Today's Message Index:
----------------------
1. 05:38 AM - Questions about circuit protection ()
2. 06:58 AM - Re: Question about 16V POLYFUSER Radial Leaded Resettable PTC Available at Digi-Key (Robert L. Nuckolls, III)
3. 07:04 AM - Re: Re: Questions about circuit protection (Robert L. Nuckolls, III)
4. 07:09 AM - Re: Question about 16V POLYFUSER Radial Leaded Resettable PTC Available at Digi-Key (Robert L. Nuckolls, III)
5. 07:12 AM - Re: Re: Question about 16V POLYFUSER Radial Leaded Resettable PTC (Robert L. Nuckolls, III)
6. 07:29 AM - Re: Z-14 Switch Combos (Robert L. Nuckolls, III)
7. 09:04 AM - Re: Questions about circuit protection (Robert L. Nuckolls, III)
8. 02:14 PM - Re: Battery Bus Location (PaulR)
9. 03:30 PM - Re: Battery Equalizers (Robert L. Nuckolls, III)
10. 03:33 PM - Re: Re: Battery Bus Location (Robert L. Nuckolls, III)
11. 04:47 PM - Tachometer problems (geoff winter)
12. 05:05 PM - Re: [AeroElectric-List] Questions about circuit protection (Carlos Trigo)
13. 07:26 PM - Re: Question about 16V POLYFUSER Radial Leaded Resettable PTC (marcausman)
14. 08:14 PM - Re: Re: [AeroElectric-List] Questions about circuit protection (Bob McCallum)
15. 08:33 PM - Re: Question about 16V POLYFUSER Radial Leaded Resettable PTC (al38kit)
16. 10:22 PM - Re: Re: [AeroElectric-List] Questions about circuit protection (Jared Yates)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Questions about circuit protection |
1/3/2010 -- 1/5/2010
Hello Bob Nuckolls, May I "Make your day by showing you where you are
wrong?"
You wrote (see your posting copied below):
"First, 14 CFR 91.205 doesn't apply to an amateur built airplane."
and
"....... but you have no obligation to consult these documents that apply to
type certificated aircraft only."
Those statements are not correct. Each experimental amateur built aircraft
will be issued an initial airworthiness certificate in accordance with FAA
Order 8130.2F (or the current version of that order). That airworthiness
certificate will include a number of Operating Limitations, written in
accordance with that order, that apply to that specific aircraft.
Per FAA Order 8130.2F the Operating Limitations will state: "After
completion of Phase I flight testing, unless appropriately equipped for
night and/or instrument flight in accordance with 91.205, this aircraft is
to be operated under VFR, day only."
That sentence means that if one is operating his aircraft at night or in
instrument conditions it must be equipped in accordance with 91.205. The
attached document will provide additional details on this subject.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
==========================================================
Time: 10:38:19 PM PST US
From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
Subject: Re: AeroElectric-List: Questions about circuit protection
>Hold on, back the truck up. Are you saying that if I put the fuses
>under the panel where they aren't accessible then my airplane will still
>meet 14 CFR 91.205 (c) and that I won't need to carry spares?
>
>I would read "that are accessible to the pilot in flight" to mean that
>the fuse panel is accessible to the pilot, not the fusees since who
>cares if you can get to the fuses if you can't get to the panel.
First, 14 CFR 91.205 doesn't apply to an amateur built
airplane. That's not to imply that the FARS don't have
some things to be considered . . . but you have no
obligation to consult these documents that apply to
type certificated aircraft only. Further, 91.205 isn't
the ONLY milestone at which your project is essentially
"un-certifiable".
But assume you adopt failure tolerance as a
design goal. For every piece of equipment
"critical" for the manner in which you plan to use
the airplane, then that piece of equipment needs to
be backed up with a plan-B. There are 100 times
more failures in a piece of electronics that DOES
NOT blow a fuse than there are failures that DO
blow a fuse. If that piece of equipment is deemed
critical, then having spare fuses for the circuit
that supports that system is whistling in the dark.
So assuming you have a back up for every POTENTIALLY
critical system, then if follows that there are NO
critical systems. Hence, whether or not you can reach
breakers or fuses for any system is immaterial.
Bob . . .
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Question about 16V POLYFUSER Radial Leaded |
Resettable PTC Available at Digi-Key
At 05:36 PM 1/4/2010, you wrote:
>Polyfuses only reset themselves IF the cause that made them to trip
>disappears.
>
>Carlos
Sort of . . . the thing that trips a polyfuse is passage
of the minimum current to warm it beyond the trip point
while it is relatively cool. Once it trips, the reistance
goes to a high state where it's EASIER to keep it warm
because presumably, the power is still on, the protected
circuit is still drawing the minimal "keep it tripped"
current.
I think some folks have pointed out that depending on
the sophistication of the device on the protected circuit
the current drawn through the polyfuse in a "tripped"
state will be insufficient to keep it hot and in a
safe . . . low current condition. In some cases, one
could experience an kind of low frequency oscillation
where the circuit trips, the polyswitch cools and
resets and the process repeats.
There are so many interactive variables to consider
that I hope it's obvious that the polyfuse is NOT
a blanket replacement for fuses or breakers. Even
when all the protection dynamics are found acceptable,
there's still the problem of how do you mount these
things in a manner suited to the aircraft power
distribution system environment. Finally, one should
consider how they affect the legacy failure mode
effects study that calls for understanding how
the pilot becomes aware of a problem with the system
such that the plan-a/plan-b decision can be made.
I'm pretty confident that the designers of the
polyswitch never envisioned this device to be
a replacement in the classic applications for
breakers or fuses. The polyswitch offered designers
a NEW opportunity to add protection inside some device
where the use of a breaker or fuse was impractical.
In these situations, the designer of the appliance
can analyze the failure modes independently of the
all-up system (i.e. an airplane full of electro-
whizzies). The idea that we can simply
craft some sort of power distribution etched
circuit board to make a blanket replacement of
legacy power distribution systems is a whole new
ball game. As I've written many times . . . the
polyswitch WILL always keep a wire from catching
fire. Circuit protection safety is not the issue.
Polyswitches throw a wrench into the gears for
how we think about operating the system when the
unexpected and unwelcome event occurs.
Bob . . .
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Questions about circuit protection |
At 06:52 PM 1/4/2010, you wrote:
>Whenever this =93fuses versus circuit breakers=94
>discussion comes afloat, I always wonder why TC
>aircraft always used circuit breakers=85
>
>Carlos
They didn't. The first airplanes to get electrical
systems at Cessna used fuses. They were cartridge
fuse holders with caps that could easily be dropped
on the floor and be difficult to find. When miniature,
low cost breakers came along, they offered a means
by which operational and environmental concerns
for the use of glass cartridge fuses could be
addressed.
It wasn't until the blade fuse came along that
environmental issues were resolved for re-considering
fuses in airplanes. It wasn't until we address the
ideas of failure tolerant system design that the
operational issues were resolved.
If the TC aircraft guys were so disposed, they
could do exactly what we're doing right now. But
regulatory inertia makes this unlikely to happen.
Bob . . .
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Question about 16V POLYFUSER Radial Leaded Resettable |
PTC Available at Digi-Key
At 11:16 AM 1/4/2010, you wrote:
Hi Jeff
I designed and have been using an electrical system similar to the
EXP bus for over a year, for no reason other than experimentation. I
chose a variety of these, ranging from 1A up to 16A... They work as
advertised, and have found their trip performance similar to that of
CB's, i.e. a 2A polyswitch probably won't trip at 2A, unless the
device draws 2A for minutes almost. 2.5A will trip after a few
seconds, 5A will trip after a second, and 100A will trip almost
instantaneously.
<snip>
So to answer your questions, yes I think they can replace CB's or
standard fuses, but I don't think they should. The fact that they
reset themselves whenever power is cycled means that a tripped system
will not stay tripped if you turn off the master switch. Standard
fuses are much better-suited to the task. And that's in my humble opinion
Great observation.
Bob . . .
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Question about 16V POLYFUSER Radial Leaded |
Resettable PTC
At 08:28 PM 1/4/2010, you wrote:
>
>See AC 43.13, chapter 11 quoted below:
>
>11-50. RESETTABLE CIRCUIT PROTECTION
>DEVICES.
>a. All resettable type circuit breakers
>must open the circuit irrespective of the position
>of the operating control when an overload
>or circuit fault exists. Such circuit breakers are
>referred to as trip free.
>b. Automatic reset circuit breakers, that
>automatically reset themselves periodically, are
>not recommended as circuit protection devices
>for aircraft.
This paragraph has been in there for decades . . .
LONG before things like the polyfuse came along.
The self-resetting breakers of yesteryear were
simple adaptations of manual resetting breakers.
Many cars used self-resetting breakers on headlight
circuits in lieu of fuses.
These devices would ALWAYS reset when they cooled.
Unlike the polyfuse which will probably stay tripped
until power is removed, the self-resetting breaker
of 1950 would definitely oscillate between a zero-
current to fault-current condition as long as power
was still on.
Bob . . .
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Z-14 Switch Combos |
At 09:08 PM 1/4/2010, you wrote:
>
>Phil -
>
>I think you misinterpreted Bob's comment. It appears you read it to say
>"you're never ALLOWED to close the cross-feed switch", when Bob meant "you
>might not ever have a reason to close it".
>
>Neal
Correct. The process for deciding how to operate
Z-14 is dependent upon what devices are
fed from each bus and how you use the airplane.
Z-14 was originally crafted for a guy building
a Glasair with full up IFR capability in both
seats. Further, it was the builder's intent to
use this machine in missions that most of us
work hard to avoid.
Z-14 offers OPTIONS for deciding how you will
manage energy resources that have become limited
due to failure of some component like an alternator
or battery contactor.
There is no SET PROCEDURE I can offer you without
doing the same failure modes effects analysis
I would conduct for a TC aircraft with a similar
system installed and tailored to the most demanding
mission for which the airplane is outfitted.
Z-14's cross-feed contactor solved a problem
with attempting to PARALLEL two alternators
in a dual alternator airplane by making them
responsible for SEPARATE systems in normal
operations.
Z-13/8 was crafted to take exploit the existence
of an unused engine accessory drive pad when
a vacuum pump is removed. Some politicians hate
to waste a good crisis, I had to waste a good
drive pad. When considered against the quantum
jumps in reliability offered by modern alternators
and artfully maintained RG batteries, I believe
Z-13/8 is about the most elegant solution to
powering up the light airplane for 99 plus
percent of all OBAM aircraft.
If you have Z-14 installed, then share with us
how equipment in your airplane is powered from
the two busses along with your vision of how
you expect to use this airplane. Is it important
to you to forestall a dark-n-stormy night story
'cause you've had an alternator go belly up while
night IFR over the Rockies crossing a weather
front? If so, what items of equipment are installed
and how are they spread between the two systems?
Bob . . .
Message 7
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Questions about circuit protection |
At 07:15 AM 1/5/2010, you wrote:
>1/3/2010 -- 1/5/2010
>
>Hello Bob Nuckolls, May I "Make your day by showing you where you are
>wrong?"
>
>You wrote (see your posting copied below):
>
>"First, 14 CFR 91.205 doesn't apply to an amateur built airplane."
Thanks for posting the review of instrumentation
requirements! With your permission, I'll post it
to aeroelectric.com and index it in the reference
documents section.
Bob . . .
Message 8
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Battery Bus Location |
Bob,
Thanks for the reply. I'm not opposed to putting it outside on the firewall, I
just didn't know whether the fuse blocks from B&C would be alright out there.
I think you spell out 6" length on the feed wire. If I stick to that, which
makes sense unprotected, then I would have to put it directly on the inside of
the firewall which would be extremely difficult to get to for service. Hopefully
none will be required, but it would be easier on the hot side.
The insulator would indeed be a good method to get the wire inside, but the length
is still a factor.
Does most everyone else put them on the hot side?
Thanks
--------
Paul Rose
N417PR (res)
RV-9A
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=280287#280287
Message 9
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Battery Equalizers |
At 05:26 PM 12/29/2009, you wrote:
Bob et al,
I appreciate the architecture advice and will take it into
consideration. Unfortunately, I'm on a work-driven building hiatus
that'll probably keep me from doing any work on the Velocity for at
least a couple years, so I won't be able to give any solid feedback
on the usefulness of a battery equalizer in this setup for a
while. In the meantime, I can do a quick trade study to look at the
cost and parts count between the multiple bus setup and replacing the
hydraulic power pack and associated control circuits.
I don't know if you looked at the link to the white paper in my
previous post or not, but in it the author shows significant
experimental improvement in battery life using an equalizer in a
series string of batteries. As I need a 24V system in my aircraft
anyway and will be using two batteries in series, it makes sense to
me to take advantage of these improvements if in fact the claims are
true. Have you (or anyone on the list) looked at the white paper
and/or have any knowledge or experience in the use and efficacy of
these equalizers (regardless of whether I keep my multi-bus setup or not)?
Dan,
The IDEAL equalizer will, no doubt, make the 12v tap
on a 24v battery look transparent to the rest of
the system . . . including batteries.
By "ideal" we mean equalizers that are about as
capable as the batteries themselves . . . very
low impedance and capable of carrying what ever
loads are imposed at the tap.
As soon as you choose an equalizer smaller than
anticipated loads, then the lower battery MUST
make up the difference. Yes, it's just for a short
time and the too-small equalizer will fix things
back up once the loads go away. Nonetheless, this
means that the bottom half of the battery is
treated differently than the top half.
Terrible thing to do? Don't know. I have no experience
with it in the distinctly aviation environment
where batteries are protected against deep cycle
and monitored for minimum capacity. How does one
integrate a less than idea equalizer into the
battery maintenance protocols?
My gut feeling is that you'll be happier in the long
run with a conversion of your 14v hardware to 28v
hardware and forget the equalizer. But should you
choose to conduct this experiment, you will become
the go-to guy for guidance on how good an idea it
is.
Bob . . .
Message 10
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Battery Bus Location |
At 04:10 PM 1/5/2010, you wrote:
>
>Bob,
>Thanks for the reply. I'm not opposed to putting it outside on the
>firewall, I just didn't know whether the fuse blocks from B&C would
>be alright out there. I think you spell out 6" length on the feed wire.
That's an idealized notion. If you need to make it 12"
or even longer to satisfy design goals, the world is
not going to come to an end.
> If I stick to that, which makes sense unprotected, then I would
> have to put it directly on the inside of the firewall which would
> be extremely difficult to get to for service. Hopefully none will
> be required, but it would be easier on the hot side.
Then put it in a location for ease of maintenance.
That would be my choice as well. Think about a
way to at least cover if not box-up the fuseblock
like they do under the hood of cars.
>The insulator would indeed be a good method to get the wire inside,
>but the length is still a factor.
The length isn't a REALLY BIG thing, just a
good practice design rule adopted by the TC
side of the house many years ago. How long would
the wire be for both extending the battery
feeder AND ease of maintenance?
>Does most everyone else put them on the hot side?
Good question. How about it guys? Anyone out
there flying fuse blocks on the forward side
of the firewall?
Bob . . .
Message 11
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Tachometer problems |
Hi All
I fly a Corby Starlet using an 1835 VW with a Bendix D4 RN-2021 dual
magneto.
Both magnetos are grounded through separate magneto switches on my panel. I
use
one of these leads to also run my tachometer. This has all been working just
fine, but I've
now replaced the original Westach tacho with a new VDO tachourmeter, item #
333-035-11.
I have the VDO tacho set for 4 stroke, 4 cylinder, single coil operation.
The rpm reading appears accurate, but it is continually fluctuating. Every
second or so the
rpm drops anything from 200 to 1000 rpm momentarily, then returns to normal.
Could anyone advise what I need to do to smooth out the reading. I've tried
putting a diode inline with no joy.
Could anyone suggest some specific combination of
capacitor/resistor/diode inline or parallel to the tacho I could try to
smooth things out? Failed to get any help from VDO so any advice would be
very much appreciated.
Cheers
Geoff
Message 12
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | RE: [AeroElectric-List] Questions about circuit protection |
Bob
I really don=92t want to resuscitate this discussion but, even being
aware of
the technical advantages of fuses versus circuit breakers, it is indeed
almost impossible to convince a pilot that a fuse is better than a
circuit
breaker.
In flight, when a fuse blows, the pilot will hardly notice it, and even
if
some device (whose circuit was protected by that fuse) becomes blank, he
will not know if it was the fuse or anything else that caused that
device to
die.
If a circuit breaker pops out, there is a big probability the pilot will
immediately notice it, or at least after seeing any device die, he will
immediately look to the circuit breakers heads to look for the one that
popped out.
Being a pilot trained for so many things, he must also know that he
shall
not push that particular breaker in, unless he wants to light up the
fire
which will burn his own ass=85
It is probably easy to convince an aircraft builder to prefer fuses, but
since in the OBAM world we are builders AND pilots, circuit breakers are
certainly much more user friendly for the pilot, even knowing that the
PILOT
is the most dangerous single-point-of-failure in a flying aircraft
Carlos
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Robert L.
Nuckolls, III
Sent: ter=E7a-feira, 5 de Janeiro de 2010 15:03
Subject: RE: AeroElectric-List: Re: Questions about circuit protection
At 06:52 PM 1/4/2010, you wrote:
Whenever this =93fuses versus circuit breakers=94 discussion comes
afloat, I
always wonder why TC aircraft always used circuit breakers=85
Carlos
They didn't. The first airplanes to get electrical
systems at Cessna used fuses. They were cartridge
fuse holders with caps that could easily be dropped
on the floor and be difficult to find. When miniature,
low cost breakers came along, they offered a means
by which operational and environmental concerns
for the use of glass cartridge fuses could be
addressed.
It wasn't until the blade fuse came along that
environmental issues were resolved for re-considering
fuses in airplanes. It wasn't until we address the
ideas of failure tolerant system design that the
operational issues were resolved.
If the TC aircraft guys were so disposed, they
could do exactly what we're doing right now. But
regulatory inertia makes this unlikely to happen.
Bob . . .
Message 13
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Question about 16V POLYFUSER Radial Leaded Resettable |
PTC
"Probably" ?
--------
Marc Ausman
http://www.verticalpower.com "Move up to a modern electrical system"
RV-7 IO-390 Flying
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=280320#280320
Message 14
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | RE: [AeroElectric-List] Questions about circuit |
protection
Carlos;
Different "Bob" here, but I must disagree with your viewpoint. Please see
embedded comments.
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Carlos
Trigo
Sent: Tuesday, January 05, 2010 8:00 PM
Subject: AeroElectric-List: RE: [AeroElectric-List] Questions about circuit
protection
Bob
I really don't want to resuscitate this discussion but, even being aware of
the technical advantages of fuses versus circuit breakers, it is indeed
almost impossible to convince a pilot that a fuse is better than a circuit
breaker.
Why?? Fuse is simpler, less expensive, probably neater, and serves its
intended purpose admirably. I've been a pilot for 35 years, a builder for
only 5 and I much prefer the simplicity and economy of fuses. I consider
myself a pilot first and I don't need convincing, I know fuses are better.
(At least in my own mind they are)
In flight, when a fuse blows, the pilot will hardly notice it, and even if
some device (whose circuit was protected by that fuse) becomes blank, he
will not know if it was the fuse or anything else that caused that device to
die.
And how is that any different than the symptoms presented by a tripped
breaker? The supplied device ceases to function in either case. To the pilot
operating the aircraft there is no difference, he looses the benefit of
whatever widget was supplied power by that circuit.
If a circuit breaker pops out, there is a big probability the pilot will
immediately notice it, How or why will he notice it?? and why does it
matter?? or at least after seeing any device die, he will immediately look
to the circuit breakers heads to look for the one that popped out.
Are you making the assumption that the breakers are somehow readily
available, visible and accessible in flight?? What if the breakers are
neatly hidden away up under the panel, are on a fold down bracket, or in
some other manner not readily apparent to the pilots position or his line of
sight? What if the breaker that faults is one on the battery buss, hidden
away in the tail cone next the battery? How does that present some different
scenario to the pilot than would a fuse??
Being a pilot trained for so many things, he must also know that he shall
not push that particular breaker in, unless he wants to light up the fire
which will burn his own ass.
All the more reason for, and another demonstration of, the superiority of
hidden fuses. (Or hidden breakers for that matter) Removes the temptation
and doesn't require the discipline and willpower "not to reset".
It is probably easy to convince an aircraft builder to prefer fuses, but
since in the OBAM world we are builders AND pilots, circuit breakers are
certainly much more user friendly for the pilot, even knowing that the PILOT
is the most dangerous single-point-of-failure in a flying aircraft
I really fail to see the "user friendly" analogy. The fuses in all the cars
I've owned have been about as "user friendly" as I can imagine, and in some
of my cars I never had occasion to even learn where they were. Can't
remember the last time one ever blew. In the dozen or so types of aircraft
I'm checked out in, I can't remember the last time a fuse blew, or a breaker
tripped either. In a properly designed and functioning car or aircraft, I
wouldn't "expect" the circuit protection devices to be called upon to do
their job for the life of the vehicle, be it airborne or ground based. I
fully agree with the "insurance" provided by their presence, but wouldn't
expect them to be called upon. (If breakers are somehow superior, why do the
millions of cars on the road use fuses?) As Bob explained the main reason
aircraft migrated to expensive breakers was to mitigate the drawbacks of
"old" technology glass cartridge fuses such as loose retaining caps and low
pressure contacts prone to corrosion. We now have modern "blade" fuses
without these shortcomings.
Don't get me wrong, I fully understand and respect your opinion and
viewpoint, I just can't get a grasp on the logic behind it. As one who makes
a living as an engineer, I view simple as better and fuses are simpler and
less expensive than breakers and have much less chance of having something
go wrong with them which makes the pilot side of me much more relaxed and
comfortable with fuses than breakers.
Carlos
Respectfully,
Bob McC
Message 15
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Question about 16V POLYFUSER Radial Leaded Resettable |
PTC
I have an EXP bus that I have been considering for my project. (That I got for
a $40, delivered.) It looks like a slick unit.
I can understand the concern for a circuit resetting itself after the power is
restored...but isn't that a reason we put switches on things?...Like leave that
circuit off if it has a problem...
Sorry, just don't see the design as having much of a downside. If you think you
may accidentally turn the thing back on, put some red tape on the switch or
something...pull the wire.
Al
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=280326#280326
Message 16
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | RE: [AeroElectric-List] Questions about circuit |
protection
In some of the larger factory-made airplanes, the breakers are situated
behind the pilot's head. In this location popped breakers are only obvious
if you get up out of your seat to look. It's pretty embarrassing to call
the maintenance guys, go through some diagnostics on a non-functioning
gadget, then have them instruct you to pull the breaker and doh! It was
popped all along. One time I tried to extend the flaps for landing, but
they didn't extend because all 5 of the flap motor circuit breakers have
been pulled since before takeoff. In that case the mechanics were working
on the flaps, pulled the breakers as a normal safety measure, but then
forgot to put them in when they were done. Then two pilots didn't notice
that they were out, at least not until configuring for the landing. In that
airplane the normal flap setting for takeoff was zero. I can think of
several other similar stories that illustrate that popped breakers aren't
necessarily all that obvious. Once you realize that something isn't working
and start looking for a breaker, they might be more obvious than a fuse,
unless you spend the extra cents on the bling-bling LED fuses.
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Bob
McCallum
Sent: Tuesday, January 05, 2010 11:11 PM
Subject: RE: AeroElectric-List: RE: [AeroElectric-List] Questions about
circuit protection
Carlos;
Different "Bob" here, but I must disagree with your viewpoint. Please see
embedded comments.
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Carlos
Trigo
Sent: Tuesday, January 05, 2010 8:00 PM
Subject: AeroElectric-List: RE: [AeroElectric-List] Questions about circuit
protection
Bob
I really don't want to resuscitate this discussion but, even being aware of
the technical advantages of fuses versus circuit breakers, it is indeed
almost impossible to convince a pilot that a fuse is better than a circuit
breaker.
Why?? Fuse is simpler, less expensive, probably neater, and serves its
intended purpose admirably. I've been a pilot for 35 years, a builder for
only 5 and I much prefer the simplicity and economy of fuses. I consider
myself a pilot first and I don't need convincing, I know fuses are better.
(At least in my own mind they are)
In flight, when a fuse blows, the pilot will hardly notice it, and even if
some device (whose circuit was protected by that fuse) becomes blank, he
will not know if it was the fuse or anything else that caused that device to
die.
And how is that any different than the symptoms presented by a tripped
breaker? The supplied device ceases to function in either case. To the pilot
operating the aircraft there is no difference, he looses the benefit of
whatever widget was supplied power by that circuit.
If a circuit breaker pops out, there is a big probability the pilot will
immediately notice it, How or why will he notice it?? and why does it
matter?? or at least after seeing any device die, he will immediately look
to the circuit breakers heads to look for the one that popped out.
Are you making the assumption that the breakers are somehow readily
available, visible and accessible in flight?? What if the breakers are
neatly hidden away up under the panel, are on a fold down bracket, or in
some other manner not readily apparent to the pilots position or his line of
sight? What if the breaker that faults is one on the battery buss, hidden
away in the tail cone next the battery? How does that present some different
scenario to the pilot than would a fuse??
Being a pilot trained for so many things, he must also know that he shall
not push that particular breaker in, unless he wants to light up the fire
which will burn his own ass.
All the more reason for, and another demonstration of, the superiority of
hidden fuses. (Or hidden breakers for that matter) Removes the temptation
and doesn't require the discipline and willpower "not to reset".
It is probably easy to convince an aircraft builder to prefer fuses, but
since in the OBAM world we are builders AND pilots, circuit breakers are
certainly much more user friendly for the pilot, even knowing that the PILOT
is the most dangerous single-point-of-failure in a flying aircraft
I really fail to see the "user friendly" analogy. The fuses in all the cars
I've owned have been about as "user friendly" as I can imagine, and in some
of my cars I never had occasion to even learn where they were. Can't
remember the last time one ever blew. In the dozen or so types of aircraft
I'm checked out in, I can't remember the last time a fuse blew, or a breaker
tripped either. In a properly designed and functioning car or aircraft, I
wouldn't "expect" the circuit protection devices to be called upon to do
their job for the life of the vehicle, be it airborne or ground based. I
fully agree with the "insurance" provided by their presence, but wouldn't
expect them to be called upon. (If breakers are somehow superior, why do the
millions of cars on the road use fuses?) As Bob explained the main reason
aircraft migrated to expensive breakers was to mitigate the drawbacks of
"old" technology glass cartridge fuses such as loose retaining caps and low
pressure contacts prone to corrosion. We now have modern "blade" fuses
without these shortcomings.
Don't get me wrong, I fully understand and respect your opinion and
viewpoint, I just can't get a grasp on the logic behind it. As one who makes
a living as an engineer, I view simple as better and fuses are simpler and
less expensive than breakers and have much less chance of having something
go wrong with them which makes the pilot side of me much more relaxed and
comfortable with fuses than breakers.
Carlos
Respectfully,
Bob McC
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|