins on at least one of them. When it was done I potted the whole thing to
keep it from shorting.
As for the ptt and the rest, my intercom might have been a little bit
different. I had an input pin for each front seat occupant, so that when
the right front keys, only his mic goes to the radio, etc. Mine were also
only single wires- one end went to the intercom, then the other end went to
local ground after passing through the switch.
Another problem was turning big shields into wires that I could crimp into
machined pins. I used crimped on terminals of various types. If I had a
large size change, I might crimp a yellow "handshake" connector on the big
clump of shields, and then crimp a red one onto a single 22-gauge piece of
wire that went to the machined pin. Sometimes I would bring two large
clumps of shields into each end of a yellow splice, then stick a 22-gauge
wire in one of the ends along with the shields.
I'll not imply that the above is necessarily the best way- my mission
wasn't to win any awards, but just to have a reliable mode of
transportation- but so far it is all working just fine. In the end, I
wouldn't say it's a rat's nest (though some might), but perhaps more of a
bird's nest.
On Mon, May 5, 2014 at 6:59 AM, Ron Walker <n520tx@gmail.com> wrote:
>
> This is a question regarding technique rather than specific equipment.
>
> I'm about to start my third try to wire my 4 place intercom to my radio.
> My goal is to get all the wires at the connector to actually look
> semi-decent and not the fat-collection-of-rats-nest bundle that has
> resulted from my first two attempts. It CAN be done, I've seen it. I
> just don't know any of the secrets ... wondering what they are ?
>
> Is there a technique or process/pattern to this ? With all the wires
> coming in - 3 from each headset connection, 2 additional pair for ptt,
> power and then the connections to the radio - there's gotta be something
> I'm missing because I've seen it done nicely ...
>
> I checked the aeroconnections site and used a couple of the tricks
> there, but they really didn't get me very far.
>
> Any advice other than hiring the task out ?
>
> Thanks
>
> --Ron
>
>
Message 3
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Subject: | Re: How do I prevent starter engaged LED from |
failing?
At 12:07 AM 5/5/2014, you wrote:
>I have had an LED indicate "Gear in transit" for 10 years with no
>protection....
>
>Best...
>
Thanks Bob . . .I'm not surprised. Folks who don't
work up to their eyeballs in TC aviation have
some difficult grasping the significance of
the hat-dances we do to get a part holy-watered.
The control of emitted stresses and demonstrating
immunity to external stresses under DO160/MilSTD704
is a kind of 99+ percentile hedge against conditions
known to manifest in at least some situations.
There's an alternator regulator on Bonanzas and
Barons that NEVER saw the lights of a DO160
test lab. It was added to the airplane's TC
WWWAAaaayy back when . . . before Part 23
aviation got so tightly wrapped up in mandated
hat-dancing.
If the airframe manufacturer accomplished enough
testing on the airplane to demonstrate 99+
percent 'suitability to task' then the addition
was allowed.
This particular design has a vulnerability
to certain noises from brush bounce in alternators
that causes the OV protection to trip. Further,
there's a 1= percent probability that new
alternators of this vintage will exhibit
the noise.
Ever so often, on at least 3 occasions I was
involved in over the last 30 years, that
1 percent minus stress comes together with
a 1 percent minus vulnerability and you get
a rash of airplanes that can't be delivered
because the alternator(s) keep tripping off
line under certain conditions.
The obvious fix is to put a fully qualified,
regulator on. But with production
volumes so low, nobody is very excited about
launching in to a new design program . . .
even when I have the design already done!
So, a suitable 'band-aid' not unlike those
things we've resorted to for over a century
has erected a reasonable wall of separation
between the waring factions and all is now
serene in the universe.
What does this have to do with adding protection
to the LED indicators attached directly to
a bus-driven source?
Simply this: The probability that any given
led is going to get toasted by one of the
stresses predicted by DO160/MilSTD704 is
very low. But as experienced practitioners
of the design arts, probability does not
figure into robustness of a design.
DO160/MilSTD704 is not a probability
game, it's a robustness game.
As a matter of design goals, I recommend the diode
as depicted in the drawings. But as Bob (and no doubt
many others) has observed . . . Gee, been
doing this for years without the protection
and I've had no problems.
The lesson-learned here has nothing to
do with holding the LED-toasting dragons
at bay and leaving the pilot unaware of
a stuck contactor . . . it's about ROBUST
design that chooses to ignore low probability
events and design for worst case.
Here's where your failure mode effects analysis
tools come into play. Suppose the LED DOES
get toasted. How long will it take you to
discover that fact and what is the probability
that LED failure will be co-incident with
an LED-toasting dragon?
If your checklist for engine cranking
includes something like:
STARTER - Engage. Observe STARTER ENGAGED
light is illuminated.
When engine starts
STARTER - Disengage. Observe START ENGAGED
light is dark.
. . . and you're covered with the same
blanket that has enveloped many other
'unprotected' installations.
DO160/MilSTD704 robustness is but one of
many tools we can apply to reduction
of risk. Knowledge and understanding is
the most powerful of those tools.
Bob . . .
Message 4
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Subject: | Re: Intercom to Radio Wiring |
At 06:51 AM 5/5/2014, you wrote:
>Hi Ron, I ran into the same problem. =C2 This was
>my solution to combining the left audio, right
>audio, and ground signals for the right front and rear passengers:
>
><http://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg>htt
p://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg
Looks like a good lick to me . . .
One of my pet peeves concerning the design of many
appliances is the dearth of pin-outs necessary
for graceful termination of wires in a common
installation.
Many times it's not a big deal to the next
larger size d-sub connector on the product to
assist the installer in termination of multiple
wires to grounds or paralleled loads.
Mr. Yates' solution is a rational and robust
solution to your installation problem . . .
perhaps a bit more 'bulk' than soldering
them into heat-shrink covered lumps . . . but
certainly more elegant in appearance and
maintainability.
Bob . . .
Message 5
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Subject: | Re: Intercom to Radio Wiring |
If your using Bob's technique to terminate the shields, make the pig tails long
enough so they are just outside the hood of the D-sub. The short length of un-shielded
wire should not cause any problem. You can also daisy chain all the
grounds into the minimum required number before it enters the hood. Otherwise
there may be too much bulk to get the hood on.
Tim
> On May 5, 2014, at 3:59 AM, Ron Walker <n520tx@gmail.com> wrote:
>
>
> This is a question regarding technique rather than specific equipment.
>
> I'm about to start my third try to wire my 4 place intercom to my radio.
> My goal is to get all the wires at the connector to actually look
> semi-decent and not the fat-collection-of-rats-nest bundle that has
> resulted from my first two attempts. It CAN be done, I've seen it. I
> just don't know any of the secrets ... wondering what they are ?
>
> Is there a technique or process/pattern to this ? With all the wires
> coming in - 3 from each headset connection, 2 additional pair for ptt,
> power and then the connections to the radio - there's gotta be something
> I'm missing because I've seen it done nicely ...
>
> I checked the aeroconnections site and used a couple of the tricks
> there, but they really didn't get me very far.
>
> Any advice other than hiring the task out ?
>
> Thanks
>
> --Ron
>
>
>
>
>
>
Message 6
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|
Subject: | Re: Intercom to Radio Wiring |
I totally agree. One of the benefits of packaging the audio products that I
have developed in d-sub backshells is that there are a lot more pins availa
ble for grounds. In fact, I usually reserve a whole row of pins for ground,
whether they are needed or not.
This simplifies installation and saves time and money.
The availability of a whole class of through-hole components that have a max
imum height sized to fit in these packages makes even small volume designs f
easible without having to resort to surface mount devices.
Cheers,
Vern Little
Vx Aviation
==========================
==========================
Sent from my iThing. It is responsible for all gramma and typo terrors.
> On May 5, 2014, at 6:46 AM, "Robert L. Nuckolls, III" <nuckolls.bob@aeroel
ectric.com> wrote:
>
> At 06:51 AM 5/5/2014, you wrote:
>> Hi Ron, I ran into the same problem. =C3=82 This was my solution to combi
ning the left audio, right audio, and ground signals for the right front and
rear passengers:
>>
>> http://jaredyates.com/bearhawk/wp-content/uploads/2011/06/P1010720.jpg
>
> Looks like a good lick to me . . .
>
> One of my pet peeves concerning the design of many
> appliances is the dearth of pin-outs necessary
> for graceful termination of wires in a common
> installation.
>
> Many times it's not a big deal to the next
> larger size d-sub connector on the product to
> assist the installer in termination of multiple
> wires to grounds or paralleled loads.
>
> Mr. Yates' solution is a rational and robust
> solution to your installation problem . . .
> perhaps a bit more 'bulk' than soldering
> them into heat-shrink covered lumps . . . but
> certainly more elegant in appearance and
> maintainability.
>
>
> Bob . . .
>
>
>
3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3
D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
Message 7
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Subject: | Alternative battery technologies . . . |
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Sunday, May 04, 2014 9:16 AM
Subject: AeroElectric-List: Alternative battery technologies . . .
The battery-buzz these days is focused on lithium . . .
and for good reason. They ARE lighter yet retain many
of the desirable qualities of a lead=acid battery
for engine cranking.
Another rising-star wannabe is a product by FireFly
Energy . . . an svrla battery that features a carbon foam
plate material with a advertised gee-whiz feature
of offering a lower weight replacement for the legacy
lead grids.
This is not a 'new' idea . . . I think the patents
have already been renewed once . . . but only recently
have potential consumers of this technology been able
to put their hands on real product.
http://tinyurl.com/kfzsj5p
This is a group 31 battery (read BIG) that weighed in
at 73.6 pounds and presented and open circuit voltage
of 13.09V at ~20C right out of the box. A 600A load
drops voltage to 9.30V. Therefor (13.1 - 9.30)/600 = 0.00633 Ohms
internal resistance. Okay, how about available capacity
under various loads?
Emacs!
When discharged at 5A, it took 20+ hours to take it down
to 10.0V. So one could say that the capacity of this
battery at 20-hour rate is over 100aH. Not bad for a
75# battery.
At higher rates, we see that the capacity drops off pretty
much like all other batteries . . . the 50A discharge
delivered only 80Ah . . . one might extrapolate from this
data that the battery's one-hour rate (as an aircraft battery
would clock in at about 65Ah. Again, not bad for a 12V,
75# battery.
>From the data taken, we can estimate that a 24V cousin
of the same active materials would be slightly more than
the 75# due to addition of extra cell walls. The internal
resistance would go up by a factor of 4. Twice as many
half-sized cells in series.
A 4x increase in internal resistance would have a profound
effect on delivered capacity at the higher rates. In other
words, when sliced up and reassembled as a 24V battery, this
device would not be able to deliver 1/2 the one-hour rate
deduced above . . . it's more likely to be down to something
like 20Ah or so.
I'm going to see if I can model the 24v version and do
some predicted plots.
>From the aircraft perspective, the 24v version would
be unable to start a turbine engine. While the capacity
is there at moderate discharge rates . . . internal
resistance kills its cranking abilities.
The plots above include some charging performance data
on a Schumacher XC75W picked up new at a Walmart store
a few weeks ago.
http://tinyurl.com/k7fatrm
On the outside of the box it says 3A charger/maintainer,
5A charger, 20A charger and 75A engine cranking output.
Okay, the first recharge cycle of the 100Ah "AGM" battery
under test produced the recharge curve in black. It
topped off at about 15.7 volts and had the battery 'wheezing'
from the vent valves.
The second recharge in the "GEL" mode produced the curve
in blue which topped off at 14.8 volts. MUCH better.
The third recharge in the "STD" mode produced the curve
in red which again topped off at 15.7 volts and squeezed
a few more molecules of disassociated hydrogen and oxygen
from the cell vents.
Clearly, this charger is not programmed for the advertised
service. Either I have a bad charger or Schumacher has
stubbed their toe. This is like finding a Fluke voltmeter
that's only good to 2% or so . . . I am told that Schumacher's
engineering staff is willing to talk. I'll be looking for
a contact in that venue to discuss my findings on this
particular Schumahcer product.
In the mean time, know that the 20A rate appears to be
a modulated 'peak' rate. Time to stuff 100Ah plus back
into this battery at the 20A setting on the charger
took 8+ hours. Not a big deal. It was reasonably expeditious
and didn't abuse the battery in the GEL mode . . . other
modes are yet to be explained/understood.
So what about these 'new' technologies? Mixed bag. Clearly
the carbon foam battery plate is not ready for prime-time
in aviation. Service in anything but moderate rate discharge
in RV's, boats, etc would be disappointing at anything over
.3C rates. Pretty sure I'm not ready to poke out $375 for
one of these things. Tho I AM glad my client was willing . . .
The charger was disappointing on two fronts. It's clearly
NOT a 20A fast charger. It's also unsuited to the tasks
advertised for maintenance of AGM/Flooded batteries. MUCH
too abusive.
A learned professor once opined "Numbers not accompanied
by degrees of uncertainty are meaningless" (Walter
Lewin). Another pretty sharp cookie was known to have
said, " . . . when you cannot measure [a thing], when you
cannot express it in numbers, your knowledge is of a meagre
and unsatisfactory kind . . ."(Lord Kelvin).
This is a good illustration of the difficulties encountered
by the CONSUMING community when factions of the SUPPLIER
community get into rock-throwing contests (Recall the
tiff that Odyssey got into with one of the battery maintainer
guys? I forget which). It would have been good and responsible
for both parties to publish the numbers instead of throwing
rocks with consumers caught in the middle.
Now that I have the numbers . . . I can go back to the folks
who have claimed certain kinds of performance based on
those numbers for clarification . . .
Watch this space.
Bob . . .
Message 8
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Subject: | Alternative battery technologies . . . |
Excellent study and report Bob. Thanks for sharing.
Bevan
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: Sunday, May 04, 2014 9:16 AM
Subject: AeroElectric-List: Alternative battery technologies . . .
The battery-buzz these days is focused on lithium . . .
and for good reason. They ARE lighter yet retain many
of the desirable qualities of a lead=acid battery
for engine cranking.
Another rising-star wannabe is a product by FireFly
Energy . . . an svrla battery that features a carbon foam
plate material with a advertised gee-whiz feature
of offering a lower weight replacement for the legacy
lead grids.
This is not a 'new' idea . . . I think the patents
have already been renewed once . . . but only recently
have potential consumers of this technology been able
to put their hands on real product.
http://tinyurl.com/kfzsj5p
This is a group 31 battery (read BIG) that weighed in
at 73.6 pounds and presented and open circuit voltage
of 13.09V at ~20C right out of the box. A 600A load
drops voltage to 9.30V. Therefor (13.1 - 9.30)/600 = 0.00633 Ohms
internal resistance. Okay, how about available capacity
under various loads?
Emacs!
When discharged at 5A, it took 20+ hours to take it down
to 10.0V. So one could say that the capacity of this
battery at 20-hour rate is over 100aH. Not bad for a
75# battery.
At higher rates, we see that the capacity drops off pretty
much like all other batteries . . . the 50A discharge
delivered only 80Ah . . . one might extrapolate from this
data that the battery's one-hour rate (as an aircraft battery
would clock in at about 65Ah. Again, not bad for a 12V,
75# battery.
>From the data taken, we can estimate that a 24V cousin
of the same active materials would be slightly more than
the 75# due to addition of extra cell walls. The internal
resistance would go up by a factor of 4. Twice as many
half-sized cells in series.
A 4x increase in internal resistance would have a profound
effect on delivered capacity at the higher rates. In other
words, when sliced up and reassembled as a 24V battery, this
device would not be able to deliver 1/2 the one-hour rate
deduced above . . . it's more likely to be down to something
like 20Ah or so.
I'm going to see if I can model the 24v version and do
some predicted plots.
>From the aircraft perspective, the 24v version would
be unable to start a turbine engine. While the capacity
is there at moderate discharge rates . . . internal
resistance kills its cranking abilities.
The plots above include some charging performance data
on a Schumacher XC75W picked up new at a Walmart store
a few weeks ago.
http://tinyurl.com/k7fatrm
On the outside of the box it says 3A charger/maintainer,
5A charger, 20A charger and 75A engine cranking output.
Okay, the first recharge cycle of the 100Ah "AGM" battery
under test produced the recharge curve in black. It
topped off at about 15.7 volts and had the battery 'wheezing'
from the vent valves.
The second recharge in the "GEL" mode produced the curve
in blue which topped off at 14.8 volts. MUCH better.
The third recharge in the "STD" mode produced the curve
in red which again topped off at 15.7 volts and squeezed
a few more molecules of disassociated hydrogen and oxygen
from the cell vents.
Clearly, this charger is not programmed for the advertised
service. Either I have a bad charger or Schumacher has
stubbed their toe. This is like finding a Fluke voltmeter
that's only good to 2% or so . . . I am told that Schumacher's
engineering staff is willing to talk. I'll be looking for
a contact in that venue to discuss my findings on this
particular Schumahcer product.
In the mean time, know that the 20A rate appears to be
a modulated 'peak' rate. Time to stuff 100Ah plus back
into this battery at the 20A setting on the charger
took 8+ hours. Not a big deal. It was reasonably expeditious
and didn't abuse the battery in the GEL mode . . . other
modes are yet to be explained/understood.
So what about these 'new' technologies? Mixed bag. Clearly
the carbon foam battery plate is not ready for prime-time
in aviation. Service in anything but moderate rate discharge
in RV's, boats, etc would be disappointing at anything over
.3C rates. Pretty sure I'm not ready to poke out $375 for
one of these things. Tho I AM glad my client was willing . . .
The charger was disappointing on two fronts. It's clearly
NOT a 20A fast charger. It's also unsuited to the tasks
advertised for maintenance of AGM/Flooded batteries. MUCH
too abusive.
A learned professor once opined "Numbers not accompanied
by degrees of uncertainty are meaningless" (Walter
Lewin). Another pretty sharp cookie was known to have
said, " . . . when you cannot measure [a thing], when you
cannot express it in numbers, your knowledge is of a meagre
and unsatisfactory kind . . ."(Lord Kelvin).
This is a good illustration of the difficulties encountered
by the CONSUMING community when factions of the SUPPLIER
community get into rock-throwing contests (Recall the
tiff that Odyssey got into with one of the battery maintainer
guys? I forget which). It would have been good and responsible
for both parties to publish the numbers instead of throwing
rocks with consumers caught in the middle.
Now that I have the numbers . . . I can go back to the folks
who have claimed certain kinds of performance based on
those numbers for clarification . . .
Watch this space.
Bob . . .
Message 9
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|
Subject: | Re: Intercom to Radio Wiring |
At 10:38 AM 5/5/2014, you wrote:
>I totally agree. One of the benefits of packaging the audio
>products that I have developed in d-sub backshells is that there are
>a lot more pins available for grounds. In fact, I usually reserve a
>whole row of pins for ground, whether they are needed or not.
>
>This simplifies installation and saves time and money.
>
>The availability of a whole class of through-hole components that
>have a maximum height sized to fit in these packages makes even
>small volume designs feasible without having to resort to surface
>mount devices.
Isn't this business fun?
Bob . . .
Message 10
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Subject: | Alternative battery technologies . . . |
At 10:41 AM 5/5/2014, you wrote:
>Excellent study and report Bob. Thanks for sharing.
>
>Bevan
You're welcome. The next phase of the
study will involve disassembly of the
battery. We want to see if our 'predictors'
based on experience and deduction about this
technology were correct. About 8 years
ago we spent a little money getting
to know the designers a little better.
Funny thing about that physics-stuff . . .
you cannot shuffle the numbers and simple-
ideas at the convenience of marketing
department. Attempts to ignore -or-
shuffle can be embarrassing, expensive
and sometimes dangerous.
Bob . . .
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Subject: | Re: How do I prevent starter engaged LED from failing? |
Joe and Bob,
I thought that an LED was a type of diode. It seems like one should not have to
stick a second diode on the circuit when using an LED.
For your review, here is an attachment of my solution. My engine/starter is in
a state of storage so the LED based circuit cannot be tested yet. I chickened
out and replaced the diode with a mini bulb. Seemed like the simplest way in my
case.
Thank you,
Eric Schlanser
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=422865#422865
Attachments:
http://forums.matronics.com//files/starter_warn_light_circuit3_451.pdf
Message 12
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Subject: | Re: trim indicator buffer |
> Well considered critical review from kindred herders
> of electrons is solicited and welcome.
I would add another 0.1 from pin 3 to ground, to keep noisy trim pots from making
the reading jumpy, and maybe another one between pins 2 and 6 to slow down
the op amp.
Message 13
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Subject: | Re: How do I prevent starter engaged LED from |
failing?
At 05:48 PM 5/5/2014, you wrote:
>
>Joe and Bob,
>
>I thought that an LED was a type of diode. It seems like one should
>not have to stick a second diode on the circuit when using an LED.
It IS a diode. It has ratings and limits like any other
diode. When caused to conduct current in a forward direction,
it exhibits a voltage drop quite a bit higher than power
steering or detection diodes . . . and it emits light while
doing it. Apply voltage in the reverse direction and
you not only get no light . . . you may punch out the
magic stuff between the terminals that emits the light.
Here's an exemplar set of plots on a bright, white LED.
http://tinyurl.com/q4f25xe
Emacs!
For a diode rated at 30 mA, one selects a resistor that
produces no more than 30 mA at maximum expected system
voltage (call it 15v). In the curve above we see that
voltage drop is 3.4V at 30 mA. (15-3.4)/.030 = 386
ohms. So the resistor to choose is no smaller than
this calculated value to stay below the diode's rated
maximum operating current.
Emacs!
Reverse voltage is another mater. Note that around
18volts, the current takes a sharp spike toward
very high . . . read damaged junction.
Now, the SOURCE of a reverse voltage in our applications
MUST be reactive. I.e., inductive response to rapid
drop in applied current . . . like a contactor opening
up. The inductive culprit is not necessarily a
DEVICE . . . even long wires between the battery
and the victim device can offer the inductive
storage need to offer a reverse voltage spike.
It WILL be short, it may not have much energy
in it . . . but it quite likely to exceed 18 volts.
Hence, legacy design goals include the addition of
a diode across the LED wired to conduct in case
such a led-killing dragon should come along.
Not saying it WILL . . . in fact, many builders
are flying 'unprotected' leds with no regrets.
There are Bonanzas with low probability of an
antagonist jumping up to irritate a less-than-
robust regulator . . . rare but not zero.
>
>
>For your review, here is an attachment of my solution. My
>engine/starter is in a state of storage so the LED based circuit
>cannot be tested yet. I chickened out and replaced the diode with a
>mini bulb. Seemed like the simplest way in my case.
Can you articulate the source of your 'fear?'
I thought that the explanations and experiences
shared here on the List would have assuaged your
concerns. By all means, use the LED without protection . . .
and simply watch it for failure. It's a no-risk
event easily spotted throughout its lifetime on
the airplane.
I'm concerned that you were offered 'too much'
information . . . that's always a risk in this
data exchange venue . . . it was never intended
to be a 'cook book . . . do this and trust
me'. But the fact that you 'chickened out' and
regressed to a legacy technology suggests that
the List did not serve you well.
Don't hesitate to bring perceptions of poor
service to my attention or anyone else's . . .
this List is all about reducing risk through
knowledge and understanding . . . not about
anointing any one process or technology.
Bob . . .
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