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How do I prevent starter engaged LED from failing?

 
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nuckolls.bob(at)aeroelect
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PostPosted: Sat May 03, 2014 7:09 am    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 06:40 PM 5/2/2014, you wrote:
Quote:


Bob et group,

In wiring a starter engaged annunciator, I am using an
off-the-shelf LED fixture with an appropriate resistor already
integrated into it. The resistor is actually soldered directly to
the LED lead inside of the fixture.

The two attached diagrams from the archives differ in how the
diode is added. (I put a 1A inline fuse where both of the attached
drawings shows a resistor.) In either drawing, it won't be possible
to place the legs of the resistor outside of the legs of a diode in
my LED circuit with the integrated resistor. Is that going to be a problem?
Would one circuit drawing be preferred over the other?

They are the same. The protection diode is wired
in parallel with the led to clamp off any reverse
voltage transient. The resistor is shown upstream
and close to the monitored power at the starter.
Having this resistor located remotely eliminates
the need for fusing the sense lead.

Suggest you modify the fixture to move the resistor
out to the source end of the wire and add the diode
in parallel with the led.

Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Sat May 03, 2014 2:07 pm    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 04:02 PM 5/3/2014, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

Eric,
I am not knowledgeable enough about the characteristics of a starter motor to answer. In my circuit, any diode, zener or not, will short out a negative voltage. A 16 volt zener will short out any positive voltage above 16. Attach your latest circuit idea for others to comment on.
It would be interesting to learn more about starters, any induced voltages during normal operations and also the voltage output and current capabilities of a starter that remains engaged with the engine after starting.

Joe's circuit would be fine for fixtures with integrate
resistors . . . and in fact, it wouldn't need to be a zener.
The 'concern' is minor and speaks to the potential for a negative
going transient to punch the junction in the LED . . .

Now, given that LEDs with integral resistors abound in
other vehicular systems . . . and no doubt few if any
have a protection diode for the LED.



If I were qualifying the LED fixture for use on aircraft,
I would be obligated to prove it invulnerable to both
positive and negative going spikes . . . albeit very short
ones . . . at voltages considerably greater than
the LED's reverse voltage stand-off characteristics.

For my purposes, I choose to simply include the diode and
not worry about it. The fact that we put such protection
in has more to do with legacy qualification philosophies that
go back 50+ years . . . but given that the LED is attached
to a starter motor terminal DOWNSTREAM of a starter contactor,
then the concerns are more profound. It's a simple experiment.
Just hook it up and see what happens. You're unlikely to have
BOTH a stuck starter contactor and a toasted LED in the same
event. If your bare-foot LED fixture stands up to the first
few dozen starts, it seem likely that a few hundreds more
is not going to be any more likely to toast it.


Bob . . . [quote][b]


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PostPosted: Mon May 05, 2014 5:42 am    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 12:07 AM 5/5/2014, you wrote:
Quote:
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 . . . [quote][b]


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nuckolls.bob(at)aeroelect
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PostPosted: Mon May 05, 2014 5:35 pm    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 05:48 PM 5/5/2014, you wrote:
Quote:
--> AeroElectric-List message posted by: "eschlanser" <eschlanser(at)yahoo.com>

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


[img]cid:.0[/img]

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.

[img]cid:.1[/img]

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.
Quote:


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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nuckolls.bob(at)aeroelect
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PostPosted: Tue May 06, 2014 3:34 am    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 05:59 AM 5/6/2014, you wrote:
Quote:

> 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.

I do not think that either Bob or I recommending using a protection diode.

Correct. My assertions went to the point of
robust design goals. Here's how the protection
diode works should one choose to include it.
There are lots of airplanes flying with commerical
off the shelf, internally regulated alternators
too . . . without the legacy ov protection.
Again, builder's choice.

Quote:
I only offered a circuit containing one to help answer the
question. Actually, I think that an incandescent lamp is more
likely to fail than a LED.

Agreed although in this case were talking about
two different failure modes. Incandescent lamps
will wear out and are subject to vibration.
LEDs are essentially longer lived than the
airplane itself assuming that it's free
of all electrical over-stresses.

Quote:
I think an indicator light (if used) should be connected in
parallel with the starter motor, and not connected to the contactor coil.

Good catch. I missed that feature. Yes,
the purpose of the light is to warn of
a stuck starter contactor. Hence, it
would be wired to the motor terminals.

Quote:
Then the lamp will illuminate whenever the starter motor is
rotating and for whatever reason. Someone correct me if I am wrong.



Bob . . .


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jluckey(at)pacbell.net
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PostPosted: Tue May 06, 2014 6:09 am    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

comments a the bottom...
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Tuesday, May 6, 2014 4:33 AM
Subject: Re: Re: How do I prevent starter engaged LED from failing?


--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

At 05:59 AM 5/6/2014, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
> 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.

I do not think that either Bob or I recommending using a protection diode.

Correct. My assertions went to the point of
robust design goals. Here's how the protection
diode works should one choose to include it.
There are lots of airplanes flying with commerical
off the shelf, internally regulated alternators
too . . . without the legacy ov protection.
Again, builder's choice.

Quote:
I only offered a circuit containing one to help answer the
question. Actually, I think that an incandescent lamp is more
likely to fail than a LED.

  Agreed although in this case were talking about
two different failure modes. Incandescent lamps
will wear out and are subject to vibration.
LEDs are essentially longer lived than the
airplane itself assuming that it's free
of all electrical over-stresses.

Quote:
I think an indicator light (if used) should be connected in
parallel with the starter motor, and not connected to the contactor coil.

Good catch. I missed that feature. Yes,
the purpose of the light is to warn of
a stuck starter contactor. Hence, it
  would be wired to the motor terminals.

Quote:
  Then the lamp will illuminate whenever the starter motor is
rotating and for whatever reason. Someone correct me if I am wrong.

The original drawing submitted by the original poster showed the light across
the motor terminals of the starter.

Care must be taken to get on the correct terminal on the starter. If you get
an indicator, LED or incandescent, across the starter "shift" solenoid (that's
the one built into the starter which engages the drive pinion) you
will indeed have a dragon by the tail. The inductive kick when the shift
solenoid de-energizes is a flame-thrower.

-Jeff
Bob . ric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectric --> http://f= nbsp; ronics.com/contribution" target="_blank">http://www.matronics.com/contrib===============



[quote][b]


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eschlanser



Joined: 08 Apr 2010
Posts: 60

PostPosted: Tue May 06, 2014 2:41 pm    Post subject: Re: How do I prevent starter engaged LED from failing? Reply with quote

Bob(s) and Joe,

It's not about poor "service" from this list. Quite the contrary. And the great body of knowledge herein is why I came to this list to find out the answer to my questions. I have learned so much here it's why I have been able to create and wire my plane. Couldn't have done it without you.
Not having full understanding of an LED is why I used the mini bulb. Your explanations made the use of the LED so much clearer that I could have used it had I seen your posts before I chickened out and installed the mini bulb. When the mini bulb fails, I'll try the LED. Although, the mini bulb has a 5k hours ave life! Also, I was not able to test the LED by running the starter. Also, the two original diagrams showing two different ways to add the diode to the circuit had me wondering which was correct.
As far as monitoring the starter contactor rather than the terminals on the starter, I have to say I followed an old drawing I had from the aeroelectric.com site. It was

http://www.aeroelectric.com/Pictures/Contactors/Starter_Contactor/s702wire.jpg

When I search for it now, I find I am not able to access it. It was a picture of an auto style start contactor with two large posts and two small posts. The small posts were labelled S and I. The picture said the I post could be used for a starter monitoring light. I'll agree the starter would be a better device to monitor. THanks for the tips.

Eric Schlanser
.


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nuckolls.bob(at)aeroelect
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PostPosted: Tue May 06, 2014 6:34 pm    Post subject: How do I prevent starter engaged LED from failing? Reply with quote

At 05:41 PM 5/6/2014, you wrote:
Quote:
--> AeroElectric-List message posted by: "eschlanser" <eschlanser(at)yahoo.com>

Bob(s) and Joe,

It's not about poor "service" from this list. Quite the contrary. And the great body of knowledge herein is why I came to this list to find out the answer to my questions. I have learned so much here it's why I have been able to create and wire my plane. Couldn't have done it without you.
Not having full understanding of an LED is why I used the mini bulb. Your explanations made the use of the LED so much clearer that I could have used it had I seen your posts before I chickened out and installed the mini bulb. When the mini bulb fails, I'll try the LED. Although, the mini bulb has a 5k hours ave life! Also, I was not able to test the LED by running the starter. Also, the two original diagrams showing two different ways to add the diode to the circuit had me wondering which was correct.

I saw those . . . and didn't see a difference in them . . .


Quote:
As far as monitoring the starter contactor rather than the terminals on the starter, I have to say I followed an old drawing I had from the aeroelectric.com site. It was

http://www.aeroelectric.com/Pictures/Contactors/Starter_Contactor/s702wire.jpg

it's still there. it got filed under "Starter Contactors"

http://tinyurl.com/o5turon


Quote:
When I search for it now, I find I am not able to access it. It was a picture of an auto style start contactor with two large posts and two small posts. The small posts were labelled S and I. The picture said the I post could be used for a starter monitoring light. I'll agree the starter would be a better device to monitor. THanks for the tips.

The wiring suggested in S702wire.jpg might make more
sense if you saw the schematic . . .

Actually, the "I" terminal is just fine . . . that's a THIRD
stationary contact within the S702-1 contactor that duplicates
the connections between the two FAT terminals thusly . . .

[img]cid:.0[/img]




Bob . . .


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Airdog77



Joined: 24 Nov 2013
Posts: 80
Location: Northern Virginia

PostPosted: Mon Dec 11, 2017 8:49 am    Post subject: Re: How do I prevent starter engaged LED from failing? Reply with quote

Bob,

I'm getting to ready to build my engine the middle of next month (Jan 18 ) and wanted to clarify the starter-on warning circuit. I have mine depicted as per the Z-13/8 diagram with a connected wire off the starter contactor post.

Off the starter contactor, the lead then runs through a 2A inline fuse, then a 2K ohm resistor (as per AG6 instructions) and then runs back to the panel (I'm in a Long-EZ, so up to the front) and terminates into an AG6 warning annunciator as my "warning light."

First, in this configuration would there be any reason to change the starter-on warning wire lead connection point from the contactor post to the actual starter?

Second, I'm thinking for the protection of the AG6 I should add a protective diode hanging off the circuit either as you and/or Joe depicted. Do you think this is advisable for my configuration?

Thanks,
Wade


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Wade Parton
Building Long-EZ N916WP
www.longezpush.com
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