nuckolls.bob(at)aeroelect
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 Posted: Wed Mar 16, 2011 8:24 pm Post subject: Transient_voltage_suppression_diode failure |
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At 06:44 PM 3/16/2011, you wrote:
| Quote: | 3/16/2011
Hello Fellow Aeroelectric Listers, You may be interested in the
attachment and the below information:
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Interesting. I had a chance to review some power distribution
diagrams for Cirrus products several years ago . . . it
was about the time they were incorporating the SD-20
alternator into one or more models.
Many of their architecture decisions were, shall we say,
novel? It would be interesting to see the details of
the service bulletin . . . the wording in the notice
sounds like they 'sprinkled' transorbs around the system
with some notion that it was a good thing to do.
Any of you who have been on the List for 13 years or
so will remember some discussions about transorbs.
Several of our members were proponents of transorb
"sprinkling" . . . but without having a terribly
good notion of how these critters are rated and how
they behave.
http://www.aeroelectric.com/articles/spike.pdf
There's another transorb issue that popped up a few
years ago. It was centered on this critter:
http://www.aeroelectric.com/Mfgr_Data/Semiconductors/704-15k36t.pdf
Seems that somebody got the cool idea that you could
PARALLEL numerous smaller devices and come up with
an array good for soaking up lots of energy. This
sorta works and a few manufacturers managed to
qualify devices to this spec. But process control
for having tightly matched devices to parallel
was critical.
I think Mooney had some of these critters "sprinkled"
in their airplanes and suffered some smokey events.
I discovered that situation when a hopeful supplier
to Hawker-Beech proposed a new starter-generator controller-
regulator. The thing had TWO of those monster transorbs
paralleled in the box. Seems that lightning issues in
composite airplanes drove the DO-160 qualification
stresses out to the moon.
Some of you may recall that I sketched a circuit
for adding a transorb to the main bus of an airplane
with the goal of standing off all evils.
http://aeroelectric.com/Pictures/Schematics/SpikeTrap.gif
The idea was that if something evil came along, the
transorb would catch it . . . that's what transorbs
do. But if it were so severe as to trigger transorbicide
(transorbs do that too), then the fuse would blow and
you would get an indicator light.
In any case, transorbs are quite helpful for getting
a black box to pass DO-160 + lightning tests. But as
soon as you see these critters scattered around an
airplane's electrical system, well . . . 'nuf said.
What was it somebody said about latching contactors
. . . "a solution looking for a problem?"
Bob . . .
Bob . . .
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