Today's Message Index:
----------------------
1. 05:47 AM - Flap Schematic Question (Grosvenor, Gary L [CC])
2. 06:51 AM - Heat Shrink on Coax (Larry Colley)
3. 07:01 AM - Re: Emergency Buss/Standby Alternator (Robert L. Nuckolls, III)
4. 07:02 AM - Re: Alternator Wiring Question (Robert L. Nuckolls, III)
5. 07:21 AM - Re: Re: Load Dumps (Robert L. Nuckolls, III)
6. 07:41 AM - Re: Re: Load Dumps (Paul Messinger)
7. 07:59 AM - Re: Emergency Buss/Standby Alternator (flyv35b)
8. 09:31 AM - Re: Emergency Buss/Standby Alternator (Robert L. Nuckolls, III)
9. 09:33 AM - Re: Heat Shrink on Coax (Robert L. Nuckolls, III)
10. 09:47 AM - Re: Flap Schematic Question (Robert L. Nuckolls, III)
11. 09:57 AM - Re: Re: Load Dumps (Robert L. Nuckolls, III)
12. 01:33 PM - Re: Re: Load Dumps (Paul Messinger)
13. 01:40 PM - Re: Re: Load Dumps (Rogers, Bob J.)
14. 06:24 PM - Alternator (Bobdeva@aol.com)
15. 06:55 PM - Re: Alternator (Benford2@aol.com)
Message 1
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| Subject: | Flap Schematic Question |
--> AeroElectric-List message posted by: "Grosvenor, Gary L [CC]" <Gary.Grosvenor@mail.sprint.com>
Bob - Here's a newbie question for you but please forgive my parochial cerebral
base. I was studying your flap schematic.
Question: What are the inverted triangle symbols with the letter L in them? These
symbols are at the end of what I think are conductors coming off a connection
point on the retract and extend relays.
Thanks so much for your expertise and willingness to share!
I'm still tryin' to learn the lingo.
Gary
Message 2
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| Subject: | Heat Shrink on Coax |
--> AeroElectric-List message posted by: Larry Colley <larry@grrok.com>
I have seen notes stating not to use heat shrink tubing on coax because the
heat will destroy the coax insulation. ??Does this apply to both RG58 and
RG400??
Message 3
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| Subject: | Re: Emergency Buss/Standby Alternator |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 02:16 PM 2/26/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: "flyv35b"
><flyv35b@ashcreekwireless.com>
>
>Bob,
>
>I have a 71 V35B Bonanza which I am in process of modifying the instrument
>panel and the electrical system to improve it's IFR capability and
>incorporate some backup systems. The original main bus (copper strip) was
>cut and a separate avionics bus is now supplied through a 35amp breaker
>switch via a 10 gauge wire. I have added an electric attitude indicator as
>a backup for a vacuum failure and am planning on installing the B&C 20amp
>standby alternator system. Even though this is not an OBAM aircraft, as an
>A&P/IA I do all the modifications and maintenance. I would welcome your
>opinion about some questions I have and others might be interested as well.
>
>I would like to install an emergency buss with an always-hot feed off the
>battery bus as a backup and to eliminate the single-point-of-failure
>avionics switch.
Why a separate bus? Make your current "avionics" bus an endurance
bus, ad a diode in series with the current avionics master so as
to avoid inadvertent back-feeding of the bus via alternate feed.
Then add an alternate feedpath from the battery. The fuse will be
bigger than 5A so to satisfy the feds you'll need the disconnect
relay shown in:
http://www.aeroelectric.com/temp/E-BusFatFeed.gif
> The EB would have numerous items, including an S-Tec 50
>AP, (removed from the existing avionics and main bus) with a total MAX
>current of nearly 20amp. Typical current would be more like 12amp, or less
>if load was shed. The EB would be supplied with a 12ga wire/16ga fusible
>link through a 20amp (or maybe 15a) breaker switch and normally through the
>D-25 essential bus diode from the main or avionics bus automatically. I
>would like the breaker switch to open before the fusible link fails so that
>load could be shed and then the switch could be closed again.
>
>1. Is the idea of having an EB even worthwhile if I incorporate the B&C
>standby alternator system?
This is a big change as far as the feds are concerned. You'll need
an STC. The B&C standby alternator is easy to get approved (it has
an STC) so having dual feedpaths for the e-bus is the only thing
you need to add . . . even THAT may get you up to your eyeballs in
paperwork . . . but it's as effective as a whole new bus structure
and easy to install.
>2. If it is, or if I don't incorporate the B&C alternator, does the D-25
>essential bus diode have the capacity to handle the proposed current in the
>normal direction? I assume this is the easiest way to supply the EB and the
>0.6v drop is of no concern?
Correct. Mount the diode on 25 square inches of aluminum surface
or more to dump the heat.
>3. How would the D-25 fail if it did? Open circuit or what?
It generally shorts (you need to preflight test this) and if it
opens, you have the alternate feed path.
>4. Is there a better way to protect the always-hot feed line such as with a
>20amp current limiter (I haven't seen any with that low of rating)?
>5. If I don't incorporate the EB should I install another breaker-switch in
>parallel with the existing avionics master switch to eliminate the
>single-point-of-failure?
>
>Although the B&C system is STC'd for the Bonanza, would the addition of an
>emergency buss constitute a major alteration in your opinion (changes to the
>basic design of the electrical system - per FAR Part 43, Appendix A)?
If you made your airplane look like figure Z-12 except you add
relay cited above, we're not going to read any dark-n-stormy-night
stories authored by you about how your electrical system came
up short.
Bob . . .
Message 4
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| Subject: | Re: Alternator Wiring Question |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 04:38 PM 2/26/2004 -0600, you wrote:
>--> AeroElectric-List message posted by: "Metcalfe, Lee, AIR"
><Lee.Metcalfe@jocogov.org>
>
>My flying Lancair 320 (not built by me) has an automotive-type,
>externally-regulated alternator with absolutely no identifying markings
>on it other than "Made In Japan" and identifiers next to the
>connections. The alternator is a belt-driven, boss-mount type on a Lyc
>320. It has binding posts for all connections plus a provision for a
>three-spade connector, which is where it is connected to the regulator
>in this particular installation. Here is the shape of the connector and
>the markings...
>
> E
> _____
> | ___ |
> __| |__
>| |
>| | | |
>| | | |
>| |
>-------------
> F N
>
>The N spade is unused. The F spade is connected to the "FLD" connection
>on the regulator. The E spade is connected to the case ground of the
>regulator (mounted on the firewall).
>
>My question is, what is the purpose of the E connection, and is it
>necessary? I ask because I'm about to swap out the generic
>automotive-type regulator for a B&C LR3C and need to know whether I need
>to keep that E connection and why.
I'm guessing but I'll suggest the "E" is the ground connection
for the second field brush. Leave it in place to use the
LR3 regulator.
Bob . . .
Message 5
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 06:57 PM 2/26/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
>Load Dump occurs anytime the generator sheds its load (like turning
>something off), because the generator/alternator stator must reduce its
>magnetic field. This takes a while---almost half-a-second in the worst case.
>Load Dump is at it's worst when nothing but a flat battery is being honked
>on by the alternator/ generator and every other load is off---THEN the
>battery gets disconnected.
>
>I've been watching this load dump stuff with interest. I designed a
>combination lightning suppressor and load dump suppressor which will see the
>light of day soon. But I could not calculate the energy sufficiently to size
>the Transient Voltage Suppressor network. But realistically the automotive
>people had this figured out a long time ago. The chief document seems to be
>SAE J1113-11 but you have to pay big bucks to get a look at it, and there's
>that secret pledge thingy.... But the other guys have published standards
>which presumably are technically close, and they can be found online.
>
>Standard Open-Circuit Volts Rise Time (10%-90%) Pulse duration
>(10%-10%)
>
>SAE J1113-11 ???? ???? ????
>Chrysler PF9326 91.5 V 5-10 mS 300 mS
>Ford CL240 60 V 1-10 mS 300 mS
>ISO 7637 ?? 5-10 mS 50-400 mS
>
>All these standards presume a quick rise from nominal to some higher
>voltage, then a slower exponential decay back to the nominal base. So they
>have the similar graphs but different values. All these standards also have
>a particular repetition rate, a load impedance, and some minor details, but
>they are quite similar.
>
>Chrysler standard PF9326 (good published information can be found online)
>presumes there is some load on the system. There is a circuit called the
>"Load Dump Vehicle Suppression Model" that simulates what one would expect
>to find in a real-world vehicle (whether or not it keeps its wheels on the
>ground.).
>
>According to the Chrysler standard, the peak voltage under these condition
>is 38 volts for a nominal operating voltage of 13.5V and of course a load
>given by the LDVSM, but about 0.5 ohms..
>
>To properly design a system to squash this stuff we need to know the worst
>case system energy (in Joules), which, we all remember, is a Watt-second.
>These are hard numbers to come by, but we can tease them out of the
>published data: Chrysler presumes a Load Dump pulse of 91.5 Volts into a 0.5
>ohm load. The 91.5 volts is the alternator/generator potential, and the peak
>current is therefore 91.5/0.5=183 Amps. And peak watts (power) is therefore
>16.7 kW. The exponential decay is 0.300 Seconds. So that's (...are you
>following this?) 16.7 kW X 0.300 S=5 kW seconds X the correction factor for
>the exponential decay which is about 1/3-1/2. So we can use a 2.5 kW(S)
>Transient Voltage Suppressor. If we use two we buy a little margin.
>
>George's experience with a 5 kW TVS blowing up....I don't know, but if it
>was across the generator or close enough so that the 0.5 ohms didn't
>apply...ka-blammmm.
I'm suspicious of how a device rated to produce 50A output
and magnetically limited to some value just above that
can produce a 183A spike . . .
I suspect we're going to find that 90v is open circuit, and that
when the transient is clamped off at some lower level that the
current is no higher than what the alternator puts out.
Total energy is still the key. Consider the battery-dump under
consideration: An heavily loaded alternator with built in regulator
is unhooked from the battery. The alternator isn't defective
before the event. NOW . . . it's running self excited into an
open circuit. I suspect this event is neither inductive or transient
(short duration typical of an L/R or R-C timed event).
The big question is how the alternator's built in regulator behaves.
If the regulator can open the field circuit before voltages get
so high that the regulator itself is damaged, then everything
comes to rest in an orderly manner. Depending on response time
of the REGULATOR, the TVS has to grunt 50A or so of current for
DURATION OF RESPONSE TIME . . . this is how George's TVS got
launched into orbit.
Response time can be a huge variable from one make of regulator
to the next. I'm hoping that we can deduce enough information
from the testing to modify recommendations for implementing
Z-24 with some degree of comfort. If not (and the pilot
really feels a need to flip alternator switches on and off
while the engine is running), then I may have to retreat
to the original philosophy of recommending that airplanes
fly only with externally regulated alternators.
Keep in mind that the investigation before us is needed
only to protect an alternator from the pilot. Z-24 provides
the ov protection desired for the rest of the system and
becomes problematical only if switches are operated
unnecessarily and at inappropriate times. Figure Z-24 is
going to disconnect an alternator wherein the regulator
has ALREADY FAILED. Anyone with Z-24 up and running
has no cause for concerns as long as he/she operates
the alternator in a manner that is consistent
with 99.999% of the flights conducted every day.
Bob . . .
Message 6
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--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
GREAT INFO.
Given the normal connection of the alternator directly connected to the main
bus and the battery connected via a contactor to the same bus; IF the
battery is disconnected when taking a charge we get the load dump and the
voltage on the main bus rises to what ever it takes until that charge
current is consumed. This can result in what ever is "ON" at the time seeing
very high voltages (compared to their rated max) and for durations much
longer than they are designed to accommodate. Ref your data.
Use of a TVS should keep the current to no more than the "dumped" current
(it seems to me) so in that respect I question that part of your info.
However shorting to ground with low resistance can cause higher momentary
currents as you suggest. The use of a TVS will not provide a simple 0.5 ohm
load but provides a simulated battery so the alternator "sees" the removal
of the battery as a slight increase in the output voltage and the TVS simply
dumps the excess current at the expense of the higher "BUS" voltage. The
alternator does not see a load dump in this case, just a slight jump in the
load voltage. In a non failed condition the regulator takes over and the
voltage returns to normal. The TVS bridges the time between the battery
removal and the response by the regulator.
This higher bus voltage may trigger the OVP circuit and terminates the
energy and limits the heat in the TVS to prevent damage to the TVS.
Thus we need both designs in a system. The TVS keeps the voltage down and
the OVP shuts the alternator down (in severe cases).
The TVS is designed to short if it over heats and that short will open blow
the in line fuse "Bob" shows in the "B" lead if the OVP fails or the
alternator has failed.
This leaves the question of what the bus voltage rises to during the load
dump.
I have experimented with 5KW 18V and it clamps fine but at a voltage above
20V (more data in a few days). It does appear that the voltage will rise to
above the max at least for some of my equipment.
This is the final concern to me. That is limiting the bus "over voltage" to
what the attached equipment can tolerate. A few milliseconds is typically
tolerated in the devices input circuit filters but your 200-300 ms duration
may not be tolerated.
At least the above is how I see the problem.
Paul
----- Original Message -----
From: "Eric M. Jones" <emjones@charter.net>
Subject: AeroElectric-List: Re: Load Dumps
> --> AeroElectric-List message posted by: "Eric M. Jones"
<emjones@charter.net>
>
> Load Dump occurs anytime the generator sheds its load (like turning
> something off), because the generator/alternator stator must reduce its
> magnetic field. This takes a while---almost half-a-second in the worst
case.
> Load Dump is at it's worst when nothing but a flat battery is being honked
> on by the alternator/ generator and every other load is off---THEN the
> battery gets disconnected.
>
> I've been watching this load dump stuff with interest. I designed a
> combination lightning suppressor and load dump suppressor which will see
the
> light of day soon. But I could not calculate the energy sufficiently to
size
> the Transient Voltage Suppressor network. But realistically the automotive
> people had this figured out a long time ago. The chief document seems to
be
> SAE J1113-11 but you have to pay big bucks to get a look at it, and
there's
> that secret pledge thingy.... But the other guys have published standards
> which presumably are technically close, and they can be found online.
>
> Standard Open-Circuit Volts Rise Time (10%-90%) Pulse duration
> (10%-10%)
>
> SAE J1113-11 ???? ???? ????
> Chrysler PF9326 91.5 V 5-10 mS 300 mS
> Ford CL240 60 V 1-10 mS 300 mS
> ISO 7637 ?? 5-10 mS 50-400 mS
>
> All these standards presume a quick rise from nominal to some higher
> voltage, then a slower exponential decay back to the nominal base. So they
> have the similar graphs but different values. All these standards also
have
> a particular repetition rate, a load impedance, and some minor details,
but
> they are quite similar.
>
> Chrysler standard PF9326 (good published information can be found online)
> presumes there is some load on the system. There is a circuit called the
> "Load Dump Vehicle Suppression Model" that simulates what one would expect
> to find in a real-world vehicle (whether or not it keeps its wheels on the
> ground.).
>
> According to the Chrysler standard, the peak voltage under these condition
> is 38 volts for a nominal operating voltage of 13.5V and of course a load
> given by the LDVSM, but about 0.5 ohms..
>
> To properly design a system to squash this stuff we need to know the worst
> case system energy (in Joules), which, we all remember, is a Watt-second.
> These are hard numbers to come by, but we can tease them out of the
> published data: Chrysler presumes a Load Dump pulse of 91.5 Volts into a
0.5
> ohm load. The 91.5 volts is the alternator/generator potential, and the
peak
> current is therefore 91.5/0.5=183 Amps. And peak watts (power) is
therefore
> 16.7 kW. The exponential decay is 0.300 Seconds. So that's (...are you
> following this?) 16.7 kW X 0.300 S=5 kW seconds X the correction factor
for
> the exponential decay which is about 1/3-1/2. So we can use a 2.5 kW(S)
> Transient Voltage Suppressor. If we use two we buy a little margin.
>
> George's experience with a 5 kW TVS blowing up....I don't know, but if it
> was across the generator or close enough so that the 0.5 ohms didn't
> apply...ka-blammmm.
>
> Regards,
> Eric M. Jones
> www.PerihelionDesign.com
> 113 Brentwood Drive
> Southbridge MA 01550-2705
> Phone (508) 764-2072
> Email: emjones@charter.net
>
> "I only regret my economies."
> Reynolds Price
>
>
Message 7
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| Subject: | Re: Emergency Buss/Standby Alternator |
--> AeroElectric-List message posted by: "flyv35b" <flyv35b@ashcreekwireless.com>
> Why a separate bus? Make your current "avionics" bus an endurance
> bus, ad a diode in series with the current avionics master so as
> to avoid inadvertent back-feeding of the bus via alternate feed.
> Then add an alternate feedpath from the battery. The fuse will be
> bigger than 5A so to satisfy the feds you'll need the disconnect
> relay shown in:
>
> http://www.aeroelectric.com/temp/E-BusFatFeed.gif
Yes, that would be simpler. Why is 5amp the maximum that the FAA seems to
be happy with on always-hot feed lines? If that is the case why not run 3
separate wires that are each fused (5amp) and connect them together at the
EB to feed it a total of 15amp? Would this keep the FAA happy?
Thanks for your advice.
Cliff
----- Original Message -----
From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Subject: Re: AeroElectric-List: Emergency Buss/Standby Alternator
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
>
> At 02:16 PM 2/26/2004 -0800, you wrote:
> >--> AeroElectric-List message posted by: "flyv35b"
> ><flyv35b@ashcreekwireless.com>
> >
> >Bob,
> >
> >I have a 71 V35B Bonanza which I am in process of modifying the
instrument
> >panel and the electrical system to improve it's IFR capability and
> >incorporate some backup systems. The original main bus (copper strip)
was
> >cut and a separate avionics bus is now supplied through a 35amp breaker
> >switch via a 10 gauge wire. I have added an electric attitude indicator
as
> >a backup for a vacuum failure and am planning on installing the B&C 20amp
> >standby alternator system. Even though this is not an OBAM aircraft, as
an
> >A&P/IA I do all the modifications and maintenance. I would welcome your
> >opinion about some questions I have and others might be interested as
well.
> >
> >I would like to install an emergency buss with an always-hot feed off the
> >battery bus as a backup and to eliminate the single-point-of-failure
> >avionics switch.
>
> Why a separate bus? Make your current "avionics" bus an endurance
> bus, ad a diode in series with the current avionics master so as
> to avoid inadvertent back-feeding of the bus via alternate feed.
> Then add an alternate feedpath from the battery. The fuse will be
> bigger than 5A so to satisfy the feds you'll need the disconnect
> relay shown in:
>
> http://www.aeroelectric.com/temp/E-BusFatFeed.gif
>
> > The EB would have numerous items, including an S-Tec 50
> >AP, (removed from the existing avionics and main bus) with a total MAX
> >current of nearly 20amp. Typical current would be more like 12amp, or
less
> >if load was shed. The EB would be supplied with a 12ga wire/16ga fusible
> >link through a 20amp (or maybe 15a) breaker switch and normally through
the
> >D-25 essential bus diode from the main or avionics bus automatically. I
> >would like the breaker switch to open before the fusible link fails so
that
> >load could be shed and then the switch could be closed again.
> >
> >1. Is the idea of having an EB even worthwhile if I incorporate the B&C
> >standby alternator system?
>
> This is a big change as far as the feds are concerned. You'll need
> an STC. The B&C standby alternator is easy to get approved (it has
> an STC) so having dual feedpaths for the e-bus is the only thing
> you need to add . . . even THAT may get you up to your eyeballs in
> paperwork . . . but it's as effective as a whole new bus structure
> and easy to install.
>
> >2. If it is, or if I don't incorporate the B&C alternator, does the D-25
> >essential bus diode have the capacity to handle the proposed current in
the
> >normal direction? I assume this is the easiest way to supply the EB and
the
> >0.6v drop is of no concern?
>
> Correct. Mount the diode on 25 square inches of aluminum surface
> or more to dump the heat.
>
> >3. How would the D-25 fail if it did? Open circuit or what?
>
> It generally shorts (you need to preflight test this) and if it
> opens, you have the alternate feed path.
>
> >4. Is there a better way to protect the always-hot feed line such as
with a
> >20amp current limiter (I haven't seen any with that low of rating)?
> >5. If I don't incorporate the EB should I install another breaker-switch
in
> >parallel with the existing avionics master switch to eliminate the
> >single-point-of-failure?
> >
> >Although the B&C system is STC'd for the Bonanza, would the addition of
an
> >emergency buss constitute a major alteration in your opinion (changes to
the
> >basic design of the electrical system - per FAR Part 43, Appendix A)?
>
> If you made your airplane look like figure Z-12 except you add
> relay cited above, we're not going to read any dark-n-stormy-night
> stories authored by you about how your electrical system came
> up short.
>
> Bob . . .
>
>
Message 8
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| Subject: | Re: Emergency Buss/Standby Alternator |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 07:58 AM 2/27/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: "flyv35b"
><flyv35b@ashcreekwireless.com>
>
> > Why a separate bus? Make your current "avionics" bus an endurance
> > bus, ad a diode in series with the current avionics master so as
> > to avoid inadvertent back-feeding of the bus via alternate feed.
> > Then add an alternate feedpath from the battery. The fuse will be
> > bigger than 5A so to satisfy the feds you'll need the disconnect
> > relay shown in:
> >
> > http://www.aeroelectric.com/temp/E-BusFatFeed.gif
>
>Yes, that would be simpler. Why is 5amp the maximum that the FAA seems to
>be happy with on always-hot feed lines?
Crash safety.
> If that is the case why not run 3
>separate wires that are each fused (5amp) and connect them together at the
>EB to feed it a total of 15amp? Would this keep the FAA happy?
No. A fault anywhere downstream of the fuse array
can produce current flows and durations in excess
of that which a single 5A fuse would offer.
Bob . . .
Message 9
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| Subject: | Re: Heat Shrink on Coax |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 07:57 AM 2/27/2004 -0700, you wrote:
>--> AeroElectric-List message posted by: Larry Colley <larry@grrok.com>
>
>I have seen notes stating not to use heat shrink tubing on coax because the
>heat will destroy the coax insulation. ??Does this apply to both RG58 and
>RG400??
No, only the RG58 which uses 1940's era plastics. Any modern
coax which includes RG-400/RG-142 styles.
Bob . . .
Message 10
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| Subject: | Re: Flap Schematic Question |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 07:46 AM 2/27/2004 -0600, you wrote:
>--> AeroElectric-List message posted by: "Grosvenor, Gary L [CC]"
><Gary.Grosvenor@mail.sprint.com>
>
>Bob - Here's a newbie question for you but please forgive my parochial
>cerebral base. I was studying your flap schematic.
>
>Question: What are the inverted triangle symbols with the letter L in
>them? These symbols are at the end of what I think are conductors coming
>off a connection point on the retract and extend relays.
>
>Thanks so much for your expertise and willingness to share!
>I'm still tryin' to learn the lingo.
Yup, most folks come into this arena with the belief that
that technology is the biggest barrier to understanding.
Whether you're working to become a chef or electronic technician, the
biggest barrier to understanding is language. Every fundamental
of cooking or assembling an electrical system is stone simple.
The science of any activity involves a working knowledge of the
fundamentals which includes learning a new language.
After that, the art of assembling simple-ideas into useful
products is easy, fun and limited only by your willingness
to exercise critical thought. And it IS an art for there
are many ways to assemble the simple-ideas into serviceable
systems.
Check out Chapter 1 of the 'Connection at:
http://www.aeroelectric.com/articles/Rev10/ch1.pdf
Figure 16 of this chapter speaks to the symbol you've
cited above along with an illustration of how it can
be labeled to show where it connects to the system. In
the case of an "L", I'm suggesting that this is a
"local" ground.
Bob . . .
Message 11
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
>
>I can not find a single reason why the alternator would suddenly like to
>increase the output current to some unrealistic values, at the same
>time increasing the output voltage. Inductivities do not behave that way.
The alternator is the energy source but only because of what
it's being told to do by the regulator . . .
>A transorg is to small, It seems that coupling a transorb with a high
>power bipolar or mosfet transistor could be the way to go. Definitely a
>large transistor can take much more power than a small transorb. A npn
>transistor powerful enough to take 50A or may be 100A current at 14 V
>for the required time of say 0.1s is needed. Connect a 14 V transorb
>or a zener diode between collector and base. Connect collector to the +
>output of the alternator, and ground the emiter. Now it is the
>transistor rather than the transorb taking most of the current. There
>are many high power transistors to choose from, and prices for low
>voltage transistors are low .
We looked at this at Cessna back in the 60's . . . The "FAT" transistor
of choice was the 2N174
http://www.pemberton.electronics.btinternet.co.uk/transistors/2n/2N174.html
and the fact that it was a PNP device made it easier to install.
The metal case (collector) could be bolted right to the airframe.
We built it up and showed that it would "grab spikes". I left
about that time and I don't recall if it ever found its way onto
the airplanes. I don't think it did. Some bean counter probably
asked, "what is the return on investment for adding this feature
to our products?" Unless he/she got a satisfactory answer, it
didn't happen. Given our level of understanding at that time,
I suspect it never made it to the production line.
You're correct in your suggestion that modern transistors are
capable of grunting some big currents. It may be that the
elegant solution would include a fat transistor.
Bob . . .
Message 12
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--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
---- Original Message -----
From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Subject: Re: AeroElectric-List: Re: Load Dumps
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
> The big question is how the alternator's built in regulator behaves.
> If the regulator can open the field circuit before voltages get
> so high that the regulator itself is damaged, then everything
> comes to rest in an orderly manner. Depending on response time
> of the REGULATOR, the TVS has to grunt 50A or so of current for
> DURATION OF RESPONSE TIME . . . this is how George's TVS got
> launched into orbit.
>
> Response time can be a huge variable from one make of regulator
> to the next. I'm hoping that we can deduce enough information
> from the testing to modify recommendations for implementing
> Z-24 with some degree of comfort. If not (and the pilot
> really feels a need to flip alternator switches on and off
> while the engine is running), then I may have to retreat
> to the original philosophy of recommending that airplanes
> fly only with externally regulated alternators.
I do not see how there is any basic difference (with regard to LOAD DUMP)in
internally regulated VS externally regulated Alternators; in the case of the
Battery contactor opening up from either pilot operation (other than
progressive switch use) or simply contactor failure. Either way IF the
alternator is charging the battery at that time, you end up with a partial
load dump as some of the load is supporting the acft systems thru the main
bus. The response time of the regulator will vary as you have said but there
is still a load dump, of some magnitude, in ALL cases that needs to be
addressed.
As the OVP simply takes the alternator off line by cutting the field and/or
allowing the "B" lead contactor to open there is still a few ms reaction
time in the contactor and the energy is dumping for that time.
Either way the TVS current is limited to a few ms and can be tolerated by
the proper TVS. however the TVS may allow a few ms of relatively HV to
appear on the main buss that can exceed the equipment ratings.
> Keep in mind that the investigation before us is needed
> only to protect an alternator from the pilot. Z-24 provides
> the ov protection desired for the rest of the system and
> becomes problematical only if switches are operated
> unnecessarily and at inappropriate times. Figure Z-24 is
> going to disconnect an alternator wherein the regulator
> has ALREADY FAILED. Anyone with Z-24 up and running
> has no cause for concerns as long as he/she operates
> the alternator in a manner that is consistent
> with 99.999% of the flights conducted every day.
>
> Bob . . .
Mostly agree on Z-24, however, protection from pilot is only part of the
concern. I really do not like the use of procedures to prevent equipment
damage. Throwing the incorrect switch should never cause damage!
I am addressing a different case. First, not everyone has your progressive
switches; and you do not seem to address contactor failure. (however
unlikely its not zero). The importance of your progressive switch as the key
to your above statement should be included.
Failure of one device should never cause additional failures. I suggest that
a battery contactor failure should not result in a load dump where the
alternator is still connected to the main bus. Regardless of the potential
damage of the alternator regulator the main bus gets the impact of the load
dump and prtection needs to be added in my opinion.
My testing to date has shown to me that the remaining issue is the peak
voltage and duration during the TVS protected load dump VS the ability of
the equipment to tolerate that transient.
Paul
Message 13
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--> AeroElectric-List message posted by: "Rogers, Bob J." <BRogers@fdic.gov>
I plan to have an internally regulated 80-amp alternator (from a Mazda RX-7)
as my primary electrical energy source, with a second 35-amp permanent
magnet internally regulated alternator as a back up source of electricity.
I will have only one battery.
I need to be able to test the back-up alternator before I fly, which
involves turning at least one alternator off while the engine is running (or
switching from one alternator to the other). What is the correct procedure
to insure that I do not accidentally destroy an alternator or any other
electrical component of my system?
-----Original Message-----
From: Robert L. Nuckolls, III [mailto:bob.nuckolls@cox.net]
Subject: Re: AeroElectric-List: Re: Load Dumps
<snip>
Keep in mind that the investigation before us is needed
only to protect an alternator from the pilot. Z-24 provides
the ov protection desired for the rest of the system and
becomes problematical only if switches are operated
unnecessarily and at inappropriate times. Figure Z-24 is
going to disconnect an alternator wherein the regulator
has ALREADY FAILED. Anyone with Z-24 up and running
has no cause for concerns as long as he/she operates
the alternator in a manner that is consistent
with 99.999% of the flights conducted every day.
Bob . . .
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<META NAME"Generator" CONTENT"MS Exchange Server version 5.5.2656.83">
RE: AeroElectric-List: Re: Load Dumps
I plan to have an internally regulated 80-amp alternator (from a Mazda RX-7) as
my primary electrical energy source, with a second 35-amp permanent magnet internally
regulated alternator as a back up source of electricity. I will have
only one battery.
I need to be able to test the back-up alternator before I fly, which involves turning
at least one alternator off while the engine is running (or switching from
one alternator to the other). What is the correct procedure to insure that
I do not accidentally destroy an alternator or any other electrical component
of my system?
-----Original Message-----
From: Robert L. Nuckolls, III [mailto:bob.nuckolls@cox.net]
Subject: Re: AeroElectric-List: Re: Load Dumps
snip
Keep in mind that the investigation before us is needed
only to protect an alternator from the pilot. Z-24 provides
the ov protection desired for the rest of the system and
becomes problematical only if switches are operated
unnecessarily and at inappropriate times. Figure Z-24 is
going to disconnect an alternator wherein the regulator
has ALREADY FAILED. Anyone with Z-24 up and running
has no cause for concerns as long as he/she operates
the alternator in a manner that is consistent
with 99.999% of the flights conducted every day.
Bob . . .
Message 14
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--> AeroElectric-List message posted by: Bobdeva@aol.com
Anyone have a source for a good alternator? (Other than B&C.) I want a good
alternator that is NOT internally regulated. Price is not important, you
usually
get what you pay for. 40 or 60 amp. for Lyc. O320.
Thank you,
Bob Devaney
Message 15
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--> AeroElectric-List message posted by: Benford2@aol.com
In a message dated 2/27/2004 7:26:51 PM Mountain Standard Time,
Bobdeva@aol.com writes:
>
> Anyone have a source for a good alternator? (Other than B&C.) I want a good
>
> alternator that is NOT internally regulated. Price is not important, you
> usually
> get what you pay for. 40 or 60 amp. for Lyc. O320.
> Thank you,
> Bob Devaney
>
Hell,, March on down the the local Piper or Cessna dealer and buy ya one. So
what if it cost a few thousand dollars. Remember,,, you get what you pay for.
Well, at least you do building a experimental plane. The certified guys might
as well buy KY jelly by the case.. Ha ha .
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