Today's Message Index:
----------------------
1. 06:20 AM - Re: Antenna Questions (Robert L. Nuckolls, III)
2. 06:40 AM - Re: Electric fuel pump circuit (Robert L. Nuckolls, III)
3. 08:24 AM - Re: Flap motor testing (Kenneth Melvin)
4. 11:13 AM - Inverting a signal condition ('Scott Richardson')
5. 12:38 PM - Re: Inverting a signal condition (Dave Morris)
6. 12:50 PM - Re: Inverting a signal condition (Chad Robinson)
7. 01:22 PM - ND Alternators (David Shani)
8. 02:17 PM - Emergency Buss/Standby Alternator (flyv35b)
9. 02:38 PM - Alternator Wiring Question (Metcalfe, Lee, AIR)
10. 02:51 PM - Re: Flap motor testing (Robert L. Nuckolls, III)
11. 02:57 PM - Re: Electric fuel pump circuit (Ed Anderson)
12. 04:00 PM - Re: Load Dumps (Eric M. Jones)
13. 08:56 PM - Re: Re: Load Dumps (Jerzy Krasinski)
Message 1
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| Subject: | Re: Antenna Questions |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 11:54 PM 2/25/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: Don Boardman <dboardm3@twcny.rr.com>
>
>Hi All,
>
>As mentioned on the list earlier, we are installing a Loran as a second nav
>to our KMD 150 GPS. A friend had an antenna that he gave us. It is a
>physical match to the Com Antennas found on most Cessnas. It indicates it is
>a Loran antenna on the bottom.
>
>Do I need to use the pre-amp that came with the Loran with this type
>antenna?
probably for best performance
>I can always experiment and look at the results with and without the
>pre-amp. Will it hurt to use the pre-amp if in fact it is not essential to
>use?
you can't hurt anything by leaving it off. if you're satisfied
with performance without it, then it's your choice.
>My friend also brought with him an identical looking antenna with graphics
>on its base that say: STS avionics. The identification tag on the bottom is
>mostly gone. Does anyone know if this is a Com antenna or another Loran
>antenna? The friend did not know.
>
>Is there a way to tell which type it is?
>
>Is there a way other than hooking an antenna to a unit to tell if it is good
>to go.
that's the best. mount it on a piece of aluminum, put an
antenna analyzer on it or transmitter and swr bridge and
see what it looks like.
>A last question. At one time I was told that is was not good to have a
>transmitter powered up without a functioning antenna attached. That
>transmitting with no antenna could damage the transceiver. Is this true?
When solid state transmitters first started showing up in
airplanes, they were particularly intolerant of high
standing wave ratio at the antenna terminal. There was
a standard caution about operating the transmitter into
an open coax . . . nowadays, any transmitter worth the
money has modern, more robust transistors in the output
stage and some designs include built in swr detection
schemes that automatically throttle back an at-risk
output stage so that high swr won't damage it.
You'd have to look at the schematic for your particular
radio to deduced whether or not this feature is in place.
What does your installation manual say about the
radio?
Bob . . .
-----------------------------------------
( Experience and common sense cannot be )
( replaced with policy and procedures. )
( R. L. Nuckolls III )
-----------------------------------------
Message 2
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| Subject: | Re: Electric fuel pump circuit |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 06:52 PM 2/25/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: Charlie Kuss <chaskuss@bellsouth.net>
>
>Bob,
> I was hoping you'd say that. (forget the relay) Do I understand you
> correctly? You feel the pump should be wired to the battery bus?
>Charlie
I think I would. There's some compelling thought for being
able to make the panel completely dark without affecting
anything needed to keep the engine running.
Bob . . .
Message 3
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| Subject: | Flap motor testing |
--> AeroElectric-List message posted by: Kenneth Melvin <melvinke@direcway.com>
I run a Cessna flap motor with 10A fuse in my RV4, and have bent the
actuating rods without ever blowing a fuse!
Ken Melvin
N36KM
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Fiveonepw@aol.com
Subject: Re: AeroElectric-List: Flap motor testing
--> AeroElectric-List message posted by: Fiveonepw@aol.com
In a message dated 02/25/2004 3:18:46 PM Central Standard Time,
bob.nuckolls@cox.net writes:
I'm mystified as to why this issue has jumped up on Mark's
airplane. There are LOTS of RV's flying with fused flap motor
circuits. Is there anyone flying that found it necessary to
fuse an RV flap motor at more than 10A?
Flew again today with an LED front & center on the panel tied directly
to the
fuse output- did many landings and, several "not so pretty" combined
with a
fair amount of "flap abuse", and the damn fuse never blew- go figure...
I'm gonna keep the "idiot light" connected for a while and see what goes
down- if I learn anything, I'll letcha know!
Mark
==
==
==
==
Message 4
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| Subject: | Inverting a signal condition |
--> AeroElectric-List message posted by: "'Scott Richardson'" <scott_m_richardson@sbcglobal.net>
Hi all,
I've constructed an annunciator panel along the lines of the one that
Mark Phillips described on this list back in December, but had a
question for some of the electronic circuit guys on the list. Most of
my signal conditions are such that when I want the indicator to light
(boost pump on, fuel low, etc.), the signal line goes high (bus voltage,
13.8v). However I have a couple of signals where the signal is
indicated by the signal line going to ground (the Low Volt light on the
B&C regulator for example). I'm looking for some mechanism to
effectively switch this type of low indication to high. I'd need
something that would:
a) drive the output voltage at the normal electrical bus voltage (since
I'm using a zener diode for dimming, I need all LED driver voltages the
same)
b) be able to drive upwards of 40ma to drive my LED indicator
Because of (a), I can't simply use a inverter IC circuit - at least I
can't find one that drives at that type of output voltage AND can take
it's supply at bus voltage. My first response is to use a simple relay
like Digi-key part PB371-ND (12V, 3A, SPST:NO, PCB mount, about $1.50)
and make up a little PCB to hold a couple of them and a connector.
I don't see anything wrong with this method, just wondering if anyone
had any other suggestions. Thanks as always...
Scott
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Scott M Richardson scott_m_richardson@sbcglobal.net
Message 5
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| Subject: | Re: Inverting a signal condition |
--> AeroElectric-List message posted by: Dave Morris <dave@davemorris.com>
Install those LEDs backwards and wire the other lead to 12VDC.
Dave Morris
At 11:12 AM 2/26/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: "'Scott Richardson'"
><scott_m_richardson@sbcglobal.net>
>
>Hi all,
>
>I've constructed an annunciator panel along the lines of the one that
>Mark Phillips described on this list back in December, but had a
>question for some of the electronic circuit guys on the list. Most of
>my signal conditions are such that when I want the indicator to light
>(boost pump on, fuel low, etc.), the signal line goes high (bus voltage,
>13.8v). However I have a couple of signals where the signal is
>indicated by the signal line going to ground (the Low Volt light on the
>B&C regulator for example). I'm looking for some mechanism to
>effectively switch this type of low indication to high. I'd need
>something that would:
>
>a) drive the output voltage at the normal electrical bus voltage (since
>I'm using a zener diode for dimming, I need all LED driver voltages the
>same)
>b) be able to drive upwards of 40ma to drive my LED indicator
>
>Because of (a), I can't simply use a inverter IC circuit - at least I
>can't find one that drives at that type of output voltage AND can take
>it's supply at bus voltage. My first response is to use a simple relay
>like Digi-key part PB371-ND (12V, 3A, SPST:NO, PCB mount, about $1.50)
>and make up a little PCB to hold a couple of them and a connector.
>
>I don't see anything wrong with this method, just wondering if anyone
>had any other suggestions. Thanks as always...
>
>Scott
>*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
>Scott M Richardson scott_m_richardson@sbcglobal.net
>
>
Message 6
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| Subject: | Re: Inverting a signal condition |
--> AeroElectric-List message posted by: Chad Robinson <crobinson@rfgonline.com>
'Scott Richardson' wrote:
> --> AeroElectric-List message posted by: "'Scott Richardson'" <scott_m_richardson@sbcglobal.net>
>
> Hi all,
>
> I've constructed an annunciator panel along the lines of the one that
> Mark Phillips described on this list back in December, but had a
> question for some of the electronic circuit guys on the list. Most of
> my signal conditions are such that when I want the indicator to light
> (boost pump on, fuel low, etc.), the signal line goes high (bus voltage,
> 13.8v). However I have a couple of signals where the signal is
> indicated by the signal line going to ground (the Low Volt light on the
> B&C regulator for example). I'm looking for some mechanism to
> effectively switch this type of low indication to high. I'd need
> something that would:
>
> a) drive the output voltage at the normal electrical bus voltage (since
> I'm using a zener diode for dimming, I need all LED driver voltages the
> same)
> b) be able to drive upwards of 40ma to drive my LED indicator
>
> Because of (a), I can't simply use a inverter IC circuit - at least I
> can't find one that drives at that type of output voltage AND can take
> it's supply at bus voltage. My first response is to use a simple relay
> like Digi-key part PB371-ND (12V, 3A, SPST:NO, PCB mount, about $1.50)
> and make up a little PCB to hold a couple of them and a connector.
>
> I don't see anything wrong with this method, just wondering if anyone
> had any other suggestions. Thanks as always...
There are dozens of ways to do this. Your way with relays works fine, although
it's a mechanical part that you might want to eliminate. It also requires
enough power to hold the relay closed, although generally not much. Or you
could just use a transistor and two resistors. My schematic capture app is
down right now (reloading my system), but in rough ASCII art it would be:
1k
+12V supply ----\/\/\--------Collector of T1, and output
1k
Input signal ---\/\/\---Base of T1
Ground ----------------------Emitter of T1
where T1 is a 2N2222 or similar NPN transistor. The 2N2222 can sink about
800mA of current if it's heatsinked in this case. You can use a larger NPN
transistor, like the ZTX1053A (handles up to 3A) if necessary, but your 40mA
requirement is way lower than this even if you drive multiple indicators.
This is a pretty simple circuit. While the input is 0 (off) the transistor is
also off, so the output "sees" 12V through the 1K pull-up resistor. In fact,
if you're directly driving an LED you won't need a current limiter on it. You
can just adjust the value in this circuit.
If the input becomes 1, the transistor turns on, and the output "sees" a more
direct path to ground through it (output is thus ground, or 0). The resistor
on the base of the transistor is a current limiter for the device itself.
Regards,
Chad
Message 7
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--> AeroElectric-List message posted by: "David Shani" <David.Shani@sanmina-sci.com>
Hello Listers,
Who have information about a good source (hopefully inexpensive) for ND
alternator ?
I am looking to use a 50 amp. one on an O-320.
Thanks,
David
Message 8
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| Subject: | Emergency Buss/Standby Alternator |
--> 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. 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?
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?
3. How would the D-25 fail if it did? Open circuit or what?
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)?
List of items planned for the Emergency Buss
SL-30 Nav/Com 2.4a typ. 3.7a max.
GX-50 GPS 0.5a typ. 0.75a
max.
Electric AI 2.4a start
0.9a run
NSD-360 HSI 0.5a
KT-76C transponder 1.6a max.
Electronics Int'l VA-1A (volt/amp) 0.2a
EI OPT-1 (oil press/temp) 0.1a
EI FP-5L (fuel flow/qty) 0.1a
Horizon digital tach 0.2a
S-TEC 50 AP 1.0 ave. 5.0a max.
S-TEC turn coordinator 3.0a
MX-20 (optional) 2.0a typ. 3.0a
max.
Panel light LED
(negligible)
As always, I appreciate your expertise and vast knowledge and especially the
time you take to share it with others here on the web and in the Aero
Electric Connection.
Cliff Hanson A&P/IA
-- Original Message -----
From: "Robert L. Nuckolls, III bat teries" <bob.nuckolls@cox.net>
Subject: RE: AeroElectric-List: Essential bus alternate feed from two bat
teries
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net> bat teries
>
> At 02:42 PM 2/24/2004 -0500, you wrote:
> >--> AeroElectric-List message posted by: Ken Harrill
> ><KHarrill@osa.state.sc.us>
> >
> >--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> ><bob.nuckolls@cox.net> batteries
> >
> >
> > >During start I thought I would use the main battery for cranking
engine,
> > >the aux battery for powering the electronic ignition (to avoid any
> > >possibility of kick back in the event main battery voltage drops below
> > >min required for electronic ignition).
> >
> > ???? Is it the stated policy/recommendation by the manufacturer
> > of the ignition system that you do this? I'm increasingly mystified
> > by what I perceive as an upsurge in worries about this. Perhaps
> > it's just that the economy is improving and more folks are building
> > airplanes with electronic ignition. Market forces notwithstanding,
> > I'm wondering if the risk is real and whether or not the
manufacturers
> > of these products are acknowledging a shortcoming in their product's
> > design. The low voltage event during cranking is tens of milliseconds
> > long as the starter motor spins up. There is no good reason why
> > you as the user should have to be concerned about this. Designing
> > sensitivity to this phenomenon out of the ignition system is
> > a rudimentary technique of circuit design.
> >
> >Bob,
> >
> >This may be a legitimate "worry". I spent quite a bit of time and energy
> >attempting to resolve the starting problems with my LSE ignition system.
I
> >have a permanent magnet Lycoming starter, a 17 AH battery, and I start
the
> >engine on the electronic ignition only. My engine would only start when
I
> >released the starter button. It always started, but it left me with an
> >uneasy feeling that sometime, far away from home, it may not. The
voltage
> >(measured at the ignition module) drops to around 8 volts with the
starter
> >engaged, and the LSE does not fire at that voltage, regardless of what
> >Klause claims. I resolved the problem for now by switching to an Odyssey
> >battery, which does not produce quite as much voltage drop. A better
> >solution is a B & C starter that draws less current, but that cost $$$.
If
> >I were building an airplane with two batteries, I would certainly
consider
> >starting on one and powering the electronic ignition from the other.
>
> Hmmm. Did you try leaving the ignition switch off until after
> the engine was rotating?
>
> Bob . . .
>
>
Message 9
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| Subject: | Alternator Wiring Question |
--> 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.
Lee Metcalfe
N320WH - Kansas City
Message 10
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| Subject: | Flap motor testing |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
At 08:23 AM 2/26/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: Kenneth Melvin
><melvinke@direcway.com>
>
>I run a Cessna flap motor with 10A fuse in my RV4, and have bent the
>actuating rods without ever blowing a fuse!
>Ken Melvin
>N36KM
Which doesn't surprise me. The mechanical advantage
that motor has is phenomenal . . . the problem isn't
one of TORQUE from the motor but INRUSH currents
presented by the permanent magnet motor in the milliseconds
after application of power but before it develops much
speed.
Bob . . .
Message 11
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| Subject: | Re: Electric fuel pump circuit |
--> AeroElectric-List message posted by: "Ed Anderson" <eanderson@carolina.rr.com>
----- Original Message -----
From: "Robert L. Nuckolls, III" <bob.nuckolls@cox.net>
Subject: Re: AeroElectric-List: Electric fuel pump circuit
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<bob.nuckolls@cox.net>
>
> At 06:52 PM 2/25/2004 -0500, you wrote:
> >--> AeroElectric-List message posted by: Charlie Kuss
<chaskuss@bellsouth.net>
> >
> >Bob,
> > I was hoping you'd say that. (forget the relay) Do I understand you
> > correctly? You feel the pump should be wired to the battery bus?
> >Charlie
>
> I think I would. There's some compelling thought for being
> able to make the panel completely dark without affecting
> anything needed to keep the engine running.
>
> Bob . . .
I agree with Bob. My rotary powered RV-6A has all critical items, fuel
pump, ignition and fuel injection system wired off the battery bus. Only
thing between the subsystems and the battery is a high grade toggle switch
and circuit breaker. Then being somewhat anal retentive about failure of
mechanical switches, I hot wire all these subsystems to the battery through
one 20 amp circuit breaker which is normally open. If you push in the
circuit breaker it routes power around all switches to the critical systems.
Never had to use it (and probably never will) but it is comforting and light
and cheap to implement.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
Message 12
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--> 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 13
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--> AeroElectric-List message posted by: Jerzy Krasinski <krasinski@provalue.net>
Eric,
I do not think this calculation is right.
I think we should model the alternator as an inductivity with current.
After opening the circuit the inductivity increases output voltage
attemting to keep the output current constant, with gradual reduction
of current as the energy from the inductivity is dissipated.
This model, produces output current equal or less than the alternator
output current just before disconnecting action.
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.
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 .
Jerzy
Eric M. Jones 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.
>
>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
>
>
>
>
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