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david(at)carter.net
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 Posted: Tue Jun 16, 2020 1:58 pm Post subject: SDS CPI-2 internal crowbar |
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This thread over on VAF is interesting. I have the CPI-2 with their recommended small backup battery in my single-alternator, single-battery (for the main electrical system) VFR-only airplane.Â
I'm planning an IFR upgrade with a full suite of Garmin G3X goodies, and want to follow the Z101 architecture. Â
It seems that their internal crowbar & fuse leave me stuck with their backup battery. Â
http://www.vansairforce.com/community/showthread.php?t=154648&page=34
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David Carter
david(at)carter.net (david(at)carter.net)
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nuckolls.bob(at)aeroelect
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| Posted: Wed Jun 17, 2020 10:45 am Post subject: SDS CPI-2 internal crowbar |
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At 04:44 PM 6/16/2020, you wrote:
| Quote: | This thread over on VAF is interesting. I have the CPI-2 with their recommended small backup battery in my single-alternator, single-battery (for the main electrical system) VFR-only airplane.Â
I'm planning an IFR upgrade with a full suite of Garmin G3X goodies, and want to follow the Z101 architecture. Â
It seems that their internal crowbar & fuse leave me stuck with their backup battery. Â
http://www.vansairforce.com/community/showthread.php?t=154648&page=34 |
This thread is a bit mystifying. OV conditions come from
one and only one source(s) . . . alternators with failed
regulators.
An OV condition is not a transient event . . . it's
a consistently rising voltage that will generally
be limited by the battery(ies) as their chemistry
gamely absorbs the excess energy condition. Hence
the voltage does not rise quickly (i.e. volts per
second) but rather sedately in electronic terms.
For decades we have been designing, qualifying and
integrating aviation electro-whizzies that are
capable players in the wild and wooley world
of vehicular DC power systems . . . matters not
whether cars, trucks, earth movers . . . or
airplanes.
In 1935 some pretty smart cookies in
the aviation industry got together in Washington
DC and founded the Radio Technical Commission
for Aeronautics (known today as RTCA).
https://tinyurl.com/y78zvrt8
For 85 years these folk have been sifting the
sands of physics in performance of electrical
and electronics systems for aircraft. Their
goal was to craft guidelines for the design
and qualification of all manner of electrical
accessory to (1) insure design performance
under all anticipated conditions and (2)
make sure that all accessories 'play nice'
in the same sandbox such that arguments
and spats do not put airframe or crew
at risk.
When it comes to ov definition, detection
and response, the attached figures speak
to 70+ years of design philosophy in
aviation electrical systems. 14V devices
are TESTED to withstand 20V perturbations
for 1S and 30 (or 40) Volt perturbations
for 100mS.
Every device bolted to an airplane is
expected to shrug off bus voltage
perturbations between the high and
low voltage plots for intervals of
time laid out on the x-axis. When
tasked with my first ov relay design
about 1975, the rule of thumb was to
design for a 50mS response to a step
increase in bus voltage from 14.2
to 20 volts.
While the electronics were solid-state,
the 'timers' were pretty crude by contemporary
standards. Today, micro-controllers
allow us to start a timer when the
voltage exceeds some lower discriminator,
say 15 volts. If the voltage stays above
that value for 500 milliseconds, we
trip the ov protection system. If the
voltage falls below 15v before
time-out, the timer resets and the process
starts over.
This all but eliminates nuisance tripping
of an ov protection system while offering
robust but timely management of a recalcitrant
regulator/alternator.
Contemporary design recommendations are
not difficult to accommodate . . . been
doing it for decades. I've designed
many products, some incorporating delicate
silicon, wherein power was supplied
directly from ship's bus . . .
Often we were requested to qualify for
indirect effects of lightning strike. Again,
not difficult.
I hope this lays foundation for consternation
felt when I read about difficulties builders are
having with the built-in ov protection on
some product. It's even more difficult
to understand how suppliers can offer
what appears to be capable of producing
really gee-whiz performance in some device
but are unable to tailor electrical input-output
ports to comfortably thrive in the aircraft
environment. Adding any form of OV 'protection'
to an accessory is completely redundant; i.e.
unnecessary.
Bob . . .
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