REFLECTOR: Reflector Digest, Vol 100, Issue 10
Dave T Nelson
dtnelson at us.ibm.com
Thu Jul 4 09:09:01 CDT 2013
Brooke - well said, Sir!
The comparison to other no redundancy systems (like your entire airframe)
is spot on, and reinforces my philosophy - stay away from complexity, and
build it really, really well - but just once. Adding all the stuff I hear
about is adding extra weight, complexity, and failure modes.
How many Cessnas, Pipers, Beechcrafts, Mooneys, etc., are lost due to the
lack of an extra alternator? An extra battery? Where you see a store
bought airplane accident due to an electrical failure, it's pretty much
always due to smoke or fire in the cockpit... How much extra risk are you
adding for that kind of problem with all of your additional redundant
systems?
Take great care in building, but build it once and keep it simple.
Dave
Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering
----- Message from Brooke Wolf <bwolf1 at tds.net> on Wed, 3 Jul 2013 21:32:32
-0400 -----
To: reflector at tvbf.org
Subject: REFLECTOR: Electrical
system
Reiff
As we go through the mental gymnastics of 2 alternators or 2 batteries or
primary busses or essential busses or main busses or emergency busses or
battery busses and redundancy galore, let us not forget we have only one
engine. Safety and associated redundancies should balance. Just food of
thought.
Brooke
On Jul 3, 2013, at 4:11 PM, reflector-request at tvbf.org wrote:
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Today's Topics:
1. Re: Electrical system (Jack Prock)
From: "Jack Prock" <jackprock at wavecable.com>
Subject: Re: REFLECTOR: Electrical system
Date: July 3, 2013 4:10:30 PM EDT
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Reply-To: Velocity Aircraft Owners and Builders list
<reflector at tvbf.org>
Reiff,
The only thing that I would add is that you start your engine using
the battery, but fly using your alternator(s). If you were going
to decide between having a duplicate of one OR the other, I would go
with a duplicate alternator.
If the battery goes out, you can’t start... get jumper cables, start
the engine, you’re on your way... just like a car. (assuming 12 volt
system )
If your single alternator goes out, you run on your battery(s) until
it/they die (while you look for a place to land)...
at night... over mountains, not a good scenario!! Other backups will
help... but the pucker factor goes way up when
(almost) everything goes dark!
The consequences of one, far outweigh the consequences of the other.
That is just my opinion... and just like assholes, everyone has one!!
Jack
From: Reiff Lorenz
Sent: Wednesday, July 03, 2013 12:24 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Electrical system
Terry,
Thank you for all the details. This is all very helpful. I like your
suggestion about the heat-shrink labeling, even though it's
expensive. For planning/drawing software I'm leaning toward Visio.
(Turbo-CAD does have some good features, too.)
I'm still working on the right tradeoff between redundancy and
complexity. Lots of suggestions from other builders to do 2
batteries. Others say 1 battery and 2 alternators. Andy Millin sent
me his diagram and he's got 3 batteries! The Vertical power system
simplifies some of this. They have multiple configurations for dual
batteries and/or dual alternators and/or ground power plugs, but it's
still not as easy as connecting everything to one box.
Builder Bill Stockman lives near me. He's retro-fitting his long-wing
SE with a Vertical Power system and a Garmin G3X. I'm hoping to be
able to help him and learn about wiring a VP system in the process.
I may have similar W&B issues to what you describe. I'm a skinny guy
and don't want to have trim issues, but I also want to take some of
my larger friends in the front seat (6'3 & 260 lbs.) Maybe there's
some middle ground between the two extremes?
Looking forward to talking to you at Oshkosh!
Reiff
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
On Behalf Of Terry Miles
Sent: Tuesday, July 2, 2013 11:46 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Electrical system
Wow. Dave, that is a very nice summary. I did all of my
wiring...every inch, every connector, every everything. I would
repeat a lot of what you offered, if asked, and that is: keep track
of wire size to fit the current load, secure stuff properly so it
cannot rub against anything, (I used that black wax lace stuff.
Yank on every connector after you make it to test it. Check every
BNC you make for continuity and twist it around a little before you
declare it sound. If you make 25 pin connectors becareful with pin
crimps, and especially the outboard most pins when you go to secure
the entire bundle. (You can google how to tied the knots.) I read
all the Nuckols stuff faithfully as I educated myself and choose
against the double alternators, but I do have a pair of Odessey 925
batteries located forward of the carnard bulkhead in the RG and have
not had water issues so far. The main distribution is after of the
carnard bulkhead. I did the 2 batts in part for wgt and bal since I
am 150 pounds and heard stories of trim issues. While it is another
discussion, the decision for one or two batts was and always will be
debatable. It might have been better for me to use removable ballast
since I cannot take anybody much over 200 lbs and put them in the
front seat. My inflight draw is about 4 amps, much much different
from days gone by. I will run out of gas before I every run out of
batt power. I replace one batt every 18 months to two years.
Making wire streams (I like that term) would have been some good
advice for me. I didn't do that and actually installed the wiring a
little at a time and added a lot of after the fact stuff....and I do
have a lot of loose single wires going hither and yon (sp?) back and
forth from port to starboard behind the instrument panel. I used
auto fusing mostly but do have about a dozen in view aircraft grade
CB's for stuff I want to know about...ignition, transponder, hydro
pump and gear control gizmo...stuff like that. There are also
decisions about putting more than one component into a single
fuse/breaker.
I bought a $300 plus wire labeling system that uses heat shrink. The
dam heat shrink refills were about 35 cents an inch, but I thought
that was money well spent, as well as being able to work at a base
level with turbo-cad to do the drawings since I experienced endless
edits in that department from my first paper drawings.
If you do your own wiring, I would call Dave first since he offered.
I am only a Saturday afternoon electrician-avionics tech, but I can
certainly add my name if you want an opinion about doing your own
harness and/or tacking the job of installing all of the avionics and
doing those 2 gazillion settings on your own. Being able to buy both
an AHRS and an autopilot from the same vendor is a big plus not
available to me. I have GRT stuff and I like it. Besides buying mil
spec wire, buying high grade teflon tape is a good idea too.
Terry
To: reflector at tvbf.org
From: dtnelson at us.ibm.com
Date: Sun, 30 Jun 2013 10:36:59 -0500
Subject: Re: REFLECTOR: Electrical system
Hi Reiff,
The power and ground bus bars I'm talking about is behind the canard
bulkhead in the area behind the panel - not forward of the bulkhead
and exposed.
In general, for exposed connections, the worry wouldn't be failure
due to shorting from the water, it'd be corrosion. In general,
galvanic corrosion should be considered, but can be easily controlled
with HW store electrician's grease. The relays and connections that
I do have on the forward (exposed) side of my bulkhead all have a dab
of that stuff (main contactor, hydraulic pump relays, battery
connections, etc.).
I've never seen galvanic corrosion on my homemade brass bus bars &
the bimetal ring connectors I've used.
I've seen the other comments re. use of two alternators, etc. I agree
with the guidance from Richard Gentil - if you've got an electrical
problem you're going to want to land and fix it anyway. Keeping your
system as simple as possible and building your simple system with
reliability in mind makes much more sense to me than trying to add
all kinds of redundancy... which just gives Murphy more opportunities
to ruin your day. I'd think really hard before installing a system
with two alternators, two batteries, all kinds of switching relays,
lots of extra wiring... failure points... and things to go wrong.
My two cents.
Dave
Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering
Dave,
Terrific advice! Thanks for all the help.
Did you cover the power buss with anything? Is there any concern of
having a "naked" power buss in the nose? I have an RG, so I'm
imagining the entire inside of the nose will get wet if I take off or
land in the rain.
I really appreciate all the info!
Reiff
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
On Behalf Of Dave T Nelson
Sent: Saturday, June 29, 2013 1:12 PM
To: reflector at tvbf.org
Subject: Re: REFLECTOR: Electrical system
This is an excellent area for KISS.... Keep It SIMPLE!
In my installation, I used two connection blocks in the area behind
the instrument panel for both 12V and ground (4 total), one of each
flavor on the left and on the right. I made them myself by soldering
brass screws into a brass plate. I then used ring terminals on the
wire ends. The terminals are then held tight with MS21042 nuts. The
idea is to avoid having to have wires seeking 12V or ground from
having to cross the whole panel from the left side to the right (or
vise-versa). The ground system should be simple - everything has
only one grounding point (to avoid ground loops). On both power and
ground, the buss bars are powered (or grounded) via two wires for
redundancy.
I used switch circuit breakers instead of switches with separate
circuit breakers (or fuses). I wouldn't recommend that... I've had a
couple of them fail.
I used circuit breakers instead of fuses. My reasoning was that I
want to be able to see at a glance if one had popped (hard to do with
a fuse). I wish I'd used the type that allow you to pull the end of
the circuit breaker to switch a circuit off.
Don't buy used circuit breakers!
Use real aviation grade wire, not Radioshack junk.
I used, carefully and religiously, a wire size chart. I've seen
many, many installations where folks use wire of way to low of a
gauge (too thick and heavy). You'll be surprised how often you can
use 20 or even 22 gauge based on the current requirements. Make sure
the wiring chart you use is for bundled wire, not single strand.
Make sure you use the right size terminal for each wire.
I sized the circuit breakers for the load, not for the wire carrying
capacity. There has been some debate on this, as Nuckolls would size
the fuse/circuit breaker for the wire, not the load. IMHO I'm trying
to protect the expensive load (radio), and the wire will always be
sized with a much greater capacity anyway... so the wire is protected
if I size the fuse for the load.
Pay attention to wire dress... think about your major wiring lanes...
try to get the wiring to all flow into and out of a lane... which
allows you to secure a bundle instead of trying to secure individual
wires.
Ensure you've got wires secured within a few inches of the connection
point. You don't want vibration load to be taken by the connector.
It will fail for sure.
If you are handy with a soldering iron, don't be afraid to use it -
as long as you are securing the soldered joint from vibration.
As I said, I chose ring terminals instead of spades... I want to be
able to count on a lock nut for security. Don't by hardware store
connectors - don't! Get good quality bimetal crimp connectors (3M
makes good ones). Use a real rachetting crimp tool, not a hardware
store special.
I *hate* cable ties... no matter how carefully you cut the ends off,
they'll leave sharp edges that'll get you at some point. I used
nylon wire tie string instead... it works great, it's easy to use,
and it'll never bite you.
The only relays in my plane are the main electrical and starter
solenoids. I know they've gotten much more reliable through the
years, but I'm still shy of using them. I don't know where they'd do
something that there isn't an easy way to do without them.
I grew up as a ham radio operator, worked in a TV repair shop through
HS, and as a technician wiring satellites in college. That (and my
BSEE) form my opinions on this stuff. I enjoy pulling wire and I
believe I'm good at it. I'm coming up on 1100 hours on my Velocity,
and had 900+ hours on a Varieze I built first - with zero wiring
induced issues.
Happy to discuss if you'd like to call.
Dave
Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering
----- Message from Reiff Lorenz <Reiff at Lorenz.com> on Sat, 29 Jun
2013 09:55:22 -0400 -----
To: "reflector at tvbf.org" <
reflector at tvbf.org>
Subject: REFLECTOR: Electrical system -
basic components
I'm starting work on the electrical system. I could use some
recommendations on what to purchase (or how to make) these items and
where you installed them:
· Main bus
· Main ground block
· Firewall ground block
· Avionics ground
I'm going to use the Vertical Power system for switching & circuit
breakers so a combination bus/CB system won't be necessary. Should I
just buy some copper bar and drill screw-holes in it? Is there a
good, basic bus product that works well? Where did you mount it and
how did you protect the power buses from accidental grounding?
Thanks!
Reiff Lorenz, Dayton, OH
Velocity XL-RG, 45% complete
Currently working on: Mounting the battery, main contactor, starter
contactor, and RG control system.
Velocity Owners and Builders Association
http://www.VelocityOwners.com
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