Today's Message Index:
----------------------
1. 04:40 AM - Re(buttal) Circuit Breakers and OVPs Rebuttal (Eric M. Jones)
2. 05:32 AM - Re: Pressure altitude and short sparks (Gary Casey)
3. 08:12 AM - Re: Re(buttal) Circuit Breakers and OVPs (Robert L. Nuckolls, III)
4. 09:15 AM - Re: short Vans master relay stud length, (Robert L. Nuckolls, III)
5. 09:32 AM - Re: Re: Pressure altitude and short sparks (Trampas)
6. 09:32 AM - Re: Re: Pressure altitude and short sparks (Jim Jewell)
7. 11:31 AM - Re: Re: Coax Cable (Brian Lloyd)
8. 11:35 AM - Re: Audio Amplifier (Brian Lloyd)
Message 1
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| Subject: | Re(buttal) Circuit Breakers and OVPs Rebuttal |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
At 12:13 PM 5/3/2004 -0400, you wrote:
>>--> AeroElectric-List message posted by: "Eric M. Jones"
<emjones@charter.net>
>>
>>When an Over-Voltage Module crowbars the alternator field line to ground,
it
>>is extremely important to have a fast blow circuit breaker for the
>>Alternator Field when using a crowbar. This fine point is easy to miss.
>>Eric
>The fault current that flows in the crowbar module is
>something on the order of 200-300A when it trips. I'm aware
>of no 5A breaker that is particularly "slow" when
>presented with this condition. I can offer no
>valid "concerns" to anyone who is selecting breakers for
>their project where the use of crowbar ov protection is
>anticipated.
>Bob . . .
Now Bob....
The circuit breaker associated with the OVP crowbar is a unique case among
aircraft circuit breakers. Typically circuit breakers used for this purpose
ARE fast blow types. I merely observe that this is a good practice to
follow. Otherwise why bother with a fast SCR or Mosfet circuit at all when a
simple NTC thermistor would do fine.
>Define "fast blow circuit breaker" . . .
Okay. I looked up "fast blow circuit breaker" in the dictionary and it says:
"Circuit interrupting device with faster trip or quicker response than
normal." There is a picture of an Eaton 1500.
The idea that a circuit breaker will blow faster at higher current is not a
linear correlation. Most breakers are simple bimetal types.
You choose: Eaton model 700, at 1000% capacity 25 degC, trips from 0.5
second to 1.5 second.
Eaton model 1500, same conditions, trips at 0.025
second to 0.2 seconds.
My epiphany that this should be--was based on making some smoke and trying
to find out why. What I found out is that it is easier to sink hundreds of
amps than it is to interrupt it with a slow bimetal circuit breaker.
My good suggestion is simply to use a fast circuit breaker in the Alternator
Field line when using OVP.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
" I would have made a good Pope."
-- Richard M. Nixon (1913-1994)
Message 2
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| Subject: | Re: Pressure altitude and short sparks |
--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<Actually there is, if the atmospheric pressure drops then it is easier for
the spark to jump to neighboring tab in distributor cap. It really has
little to do with the compression pressure other than the plug on the
compression stroke requires high voltage to fire and when this voltage is
higher than the voltage required to jump to neighboring tab on distributor
cap, electricity will flow via path with least resistance.
Trampas>>
<<That may be the theory, but I have flown several Jacobs powered
aircraft that always misfired above ten or twelve thousand feet
and smoothed out nicely down low. When new wires were pulled
into the ignition loom, the high altitude problems ceased.
Old Bob>>
Trampas,
You are right in that at higher altitudes it takes less voltage to jump
between tabs in the distributor or to jump a gap from a cracked plug wire.
But the condition that creates the voltage level is the pressure in the
combustion chamber, so at higher altitude there will be less voltage
required to jump the gap in the plug, which is the dominant factor. It
should only be a problem at full throttle when combustion pressure is the
highest compared to atmospheric. Then why, as Old Bob points out, would a
non-supercharged engine have a problem at high altitude? Don't know, but
here is a theory: At low altitude the engine is always run rich at full
throttle, keeping the voltage requirement down. Only at high altitude is
the engine leaned while the throttle is full open. Under lean conditions
the voltage requirement rises by some amount and I'm not sure how much -
maybe 10 or 20%? The only other explanation I can come up with is that the
distributed capacitance of the ignition wires tends to require a higher peak
voltage that is actually necessary to jump the gap in the plug. This effect
is constant with altitude, creating a coil voltage that does not drop quite
as fast as altitude rises. Just a couple of theories. Make sense?
Gary Casey
Message 3
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| Subject: | Re: Re(buttal) Circuit Breakers and OVPs |
Rebuttal
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 08:33 AM 5/6/2004 -0400, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
> >--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
><bob.nuckolls@cox.net>
>
>At 12:13 PM 5/3/2004 -0400, you wrote:
> >>--> AeroElectric-List message posted by: "Eric M. Jones"
><emjones@charter.net>
> >>
> >>When an Over-Voltage Module crowbars the alternator field line to ground,
>it
> >>is extremely important to have a fast blow circuit breaker for the
> >>Alternator Field when using a crowbar. This fine point is easy to miss.
> >>Eric
>
>
> >The fault current that flows in the crowbar module is
> >something on the order of 200-300A when it trips. I'm aware
> >of no 5A breaker that is particularly "slow" when
> >presented with this condition. I can offer no
> >valid "concerns" to anyone who is selecting breakers for
> >their project where the use of crowbar ov protection is
> >anticipated.
>
> >Bob . . .
>
>Now Bob....
>
>The circuit breaker associated with the OVP crowbar is a unique case among
>aircraft circuit breakers.
How so unique?
> Typically circuit breakers used for this purpose
>ARE fast blow types. I merely observe that this is a good practice to
>follow.
There are volumes of "good practice" admonitions published
that offer little or no assistance to the reader. For example,
AC43-13 has a big table of wire types that may be considered
for use in the repair or modification of aircraft. I have yet
to meet the A/P that can wade through that pile "good practice"
advice and make a considered selection . . . not to mention
find a supplier that can sell him 20 feet of his wire-of-choice.
The term "fast blow circuit breaker" is non-quantified, and without
recommendations for a specific part number, gives the neophyte builder
no information upon which he/she can operate. I object to the
non-quantified,
non-specific recommendations because they raise concerns while
offering no specific solutions. Tossing out the "fast blow"
tidbit can serve only to raise anxiety levels.
> Otherwise why bother with a fast SCR or Mosfet circuit at all when a
>simple NTC thermistor would do fine.
>
> >Define "fast blow circuit breaker" . . .
>
>Okay. I looked up "fast blow circuit breaker" in the dictionary and it says:
>"Circuit interrupting device with faster trip or quicker response than
>normal."
Luv that term "normal" . . . if you ran a parts house and
an RV builder walks in to purchase a "normal" circuit breaker,
what would you sell him?
>There is a picture of an Eaton 1500.
>
>The idea that a circuit breaker will blow faster at higher current is not a
>linear correlation. Most breakers are simple bimetal types.
>
>You choose: Eaton model 700, at 1000% capacity 25 degC, trips from 0.5
>second to 1.5 second.
> Eaton model 1500, same conditions, trips at 0.025
>second to 0.2 seconds.
>
>My epiphany that this should be--was based on making some smoke and trying
>to find out why. What I found out is that it is easier to sink hundreds of
>amps than it is to interrupt it with a slow bimetal circuit breaker.
>
>My good suggestion is simply to use a fast circuit breaker in the Alternator
>Field line when using OVP.
. . . without explanations like you offered above, the
information is of little value to most of the folks who frequent
this list. The question still unanswered is what are the effects/risks
for having a model 700 versus a model 1500 breaker installed
as the field control breaker?
It's an interesting discussion for folks who make careers of
sifting the fine points of contact physics and thermodynamics.
I'll suggest that in this venue, little jewels of knowledge should
be supported by an explanation of physics and considered recommendations
for selection of parts and materials.
Bob . . .
Message 4
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| Subject: | Re: short Vans master relay stud length, |
again...
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 09:56 PM 5/2/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: czechsix@juno.com
>
>Guys,
>
>I know this has come up before...I've got the Vans master relay with the
>oh-so-short little studs which will barely hold a single terminal let
>alone the multiple ones that I need (battery lead, e-bus feed, Lightspeed
>#1, and aux battery feed).
>
>Before I toss it in the useless parts bin and order a manly B&C relay on
>Viagra with a stud size worthy of my 21st Century electrical system, I'm
>just curious as to why I can't stack the aformentioned terminals directly
>on the + battery terminal? Seems I recall hearing somewhere that this is
>bad practice, but can't think of how the physics of the connection would
>be any different (i.e. less convenient or less secure) this way as
>opposed to attaching them all to the master relay stud. But I don't have
>my battery yet (planning Odyssey PC680) so I'm not sure if there are
>issues I'm unaware of....
Normally, it's not a good idea to fiddle with the assembly
hardware on this series of contactors. Improper placement
of the stud when tightening the mounting nut for the stud
might cause mis-alignment of contact faces within the
assembly and reduce life of the contactor.
Since replacement of the contactor was already being considered,
I thought we might explore the possibility of getting more exposed
threads by replacing the existing mounting nut with a jam nut
as shown in
http://www.aeroelectric.com/Pictures/stud_length.jpg
The White-Rogers contactor on the right seemed to have
good rotational stability so that replacing the original
nut with a thinner one yielded several more threads for
terminal stacking. Unfortunatly, the Cole-Hersee part has
a SPECIAL nut that cannot simply be replaced with the
plain brass jam nut. So, I guess my best recommendation
is to get the more user friendly part from B&C - or stack
terminals on the battery post. It's a threaded brass terminal
so you'd probably get away with it. Personally, I'd
go with the longer stud on a contactor.
Bob . . .
Message 5
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| Subject: | Re: Pressure altitude and short sparks |
--> AeroElectric-List message posted by: "Trampas" <tstern@nc.rr.com>
Gary,
How about this for a theory, the air plane requires XX number of horse power
to fly at some indicated air speed. This will be regardless of altitude as
we are using indicated air speed, assume no wind and same air temperatures.
Thus to produce this horse power the pressure in the cylinders will be same
at low altitudes and high altitudes. The difference is that at low altitudes
the throttle is not opened as wide thus regulating the manifold pressure,
then at higher altitudes you have to open the throttle more to get the extra
oxygen, which will keep the manifold absolute pressure where it was at lower
altitude, again with the assumption air temperature is constant. Thus as
mentioned, in previous posts, the pressure in the cylinders is based on
manifold air pressure. Thus to produce the same horsepower at higher
altitudes you open the throttle more to match manifold pressure to the same
level as it was at low altitudes, assuming same mixture adjustment and same
air temperature.
Regards,
Trampas Stern
www.sterntech.com
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Gary
Casey
Subject: AeroElectric-List: Re: Pressure altitude and short sparks
--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<Actually there is, if the atmospheric pressure drops then it is easier for
the spark to jump to neighboring tab in distributor cap. It really has
little to do with the compression pressure other than the plug on the
compression stroke requires high voltage to fire and when this voltage is
higher than the voltage required to jump to neighboring tab on distributor
cap, electricity will flow via path with least resistance.
Trampas>>
<<That may be the theory, but I have flown several Jacobs powered
aircraft that always misfired above ten or twelve thousand feet
and smoothed out nicely down low. When new wires were pulled
into the ignition loom, the high altitude problems ceased.
Old Bob>>
Trampas,
You are right in that at higher altitudes it takes less voltage to jump
between tabs in the distributor or to jump a gap from a cracked plug wire.
But the condition that creates the voltage level is the pressure in the
combustion chamber, so at higher altitude there will be less voltage
required to jump the gap in the plug, which is the dominant factor. It
should only be a problem at full throttle when combustion pressure is the
highest compared to atmospheric. Then why, as Old Bob points out, would a
non-supercharged engine have a problem at high altitude? Don't know, but
here is a theory: At low altitude the engine is always run rich at full
throttle, keeping the voltage requirement down. Only at high altitude is
the engine leaned while the throttle is full open. Under lean conditions
the voltage requirement rises by some amount and I'm not sure how much -
maybe 10 or 20%? The only other explanation I can come up with is that the
distributed capacitance of the ignition wires tends to require a higher peak
voltage that is actually necessary to jump the gap in the plug. This effect
is constant with altitude, creating a coil voltage that does not drop quite
as fast as altitude rises. Just a couple of theories. Make sense?
Gary Casey
Message 6
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| Subject: | Re: Pressure altitude and short sparks |
--> AeroElectric-List message posted by: "Jim Jewell" <jjewell@telus.net>
While following this thread on ignition wiring etc. I have not as yet
noticed any comments about the effects of spacing between the individual
high tension leads.
Coming into the wonderful world of Vans RV from the automotive field I have
often noted that generally speaking it is considered normal in the aircraft
industry to group the all the high tension leads in parallel bundles only
separating them out to reach the spark plugs. Also the wire used is most
often small diameter wire.
Most often if not always the wires are shielded but I suspect that this is
done more for radio noise suppression than ignition wire crossfire breakdown
reasons.
When I look at the "round engines" with the metal looms I often wonder how
they cope with the combined effects of packing wires into such tight spaces
along with ambient variable moisture, cleaning solvents, hot soak heat etc.
that is sure to be present. I realize that few if any other options exist
when cooling airflow considerations etc. are accounted for. I am not at all
surprised to hear more than one reference the wire harness replacement
having been the fix for misfire events.
Having spent a bit of time around an automotive chassis dynamometer at sea
level, I am satisfied that there is some value in my taking extra effort in
regard to the above. Turning the lights out in the Dyno shop during the
initial run up often provided a graphic insight as to condition of the high
tension wires. At simulated highway speeds with a mild load applied the
lightshow provided was often worth the effort. Often the application of some
wire spacers and a bit of wire re-routing provided the needed fix. Removing
contamination from distributor caps, coils etc. and a spritz or two of water
repelant also helped.
With the above in mind I have given extra effort to using the supplied MSD
separators provided with the LSE Plasma II system. In fact I bought more of
them and applied them to the left side Slick mag wires. The result is
improved wire mounting stability but at half inch spacing between the wires
still less than ideal wire spacing.
I will leave how this applies to altitude related misfiring troubles for the
engineers and therorists to work out amoug them selves. Keep in mind though
that automobiles do get to some quite high mountain altitudes pulling big
loads.
Jim in Kelowna do not archive
Message 7
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--> AeroElectric-List message posted by: Brian Lloyd <brianl@lloyd.com>
McFarland, Randy wrote:
> --> AeroElectric-List message posted by: "McFarland, Randy" <Randy.McFarland@novellus.com>
>
> Along the lines of RG 400 use, can anyone tell me why the Garmin 327
> Transponder installation manual suggests in their Antenna Cable table 2-1
> the max length for the cable is 8.8 feet if using RG 400?
> Is this length specific to the transponder antenna only?
Yes. If you have a DME you can consider that it has the same limitation since
it runs at approximately the same frequency as the transponder.
> Can I run RG 400
> for Com / Nav antennas longer than 8.8 feet? (like about 20' out to the
> wingtip?)
Yes.
When you run a signal through coax some of it is lost in heating the dielectric
between the center conductor and the shield. The loss at 1000 MHz (where the
transponder signal is) is much higher than the loss at 118 MHz. There should
be no problem running VHF comm and nav signals anyplace in the airplane using
RG-400.
--
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
http://www.lloyd.com St. Thomas, VI 00802
+1.340.998.9447 (voice) +1.360.838.9669 (fax)
There is a time to laud one's country and a time to protest.
A good citizen is prepared to do either as the need arises.
Message 8
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| Subject: | Re: Audio Amplifier |
--> AeroElectric-List message posted by: Brian Lloyd <brianl@lloyd.com>
Leo Gates wrote:
> --> AeroElectric-List message posted by: Leo Gates <leogates@allvantage.com>
>
> I would like to build an audio amplifier for my Zenith CH601HDS. I want
> to mount a 3 way bookshelf speaker in the baggage compartment and feed
> the headset audio to it. The speaker I have will handle 40 watts but I
> think driving it with 10 -20 watts should be adequate - any thoughts?
> The amplifier needs 150 Ohm input and 4 - 8 Ohm output, 12 V. DC power.
> Anyone know of a source, either diagram or ready made?
You can find an entire range of high-power automotive amplifiers that should do
the job for you. Get one that has line-level inputs and try that. Get one that
has an adjustable input attenuator (volume control). Most can be bridged
so that they provide more power to one output, such as a subwoofer.
--
Brian Lloyd 6501 Red Hook Plaza
brianl@lloyd.com Suite 201
http://www.lloyd.com St. Thomas, VI 00802
+1.340.998.9447 (voice) +1.360.838.9669 (fax)
There is a time to laud one's country and a time to protest.
A good citizen is prepared to do either as the need arises.
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