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nuckolls.bob(at)aeroelect
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 Posted: Mon Apr 02, 2012 12:02 pm Post subject: Converting to externally reg alternator |
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At 08:43 AM 4/2/2012, you wrote:
| Quote: |
Eric is easily amused...
try:
http://lmgtfy.com/?q=Converting+to+externally+regulated+alternator
But here is where I will annoy Bob N.: Consider the fact that if
automobile regulators had a lower failure rate if they were
externally regulated, auto makers would use them. The fact is that
BRAND NEW (not rebuilt) Nippon Denso alternators seem to have a
nearly-zero failure rate.
Then make your decision. I have had several builders send me their
external regulators for examination. This cemented my opinion permanently.
|
Eric my man! This has never been a discussion
about comparative failure rates. If I've failed
to illuminate the logic behind my writings, indulge
me please with the following:
Without doing a very hi-labor study to discover
practical failure rates of any design philosophy, one
is presented with the question:
"Knowing that the failure rate of neither philosophy
is zero, what is the potential return on investment
for some active form of over-voltage management?"
In retrospect, had we considered and implemented
the PlanePower approach for ADDING ov protection
to an existing IR alternator design, it's an indisputable
fact that B&C could have brought a lower cost alternator/
regulator design to the OBAM aircraft marketplace than
the products which ultimately became the LR series
regulators and L series alternators.
But even with the PP philosophy in our hip pocket, it
did not address another feature of the design
philosophy for having ACTIVE notification of low
voltage as part of the package. So once you
have . . .
(1) a black box with LV warn and OV management
features and . . .
(2) we still have to open the alternator to make
the necessary interface that provides positive,
any time control over the alternator's output
(a legacy design goal carried across from TC
aviation).
(3) it just made more sense to us at the time to
offer one black box that offered the features
of three functions classically accomplished
by three separate devices, hence the LR1, 2 and
3 series regulators were crafted and offered to
OBAM aviation.
I'm still amazed that folks get so embroiled over
the idea of "my alternator is more RELIABLE than
your alternator." It's not about relative
reliability. It's about delivering to design goals
that have served us well in airplanes for nearly
100 years.
The simple-idea behind OV protection has
ALWAYS been an assumption that ANY regulator can
fail in a runaway condition. Unless KNOW that
a particular design combined with proper
installation and maintenance has a 10 to the
minus 9 failure rate, then the FAA doesn't
care if one alternator is 1.5 x 10 to the
minus 7 and the other is 1.0 x 10 to the
minus 8 and perhaps a third can be expected
to crap out in less than 2000 hours.
The working assumption is that they are not
perfect and building an automated response
to acknowledged imperfections is not only
a good idea, it's mandated:
FAR23.2451(c)(5) "Each generator/alternator must have an overvoltage
control designed and installed to prevent damage to the electrical
system, or to equipment supplied by the electrical system that could
result if that generator/alternator were to develop an overvoltage condition."
Notice that no relief is offered for the
more "reliable" of two systems.
I have always said that the modern automotive
products are of stellar value and performance.
I also elaborated on the potential for equal or
better value in remanufactured alternators in
the latest revision to chapter 3 in the 'Connnection.
http://tinyurl.com/cx6426c
So in retrospect, I still believe that the
B&C LR/L combo was a good decision. We
could probably redesign for ease of manufacturing
and reducing costs, I don't see an alternative
architecture that still stands up to design
and marketing goals we adopted at that time.
Even if we left the stock regulator in place,
we still have to open the alternator for
other reasons. So why not keep the internal
mods simple . . . and make the most vulnerable
parts easily trouble shot and replaced without
pulling a very reliable alternator off the
engine?
The fact that perhaps thousands of OBAM
aircraft are flying successfully with un-
modified IR alternators doesn't even merit
honorable mention in the discussion. It's
not about comparative reliability. It's
about perceptions of perfection. I'm aware
of no suppliers of perfect alternators . . .
nor is the FAA.
Even PlanePower subscribes to legacy
design goals when they modify commercial-
off-the-shelf alternators to provide OV
management and any-time, any-conditions,
positive control from the cockpit. I have
recommended nothing more . . . . or less.
If I am annoyed, its because there are those
among us that cast me in the role of Ralphie's
mother who admonishes, "Don't shoot that
B-B gun, you'll put your eye out!" My concerns
are not about the very low risk for loosing
one's eyesight. They're about understanding
and managing risks that are NOT zero. We're not
even talking about safety. I'm aware of no fatal
accident where an unmitigated ov condition
precipitated the event. . . . risk with potential
for damage that far exceeds the cost of a
mitigating feature.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Mon Apr 02, 2012 6:41 pm Post subject: Converting to externally reg alternator |
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At 10:24 AM 4/2/2012, you wrote:
| Quote: | --> AeroElectric-List message posted by: Bob Verwey <bob.verwey(at)gmail.com>
Does the crowbar module not offer enough protection? With a VFR day
only, electronic ignition setup, minimal elctrogizmos, does not the
reserve battery power give a safe reserve?
|
The ov protection systems can be crafted from a variety
of technologies and design goals . . . of which "crowbar"
modules is one.
ANY technology is better than none. The rational is based
on the fact that unlike a generator, alternators are capable
of over 100 volts of output as I discussed in this article:
http://tinyurl.com/6m3uyqz
What's more, this voltage is available at the same current
rating as the alternator. Nobody's avionics takes kindly
to such abundance of energy.
For an OV protection system to qualify onto a Type Certificated
aircraft, it must meet certain requirements for SPEED or time
it takes to respond to an OV condition. This is on the order
of 100 milliseconds or less. MUCH faster than any pilot will
perceive a failure and then react fast enough to preclude
damage to other parts of the airplane.
So an OV protection system has but one purpose . . . bring a
failed alternator system to heal in a timely manner. When
you ACTIVE NOTIFICATION OF LOW VOLTAGE light comes on a few
seconds later, THEN you transition to Plan-B and start the
process of getting back on the ground comfortably. Whether
or not your battery is capable of proving "safe reserve"
is an entirely separate matter.
Bob . . . [quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Fri Apr 06, 2012 4:55 am Post subject: Converting to externally reg alternator |
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At 08:43 PM 4/4/2012, you wrote:
| Quote: |
Ah! Since anecdotal evidence is apparently compelling, my Ford had
a runaway alternator, which resulted in a battery explosion, which
peppered the underside of the hood with acid burns. Bummer.
Paul
|
Good morning Paul, long time no hear!
As I was talking to the chief engineer at
MPA about this experiences with alternators,
it would have been interesting to know how
what percentage of alternators coming in
the door had failed regulators . . . and what
the failure modes were.
The only alternators that they routinely examined
for fault analysis were those returned on
warranty. As I stated in the narrative of my visit
the rate of returns had mostly to do with the
skills of the installer. An exceedingly small
number of warranty returns had any failures at
all.
Of course, ALL alternators coming through the
rebuild stream had been replaced for reasons
some mechanic thought were good. At the same
time, I've encountered few mechanics that
REALLY understand how the alternator works and
how to accurately troubleshoot systems that
exhibit less than gross failure.
Virtually none of the normal work stream was
evaluated for failure modes. It would have
been VERY interesting to see how many had
failed regulators in a runaway mode. But alas,
22,000 items passed through that facility
every day. Any effort to glean such information
from those carcasses would have been very
difficult/expensive.
The bottom line is that the best source of
data we have comes from the aviation community
. . . and that data will be anecdotal at best.
The bright side is that the astute system
designer needs only to know that risk for
regulator failure in any system is not zero
and happily, insurance against such failures
is inexpensive.
As the personable spokesperson for Allstate
might suggest, "You're in good hands with
OV protection."
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Apr 07, 2012 6:44 am Post subject: Converting to externally reg alternator |
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At 10:32 PM 4/6/2012, you wrote:
| Quote: | Bob, all, Forgive my lack of knowledge here, but I don't understand the problem here. I use the Z-17 architecture that has the Rotax dynamo output connected to the battery via relay. If the relay is powered down the dynamos output goes to ground through a capacitor. At least that's my understanding. If that is correct, why can't a single wire alternator be controlled in the same way. In the event of a voltage regulator failure and a runaway alternator ensues would not the overvoltage module do the same to a relay connecting the single wire to the battery? Obviously this sounds simple for an electronic illiterate like me. What am I missing that makes such a scenario unworkable.
Rick Girard
On Fri, Apr 6, 2012 at 7:53 AM, Robert L. Nuckolls, III < nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" < nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 08:43 PM 4/4/2012, you wrote:
--> AeroElectric-List message posted by: Paul Millner <millner(at)me.com (millner(at)me.com)>
Ah! Since anecdotal evidence is apparently compelling, my Ford had a runaway alternator, which resulted in a battery explosion, which peppered the underside of the hood with acid burns. Bummer.
Paul
Good morning Paul, long time no hear!
As I was talking to the chief engineer at
MPA about this experiences with alternators,
it would have been interesting to know how
what percentage of alternators coming in
the door had failed regulators . . . and what
the failure modes were.
The only alternators that they routinely examined
for fault analysis were those returned on
warranty. As I stated in the narrative of my visit
the rate of returns had mostly to do with the
skills of the installer. An exceedingly small
number of warranty returns had any failures at
all.
Of course, ALL alternators coming through the
rebuild stream had been replaced for reasons
some mechanic thought were good. At the same
time, I've encountered few mechanics that
REALLY understand how the alternator works and
how to accurately troubleshoot systems that
exhibit less than gross failure.
Virtually none of the normal work stream was
evaluated for failure modes. It would have
been VERY interesting to see how many had
failed regulators in a runaway mode. But alas,
22,000 items passed through that facility
every day. Any effort to glean such information
from those carcasses would have been very
difficult/expensive.
The bottom line is that the best source of
data we have comes from the aviation community
. . . and that data will be anecdotal at best.
The bright side is that the astute system
designer needs only to know that risk for
regulator failure in any system is not zero
and happily, insurance against such failures
is inexpensive.
As the personable spokesperson for Allstate
might suggest, "You're in good hands with
OV protection."
Bob . . .
====================================
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Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
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Bob . . . [quote][b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Apr 07, 2012 8:00 am Post subject: Converting to externally reg alternator |
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|
At 10:32 PM 4/6/2012, you wrote:
| Quote: | Bob, all, Forgive my lack of knowledge here, but I don't understand
the problem here. I use the Z-17 architecture that has the Rotax
dynamo output connected to the battery via relay. If the relay is
powered down the dynamos output goes to ground through a capacitor.
At least that's my understanding. If that is correct, why can't a
single wire alternator be controlled in the same way. In the event
of a voltage regulator failure and a runaway alternator ensues would
not the overvoltage module do the same to a relay connecting the
single wire to the battery? Obviously this sounds simple for an
electronic illiterate like me. What am I missing that makes such a
scenario unworkable.
|
Actually, it can. In fact, that is the control philosophy
originally depicted in Z-24 found at:
http://tinyurl.com/7z6yzv9
The reasoning behind this configuration was
simple. If you've got a runaway alternator for
which there are no external controls, the only
remedy left is to simply isolate the offending
machine from the rest of the aircraft's electrical
system.
Notice the similarity of the Z-24 architecture
with that of Z-17 found at:
http://tinyurl.com/7mh9k3c
Again, the engine driven power source (whether fielded
by a permanent magnet -OR- a fixed magnet) offers
no means by which one may apply external controls.
At some time (post Z-17) it was reasoned that the
root cause for any runaway condition on an alternator
was a regulator failure. In the case of PM alternators,
we had ready access to the AC output of the energy
source driving the rectifier/regulator. Given that
AC current is many times less abusive to relay contacts
in the disconnect mode, it seemed prudent to MOVE
the disconnect relay to the windings of the PM
alternator BEFORE the regulator. Hence Z-16 was
offered:
http://tinyurl.com/7vp9g4e
EITHER philosophy of OV management described above
meets design goals for isolation of the offending
alternator from the rest of the system. Z-16 might
be described as more elegant.
Now, let's take what we've discussed above and
see how it speaks to Z-24. Further, let's discuss
some special cases for the b-lead disconnect
philosophy as it relates to self excited, electrically
fielded alternators.
The PM alternator is fixed field . . . PERIOD. Maximum
output voltage is a function of RPM . . . PERIOD.
The electrically excited alternator with a field coil
connected internally to the B-lead is another breed
of animal entirely. As I discussed in the article
at:
http://tinyurl.com/7cormux
the automotive alternator is demonstrably capable of
very high output voltages when supplied with a fixed
field (like a PM alternator) and still higher voltages
when the field is supplied from the alternator's own
runaway output . . .
A stone-simple b-lead disconnect system was conceived
for the larger wound-field machines and published as
Z-24. In the article published at:
http://tinyurl.com/5n989y
we explore the special cases for using this control
philosophy. The new considerations for design arose
from two major differences between the PM alternator
control (z-17/z-16) and wound field alternator control
(z-24).
(ISSUE 1) As one attempts to open the b-lead on a runaway
alternator, the contactor is opening against a tightly
wound voltage 'spring' if you will. In the first few
milliseconds after onset of the ov condition, the
alternator is attempting to push the bus voltage up
but will be held at bay by the valiant efforts of the
battery. None the less, output current for the alternator
will be at the machine's magnetic limits, probably just
above rated design current.
As the contacts open, voltage rise across the spreading
contacts is very fast and will no doubt establish an
arc in the widening space that is not unlike that which
I described in the narrative about MPA's demonstrations
of b-lead disconnects in the latest revision to chapter
3 of the connection.
The flash of fire was so intense as to blinding to both
the human observer -AND- the lowly video camera. Deleterious
to the contactor? Probably. But even if the contactor is
toasted by the effective disconnection of a runaway
alternator, the original design goal is achieved. The
radios are not toasted too. Remedy? One could install
a contactor with better ratings for high voltage disconnect
like:
http://tinyurl.com/83kf237
(ISSUE 2) Early in the history of Z-24, it seems that
some OBAM aircraft builders used the control switch
to cycle their alternators ON/OFF while under load.
This lead to what the automotive industry calls a
"load dump" wherein the built in regulator is unable
to respond fast enough to bring a suddenly unloaded
alternator back under control. Hence, the alternator's
output launches for the moon. In a load-dump case, the
rise is expected to be transient. Assuming the alternator
is well designed, the short term ov condition is quickly
brought to heel and all is right with the universe.
Unfortunately, all alternators are not created equal.
The alternators installed on these airplanes were demonstrably
incapable of standing off the b-lead disconnect transients
demonstrated for me in MPA's laboratories. These alternators
suffered failures attributed to poor design of Z-24. I suspect
that individuals who experienced these failures abandoned use
of any form of automatic OV runaway management.
Over the years, we've learned that Z-24, when applied to
a realistically designed alternator and fitted with
a robust contactor is probably about as bullet-proof
as design goals dictate.
"But wait, call in the next ten minutes and we'll
. . . .", heard that one before.
In this case, the feature just out of reach is described
in the article cited above . . . don't click this link
again, you already have http://tinyurl.com/5n989y
Here I've proposed a next generation control philosophy.
A philosophy dependent on being able to run alternators
at their rated outputs in a test environment. To that end
I acquired an alternator test stand
http://tinyurl.com/79k9lm2
and set out to modify it for emulation of the architecture
of every architecture in the z-figures up to and including
Z-14. This offered some obstacles not the least of which
was a big honk'n 3-phase motor . . .
http://tinyurl.com/7qlhaqf
which demanded an adapter be added at the end of a 60 amp
feeder I ran out to my garage on Bainbridge. The modification
was well along when it was interrupted by a move to
Medicine Lodge with a host of new demands on my time.
However, it would be useful to describe the functionality
of the next generation controller.
The AEC9004 'black box' contains a micro-controller programmed
to do the following. (a) watch the b-lead terminal for signs
of overvoltage. (b) when and if an ov condition is detected,
power is removed from the b-lead contactor coil. (c) the
differential voltage across the contactor is monitored for
first signs of the alternator side being more positive than
the battery side by say 1 volt or so. (d) at that time a
power MOS-FET good for hundreds of amps is biased on hard
and throws a dead short across the b-lead terminals of the
alternator. A kind of "software crowbar" approach to ov
management.
This sounds brutal . . . but is in fact quite gentle.
An alternator is incapable of delivering much more output
current than it's nameplate rating. Hence, the FET need only
sink perhaps 60 or 70 amps to ground as soon as it is safe
to do so. I.e. the BATTERY must be disconnected before
the crowbar is triggered. Since the alternator's output
is folded back to the field winding, the act of pulling
the b-lead to ground deprives the field of voltage necessary
to feed and sustain the runaway. Hence, everything comes to
a benign state of rest in milliseconds after the FET is
turned on. I've not been able to test it yet but it is
my expectation that the 'current' flowing in the crowbar
FET during the OFF condition for an alternator will be
under 1 amp. That current being delivered by the residual
magnetism of the rotor.
The cool thing about this philosophy is that all the issues
for voltage rating of the contactor -AND- worries about
load-dump transients are mitigated. This control system could
be applied to an alternator of any pedigree with minimal
concerns for damage. Further, it installs a one-wire alternator
in an airplane while offering the legacy design goals for
(1) any-time/any-condition ON/OFF control of the alternator
and (2) timely response to mitigation of an OV condition.
I'm now considering the use of my truck engine driven
alternator test bed. Some years ago, a List member donated
a new one-wire alternator to the task and it has been
mounted on a frame to belt drive it from a 2 hp tread-mill
motor. Preliminary work at low power can be accomplished
with this fixture with high power work to be done on the
truck.
In the mean time, Z-24 as published is a valid philosophy
for getting a one-wire alternator installed today. Further,
Z-24 easily morphs to the next generation configuration
when that hardware achieves production reality.
Bob . . .
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millner(at)me.com
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