Today's Message Index:
----------------------
1. 12:38 AM - Re: OV Protection (Howard Ogle)
2. 03:24 AM - Seminar (Donald Maziarz)
3. 05:30 AM - snubbers (Gary Casey)
4. 05:30 AM - autopilots (Gary Casey)
5. 06:09 AM - Re: Fw: Spike-catcher diode failures (KITFOXZ@aol.com)
6. 06:49 AM - Re: snubbers (Jos Okhuijsen)
7. 06:49 AM - Re: snubbers (Canyon)
8. 07:36 AM - Re: Fw: Spike-catcher diode failures (Paul Messinger)
9. 07:54 AM - Re: Fw: Spike-catcher diode failures (Canyon)
10. 08:54 AM - Re: Altitude control (Eric M. Jones)
11. 09:54 AM - Re: snubbers (Jerzy Krasinski)
12. 10:17 AM - Re: snubbers (Canyon)
13. 11:53 AM - Re: snubbers (Jerzy Krasinski)
14. 12:39 PM - Re: snubbers (Canyon)
15. 12:47 PM - PLEASE READ - Pending ISP Upgrade For Matronics... (Matt Dralle)
16. 06:44 PM - Re: Starter concerns with FADEC and EFIS (Leonard Garceau)
17. 08:02 PM - Re: snubbers (CBFLESHREN@aol.com)
Message 1
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| Subject: | Re: OV Protection |
--> AeroElectric-List message posted by: Howard Ogle <pub@macrotechcorp.com>
Circuit protection devices, like fuses, breakers, fusible links, are only
intended to protect the WIRE from an overload condition (to much amperage). The
danger when a wire conducts two much current is overheating of the wire and the
resulting damage that can occur.
Electricity 101: Using water theory to explain electricity... You can think of
voltage as pressure in a pipe. Whereas amperage can be thought of as volume of
water flowing past a point, just as it is the number of electrons flowing past
a
point in a wire. (For this discussion, I'm going to keep it simple and leave
resistance out of the picture.)
So, your fuses and circuit breakers protect you from to much current or amperage
flowing through a given wire. But, they do nothing to prevent a run away
alternator from offering up to much voltage which can destroy avionics or other
electrical equipment. It can only take a fraction of a second for high voltage
to do it's damage.
A fusible link or other current protection device inline with the alternator
B-lead is designed to prevent a shorted B-lead or shorted alternator from
killing the battery or smoking the B-lead wire. If we lose the alternator, it
sure would be nice (in some cases absolutely necessary) to still have the
battery to get us on the ground. Not to mention, if we didn't have some sort of
current limit on the B-lead, we could end up with an electrical fire.
There are several ways an alternator can fail. However, the one that we are not
protected from yet, unless we have OV protection, is the so called run away
condition. This is where the alternator can supply relatively high voltage to
our system. Current protection does nothing here. The OV protection that Bob
recommends, and I agree, shorts the field lead of the alternator to ground as
soon as an OV condition is detected. This causes the alternator's magnetic field
to immediately collapse (within milliseconds). This is followed by the
alternator field circuit breaker popping, due to the field circuit being shorted
to ground by the OV circuitry. This happens so fast that this is your clue that
you just had an OV condition. The good news is that you still have battery
power, radios and avionics.
A proper system should have both current (fuses, breakers, fusible links)
protection as well as OV protection.
Howard Ogle
--> AeroElectric-List message posted by: "Tinnemaha" <Tinnemaha@charter.net>
> I'm in the (very frustrating) process of designing an electrical system for my
> first experimental (Kitfox w/ Lyc O-235):
> I'm confused about over voltage protection devices(for alternators):
> I understand that their basic purpose is to protect the electrical system if
> the voltage output gets too high, but isn't that the function of any other
type
> of cirquit protection device (fuses, breakers, fusible links)? I'm planning
> on installing a 35 amp fusible link between the alternator and the main bus.
> Does that only protect against over-amperage? I saw the 'crow-bar' type of
> OV protection devices from B&C on the web site - does that get installed
between
> the alternator and the fusible link?
> Any comments or clarifications would be helpful
> Thanks,
> Grant
Message 2
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--> AeroElectric-List message posted by: "Donald Maziarz" <n2va@arrl.net>
You Can Fly Them,
But Can You Wire Them?
What: Weekend seminar presented by The AeroElectric
Connection
Hosted by the National Capital Area
Chapter 186,
Experimental Aircraft Association (EAA)
When: June 7 0800 - 1700
June 8 0800 - 1200
Where: Manassas, VA at the Manassas Regional Airport
(HEF),
EAA 186 Chapter House, at the base of the
tower
Learn the ins and outs of wiring your homebuilt or
restoration project airplane.
Not building or restoring, then get a general
understanding of the aircraft
electrical systems.
Bob Nuckolls has 40 years of knowledge to share with
you.
Cost: $150 per person including a copy of Bob's super
book The AeroElectric Connection
Door Prizes
For more information and to register go to the seminar
area at http://www.aeroelectric.com/
Also note Bob's satisfaction guarantee.
Message 3
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--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<< My Conclusion: DO NOT put a diode across a relay where the relay coil is
in a
circuit that closes to ground. In fact; look closely at any circuit where
you
have used diodes to increase the life of the contacts in a switch or relay
and
consider the consequences of a shorted diode.
another post:
There are two other "snubbing" approaches you can use which won't have a
single
point failure.
1) Diode and resistor in series. Resistor value would be chosen to match
resistance
of coil. Unlike the purely resistive snubbing which would place additional
drain on the battery, the diode will prevent the current from flowing
through
the resistor in normal mode. The resistor protects your circuit in the
event of a diode failure, and still allows the relay to operate. In
snubbing
mode, the current flows through the resistor and the diode.
2) Resistor and capacitor in series. With this approach, the capacitor
is chosen
to "absorb" the energy from the coil. However, the circuit will now
resonate.
The resistor is added to dampen the resonance.>>
Very interesting, and excellent thoughts. But I don't think it matters
whether or not the relay coil goes to ground - the failure mode would be the
same if the switch was in the ground leg. One problem with method 1 above
is that with that value resistor the heat dissipation in the diode-shorted
mode would likely be greater than the rating of the resistor, causing the
resistor to fail as well. I wonder if there isn't a 3rd method - and that
is to simply put a capacitor across the coil without the series resistor (in
fact, I've seen some done this way). Sure, the coil/capacitor will
oscillate, but why do I care? The only thing I'm trying to accomplish is to
increase the life of the switch by reducing the arcing, which the capacitor
will do, even if it's not perfect. I assume it would have to be a fairly
large capacitor and it needs to be rated at a fairly high voltage of maybe
50 volts (a 1 mfd, 50-volt electrolytic?) Further, I would think the
capacitor would be more effecting in reducing the EMC signature as it will
conduct with less delay. A diode requires time to turn on and hence there
is always a voltage spike of very short duration just prior to turn-on. It
is my understanding that these diode turn-on spikes are the principle source
of noise in an alternator, not the voltage ripple. In the passenger car
world there are no parallel diodes to my knowledge as it was found to be
cheaper and more reliable to beef up the switches to tolerate the arcing.
Any exposed semiconductors (not in boxes on circuit boards) are avoided like
the plague due to vibration and reliability issues.
Gary Casey
Message 4
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--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<I found this web page and built the EZ Trim. It works with the Electric
trim that I already had installed.
http://hometown.aol.com/ccady/eztrim.htm
Cliff Shaw
1041 Euclid ave.
Edmonds WA 98020
(425) 776-5555
N229WC "Wile E Coyote"
> >about 1/10 of the above, or 27 feet at sea level and 52 feet at 20,000
feet.
> >I would think that would be about as accurate as we care about and all
that
> >can be had today with sensors built in quantities of several million a
year.
> >>>
The sensor in the "EZ Trim" shown above is exactly what I was talking
about - it is a MAP sensor in a catalog-available package. Unfortunately,
it is from one of our competitors. But it brings up another question,
especially related to the ES I'm building that has 3-axis electric trim.
What is the disadvantage of using the trim as the autopilot actuator? That
would certainly reduce the overall weight and potential cost. The problem I
see is that there is no convenient way to override the system. For
instance, if it makes an uncommanded dive and the pilot pulls it back up the
trim will continue to go to full nose-down position. I suppose the reaction
could be to disconnect and then manually correct the trim? Is the trim
typically fast enough to make for a good autopilot response? I have played
with the manual pitch trim in my Cardinal and with a little practice I can
do a very nice job of flying the plane with the trim only. The EZ Trim idea
is an intriguing one. Comments anyone?
Gary Casey
Message 5
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| Subject: | Re: Fw: Spike-catcher diode failures |
--> AeroElectric-List message posted by: KITFOXZ@aol.com
In a message dated 3/15/2003 11:22:23 PM Eastern Standard Time,
KeithHallsten@quiknet.com writes:
> AeroElectric-List message posted by: "KeithHallsten" <
> KeithHallsten@quiknet.com>
>
> Here's a thread that's been going on the Velocity builder's list server.
> Food for thought for all!
>
>
> ---- Original Message -----
>
> From: Al Gietzen
>
> Sent: Friday, March 14, 2003 11:55 AM
> Subject: REFLECTOR: Speaking of diodes
>
>
> It is obviously common practice to use diodes and Transient voltage
> suppressors (TVS) to kill the backward inducted current from devices with
> coils (relays, motors, etc.) to protect the contacts in switches and relys
> from arcing. Have we also considered the consequences of these little
> jewels failing; especially failing in a shorted condition; which, I believe
> is the most likely failure mode.
>
>
> I had installed a TVS (a P6KE27DICT TVS from Digikey rated 27v 600W)
> across the coil on a battery contactor. It has been there for a year or
> two and has worked well as I cycled the gear or whatever. Also in testing
> circuits I have many times closed the contactor by touching an alligator
> clip from battery - to the ground terminal of the coil for momentary
> closing, and was pleased to note that there was little or no arcing. Until
> the other day, when I went to do that and got a bunch of sparks. What! I
> put it on again and realized quickly that I had a dead short and things
> were getting hot in a hurry. The TVS had failed shorted.
>
>
> In a typical circuit, the battery switch on your panel closes that
> contactor coil circuit to ground. A shorted TVS, or diode, makes that an
> unprotected short to ground, and I'd think could smoke some #22 awg pretty
> fast. What's wrong with this picture? Are we assuming that these things
> don't fail?
>
>
> Similarly; a shorted diode that you have across your trim motor relay
> would cause the trim to run all the way to one extreme and stay there. Can
> you fly and land your plane with full up or down trim? Could be be real
> tough, especially if you haven't trimmed the trim spring to allow full
> travel in the opposite direction with some hard pulling on the stick.
>
>
> I have a bunch of the 1N4001 diodes that I planned using across small
> relays. I think a diode across a contactor needs a higher current rating,
> but how high? And how does one determine the rating required. Us
> electronically challenged nuclear engineers, educated mostly before the
> advent of semiconductors, want to know.
>
>
> Thanks,
>
> Al
>
The first thing that caught my eye in this posting from Al Gietzen begs the
question: Why is he using a transorb rated at 27 V for this application? He
is obviously trying to absorb the inductive kick from his battery contactor's
coil in order to protect his master switch's contact life. He doesn't say
whether his electrical system is 14 or 28 volt. If it is a 28 V system, his
27 V transorb will conduct anyway the first time he brings his alternator
online. He is in the building phase right now I am assuming because he says
that he has "made" the battery contactor in order to swing his (landing)
gear. This transorb's failure is a good event for him now instead of on
engine start day.
If he has a 14 V system, using a 27 V transorb is short changing himself and
his system. The transorb he has chosen only begins to conduct above 27
volts. This means that in practice, the kick from his coil is only
suppressed above 27 volts. This will allow an amount of energy to be handled
by his master switch's contacts that need not be. Using a diode across the
coil will bring it's kick all the way down to .6 V.
He mentions the fear of such an event occurring on his trim relay circuit
causing a trim motor to run away. No matter what device is used to absorb
the kick from the coil of a relay/contactor, be it a transorb, diode,
capacitor, neon, etc., if that device shorts it will not cause a run away
relay/contactor because the relay/contactor's coil is shorted by the bad
device in parallel with that coil. The over current protector (circuit
breaker, fuse, fusible link) will open the circuit.
What Al's issue is, is the lack of over current protection of the 22ga. wire
in his battery contactor coil's grounding circuit. The only failure that
would make this an issue is if the coil's suppression device shorted (or the
coil itself). A diode across the contactor's coil is probably best overall
here. This diode should be robust enough to do the job well. A fusible link
or a fuse could be added in series with the diode/coil ground circuit but
that would be overkill in my opinion. Chose a good diode that will do the
job. A 1N4001 is ideal in all respects here.
John P. Marzluf
Columbus, Ohio
Kitfox Outback (out back in the garage)
Message 6
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--> AeroElectric-List message posted by: Jos Okhuijsen <josok@ukolo.fi>
The diode in this case will die of overvoltage only. The better the
switch, the shorter the cutoff time, and the higher the spike which
will stand over the diode. Overvoltage kills a diode instantly, as
opposed to overcurrent, which will first heat up and then kill.
Adding a capacitor to a coil changes the circuit into a tuned circuit,
much like a magneto, and if the components are sufficiently wrong
chosen, the end result will be more destructing then imaginable. A large
capacitor has an notable impedance of it's own, so is out of the
question. So the first step is to choose the diode with an sufficienty
high reverse voltage, the 1n4001 is (or was) availble from 100 to 800
volts. 800 is the minimum. If nethertheless the diode would fail a
fusable! resistor could prevent the next disaster. Fusable resistors
will not induce a fire hazard, not on 12 volts at least. A normal
resistor will, and could even short out instead of open.
Problem here is that the the resister would have to be inspected at
regular intervals, otherwise a failed diode would never be noticed.
Jos
Gary Casey wrote:
>--> AeroElectric-List message posted by: "Gary Casey" <glcasey@adelphia.net>
>
><< My Conclusion: DO NOT put a diode across a relay where the relay coil is
>in a
>circuit that closes to ground. In fact; look closely at any circuit where
>you
>have used diodes to increase the life of the contacts in a switch or relay
>and
>consider the consequences of a shorted diode.
>
>another post:
>
> There are two other "snubbing" approaches you can use which won't have a
>single
>point failure.
>
> 1) Diode and resistor in series. Resistor value would be chosen to match
>resistance
>of coil. Unlike the purely resistive snubbing which would place additional
>drain on the battery, the diode will prevent the current from flowing
>through
>the resistor in normal mode. The resistor protects your circuit in the
>event of a diode failure, and still allows the relay to operate. In
>snubbing
>mode, the current flows through the resistor and the diode.
>
> 2) Resistor and capacitor in series. With this approach, the capacitor
>is chosen
>to "absorb" the energy from the coil. However, the circuit will now
>resonate.
>The resistor is added to dampen the resonance.>>
>
>Very interesting, and excellent thoughts. But I don't think it matters
>whether or not the relay coil goes to ground - the failure mode would be the
>same if the switch was in the ground leg. One problem with method 1 above
>is that with that value resistor the heat dissipation in the diode-shorted
>mode would likely be greater than the rating of the resistor, causing the
>resistor to fail as well. I wonder if there isn't a 3rd method - and that
>is to simply put a capacitor across the coil without the series resistor (in
>fact, I've seen some done this way). Sure, the coil/capacitor will
>oscillate, but why do I care? The only thing I'm trying to accomplish is to
>increase the life of the switch by reducing the arcing, which the capacitor
>will do, even if it's not perfect. I assume it would have to be a fairly
>large capacitor and it needs to be rated at a fairly high voltage of maybe
>50 volts (a 1 mfd, 50-volt electrolytic?) Further, I would think the
>capacitor would be more effecting in reducing the EMC signature as it will
>conduct with less delay. A diode requires time to turn on and hence there
>is always a voltage spike of very short duration just prior to turn-on. It
>is my understanding that these diode turn-on spikes are the principle source
>of noise in an alternator, not the voltage ripple. In the passenger car
>world there are no parallel diodes to my knowledge as it was found to be
>cheaper and more reliable to beef up the switches to tolerate the arcing.
>Any exposed semiconductors (not in boxes on circuit boards) are avoided like
>the plague due to vibration and reliability issues.
>
>Gary Casey
>
>
>
>
Message 7
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--> AeroElectric-List message posted by: Canyon <steve.canyon@verizon.net>
Gary Casey wrote:
>A diode requires time to turn on and hence there
>is always a voltage spike of very short duration just prior to
>turn-on. It
>is my understanding that these diode turn-on spikes are the principle
>source
>of noise in an alternator, not the voltage ripple. In the passenger car
>world there are no parallel diodes to my knowledge as it was found to be
>cheaper and more reliable to beef up the switches to tolerate the arcing.
>Any exposed semiconductors (not in boxes on circuit boards) are
>avoided like
>the plague due to vibration and reliability issues.
---
All of this is far afield of the reality and/or actual physics of
proper suppression of transient energy developed when circuits through
coils are suddenly broken. In truth, the best, most effective and
safest transient suppression is accomplished with a diode placed
immediately across the inductive element - period. All other methods
using resistors, capacitors, varistors, transorbs etc are far inferior
and thus far less desirable. Don't know how these myths get started...
Steve
Message 8
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| Subject: | Re: Fw: Spike-catcher diode failures |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@tenforward.com>
Transorbs act the same way as a normal diode in the forward direction (they
conduct at under 1 v ) so using the normal transorb or a 1N4001 works the
same when placed across the relay coil to protect the coils inductive "kick"
from potential upstream switch contacts. There are also bi-directional
transorbs same part number but with a "C" after the voltage.
Basically a transorb is a special purpose Zener diode designed for high peak
currents and extremely fast action.
ANY diode can fail short and the primary diode failure is short. In a 12V
acft the failure of a 27V transorb is likely completely random and could
have happened with a 1N4001. The peak current rating of the transorb is huge
compared to the 1N4001. The steady state current rating is similar and is
limited by the package getting too hot.
The intent of a transorb is to clip any high voltage that might get back to
electronics and cause a failure from the HV spike. A 1N4001 diode across the
relay coil is used to continue the coils current around and around the coil
and let the coils resistance absorb the potential inductive spike.
In spacecraft applications we used two diodes in series across every relay.
The dual diodes were special two diodes in a single package. Thus a single
failure of a diode did no harm.
In any case properly fused circuits would prevent any wire overheating etc.
Paul
----- Original Message -----
From: "KeithHallsten" <KeithHallsten@quiknet.com>
Subject: AeroElectric-List: Fw: Spike-catcher diode failures
> --> AeroElectric-List message posted by: "KeithHallsten"
<KeithHallsten@quiknet.com>
>
> Here's a thread that's been going on the Velocity builder's list server.
Food for thought for all!
>
>
> ---- Original Message -----
>
> From: Al Gietzen
>
> Sent: Friday, March 14, 2003 11:55 AM
> Subject: REFLECTOR: Speaking of diodes
>
>
> It is obviously common practice to use diodes and Transient voltage
suppressors (TVS) to kill the backward inducted current from devices with
coils (relays, motors, etc.) to protect the contacts in switches and relys
from arcing. Have we also considered the consequences of these little
jewels failing; especially failing in a shorted condition; which, I believe
is the most likely failure mode.
>
>
> I had installed a TVS (a P6KE27DICT TVS from Digikey rated 27v 600W)
across the coil on a battery contactor. It has been there for a year or two
and has worked well as I cycled the gear or whatever. Also in testing
circuits I have many times closed the contactor by touching an alligator
clip from battery - to the ground terminal of the coil for momentary
closing, and was pleased to note that there was little or no arcing. Until
the other day, when I went to do that and got a bunch of sparks. What! I
put it on again and realized quickly that I had a dead short and things were
getting hot in a hurry. The TVS had failed shorted.
>
>
> In a typical circuit, the battery switch on your panel closes that
contactor coil circuit to ground. A shorted TVS, or diode, makes that an
unprotected short to ground, and I'd think could smoke some #22 awg pretty
fast. What's wrong with this picture? Are we assuming that these things
don't fail?
>
>
> Similarly; a shorted diode that you have across your trim motor
relay would cause the trim to run all the way to one extreme and stay there.
Can you fly and land your plane with full up or down trim? Could be be real
tough, especially if you haven't trimmed the trim spring to allow full
travel in the opposite direction with some hard pulling on the stick.
>
>
> I have a bunch of the 1N4001 diodes that I planned using across
small relays. I think a diode across a contactor needs a higher current
rating, but how high? And how does one determine the rating required. Us
electronically challenged nuclear engineers, educated mostly before the
advent of semiconductors, want to know.
>
>
> Thanks,
>
> Al
>
>
> ----- Original Message -----
>
>
> Al
>
>
> You are correct, this had been a problem and has resulted in problems with
general and commercial aircraft. I could not find my notes for an IA
conference in early 90's but did find info in notes from a conference this
year. AD 90 03 19 R1 required all spike suppression devices to be removed
from a commercial transport because of fire in the heater elements that was
caused by the spike diode that shorted the relay to ground. The FAA will not
allow any electrical system to be installed in an aircraft that has a spike
suppression device across the coil of a relay that is connected to a high
current power source. The key is "HIGH CURRENT".
>
>
> On low-current systems it is still ok but as you noted this type of system
will almost always bypass the circuit breaker and burn something up. If
using a spike suppression device, try to use a transorb (Mosorb), try
1N6284A/ 1.5kE36A, Motorola. Cost less than $1 and works much much faster.
Remember, low current only.
>
>
> Johnny Thompson XLRG N5UP
>
>
> ----------------------------------------------
>
> ----- Original Message -----
>
> Subject: Re: REFLECTOR: Speaking of diodes
>
>
> It would be informative to connect the shorted diode to a piece of 22 ga
mil spec wire then apply 13 volts and see which melts first. I'll bet the
diode burns open before the insulation is damaged.
>
>
> ----- Original Message -----
> From: Al Gietzen
> To: reflector@tvbf.org
> Sent: Saturday, March 15, 2003 5:58 PM
> Subject: RE: REFLECTOR: Speaking of diodes
>
>
> Well; I did just that. Based on two tests, you lose your bet 50% of the
time. I first did the test on the TVS that had failed short the other day.
Recall that it had heated pretty seriously before I opened the circuit. I
put it between two 10" lengths of #22 wire and applied 12 volts. The TVS
opened in less than a second and not much else happened.
>
>
> I then failed a 1N4001 diode by passing a pulse of forward current
exceeding its rating. I then connected 12v in the other direction. The
results were dramatic. The diode and its leads were the first things that
got red hot; followed quickly by the #22 wire becoming red hot and
essentially vaporizing all of the tefzel insulation. A couple seconds more
(at least it seemed that long) and the insulation began melting on my #18
wire jumper; at which point I gave quick tug on the alligator clips which
pulled the diode apart.
>
>
> My Conclusion: DO NOT put a diode across a relay where the relay coil is
in a circuit that closes to ground. In fact; look closely at any circuit
where you have used diodes to increase the life of the contacts in a switch
or relay and consider the consequences of a shorted diode.
>
>
> Possible solution:
>
>
> My son (who is not electronically challenged, and makes his living
designing microprocessors and other circuits, suggests the following:
>
>
> There are two other "snubbing" approaches you can use which won't have a
single point failure.
>
> 1) Diode and resistor in series. Resistor value would be chosen to
match resistance of coil. Unlike the purely resistive snubbing which would
place additional drain on the battery, the diode will prevent the current
from flowing through the resistor in normal mode. The resistor protects
your circuit in the event of a diode failure, and still allows the relay to
operate. In snubbing mode, the current flows through the resistor and the
diode.
>
> 2) Resistor and capacitor in series. With this approach, the capacitor
is chosen to "absorb" the energy from the coil. However, the circuit will
now resonate. The resistor is added to dampen the resonance. Choosing the
values of both the R and C would depend on the inductance of the coil, which
is something you probably don't know. So, there would be some trial and
error involved with choosing values.
>
> I think approach #1 will work very well.
>
>
> Sounds right to me. The resistance of the battery contactor coil is
about 15 ohms. Put a 15 ohm resistor in series with the diode, and the
current in the rare event of the shorted diode would be less than an amp.
Keep the resistor in the open air where it can dissipate some heat. Typical
15 A relays have coil resistance of about 150 Ohms. Put in a 150 Ohm
resistor with your diode and shorted current is limited to less than 0.1
amps. Not enough to drive your trim motor.
>
>
> Anyway; it makes sense to me not to risk myself and my plane in an
effort to prolong the life of the contacts in a relay. Failure of the relay
is likely to be inconsequential.
>
>
> Best, Al
>
>
Message 9
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| Subject: | Re: Fw: Spike-catcher diode failures |
--> AeroElectric-List message posted by: Canyon <steve.canyon@verizon.net>
Paul Messinger wrote:
>ANY diode can fail short and the primary diode failure is short. In a 12V
>acft the failure of a 27V transorb is likely completely random and could
>have happened with a 1N4001. The peak current rating of the transorb
>is huge
>compared to the 1N4001. The steady state current rating is similar and is
>limited by the package getting too hot.
---
Paul, can't argue the point -- it's true. However, it leads one not
skilled in the art to think they have protection they don't have for
OV. 27V is far too late to help any typical sophisticated
system/device likely to be in the circuit. There are simply better
ways to handle OV, IMO. And in fact, 1N4001 diodes are rated at only
50V, IIRC -- the ones that should be used are at least 1N4006 and IIRC,
the IN52XX (? it's been awhile) series would be even better, and two in
series should be fine, though not many folks are likely to ever be
aware if one of them shorted and then you're back to a single. :-)
Steve
Message 10
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| Subject: | RE: Altitude control |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
Altitude....
The Swiss make a wristwatch for climbers that has an barometric altimeter function
accurate to 1 meter at 10,000 meters. So 0.001% accuracy ON YOUR WRIST! is
no big deal. Fifteen years ago at an aerospace show, I saw a (REAL BIG DEAL)
laboratory altimeter that had ten decimal places and the last couple digits were
dancing. I asked about its precision and the salesman said, "watch this", and
he slipped a thin product flyer under the sensor. The 8th place (or so) jumped
up a digit and stayed there. It hurts my head to think how good that thing
was.
Theoretically, ultimate barometric altitude precision is exactly equivalent to
the size the smallest bubble that has buoyancy. There it goes, ouch, my head hurts
again.
It is important to realize that barometric altitude is sloppy compared to other
ways of measuring altitude. Differential GPS, radar, and all the fancy ways formerly
unaffordable to home builders are becoming affordable.
Regards,
Eric M. Jones
Message 11
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--> AeroElectric-List message posted by: Jerzy Krasinski <krasinski@direcway.com>
>
>
> All of this is far afield of the reality and/or actual physics of
> proper suppression of transient energy developed when circuits through
> coils are suddenly broken. In truth, the best, most effective and
> safest transient suppression is accomplished with a diode placed
> immediately across the inductive element - period. All other methods
> using resistors, capacitors, varistors, transorbs etc are far inferior
> and thus far less desirable. Don't know how these myths get started...
>
> Steve
>
>
Steve,
I wonder what is wrong with varistors. These seem to be among the most
reliable electronic elements. The damage mechanism of varistors is
thermal, however, you have to heat all the big device, rather than a
tiny junction of the diode. Varistors can take incredible abuse, they
can absorb an incredible current with no damage, and the only limit is
the total energy of the spike. That is the reason why varistors and not
discrete diodes are used for lightning protection of power lines. In
addition they are made using ceramic process and they are cheap. Most of
them are fast enough to turn on and absorb a voltage spike generated in
a coil.
In fact varistors on a micro level are diodes. There are millions of
strings of junctions formed between the grains of the ceramic material
of varistor and that explains why varistors survive so much of bad
treatment. To ruin a varistor you would have to ruin millions of the
micro diodes and that requires to make the WHOLE pellet heated to a
very high termperature.
I use varistors in my work to protect 200V electronics from periodic (20
times a second) 20 kV voltage spikes with ~50 ns risetime. I put a 250V
big varistor across the 200V output. That took care of the problem.
These 20kV pulses just sink into the varistor. Living in a rural area I
had problems with lightning strikes in the power line wiping out my TV,
computer equipment, telephones etc. I got exhausted fighting each time
with my insurance company to get replacement $$ for lightning damaged
property, that is included in my policy. I put varistors between the
power wires, and between the wires and the ground wire. The Oklahoma
strength lightnings are still there, but neither my equipment nor
varistors failed. If something takes abuse of a lightning why it would
fail from a much weaker pulse generated in a coil? It seems that a tiny
varistor would be sufficient to handle the coil generated spikes.
Attaching a 15 - 17 V varistor across the relay coil in a 13.5V system
would limit voltage on the coil roughly to 15 - 17 V in any direction,
since voltage/current characteristic of the varistor is symmetric. That
should protect the coil.
Does anyone on this list know a reason why the varistor would be
inferior in a relay coil voltage spike protection circuit?
Jerzy
Message 12
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--> AeroElectric-List message posted by: Canyon <steve.canyon@verizon.net>
Jerzy Krasinski wrote:
>Attaching a 15 - 17 V varistor across the relay coil in a 13.5V system
>would limit voltage on the coil roughly to 15 - 17 V in any direction,
>since voltage/current characteristic of the varistor is symmetric. That
>should protect the coil.
---
Jerzy, the answer lies in the dynamics of the transient. In the case
of a diode across the coil, the transient is generated by the fact the
coil wants to continue the current flow after the current source has
been switched off and a diode will circulate that small transient
energy through the diode, quenching the transient energy, almost
instantly limiting the voltage to ~0.6 or so volts above the relatively
stiff current sink of a battery circuit voltage. What else could one
desire?
Compare the varistor clip voltage to this and I think it is obvious
which is most appropriate for the task intended.
For other applications you describe, in AC circuits, varistors are very
effective. And for your situation with lightning, if possible, bury
the power underground for the final run to your house/barn whatever and
you will also see considerable improvement in protection. Adding the
varistors as you describe then adds even more effective protection with
this arrangement for household power.
Steve
Message 13
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--> AeroElectric-List message posted by: Jerzy Krasinski <krasinski@direcway.com>
>
>
>Jerzy, the answer lies in the dynamics of the transient. In the case
>of a diode across the coil, the transient is generated by the fact the
>coil wants to continue the current flow after the current source has
>been switched off and a diode will circulate that small transient
>energy through the diode, quenching the transient energy, almost
>instantly limiting the voltage to ~0.6 or so volts above the relatively
>stiff current sink of a battery circuit voltage. What else could one
>desire?
>
>Compare the varistor clip voltage to this and I think it is obvious
>which is most appropriate for the task intended.
>
>
>
Steve,
The purpose of the circuit we discuss is to safely discharge the energy
stored in the relay core. Safely means without unnecessary overvoltage.
In case of a diode voltage will get clipped at ~ 0.6 V, in case of a 15
V varistor voltage will get clipped at ~15 V. In both cases the energy
will get dissipated safely from the coil's point of view, since 12 V
coil would handle 15 V with no problem.
Diodes are widely accepted as damping elements for inductice loads, and
if you asked me a few days ago, before I learned that diodes fail more
frequently than acceptable in aviation, I would recommend a diode for
that task. But now, having FAA against the diodes, and looking for a
difficult to damage damping element for the coil, I noticed that the
varistor's resistance to damage by current pulses or inverse voltage
spike would be very difficult to beat.
Jerzy
Message 14
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--> AeroElectric-List message posted by: Canyon <steve.canyon@verizon.net>
Jerzy Krasinski wrote:
>Diodes are widely accepted as damping elements for inductice loads, and
>if you asked me a few days ago, before I learned that diodes fail more
>frequently than acceptable in aviation, I would recommend a diode for
>that task. But now, having FAA against the diodes, and looking for a
>difficult to damage damping element for the coil, I noticed that the
>varistor's resistance to damage by current pulses or inverse voltage
>spike would be very difficult to beat.
---
Diodes are widely accepted because they are the right device in the
right application, but this is for experimental planes, right? Try it
out if you're determined and let us know how it works out. Personally,
I'll stick with diodes and avoid the +- 15V ringing of the inductor
about the power rail(s).
Steve
Message 15
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| Subject: | PLEASE READ - Pending ISP Upgrade For Matronics... |
--> AeroElectric-List message posted by: Matt Dralle <dralle@matronics.com>
Dear Matronics Listers,
Sometime during the next 72 hours, the ISP (Internet Service Provider) for
Matronics will be upgrading the level of service to 1.1Mb from the current
768k. When they reprovision the line, there will be an outage requiring
that the local router here be restarted. It is also unclear whether or not
the physical line will support the new rate, so some testing will be
required to verify the new service at the time of installation.
Unfortunately, I don't really have an idea of exactly when they will be
reprovisioning the line, so I wanted to give everyone a heads up on what's
going on. All Matronics List services such as email list redistribution,
subscriptions, and web search and browse will be unavailable during the
upgrade.
In other upgrade news, last Thursday, 3/13/03 I upgraded the firewall
appliance between the Internet and the Matronics systems. This new
firewall represents a substantial increase in performance and hopefully
reliability over the previous system. It will compliment nicely the new
level of ISP connectivity.
Finally, these are just two examples of the upgrades brought to you
compliments of the 2002 List Fund Raiser. A special thanks to all that
made a Contribution in 2002 and so far this year! Everyone that uses these
Lists appreciates your generosity!
I will post a short message again if I manage to get some clear direction
on the time-frame for upgrade, or perhaps when its been completed.
Thanks again!!
Matt Dralle
Matronics Email List Administrator
Matt G Dralle | Matronics | PO Box 347 | Livermore | CA | 94551
925-606-1001 V | 925-606-6281 F | dralle@matronics.com Email
http://www.matronics.com/ WWW | Featuring Products For Aircraft
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Long Way Home, 1982
Do Not Archive
Message 16
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| Subject: | Re: Starter concerns with FADEC and EFIS |
--> AeroElectric-List message posted by: "Leonard Garceau" <lhgcpg@westriv.com>
Hi Bob,
I have a question about wiring the fuel injected and coil over plug engines.
I see how you wire two hot busses from 2 batteries to the two computers.
But how do I wire the fuel injectors and the coils to the two separate
batteries? What do you think would work the best?
Thanks,
Leonard
----- Original Message -----
From: <TimRhod@aol.com>
Subject: AeroElectric-List: Starter concerns with FADEC and EFIS
> --> AeroElectric-List message posted by: TimRhod@aol.com
>
> In a message dated 3/14/2003 5:25:57 PM Eastern Standard Time,
> cozytom@mn.rr.com writes:
>
> > <A
HREF="mailto:aeroelectric-list@matronics.com">aeroelectric-list@matronics.co
m
>
> Bob and others:
> Ive been thinking of solutions to some of the things we have been
discussing
> concerning voltage drop when starting FADEC engines. Also concern over
> voltage spikes or low voltage problems with the EFIS/ONE during
starting.
> Here is what I came up with. Using Z-14 DBDA Put all avionics one one
bus.
> For me I think this will be a avionics bus with quad feed. One from main
bus
> through diode and avionics master switch. Second from Alternate bus
through
> diode and avionics secondary master switch. Master switches are included
in
> case EFIS systems need isolated as Greg Ricktor seems to think they should
> be. Third and fourth essential feeds from main batt buss and alternate
batt
> buss on one switch that would choose one or the other. Cross feed
contactor
> will not have starter switch included. Starter switch will be seperate.
Here
> is how I envision it working. During start up sequence the avionics bus
can
> be feed through the alternative electrical system. So the Efis/One is
powered
> up from that source. Also the FADEC ignition is powered from the Alternate
> battery. The main battery is used to start the engine The cross feed is
kept
> open at this point so the two electrical systems never affect each other.
If
> you needed both batteries to start you would not turn on avionics bus
until
> engine started. You wouldnt have you oil pressure immediatly but this
> shouldnt be a common occurance to need both batteries for starting. It
seem
> to me that this allows the Efis/One and the FADEC ing. to be at 12.5 volts
> continually during engine start-up. What do you think?
>
>
Message 17
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--> AeroElectric-List message posted by: CBFLESHREN@aol.com
Hi Jerzy, I've been lurking here & can't help but recall that "Bob" had
MOV's shown in some of his earlier drawings for the protection of various
Start & Master relays. I asked him about their use back then & as I recall,
he stated the reason for his preference over a diode, for the MOV was that no
concern for polarity made them slightly easier for us "lay" homebuilders to
cope with. FWIW ---- Chris Fleshren
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