EI Power System Review

[WingsOnWheels]

Originally Posted by Carl Froehlich

+1

Do not look at just power to your ignitions, look as total system design. Two equal batteries provides power for 2+ hours, a lot more than the typical EFIS wimpy backup battery maybe doing 30 minutes of backup power to keep your screen alive. And you get great cranking power.

Carl

I agree for an IFR aircraft. In my case, the modification is for a flying VFR airplane. I don't see significant value in adding a second full size battery at this point. The EFIS backup is good for 45-60 minutes (assuming the main battery is gone), but I don't *need* the EFIS anyway. My tablet which is used for navigation is good for about 1.5-2hrs on battery. If I do add IFR capability down the road, it will be a different story. Then a second PC680 would make a lot of sense.

[WingsOnWheels]

Originally Posted by mfshook62

Here is the wiring diagram that I used for a back up battery for my Dynon HDX and my new SDS CPI-2 EI. I used an Earth X 6.2Ah ETX-18B for my back up battery which should keep the EI and essential Dynon components active long enough to land. Please feel free to comment if there is a problem with this setup, or if I left anything out.

My only concern with that layout:
Do you leave your backup battery switch on all the time (at least when running), or do you have to turn it on?

Also, if you have a fault in your Avionics/Critical buss, you will lose both ignition systems.

[DanH]

Mike, are you sure you wish to drive both ignitions from the avionics bus?

A reasonable design goal might be to drive both ignitions from separate and independent sources while everything else is shut down, preferably by flipping one switch (the master).

Another might be to label switches for what the really do. Here we have switches identified as "avionics master" and "batt 2", which result in a stopped fan if moved to OFF.

Why a 70 amp breaker on the B lead? It means you need to run a hot B lead through the firewall to the instrument panel. An ANL or similar firewall forward ends that bit of 1950's silliness; the hot lead in the panel is protected.

I see a "backup" label just to the left of module B. What is going on there?

You realize a short anywhere between the backup battery and the two 15 amp ignition breakers will kill both ignitions?

[Bcone1381]

Since Five days have passed with no activity on this thread, I think its okay to share two ideas from Bob Nuckolls on standby batteries that some might consider hi-jacking a thread.

(If the name Bob Nuckolls does not ring a bell, the kit planes link below gives a little info for you.)

https://www.kitplanes.com/bob-nuckol...-hall-of-fame/

Batteries have been an essential component
of aircraft electrical systems from day-one.
The first airborne electrics were battery powered
by devices recharged after every flight given
that engine driven power sources were not
yet prominent fixtures. Indeed, wind-driven
generators were more prevalent (read low power
and DRAG!).

Batteries were 'wet', produced fumes when
charged. dribbled acid over themselves and
the airplane and had relatively short service
lives. I.e. they were a commodity like tires,
oil and gasoline. Their reliability as a
power source depended on constant monitoring
of condition.

While secondary (rechargeable) batteries have
become much more efficient, environmentally
friendly, more per pound and cubic foot, they
are still a commodity. You cannot install
a battery into any function expecting it to
perform as needed for more than a tiny fraction
of the airframe service life. Further, if loss
of a battery-supported system adversely impacts
probability for comfortable termination of
flight like fuel and oil . . . the battery's
condition demands reliable monitoring of
condition for continued airworthiness.

This is a burden on cost of ownership. It
expands the operator's work load for periodic
and capable preventative maintenance peppered
with the expense of replacement on condition.

Design goals for elegant electrical systems
architecture includes minimizing the need
for batteries in both number, size and expense.
The ultimate achievement for reduction of
batteries might be (1) a battery capable
of but one start cycle and (2) sufficient
capacity to operate landing lights during
the last 60 seconds of a dead-stick landing
at night.

THAT battery might indeed be quite small and
its cost of ownership very nominal. It might
even be cheap enough to simply replace it at
every annual . . . or perhaps every 100 hours
just as you might change the oil. Thus you've
eliminate the need for time, effort and test
equipment necessary to conduct preventative
maintenance on ship's battery(ies).

This line of reasoning sets the design goals
for an electrical system tailored to a project's
engine, airframe, capabilities and planned
missions. One goal is to minimize singling
out any particular set of loads as critical
but to consider the machine, pilot and
flight environment as a system.

Over the past 30 years, a family of architectures
have been proposed, refined, published and
applied to projects in the OBAM aviation
community. Some have served the builder's
design goals well . . . others not so well.
It's an iterative evolutionary process that
strives for demonstrable success.

The proposed Z01 architecture takes into account
the pronounced shift in aircraft designs that
incorporate multiple engine driven power sources,
electrically dependent engines and yes . . .
a desire to shed as much of the battery weight
and cost of ownership as practical.

Discussions here on the List and elsewhere
are needed to ferret out any failure to meet
a design goal . . . not as SUPPLIERS of any
particular electro-whizzy but as USERS
of those devices as components of the whole
FLIGHT SYSTEM.


Bob . . .

This is a thought from Bob about a second standby alternator.

An SD8 standby alternator would weigh
less than an 8Ah battery, requires
close to zero preventative maintenance
and carry 8+ amps of load as long as the
fan is running. .

[bjb3013]

Originally Posted by DanH

What Carl said.

Do this instead, isolated feeds and grounds. One diode, not three, and replace the useless breaker with a fusible link for aux battery charge. Well, "useless" may not be fair, as you could pull it to preflight check the aux battery output.

The EDIS feeds really only need 5 amp protection, as the EDIS system only needs a bit over an amp.



Been flying this for a while now. Strip off the voltage monitor, push to test aux battery voltage, and ignition map select wiring, and it's pretty much what you see above. Both batteries are behind the baggage compartment in the RV-8, so there is no battery bus or main bus in the ignition system.



Aux features stripped away:

Dan,
On the bottom simplified drawing what?s the specs on the diode to the aux battery if it is a 12 amp hour battery

[DanH]

Originally Posted by bjb3013

Dan,
On the bottom simplified drawing what?s the specs on the diode to the aux battery if it is a 12 amp hour battery

Honest answer is "I dunno". Reviewed them many moons ago, and since lost the package.

[Carl Froehlich]

Originally Posted by DanH

Honest answer is "I dunno". Reviewed them many moons ago, and since lost the package.

Many options but I?d use a 30amp dual package Schottky diode, run the diodes in parallel and mount with a heat sink. These are just a few dollars.

Carl

[bjb3013]

Good information
Why use a pair and where can I source these diodes
Thanks
Brent

[Carl Froehlich]

Originally Posted by bjb3013

Good information
Why use a pair and where can I source these diodes
Thanks
Brent

The dual package makes for easy mounting. Here is an example: https://www.alliedelec.com/product/s...3-45/70616400/

Here is a simple heatsink for mounting on a bulkhead or such: https://www.alliedelec.com/product/w...89ab/70236299/

Many options for both available at Allied Electronics.

Carl

[Walt]

I like these..

https://www.mouser.com/ProductDetail/Microchip-Microsemi/APT2X101S20J?qs=sGAEpiMZZMtQ8nqTKtFS%2FPOoKY%252BW dZ3GI0MbqjPqs%2FwzfBt9yg9g1Q%3D%3D

or this one:

https://www.newark.com/ixys-semicond...45v/dp/96K8819