Today's Message Index:
----------------------
1. 06:29 AM - Re: OVP and Load Dump (Troy Scott)
2. 07:11 AM - Re: Re: What's all this load dump stuff anyway? (Paul Messinger)
3. 08:52 AM - Re: For Bob Nuckolls (Robert L. Nuckolls, III)
4. 12:27 PM - Re: For Bob Nuckolls (Chad Robinson)
5. 01:50 PM - Re: For Bob Nuckolls (Robert L. Nuckolls, III)
6. 02:26 PM - Re: What's all this load dump stuff anyway? (jmfpublic@comcast.net)
7. 03:18 PM - Re: For Bob Nuckolls (Greg Young)
8. 03:47 PM - Re: Re: What's all this load dump stuff (Wallace Enga)
9. 05:39 PM - Re: For Bob Nuckolls (Ron Koyich)
10. 08:15 PM - For Bob Nuckolls: Roll your own crowbar module troubles ()
11. 11:13 PM - Co-ax splice method (KeithHallsten)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: OVP and Load Dump |
--> AeroElectric-List message posted by: "Troy Scott" <tscott1217@bellsouth.net>
Bob Nuckolls,
Thanks!! I'll definitely want to include this feature. I'll stay tuned.
Regards,
Troy Scott
tscott1217@bellsouth.net
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: What's all this load dump stuff anyway? |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
see embedded
----- Original Message -----
From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Subject: AeroElectric-List: Re: What's all this load dump stuff anyway?
>
> 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.
Disagree, the vast majority of devices designed for this purpose by the TVS
component industry is for parts many times higher in rating. In fact the
ONLY part I can find that is not a 5000W unit is the above referenced part
noted by "ON" Semi (not a leader on the TVS field). (This for Alternator
Load dump suppression).
It might be of interest to point out what the following spec requires.
"The DaimlerChrysler Corp EMC spec # PF-9326 change D" states.
(Not an exact word by word quote (shortened) but technically factual)
3.5.3 Load Dump Transient test specifies a transient generator that must
produce 125 joules of energy to a 0.5 ohm resistive load with an internal
source resistance of 0.5 ohms when set to an open source voltage of 105
volts. The waveform must average 45.75v minimum over 95ms duration. Further
the test circuit pulse is shown to be above 22.65V for 300ms.
The test load used consists of FIVE of the above MR2535 in parallel each
with 0.1 individual series resistors.
This load results in a suppression of the 90+V pulse to the range of 34-38
volts over the duration of the pulse exceeding this clamped voltage which
duration is not specified in numbers but appears to be in the range of 200ms
based on waveform charted.
The above shows a voltage pulse clamped to close to the DO-160 40 V pulse
but as I recall the DO-160 40 V pulse is much shorter than 200ms and thus
does not cover maximum load dump conditions, that is, if the above
automotive test is max case. In any case it shows the apparent need for much
more than one 1500W MR2535 supporting the rest of the industries contention
that a 5000watt unit is needed.
Bob please restate for us the DO-160 Over voltage tests of one second
duration and shorter including the 40v pulse test including pulse peak and
duration/pulse shape.
To many of us the problem is important, as however unlikely a damaging load
dump occurrence is, if you experience one it can damage lots of very
expensive equipment.
Consider the automobile design. The battery is hard wired to the alternator
"B" lead and the rest of the electrical system is connected by the ign
switch. Thus in an auto only a mechanical failure can cause a load dump. IE
the mechanical connection somehow opens. Then consider automobiles have
designed in TVS protection in the dozens of electrical modules and thus have
a distributed load dump/transient protection network.
In an acft however things are connected differently. The battery is not
directly connected to the alternator "B" lead. The system each are
individually connected thru power relays to the system bus and thus there
are two relays that can cause a load dump if either is opened at the wrong
time.
The opening of the "B" lead isolates the load dump to the alternator.
The opening of the battery relay results in the acft electrical system being
exposed to the load dump. It does not matter how or what caused the battery
relay to open the result is a system wide load dump.
The old spam cans are just as likely to have a load dump as the latest
designs in that respect.
Its not usually a problem however as the load dump from battery disconnect
is not a problem unless the battery is being heavily charged AT that time
and normally this is only for a short time after initial startup.
Paul
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: For Bob Nuckolls |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 07:21 PM 5/12/2004 -0400, you wrote:
>--> 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?
Yes . . . there WILL be a load dump transient but its magnitude is a
function
of total alternator load, ratio of system loads to battery recharge load,
engine rpm, and individual alternator characteristics. Consider further
that most if not all of the equipment in your airplane was designed to
EXPECT load-dump type transients and survive them.
The worst case load dump happens when the battery is deeply discharged
and accepting strong recharge current from the alternator while at cruise
rpm -AND- minimal system loads. Increasing the amount of stuff running from
the bus in comparison to total alternator loads will reduce the magnitude
of a potential load dump event. Alternator and battery switches are
generally operated on the ground with the engine either stopped or at
>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?
No, for the most part, all this discussion is a tempest in a teapot
because (1), it's a vary rare event with a huge range of variability
depending on system operating conditions and (2) we in the spam can
industry have been encouraged to design new products for aircraft with
a robust tolerance of the load-dump event. From the perspective of
Raytheon Aircraft delivering a new A-36 to a customer, concerns
for pilot induced load-dump events causing any damage is completely
off the radar screen. We've done the best we know how to do both
from regulatory and professional efforts to make this a non-issue
with certified aircraft.
It only popped up on radar screens in OBAM aircraft because
with the special case generated by Figure Z-24 OV protection applied
to internally regulated alternators where it's relatively easy
to produce a load-dump event that damages the alternator. This
happens when the alternator is cycled on and off while the engine
is running . . . and again, it probably happened on a Lycoming
engine (high alternator drive pulley ratio) and the alternator
was working hard to recharge a battery that was just used to
crank the engine. If the switch had been flipped on and off
a short time later, the event may not have been so high as
to zork the regulator.
Figure Z-24 has been in publication for about 6 years. Certainly
dozens of aircraft are flying this configuration without
having to report alternator failures because (1) they operate
the switches in the conventional manner and/or (2) load
conditions prevalent at the time of switch operation did not
produce an event with enough magnitude to damage the alternator's
regulator.
Don't loose any sleep over this my friend. 99% of what you're
seeing discussed here on the list is academic discussion
among folk who do this for a living. Like DNA where 95%
is chaos which binds together the 5% of what makes us what we are,
this voluminous discussion will lead to considered, simple and
practical solutions to something that isn't a big problem
in the first place.
I've had some private e-mails suggesting that we should take
this stuff off-list. It "confuses" or "alarms" some folks.
Well, the US Congress does a whole lot of confusing or alarming
stuff off-list too . . . and we know where that gets us. Just
be assured that when all the dust settles, those who are confused or
alarmed will be offered simple remedies while those who choose
to follow along will be richer in understanding for having
taken the time to do it.
Bob . . .
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: For Bob Nuckolls |
--> AeroElectric-List message posted by: Chad Robinson <crobinson@rfgonline.com>
Robert L. Nuckolls, III wrote:
> The worst case load dump happens when the battery is deeply discharged
> and accepting strong recharge current from the alternator while at cruise
> rpm -AND- minimal system loads. Increasing the amount of stuff running from
> the bus in comparison to total alternator loads will reduce the magnitude
> of a potential load dump event. Alternator and battery switches are
> generally operated on the ground with the engine either stopped or at
Bob, could you please elaborate on this point? I don't understand why minimal
system load is part of the worst-case. Is the implication that pre-existing
loads other than the battery could help absorb the dump? Or is this simply a
percentages thing?
> I've had some private e-mails suggesting that we should take
> this stuff off-list. It "confuses" or "alarms" some folks.
> Well, the US Congress does a whole lot of confusing or alarming
> stuff off-list too . . . and we know where that gets us. Just
> be assured that when all the dust settles, those who are confused or
> alarmed will be offered simple remedies while those who choose
> to follow along will be richer in understanding for having
> taken the time to do it.
It might be nice for you to write up one of your famous articles summarizing
the physics of what happens, how to avoid them, and where they actually matter.
Regards,
Chad
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: For Bob Nuckolls |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 03:24 PM 5/13/2004 -0400, you wrote:
>--> AeroElectric-List message posted by: Chad Robinson
><crobinson@rfgonline.com>
>
>Robert L. Nuckolls, III wrote:
> > The worst case load dump happens when the battery is deeply discharged
> > and accepting strong recharge current from the alternator while at
> cruise
> > rpm -AND- minimal system loads. Increasing the amount of stuff
> running from
> > the bus in comparison to total alternator loads will reduce the
> magnitude
> > of a potential load dump event. Alternator and battery switches are
> > generally operated on the ground with the engine either stopped or at
>
>Bob, could you please elaborate on this point? I don't understand why minimal
>system load is part of the worst-case. Is the implication that pre-existing
>loads other than the battery could help absorb the dump? Or is this simply a
>percentages thing?
It's a ratio . . . or percentage thing. Suppose total load on alternator
is 50A, 48A going to things on the bus and 2A to recharging the battery.
Now, flip ALL 40A of bus loads off and the alternator will do it's
overshoot thing but the battery is still on the bus to soak up the short
burst of energy that comes during the load-dump. Now, take the same scenario
and turn off the battery. Loads on alternator drop from 50 to 48, not a
big dump, no big deal.
Reverse the situation. Cold morning, battery in good condition but
dead from master being left on. Start with battery cart and turn
alternator on. Alternator pegs out at max capability to recharge
the dead battery. Say bus has a couple of amps worth of goodies
on and you open the battery master contactor. Alternator load drops
from max capability (which can be better than label ratings on
cold day) down to the couple of amps that the bus powered goodies
need. BIG drop in current, BIG overshoot which gets conducted to
whatever items are presently powered from the bus.
> > I've had some private e-mails suggesting that we should take
> > this stuff off-list. It "confuses" or "alarms" some folks.
> > Well, the US Congress does a whole lot of confusing or alarming
> > stuff off-list too . . . and we know where that gets us. Just
> > be assured that when all the dust settles, those who are confused or
> > alarmed will be offered simple remedies while those who choose
> > to follow along will be richer in understanding for having
> > taken the time to do it.
>
>It might be nice for you to write up one of your famous articles summarizing
>the physics of what happens, how to avoid them, and where they actually
>matter.
It's in the mill. Will be able to complete it when all the
data are in from repeatable experiments.
Bob . . .
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
<Aeroelectric-List@matronics.com> (Aeroelectric-List)
| Subject: | Re: What's all this load dump stuff anyway? |
--> AeroElectric-List message posted by: jmfpublic@comcast.net
Paul and Bob,
The MR2535 is $1.45, minimum order 10 units from Digikey. Using 5 of them should
not be a problem.
Jim Foerster
Message 7
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | For Bob Nuckolls |
--> AeroElectric-List message posted by: "Greg Young" <gyoung@cs-sol.com>
I had pretty much tuned out the earlier load dump discussions because it was
more than my electron challenged brain could handle but I now realize that I
recently experienced it and it's practical downside. During maintenance the
ammeter line on my Navion got connected to the buss side of the master CB
instead of the battery side (don't ask!). That put a 35amp CB in series with
the 60amp main breaker from my 50 amp generator. No problem until the engine
started and the generator came on line. The 35a blew disconnecting the
battery and creating what I now know to be a load dump. That blew all the
fuses in my GX-60, SL-30 and SL-70 rendering them useless - twice
before we found the problem. The radio shop was able to replace the fuses
and the radios appear otherwise undamaged but it wasn't pleasant, easy or
convenient (soldered PICO fuses). These are all current generation radios
which I assume were built to DO-160. But that gave me no comfort when I was
stranded without radios and none now knowing it could happen again if the
battery gets disconnected. Oddly, my SL-15/PS7000 audio panel, ACU and
various gauges escaped unscathed. Moral - if you have UPSAT radios, carry
your own supply of 2a & 7a PICO fuses. I may not be able to change my Navion
but I'd sure like to solve/prevent this problem in my RV-6.
Regards,
Greg Young - Houston (DWH)
RV-6 N6GY ...project Phoenix
Navion N5221K - just an XXL RV-6A
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> --> <bob.nuckolls@cox.net>
>
> At 03:24 PM 5/13/2004 -0400, you wrote:
> >--> AeroElectric-List message posted by: Chad Robinson
> ><crobinson@rfgonline.com>
> >
> >Robert L. Nuckolls, III wrote:
> > > The worst case load dump happens when the battery is
> deeply discharged
> > > and accepting strong recharge current from the
> alternator while
> > > at
> > cruise
> > > rpm -AND- minimal system loads. Increasing the amount of stuff
> > running from
> > > the bus in comparison to total alternator loads will
> reduce the
> > magnitude
> > > of a potential load dump event. Alternator and
> battery switches are
> > > generally operated on the ground with the engine
> either stopped
> > > or at
> >
> >Bob, could you please elaborate on this point? I don't
> understand why
> >minimal system load is part of the worst-case. Is the
> implication that
> >pre-existing loads other than the battery could help absorb
> the dump?
> >Or is this simply a percentages thing?
>
> It's a ratio . . . or percentage thing. Suppose total load
> on alternator
> is 50A, 48A going to things on the bus and 2A to recharging
> the battery.
> Now, flip ALL 40A of bus loads off and the alternator will do it's
> overshoot thing but the battery is still on the bus to soak
> up the short
> burst of energy that comes during the load-dump. Now, take
> the same scenario
> and turn off the battery. Loads on alternator drop from 50
> to 48, not a
> big dump, no big deal.
>
> Reverse the situation. Cold morning, battery in good condition but
> dead from master being left on. Start with battery cart and turn
> alternator on. Alternator pegs out at max capability to recharge
> the dead battery. Say bus has a couple of amps worth of goodies
> on and you open the battery master contactor. Alternator load drops
> from max capability (which can be better than label ratings on
> cold day) down to the couple of amps that the bus powered goodies
> need. BIG drop in current, BIG overshoot which gets conducted to
> whatever items are presently powered from the bus.
>
>
> > > I've had some private e-mails suggesting that we should take
> > > this stuff off-list. It "confuses" or "alarms" some folks.
> > > Well, the US Congress does a whole lot of confusing
> or alarming
> > > stuff off-list too . . . and we know where that gets us. Just
> > > be assured that when all the dust settles, those who
> are confused or
> > > alarmed will be offered simple remedies while those who choose
> > > to follow along will be richer in understanding for having
> > > taken the time to do it.
> >
> >It might be nice for you to write up one of your famous articles
> >summarizing the physics of what happens, how to avoid them,
> and where
> >they actually matter.
>
> It's in the mill. Will be able to complete it when all the
> data are in from repeatable experiments.
>
> Bob . . .
Message 8
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: What's all this load dump stuff |
anyway?
--> AeroElectric-List message posted by: Wallace Enga <wenga@svtv.com> anyway?
Jim,
The ST BZW50-22 has about the same specs and
a little higher Peak Pulse rating of 5000W.
Prob get by with 4 of them :)
http://www.datasheetcatalog.com/datasheet/B/BZW50-22.shtml
Wally Enga
At 09:23 PM 5/13/04 +0000, you wrote:
>--> AeroElectric-List message posted by: jmfpublic@comcast.net
>
>Paul and Bob,
>
>The MR2535 is $1.45, minimum order 10 units from Digikey. Using 5 of them
>should not be a problem.
>
>Jim Foerster
>
Message 9
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | For Bob Nuckolls |
--> AeroElectric-List message posted by: "Ron Koyich" <Ron@Koyich.com>
>>Well, the US Congress does a whole lot of confusing or alarming stuff
off-list too . . . and we know where that gets us. Just be assured that
when all the dust settles, those who are confused or alarmed will be
offered simple remedies while those who choose to follow along will be
richer in understanding for having taken the time to do it.<<
Thanks for the sobering thoughts, Bob.
From my years of experience with aircraft electronics and avionics, I
believe the practical answer is: load dump problems are not one of the
big problems folks need to concern themselves with. Like a spot of dust
on an elephant's butt - not a worry.
Ron
Message 10
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | For Bob Nuckolls: Roll your own crowbar module troubles |
--> AeroElectric-List message posted by: Ralph Ketter <arizonahikers@juno.com>
2.3 SUBJ_YOUR_OWN Subject contains "Your Own"
Bob,
This is a resend of previous information I posted but you didn't get.
I build my own OV crowbar module and it functions correctly except that
it operated in the 10-11 volt range. I triple checked the components
and wiring. I changed the 1.62K ohm resistor specified for a 14 volt
system to 6.04K and the circuit operates in the correct voltage range of
15.5-17 volts.
***************************
Designating Point (1) as the + end of the capacitor, and Point (2) as the
junction of the 392 ohm resistor, and GND as the negative lead, with the
pot at midrange I got the
following readings:
******
1.62 K resistor in place for 14 volt operation. - Trip point = 10.4
volts.
Point (1) - Point (2) +0.436 volts
GND - Point (2) +7.6 volts
******
6.04K resistor replacing the 1.62K one. - Trip point = 16.22 volts.
Point (1) - Point (2) +0.538 volts
GND - Point (2) +7.36 volts
******
These readings made me realize the circuit was not letting the zener
regulate at 12 volts so I did the following checks.
First I disconnected the SCR trigger lead to prevent it from firing. I
reinstalled the original 1.62K resistor.
Measuring the Zener voltage from GND to Point (2):
As I increased the input voltage the voltage across the zener increases
linearly to about 8.25 volts and then starts to decrease. The input
voltage is about 9 volts when this knee occurs.
I then disconnected the 1N4148 diode and repeated the above test with
basically the same results.
With the 1N4148 diode still disconnected, I also disconnected the NPN
collector and PNP base (they remained connected together) from the point
(2) junction. Now only the Zener and 392 ohm resistor are in series
across the supply. Again measuring the Zener voltage from GND to point
(2):
The zener voltage tracks the input voltage up to about 11.3 volts at
which point the zener begins to regulate.
With the two transistors still disconnected, I reconnected the 1N4148
diode.
Now the voltage across the zener increases linearly up to 9 volts (input
voltage is 9.35) when suddenly the voltage drops to 1.87 volts.
Do you have any suggestions to help troubleshoot of fix it.
Ralph Ketter
RV-6
Marysville, KS
***************************
Message 11
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Co-ax splice method |
--> AeroElectric-List message posted by: "KeithHallsten" <KeithHallsten@quiknet.com>
I'm about to close up the winglets on the Velocity I'm building, and I need to
extend the antenna wire first. The copper-foil type antenna came to me with a
short length of RG-58 attached, already glassed into the winglet. I intend to
extend it to the instrument panel with RG-400. The area where the splice will
be made will be inaccessible once I seal up the winglet, so I want to use the
parts and technique that has the lowest probability of a problem for the life
of the airframe. I could just install a male connector on one and a female
connector on the other, then mate them and cover with some heatshrink. Is this
the best approach to this situation? Thanks for your advice!
Keith Hallsten, Roseville, CA
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|