Today's Message Index:
----------------------
1. 02:29 AM - Re: Re: ov protection for internal v.r. alternators (Steve Sampson)
2. 05:42 AM - Re: Strain relief (Gary Casey)
3. 08:39 AM - Re: Re: ov protection for internal v.r. alternators (Clay R)
4. 08:19 PM - Re: OV protection for internally regulated alternators (Robert L. Nuckolls, III)
5. 08:34 PM - OV protection for alternators with built in regulators (Robert L. Nuckolls, III)
6. 11:33 PM - Official Usage Guideline [Please Read] [Monthly Posting] (Matt Dralle)
Message 1
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| Subject: | re: ov protection for internal v.r. alternators |
--> AeroElectric-List message posted by: "Steve Sampson" <SSampson.SLN21@london.edu>
Clay - is anyone looking into this for you? It sounds like plenty of people
are getting blown alternators after putting the B&C stuff on. Steve.
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Clay R
Subject: AeroElectric-List: re: ov protection for internal v.r.
alternators
--> AeroElectric-List message posted by: Clay R <clayr_55@yahoo.com>
Now I see the following warning on Vans web site on
the alternator page. (I think this was added this
week)
Warning!
The internally regulated 60 ampere alternator should
not be used with overvoltage protection systems. If
you open the charging circuit while it is in
operation, it will destroy the regulator.
-Clay
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Message 2
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| Subject: | RE: Strain relief |
--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<I don't mean to be defensive, and I really appreciate your point. I'm
actually thinking that some sense of strain relief can be had by
tie-wrapping the wires in an "S" (connectors in the middle of the S, so to
speak) so that there can't be any direct tension on the pin/socket
connections. I believe I have enough slack to do that.
)_( Dan>>
That's exactly what I do, and I do that for the typical "Molex" connector as
well, since they don't have a particularly robust built-in strain relief.
Gary Casey
Message 3
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| Subject: | RE: re: ov protection for internal v.r. alternators |
--> AeroElectric-List message posted by: Clay R <clayr_55@yahoo.com>
The cost to buy a 35A externally regulated alternator,
regulator, and bracket from another supplier was just
a little more than the cost to repair my Vans 60A
alternator ($70). So, that's what I did.
I still completely agree that there must be a way to
disconnect an internally regulated alternator from the
electrical system, and agree with Bob's advice there.
However, I don't like the fact that any trip of the OV
protection or the alt field switch will fry the
alternator. (or at least Vans alternator)
This is what it took to push me from the internally
regulated alternator that I already had, to an
externally regulated unit. I'm glad I found out about
this on the ground instead of at a later date.
The lesson learned is that I think this information
should be added to the wiring diagram for OV
protection so others will know about this limitation
too. (Vans has already added it to their web page,
and hopefully will add it to the instructions that
come with the alternator)
Right now, I'm planning on leaving the contactor in
place, even with the new externally regulated
alternator unless this isn't a good idea. (the only
possible downside I can think of is that the contactor
could fail and it really isn't necessary.) I WILL
test it though, to make sure the alternator stops
producing power when I turn off the Alt field switch.
All in all, this experience is just one more way we
all learn exactly how things electrical work in our
airplanes. I can tell you that after dealing with
this issue I REALLY know how the alternator and
charging system works, when I didn't before. I just
hope that sharing my experience leads to more
knowledge for others and safer planes for all to
follow.
Still looking forward to Bob's take on this too. (I
could still be wrong)
--Clay
--> AeroElectric-List message posted by: "Steve
Sampson" <SSampson.SLN21@london.edu>
Clay - is anyone looking into this for you? It sounds
like plenty of people
are getting blown alternators after putting the B&C
stuff on. Steve.
__________________________________
Message 4
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| Subject: | RE: OV protection for internally regulated alternators |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
As promised, I've been looking into this problem and I've crafted
a white paper on the topic. Here is the text of the paper . . .
-------------------------------------------
"Load Dump" Damage to Alternators with Built-in Regulators
Bob Nuckolls
1 February 2004
>AeroElectric-List message posted by: "Ned Thomas" <315@cox.net>
>
>For what it is worth, I had an internally regulated alternator
>on my RV6A. I had an overvoltage occur and had no way to
>shut it off except land and turn off the engine. When
>I smelled the battery acid cooking out I was quite concerned.
>I was able to land before ruining the battery but even tho
>I immediately turned off the master when I found the
>voltmeter reading high, I did find that one of my strobes
>had fried. After this happened I installed the OV protection
>recommended by Bob. In the event you do encounter an OV
>situation you must be able to isolate the alternator.
>I was lucky, the battery could have blown up...
>----- Original Message -----
>From: "Clay R" <clayr_55@yahoo.com>
>Now I see the following warning on Vans web site on
>the alternator page. (I think this was added this week)
>Warning!
>The internally regulated 60 ampere alternator should not
>be used with overvoltage protection systems. If you
>open the charging circuit while it is in operation,
>it will destroy the regulator.
>AeroElectric-List message posted by: "Steve Sampson"
<SSampson.SLN21@london.edu>
Clay - is anyone looking into this for you? It sounds
>like plenty of people are getting blown alternators
>after putting the B&C stuff on.
BACKGROUND
(1) The "B&C stuff" is only a collection of parts described in documents
described in the AeroElectric Connection. Let us take care as to how the
phenomenon is described with respect to implied cause and effect. It's not
B&C's architecture but AeroElectric Connection architecture . . . B&C only
sells the parts to implement it.
(2) For years and since day-one of my participation in B&C's development
and marketing of alternators, we have preached the doctrine of externally
regulated alternators. Examples of this philosophy are found throughout
early writings and particularly in chapters on alternators and regulators
in the 'Connection. A simple inspection of B&C's offerings from the
beginning will show that only externally regulated alternators are offered.
(3) There has been a lot of interest in adapting internally regulated
alternators to aircraft because they are so readily available and cheap.
Further, they've produced an excellent track record of reliability on cars
. . . it seems a shame not exploit that characteristic in aircraft.
(4) The challenge for adapting internally regulated alternators to
airplanes has always been making them behave like externally regulated
alternators and generators before them. On the instrument panel there is a
switch labeled ALT OFF/ON. One expects that operation of this switch will
produce the same result whether you're sitting in a 1965 C-172 or a 2004 RV-8.
(5) Most alternators with built in regulators, once given the ON command
via the rear-connected control wire will indeed come alive . . . but since
this wire was originally intended only as a means for the EFI controller on
a car to delay onset of engine loads after starting, there was no
requirement for being able to turn the alternator OFF via this same wire.
So, the vast majority of automotive take-offs cannot be turned OFF by
removing +14v from the control wire via panel mounted switch. This
condition was experienced by Mr. Thomas in the anecdote cited earlier.
(6) While the probability of regulator failure in cars is exceedingly low,
it is not zero. We've heard anecdotal stories of unhappy, high-dollar
events taking place in airplanes after failure of an internally regulated
alternator.
(7) With the goal of addressing a desire in the marketplace to utilize
off-the-car technology, figure Z-24 was developed to address both
controllability and overvoltage issues with the lowest practical parts
count and without modifying the alternator.
RECENT HISTORY
It seems that there have been a rash of failures of internally regulated
alternators installed per Figure Z-24. Let's review the inner workings and
shortcomings of the modern, internally regulated alternators. We know that
all alternators run best with a battery connected across their output. The
battery is an excellent filter for the noise inherent on DC power generated
by rectified 3-phase AC power. The battery also provides a flywheel effect
. . . a kind of electrical inertia that damps out the frisky nature of an
alternator's ability to quicky respond to and control its own output.
A phenomenon labeled by the automotive industry as "load dump" speaks to a
characteristic native to the physics of alternator performance. Its
existence has been known since the beginnings of alternator use in
vehicles . . . but it was only a concern after a proliferation of solid
state electronics for fuel injection systems, ignition systems, anti-lock
brakes, etc. Should an alternator producing a lot of power be suddenly
disconnected from the load, it may generate what would be properly called a
surge of voltage exceeding bus voltage by several times. If the load dump
is limited to shedding of normal system loads, the battery's electrical
inertia will be in place to smooth over the event. However, if the
disconnection includes the battery, no mitigating electrical-mass is
present to capture a significant energy transient. In aviation parlance,
a "load dump" is rapid shedding of normal system loads. The scenario we are
discussing might be more appropriately called a "battery dump".
Unlike relatively low energy spikes characteristic of switching transients
on inductive loads, a battery dump event is longer and carries a lot more
energy. In the spring of 1998, there was a romance in the OBAM aircraft
community with products called transient voltage suppressors (TVS). A
school of thought suggested that the electrical system be sprinkled with
these little critters to ward off effects of any gremlins of the
overvoltage persuasion which may be lurking about the system. The suggested
technique was to install a TVS on the power feeder for each vulnerable
accessory.
There was an extensive discussion thread. You may review published excerpts
of that discussion at:
http://aeroelectric.com/articles/spike.pdf
This was before we began to consider and refine any notions of using
internally regulated alternators in OBAM aircraft.
In that thread, I suggested it was much better to (1) identify and mitigate
such hazards at their source and/or (2) design accessories to be immune to
such hazards. For decades, DO-160 has been an effective guideline for
development of robust victims while MIL-STD-704 outlined design goals for
output quality of power generation equipment.
Here are but a few of hundreds of relevant documents on the phenomenon to
be found on the web . . .
http://www.sto-p.com/pfp/pfp-transients.htm
http://www.onsemi.com/pub/Collateral/CS3341-D.PDF
http://www.audifans.com/archives/1998/08/msg00929.html
. . . do a Google search on "load dump" and "alternator" for a wealth of
useful expansion of the topic.
WHAT'S HAPPENING?
The original discussions 4 years ago focused on the need to protect system
accessories from the effects of alternator behavior. In the cases before us
now, the victim is NOT airframe system accessories being hammered by a
skittish alternator. These are cases where the alternator is killing itself
. . . or more accurately, killing its own voltage regulator.
If you look over the specifications for modern, solid state regulator
chips, you'll find references to protection against load dump conditions
built right onto the chip. I believe what we're observing now is a
shortcoming of relatively mature automotive take-off alternators with
regulators that do not enjoy this kind of protection.
Referring to the group of block diagrams in this document, note that I've
illustrated 4 configurations of installation architecture for alternators
with built in regulators.
(download
http://www.aeroelectric.com/articles/Alternator_Failures.pdf
to get the illustration)
(1) The first diagram is captioned "AUTOMOTIVE" and it illustrates the
relationship between battery and alternator in virtually all automotive
applications. The battery is ALWAYS connected to the alternator. System
loads are controlled via panel switches and/or ignition switch but portions
of the power distribution system are always hot, even when the vehicle is
parked. Not desirable on airplanes.
(2) The second configuration is "FIGURE Z-24" referring to an architecture
described in the AeroElectric Connection to accommodate two hard-and-fast
design goals for using an alternator in an airplane: (a) absolute control
of the alternator operation from the cockpit irrespective of flight
condition and (b) protection against the very rare but potentially
hazardous and expensive overvoltage condition.
(3) The third configuration describes an ill-conceived recommendation
suggesting deletion of the alternator disconnect and wiring the alternator
to the airplane a-la-automotive. Note that while this configuration
prevents the pilot from switching an alternator off while in operation, it
does not prevent the battery from being taken off line. If we
disconnect the alternator from the system while leaving the battery on as
allowed with Figure Z-24, only the alternator is at-risk for self destruction.
When you leave the alternator connected to the system and shut off the
battery master, there is still risk of a battery-dump transient. While
system loads will soak up some transient energy and mitigate amplitude and
duration of the event, now the whole system is subjected to the transient.
In airplanes like the Baron and Bonanza where alternators and battery
master switches are separate, non-interlocked controls, switches can be
manipulated in a manner that will produce the same "battery dump" effect
that we're discussing. So the potential for this effect is not new nor is
it unique to the nifty little alternators so popular in the OBAM aircraft
community.
(4) The fourth configuration illustrates an experiment to be conducted
which may prove the usefulness of a technique intended to tame the dragon.
A PROPOSED GAME PLAN
(1) If you have Figure Z-24 installed and you're already flying or nearly
ready to fly, don't change anything. Although you may never need the
protections Z-24 offers, I don't recommend you go flying without it. It is
EASY to prevent battery dump damage to the alternator by controlling
sequence of operation for the switches.
[a] Battery master is the first switch to come on before cranking the
engine and it should stay on until after engine shutdown.
[b] The alternator control switch may be turned on before cranking the
engine but it's probably better to leave it off until after the engine is
running.
[c] At the end of the flight, shut the engine down before first turning
off the alternator . . . .
[d] . . . followed by turning of the battery master switch.
Following suggestions in any of the Z-figures in the 'Connection will
provide you with interlocked battery master and alternator control switches
wired so as to prevent an alternator from remaining on-line with the
battery disconnected.
The battery dump transient is generated by the disconnection of the battery
from the alternator b-lead terminal while the alternator is working hard.
It can't be working hard if the engine is not running. The warning
published by Van's is accurate as far as it goes but misses important
points with respect to absolute operational control of the alternator from
the cockpit and overvoltage protection. So, if you don't diddle with the
switch while the engine is running, your alternator is not at risk for
battery dump damage and you retain both operational control and overvoltage
protection.
(2) If you have yet to select an alternator but need to do it soon, you
cannot go wrong with installing an alternator designed for aircraft
service. Alternators using external regulation are easily managed for both
operational control and overvoltage protection by simply opening the field
lead. This activity does not generate the battery dump transient we're
discussing.
(3) I'm planning to test an alternator with built in regulation on a test
stand using a fat TVS device connected as shown in the last block diagram.
I'll be making measurements of worst-case transient energies and making
sure that the diode we select is adequately sized to the task.
NOTE
If anyone out there remembers the zener diode
that Pelican Aviation used to stick on the back
side of their alternators (some STC'd no less!)
while calling it "overvoltage protection" please
recall that this was neither ov protection nor
was it a practical solution to the problem
before us now.
After the bench testing studies are complete, I'll be looking for
volunteers who are already flying Figure Z-24 alternator control schemes. I
will supply a pair of TVS diodes for installation on your airplane. You
will be asked to conduct a series of battery dump simulations. After the
simulations, you'll be asked to install the second diode and return the
first one to me for inspection.
Once we've done the repeatable experiment to demonstrate suitability of the
"fix", this paper will be updated to publish the results and Figure Z-24
will be updated appropriately. In the mean time, I'll supply a copy of this
paper to Van's in with the hope that it will clarify the issues and
forestall some poorly founded modifications to electrical systems in the
OBAM aircraft community. Please feel free to circulate this document for
both its informative value and potential for critical review.
As a closing note to this document, I ran across this paper:
http://www.st.com/stonline/books/pdf/docs/4345.pdf
. . . written by the folks at SGS-Thompson on battery dump mitigation. This
paper describes a proposed technique for building battery dump management
right into the alternator . . . what a concept! Whether or not this
capability will be offered in automotive products suited to airplanes soon
is hard to predict. In the meantime, it's a no-brainer to make the
alternators we have work quite nicely.
The bottom line folks . . . I believe there is good value in the use of
internally regulated alternators on airplanes. However, it's important that
we make decisions based upon good science that helps us understand and
accommodate their unique characteristics.
Bob . . .
Message 5
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| Subject: | OV protection for alternators with built in regulators |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
I'm told that a warning notice has been published on Van's
website concerning damage to alternators having built
in regulators that are wired per Figure Z-24 in the
AeroElectric Connection.
I've researched the problem and crafted a white paper
outlining history and technical details of the phenomenon
along with an interim work-around plus plans for development
of a permanent fix.
You're welcome to download the paper at
http://www.aeroelectric.com/articles/Alternator_Failures.pdf
Feel free to link to, or re-publish all or any part of this
document as you see fit to service your customers.
Bob . . .
-----------------------------------------
( Experience and common sense cannot be )
( replaced with policy and procedures. )
( R. L. Nuckolls III )
-----------------------------------------
Message 6
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| Subject: | Official Usage Guideline [Please Read] [Monthly Posting] |
DNA: do not archive
--> AeroElectric-List message posted by: Matt Dralle <dralle@matronics.com>
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Matronics Email List Administrator
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