Today's Message Index:
----------------------
1. 06:07 AM - Re: What's all this load dump stuff anyway? (echristley@nc.rr.com)
2. 07:26 AM - LASAR Ignition Wiring (ronald jagels)
3. 08:05 AM - Re: OVP and Load Dump (Troy Scott)
4. 08:09 AM - Re: What's all this load dump stuff anyway? (Wallace Enga)
5. 08:43 AM - Re: What's all this load dump stuff anyway? (Robert L. Nuckolls, III)
6. 09:50 AM - RG142 (Eric M. Jones)
7. 09:54 AM - Single Ground (David Schaefer)
8. 11:17 AM - Re: RG142 (LarryRobertHelming)
9. 04:20 PM - For Bob Nuckolls ()
10. 10:13 PM - Re: OVP and Load Dump (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: What's all this load dump stuff anyway? |
--> AeroElectric-List message posted by: echristley@nc.rr.com
> But now imagine that you have turned on your 1000W
sound system
> ensuring that the alternator is being called on to
deliver maximum
> power. Assume you turn off the sound system, i.e.
"dump the load,"
> so that the bus voltage starts to rise. The VR
reduces the current
> in the field but it takes a finite amount of time
for the magnetic
> field in the armature to change to the new value.
In the mean time
> the bus voltage continues to rise. This sudden,
momentary over
> voltage can cause damage to electrical components.
The OVP circuit
> won't help as the VR has already turned down the
current in the field.
>
>
Excellent explanation Brian, but I'd like to add the
image that makes it blatantly clear to me.
Imagine you're trying to open a door. Really
stubborn door. You push with everything you have,
and even call in me, Bob and several others from
this list. We are all sweating and grunting to get
the door open. Suddenly, and without warning, your
wife, who is more intelligent than all the rest of
us combined, turns the door knob.
The resulting explosive release of force can be
referred to as a load dump.
Message 2
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| Subject: | LASAR Ignition Wiring |
--> AeroElectric-List message posted by: "ronald jagels" <rejnovca@hotmail.com>
Building an RV-8A with battery in the rear, LASAR electronic ignition and
planning to use Z-13 as a starting point for electrical systems. The LASAR
installation instructions I pulled off the internet apply to a backfit on
existing aircraft and indicate use of the conventional O-L-R-Both-Start
switch. Power is feed to the LASAR control box and then distributed to the
MAG backups with blue wire to the left MAG P lead and green wire to the
right MAG P lead. Question - has anyone wired the LASAR ignition using 2-3
switches as described by Bob in the AeroElectric Connection Book? If so how
did you wire it?
Message 3
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| Subject: | Re: OVP and Load Dump |
--> AeroElectric-List message posted by: "Troy Scott" <tscott1217@bellsouth.net>
Wallace,
Thanks for your response. Actually, I do understand the difference in
alternator regulator OVP and an OV event caused by Load Dump. I just
believe that a device advertised to have "over voltage protection" should
include features that provide for common possibilities like Load Dump, which
IS a short duration high-voltage-on-the-bus event. The B&C regulator is a
separate box with wires going to and coming from it. Would it be a big deal
to add the $.49 part and a few wires which would connect to the proper
places to absorb a Load Dump? With this and maybe a few other features,
maybe then you could legitimately call it a complete OVP system. And it
doesn't matter if everybody else makes OVP systems without these features.
We're supposed to be better that everybody else, right?
Regards,
Troy
tscott1217@bellsouth.net
Message 4
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| Subject: | Re: What's all this load dump stuff anyway? |
--> AeroElectric-List message posted by: Wallace Enga <wenga@svtv.com>
Brian,
Great explanation on this mysterious electron producer.
The one paragraph below, I might quibble with you on, is
regarding alternators with Internal Voltage Regulators.
These do not have the "classic field wire", but rather a control wire.
Cutting off power to this lead may not shut the alternator down in
all situations.
That is the reason for the addition of a "B Lead" Disconnect Contactor,
along with it's Load Dump issues when inadvertently opened.
Wally Enga
At 12:02 AM 5/12/04 -0400, you wrote:
>--> AeroElectric-List message posted by: Brian Lloyd <brianl@lloyd.com>
>
>
>Bob over-voltage protection circuit discovers this high voltage long
>before it is dangerous to the devices on the bus. It cuts off all power
>to the field thus turning off the alternator. Now you limp home on the
>juice left in the battery. No worries.
Message 5
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| Subject: | Re: What's all this load dump stuff anyway? |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 12:48 AM 5/12/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: "Jerzy Krasinski"
><krasinski@provalue.net>
>
>
> >............... But now imagine that you have turned on your 1000W sound
>system ensuring that the alternator is being called on to deliver maximum
>power. Assume you turn off the sound system, i.e. "dump the load," so that
>the bus voltage starts to rise. The VR reduces the current in the field but
>it takes a finite amount of time for the magnetic field in the armature to
>change to the new value. In the mean time the bus voltage continues to
>rise. This sudden, momentary over voltage can cause damage to electrical
>components. The OVP circuit won't help as the VR has already turned down
>the current in the field.
> >
> >
> > Brian Lloyd >
> >
>
>It depends what OVP circuit. A proper OVP circuit is a fast and brutally
>acting device capable to sink a lot of current from the bus whenever it
>detects a voltage increase above the norm. In other words it is a device
>momentarily increasing the load on the bus, absorbing all the excess current
>caused by the load dump. It absorbs as much current as needed to keep the
>bus voltage only slightly increased above the norm, far away from damaging
>voltages. In the mean time the regulator can reduce the field current so
>the voltage on the bus goes back to normal. That reduces the current through
>the OVP device which goes idle and the system continues to work in a
>standard way.
>Jerzy
We're stirring two separate events together in the same pot
and blurring sharp distinctions between the two along
with consideration of practical remedies.
Over Voltage Protection addresses a condition that was largely
ignored until alternators were installed on aircraft. It's
precipitated by a failure of the voltage regulator failure and
the engine driven power source begins pushing an otherwise
normal system voltage upward. This is a gross failure of a
control device where potential energy available to damage
system components is measured in Killowatt-Seconds and the
event will proceed with no practical bound on time unless
automatic protection (or pilot intervention) steps in to
shut off the failed alternator.
Voltage settings and time versus voltage operating
characteristics have been studied and defined over the
past 40 years or so and the result is a large field of
offerings in over-voltage relays and, in the AeroElectric
case, crowbar OV protection modules.
The "load dump" phenomenon is described by simple dynamics
of an alternator and it's companion regulator to respond
to sudden reduction in load. It doesn't require a 'failure'
to initiate the event. A simple operation of the alternator
control switch on a Figure Z-24 OV protection system or
operation of the battery master in a Bonanza while the
alternator is carrying a substantial load is all it takes.
This phenomenon is a relative low energy perhaps less than
100 watt-seconds and is self terminating. The classic
OV Protection system was not designed for nor should it
be expected to deal with this event.
The technology of choice is an adaptation of zener voltage
regulator diodes especially crafted to provide a temporary
but rather robust LOAD to the alternator during the
tens of milliseconds that it takes to recover from a
sudden drop on demand for its formidable output capabilities.
This class of zener is commonly referred to as a TVS or
transient voltage suppressor. It's a device
rated to soak up large (1500 Watts or more) surges of
energy for short (less than 100 milliseconds) periods of
time.
Load dump is a RARE event in normal operation. Certified
aircraft have not been fitted with prophylactic measures
because it is so rare. This topic has been stirred numerous
times here on the List and elsewhere over the past 5 years
or so. It was not until Van's Aircraft noted that flipping
the alternator control switch in an aircraft wired per
Figure Z-24 might produce a load-dump event (that could
damage the alternator only) that the topic bubbled to
the surface again.
The debate is not whether a load-dump event can happen.
We know and accept that its occurs under specific
conditions that have become less rare because one
can accidently produce the event by flipping switches
under otherwise "normal" conditions. The conversation is
not so much a debate but a desire to understand and
confirm recommendations already circulating throughout
the automotive industry for RATING the TVS device.
It may well be that a suitable device will surface
in the form of this critter:
http://www.aeroelectric.com/Mfgr_Data/MR2535L-D.pdf
They cost about $3 in low quantity and are installed
by simply attaching to the back of the alternator.
One wire to the b-lead terminal, other to ground.
I've oft cited the value of "repeatable experiments"
as the foundation for good engineering decisions.
TVS devices come in hundreds of part numbers of which
perhaps 20-30 parts are best suited to our task.
There's much published literature from the automotive
industry that suggests the part cited above will do
the trick for 99% of the installations common to
OBAM light aircraft. In fact, if any of you
are especially concerned about load dump transients,
you could acquire one of these critters and install
it this afternoon and be 99% assured of having
fabricated a firewall against a .001% event.
Incidental to the outcome of the proposed repeatable
experiments are real debates as to the need for
clamping off load-dump transients at voltage
levels far below values common in Spam cans.
DO-160 cites 40 volt withstand levels for products
intended to serve in 14 volt aircraft. Many
suppliers to the OBAM community are ignorant of
or choose to ignore this simple and easily
accommodated recommendation. They offer devices
advertised with 20-30 volt limits. Some folk suggest
it is in the consumer's best interests to
accommodate these products with extra-ordinary
efforts found no where else in the aircraft
(or automotive) industry. From the perspective
of a designer with feet in both buckets, I've
suggested that we'll better serve the OBAM
aircraft community by insisting potential
suppliers educate themselves on the simple
techniques proven effective in thousands
of products intended for a certified world.
OV protection and load dump protection are
separate tasks with different requirements.
The risks for not installing protection are
well documented and not very debatable. I
have every expectation that experiments currently
proposed will not offer new and startling
discoveries . . . the numbers gleaned will
allow us to confirm a choice of devices for
a well understood task. It's going to be
something akin to deciding whether a piece
of equipment is held to the airframe with
#6 hardware . . . or would #8 be better?
There is useful debate to be conducted on
how we view ourselves as champions and
practitioners of leading edge technology.
I prefer to take advantage of 5 decades
of knowledge base on electrical system performance
upon which we will build an ever expanding
leading edge. I don't find it useful and
cannot recommend that we step back from the
best-we-know-how-to-do just to accommodate
the new kids on the block. Let's help them
join us at the leading edge instead of
spending time and dollars to craft a
system especially friendly to sub-standard
products. In the hypotheticals I cited
yesterday, it would be like putting low
compression jugs on an engine to accommodate
Nuckolls' cheap 75 octane fuel or drilling
half again more holes to install wing attach
bolts so one can use hardware store grade 5
fasteners.
No doubt some will choose to be accommodating
and that's fine too. This is, after all, an
OBAM aircraft community. If accommodation does
not compromise safety, then I'll be the last
to get really excited about anyone's CONSIDERED
decisions on configuring their aircraft. I
won't recommend accommodation when it's easy
to avoid and when the effort is beneficial
to the OBAM aircraft community as a whole.
This I will happily debate any time . . . it's my job.
Bob . . .
Message 6
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--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
If RG142 is the only coax that is used in an airplane--about how much is
used per airplane? (Now please don't say it depends...). I am trying to find
out how much weight can be saved by changing to something else, and if
RG142 ONLY can be used for everything coaxial.
Offline is best:
Email: emjones@charter.net
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Message 7
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--> AeroElectric-List message posted by: "David Schaefer" <dschaefer1@kc.rr.com>
Bob ..
I need your thoughts on a problem I've run up against. I've followed your
single ground specifications to a tee. All my grounds are run to the single
B&C ground block. However, I have an issue. I have a 'pre-made' harness
with 8 power and 8 ground connections all on very short leads coming out of
the main cable bundle. All have ring terminals on them. I've cut off the
power side ring terminals and replace them with fast-ons to connect to my
fuse block.
However, I can't decide what to do with the ground side. Do I cut them off
and splice longer wires (3') onto the leads to get back across the plane to
the ground block? OR can I put the ring terminals on a single bolt and run
one larger wire back to the block? OR do I put a couple of bolt-studs by the
fuse blocks and ground the ring terminals to the firewall?
Will the splices 'degrade' the ground?
I'll look forward to your input.
Regards
DWS
Message 8
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--> AeroElectric-List message posted by: "LarryRobertHelming" <lhelming@sigecom.net>
If you locate your antennas only in the wing tips it will take considerable
more coax than if you locate them in the belly of the plane. * AND* How
many antennas will you have? (Now please don't say it depends...).
Your answer will not *depend* on anything but your own desires.
Indiana Larry
----- Original Message -----
From: "Eric M. Jones" <emjones@charter.net>
Subject: AeroElectric-List: RG142
> --> AeroElectric-List message posted by: "Eric M. Jones"
<emjones@charter.net>
>
> If RG142 is the only coax that is used in an airplane--about how much is
> used per airplane? (Now please don't say it depends...). I am trying to
find
> out how much weight can be saved by changing to something else, and if
> RG142 ONLY can be used for everything coaxial.
>
> Offline is best:
> Email: emjones@charter.net
>
> Regards,
> Eric M. Jones
> www.PerihelionDesign.com
> 113 Brentwood Drive
> Southbridge MA 01550-2705
> Phone (508) 764-2072
>
>
Message 9
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| Subject: | For Bob Nuckolls |
--> AeroElectric-List message posted by: <jimk36@comcast.net>
Bob--
I've been following the load dump thread with some interest, for the plane I'm
building and the one I fly. I have had a Beech C33A for 15 years and put about
2000 hours on it. It has a 70A alt. and plenty of equip. to load it up. In all
this time I had no idea until this issue came up on the Connection that there
was the potential to trash 10s of thousands of dollars of avionics and other
equip.
There is nothing in the POH about this. In fact the POH says that in the event
of an overvoltage condition, [which would be indicated by an O-V warning light],
batt and alt switch "off momentarily, then on [this resets the overvoltage
relay]". As I understand it this in itself could generate a load dump if the batt
were switched off slightly ahead of the alt.. Am I correct?
Seems strange that the issue of load dump and operation of the master sw was not
included in the POH. Are you aware of any reason for the omission other than
that pilots rarely feel the urge to turn off the master while in flight or when
on the ground with the engine running?
Jim Kaser
Message 10
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| Subject: | Re: OVP and Load Dump |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 10:02 AM 5/13/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: "Troy Scott"
><tscott1217@bellsouth.net>
>
>Wallace,
>
>Thanks for your response. Actually, I do understand the difference in
>alternator regulator OVP and an OV event caused by Load Dump. I just
>believe that a device advertised to have "over voltage protection" should
>include features that provide for common possibilities like Load Dump, which
>IS a short duration high-voltage-on-the-bus event. The B&C regulator is a
>separate box with wires going to and coming from it. Would it be a big deal
>to add the $.49 part and a few wires which would connect to the proper
>places to absorb a Load Dump? With this and maybe a few other features,
>maybe then you could legitimately call it a complete OVP system. And it
>doesn't matter if everybody else makes OVP systems without these features.
>We're supposed to be better that everybody else, right?
The LR3 regulator wires to the ship's systems with
20 and 22 awg wires of variable length. The best place
to install a TVS is as close to the source (alternator
b-lead) as practical with shortest lengths of wire. When
the TVS is finally sized, the recommended location
would not be inside the LR-3 regulator but right on
the back of the alternator. This will allow a single
recommended installation to cover all manner of load-dump
event in both externally regulated and internally regulated
machines wired per Z-24.
Bob . . .
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