Avionics News July 2020 - 23

through a second regulator so the standby generating
source comes online automatically - while illuminating
a warning light to inform the pilot of the failure of the
main generating source. This can also be made to require
pilot action, shedding load on the secondary buss to avoid
overtaxing the standby unit.
Now the job entered the territory where expert
knowledge of electrical systems is needed to protect the
gauges and instruments. The avionics shop willing to help
a builder with the design and construction of the wiring
stands a decent chance of landing that work - and more.
The generating sources should be wired through the
busses to, at a minimum, keep charged the main battery
while continuing to power the essential equipment.
Secondary batteries as standby power
While the Federal Aviation Administration wants to
see glass cockpit systems for IFR aircraft equipped with
alternative power sources, the choice of a standby source
belongs to the builder. Numerous options exist for adding
an alternative generating source, but not all aircraft can
accommodate those options.
The most-common options involve installing a standby
alternator on the engine-accessory pad once home to the
vacuum pump - now vacant because the panel is alldigital glass. But not all engines used in homebuilt EABs
offer the option of putting a standby alternator on the
engine.
With the appropriate voltage regulator and breaker
protections, a second battery offers a solution. And since
these are experimental aircraft we're discussing, some
of the new options in lightweight lithium-ion battery
technology can provide the solution at a weight no more
than the most-common standby alternators.
The choice of regulator is critical here, since one
generating source has to keep charged two batteries.
The wiring and breakers also must allow for the shift to
the standby battery from the main battery and primary
alternator.
The savvy avionics shop should also consider offering a
warning light option to alert the pilot to the main system's
failure. In some available voltage regulators, that "idiot
light" capability is built in, making the addition a simple
matter of acquiring the fixture for the light, installing it in
the panel - in the pilot's direct line of vision, please - and
wiring the light to the regulator.

Gimme a break
In the real world of experimental aviation, builders
enjoy three options for protecting the aircraft wiring
and all those pricey boxes filling the panel space: fuses;
circuit breakers; and for EAB aircraft, electronic circuit
breakers or ECB.
In all cases, regardless of which system the EAB
builder selects, a working flashlight is a must for night
flight.
First up, the fuses. Advantages: simple technology; easy
to understand; flexible; and can be replaced after blowing.
Fuses can be wired in so that one fuse protects one device
while another protects several.
The FAA provides guidance on what it considers
acceptable solutions to various systems in Part 23 aircraft
via Advisory Circular No. 23-17C, which is available
online at https://www.faa.gov/documentLibrary/media/
Advisory_Circular/AC_23-17C.pdf.
The FAA wants pilots of aircraft using fuses to carry
one complete set of spare fuses, or three spare fuses
of each kind required. And those spare fuses must be
accessible to the pilot in-flight.
Next, circuit breakers. Advantages: no need to carry
spare fuses; and circuit breakers can be reset. If tripped
again, electronics experts caution against repeatedly
resetting a tripped breaker lest it exacerbate the problem
causing the trips.
Disadvantages: they're more expensive and can take
more space behind the panel.
Finally, electronic circuit breakers. The latest
innovation for electrical systems, ECBs are solid-state
systems, adjustable, and allow for simpler wiring with
greater flexibility than thermal or automotive-style
breakers.
Some ECB options allow for the connection to a second
battery or generating source, further simplifying the
overall wiring job and aiding in redundancy. A number of
makers of avionics for the EAB and LSA segments offer
ECBs, and stand-alone makers also offer versions of the
same technology.
Penetrating the EAB world to offer help
EAB builders populate the nation in significant
numbers, at airports big and small. Many of them are
Continued on following page
avionics news

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july

2020

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https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-17C.pdf https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-17C.pdf

Avionics News July 2020

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