Today's Message Index:
----------------------
1. 06:24 AM - Re: Flyback Diodes (Bill Watson)
2. 07:36 AM - Re: Fire-Sale Phase V (Hariharan Gopalan)
3. 07:57 AM - Re: Fire-Sale Phase V (Justin Jones)
4. 08:24 AM - Re: Fire-Sale Phase V (Robert L. Nuckolls, III)
5. 11:23 AM - Re: Flyback Diodes (Robert L. Nuckolls, III)
6. 11:48 AM - Re: Re: Wiring schematic question (Peter Pengilly)
7. 12:33 PM - Re: Wiring schematic question (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: Flyback Diodes |
So, the diode we find jumpered between the coil contacts on let's say,
our starter relay, prevents a high voltage shooting back thru our
starter switch and arcing the contacts when we let go of the starter
key/switch?
Or does it prevent a power surge from hitting the entire electrical system?
Bill "waking up brain cells in disuse since early adolescence" Watson
(nice video, thanks!)
On 11/17/2014 12:07 PM, Eric Page wrote:
> The following video was just posted by a fellow on YouTube who I
> follow. It does a very nice job of illustrating the purpose and
> effect of using flyback or catch diodes on inductive loads like relay
> coils.
>
> Since the topic has arisen here a number of times, I thought this
> might be of interest.
>
> http://www.youtube.com/watch?v=c6I7Ycbv8B8
>
> Eric
>
Message 2
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Subject: | Re: Fire-Sale Phase V |
Please invoice rdu.hari@gmail.com
Thanks
Hari
On Mon, Nov 17, 2014 at 10:18 PM, Charlie England <ceengland7@gmail.com>
wrote:
> ceengland7@gmail.com>
>
> On 11/17/2014 8:37 PM, Robert L. Nuckolls, III wrote:
>
>> nuckolls.bob@aeroelectric.com>
>>
>>
>> Excellent! Please invoice to mcsophie@gmail.com (different from my
>>> aeroelectric subscription).
>>>
>>> Thanks,
>>>
>>> Charlie
>>>
>>
>> Done.
>>
>>
>> Bob . . .
>>
> And done.
>
> Thanks,
>
> Charlie
>
>
Message 3
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Subject: | Re: Fire-Sale Phase V |
Bob,
I would like one of them if you have any left.
Thanks
Justin
jmjones2000@mindspring.com <mailto:jmjones2000@mindspring.com>
> On Nov 17, 2014, at 3:30 PM, Robert L. Nuckolls, III
<nuckolls.bob@aeroelectric.com> wrote:
>
<nuckolls.bob@aeroelectric.com>
>
> I have two, legacy crowbar overvoltage modules
> left from inventory. $20 each post-paid to US
> addresses.
>
>
> Bob . . .
>
>
>
>
Message 4
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Subject: | Re: Fire-Sale Phase V |
At 09:33 2014-11-18, you wrote:
>Please invoice <mailto:rdu.hari@gmail.com>rdu.hari@gmail.com
>
>Thanks
>Hari
already sold
Bob . . .
Message 5
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Subject: | Re: Flyback Diodes |
At 08:19 2014-11-18, you wrote:
So, the diode we find jumpered between the coil contacts on let's
say, our starter relay, prevents a high voltage shooting back thru
our starter switch and arcing the contacts when we let go of the
starter key/switch?
Yes . . .
Or does it prevent a power surge from hitting the entire electrical system?
Not at all. Contactor/relay coil flyback, catch or
suppression diodes have been part-and-parcel of the
system designer's toolbox for quite a few years. While
I was a tech writer at Cessna (65-69), our chief scientist,
Gordon Wood, Phd, purchased this nifty peak-reading
voltmeter (Hewlett-Packard I think) and did some
battery and starter contactor behavior studies in the
labs.
"My gawd Mabel . . . did you see the size of that
spike?!?!?! Gee whiz . . . over 400 volts . . .
that sounds dangerous."
This was exactly the time when Aircraft Radio
Corporation, recently purchased by Cessna, was
producing Cessna branded 300, 500 and ultimately
400 Series radios and autopilots.
When the radios began to show up with transistorized
audio/modulator and dc/dc converters for vacuum
tube high voltage, we began to experience a rash of
un-explained failures in the transistors of newly
installed radios. We were building 10,000 airplanes
a year back then . . . needless to say, even a few
percent failure rate in radios was a SIGNIFICANT impact
to corporate bottom line.
The quest was on . . . if not to understand what
was really happening . . . then at least to stop
the failures. About that same time, Cessna hired
Wichita University to craft a course on "The
Industrial use of Transistors," which was well
attended by about 20 folks from both Cessna plants
and your's truly.
The instructor was extremely well versed in the topic
being that he was both a college prof and a sought
after consultant. Not a great teacher . . . but
Jerry Wedel I learned how to 'pick his brain'
in useful ways by the questions we asked. We sat
on opposite sides of the class and stroked him
to our great advantage.
Back then, the power transistors of choice were
germanium, mostly PNP devices with max operating
voltages on the order of 30 volts. Hmmmm . . .
Mean while, back at the airplane farm, Gordon was
poking around the electrical systems of our airplanes
in search of clues. It was quickly discovered that
adding the diode across the contactor coil
completely eliminated the gawd-awful spike. Whew!
Slew that dragon. But that still didn't fix the
radio failures. About then, flight test pilots
discovered that if the radios were OFF during engine
start, the did not suffer the failures.
You know what came next. The avionics master switch
was born. Simultaneously, a new line of thought was
launched into the aviation consciousness . . . and
a new phrase was oft repeated on avionics benches
across the world, "Damn, I think a spike got it."
It took about two decades before anyone really
began to sift the simple-ideas for properties of
materials and management of energy (it's called
engineering) and figure out what was really
going on. Turns out that transistor failures in
the radios were not suffering the effects of high
voltage spikes . . . but second breakdown effects
in relatively fragile transistors due to LOW voltage
effects, i.e. brownout during cranking.
Batteries back then were pretty sorry things by
today's standards. Our 'airplane patch' east of
the plant would have hundreds of new airplanes
parked out there awaiting ferry pilots. The
batteries were NEVER attended to in a manner
consistent with their physics . . . hence, more
that a few airplanes needed to be propped, jumped
and/or battery charged . . . but only AFTER
the pilot had attempted to start the airplane
perhaps with one or more radios turned ON.
It was also not well understood that those
spectacular contactor coil spikes never went
anywhere . . . at least not out onto the ship's
electrical system. 99% of energy stored on
the contactor's inductance was dissipated in
the air-gap of the spreading switch contacts
as the battery master was turned OFF or the
starter switch was released.
The diodes across the coil were a good thing,
it saved wear and tear on switches . . . but
had no significance on the life span of a radio
or any other appliance.
In still later years, there was some earnest
debate about OTHER effects of adding diodes
across relay or contactor coils. Simple
measurements demonstrated that adding the
diode caused there to be a DELAY in relay/
contactor drop-out . . . the diode cause
coil current to be sustained for some milliseconds
after the switch opened as energy stored in
the coil was dissipated in circuit resistance.
Hmmm . . . if the contactior's release
is delayed/slowed, does that also translate
into a slower contact spreading velocity
which in turn aggravates the arcing? Intuitively
it seems likely . . . indeed, many articles
have been written, some by folks working for
big-name companies that thoroughly described
the diode induced drop-out DELAY . . . and
then extrapolated that good information into
an erroneous assumption that influences
on drop-out delay were equally applicable
to contact spreading velocity . . . without
making a single measurement.
On page 4 of this document
http://tinyurl.com/n296nl6
there are 'scope displays that demonstrate
approx 5x increase in dropout delay for
having added a plain-vanilla diode across
a relay coil.
At the same time, the contact spreading
times are very similar demonstrating no
significant difference in the arc
signature.
Bill "waking up brain cells in disuse since early adolescence" Watson
(nice video, thanks!)
The youtube tutorial was nicely done and
confirms the value of adding SOME form of
coil spike suppression . . . but to extrapolate
the demonstration's significance for other
features of relay performance is fraught
with opportunity for error.
Bob . . .
Message 6
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Subject: | Re: Wiring schematic question |
If you have no master relay or starter relay then the thick wire from
the battery to the starter will be hot at all times - there are a few
accident scenarios where you could wish you hadn't done that, but its a
judgement over risk and reward!
I have a similar set up on my One Design, except that I used a starter
relay, and also brought out the wire that controls the NL solenoid to a
switch on the panel to provide an emergency off should the start relay
weld itself together (used the suggestion in the Sky-Tec documentation).
Yes that is a few additional ounces, but you already have a starter and
a battery so the penalty is not that large.
If you are worried about ounces then swap out your mags for P-mags?
Peter
On 18/11/2014 06:31, Ryan wrote:
> Thanks Bob.
>
> That all makes good sense after reading through it.
>
> Much appreciated.
>
> Ryan
>
> ------------------------------------------------------------------------
> Date: Tue, 18 Nov 2014 00:00:09 -0600
> To: aeroelectric-list@matronics.com
> From: nuckolls.bob@aeroelectric.com
> Subject: AeroElectric-List: Re: Wiring schematic question
>
> At 03:41 2014-11-17, you wrote:
> Hi Bob,
>
> I have been in email discussion with Greg Jones at B&C about a few
> things on my Pitts Special and he suggested you would be best to speak
> with about the Aerobatic Aircraft wiring schematic on their website,
> it was made mention that you drew it up.
> Drawing number 420-506
>
> http://www.bandc.biz/pdfs/420-506_Indexed_Diagram_with_BOM.pdf
> http://www.bandc.biz/pdfs/420-506_REVB.pdf
>
> <http://www.bandc.biz/pdfs/420-506_REVB.pdf>I had a couple of
> questions, hopefully you can assist a little.
>
> Looking at the mag switch portion of the diagram. Should it not be
> drawn that the impulse magneto is the OFF-START/ON?
> If the OFF-START/ON switch (Right Mag) is used and the start button
> engaged the starter would not power unless the Left Mag were also on.
> Am I missing something here?
>
> *Those drawings were sorta copied from my originals *
> * but with errors. See
>
> *
> *http://tinyurl.com/lsqz36k
>
> <http://tinyurl.com/lsqz36k> *
> * Here you see two options for toggle switch control *
> * of magnetos . . . one option uses push button to energize *
> * starter, the other uses the left mag switch to energize *
> * the starter. BOTH versions lock the starter out if *
> * the non-impulse coupled magneto is not OFF.
>
> *
>
> Might I also ask what the function of the momentary side of the mag
> switch is for - (ON)-OFF-ON?
>
> * Same as left side. It was selected to be mechanically *
> * identical to the left mag switch so that BOTH switches *
> * are MAG-ON with the switch in the middle . . . it's a *
> * carry over from the arguments I've received from human *
> * factors guys . . . NORMAL ON and OFF positions for both *
> * mags should look the same.
>
>
> *
>
> I am running an SD-8 dynamo and my intention is to have no master
> solenoid (as shown in the schematic) and also not use a starter
> solenoid, I am using the Skytec NL starter and they have an option of
> wiring the starter using the internal solenoid of the starter. Do you
> foresee any problem here?
>
> *If they use a two-stage solenoid for pinion gear *
> * extension . . .
>
> *
> *http://tinyurl.com/nx6xavk
>
> <http://tinyurl.com/nx6xavk> *
> * then there are extra-ordinary stresses on the *
> * switch that actually controls the starter solenoid. *
> * Your choice. I recommend either an external contactor *
> * or at least a buffer-relay to control starter *
> * solenoid.
>
> *
>
> My biggest concern was having the starter engage and not be able to
> shut it off. I see the B&C starter has an Emergency Starter Off how
> does this disable their system as the way I see it, if the solenoid
> contacts welded themselves closed, the starter is still feed power.
>
> * Emergency starter off? Don't know what this is *
> * other than to simply turn the battery master switch *
> * off.
>
> *
>
> I contacted Skytec and they said, due to the way their starter is made
> this can't happen so a starter 'kill' isn't required. If power is
> removed from the start solenoid the starter 'will' disengage, I guess
> the only real danger in this situation is a stuck start switch but
> turning off the master would solve that I guess.
>
> * I haven't a clue as to what they're talking about. *
> * In every Z-figure and every TC aircraft, the battery *
> * master relay is the back-up for a stuck-starter-contactor.
>
> *
>
> Bob . . .
> *
>
> ==========
> _blank">www.aeroelectric.com
> " target="_blank">www.buildersbooks.com
> ="_blank">www.homebuilthelp.com
> ="_blank">www.mypilotstore.com
> ank">www.mrrace.com
> ="_blank">http://www.matronics.com/contribution
> ==========
> -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
> ==========
> http://forums.matronics.com
> ==========
>
> *
> *
>
>
> *
Message 7
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Subject: | Re: Wiring schematic question |
At 03:41 2014-11-17, you wrote:
Hi Bob,
I have been in email discussion with Greg Jones at B&C about a few
things on my Pitts Special and he suggested you would be best to
speak with about the Aerobatic Aircraft wiring schematic on their
website, it was made mention that you drew it up.
Drawing number 420-506
http://www.bandc.biz/pdfs/420-506_Indexed_Diagram_with_BOM.pdf
http://www.bandc.biz/pdfs/420-506_REVB.pdf
I had a couple of questions, hopefully you can assist a little.
My apologies, I didn't 'scope out the rest of the diagram.
No, that general architecture was not suggested by me but
the diagram does have some features borrowed from the z-figures
of that era. For one thing, the MOV's as transient suppressors
was NOT a good idea. We abandoned that recommendation in
the AeroElectic Connection . . . oh . . .I forget. But a long
time ago.
With an SD-8, one is indeed strapped for 'surplus energy'
so elimination of the battery contactor is a useful thing
from the energy management perspective. Do you KNOW what
your ship's running loads are? How big is your battery?
What kind of strobe system . . . and current draw?
As long as your battery is in good condition and fully
charged at engine start, the probability of a contactor
sticking is very low. It's the tentative closures when
a soggy battery is trying to grunt the starter that
gets you a stuck contactor. At the same time, the
modern intermittent duty starter contactors are much
more resistant to sticking under all conditions . . . again
assuming that you 'drive 'em hard' . . . 20AWG wire
to the 5A coil is a good idea.
As far as compliance with legacy notions of seeking
'Max Cold' conditions in the wiring with all switches
OFF, you COULD use a battery master relay that did not
carry starter current while locating the external
starter contactor adjacent to the battery too.
However, your risks are low using the diagram as published.
The only changes I would recommend are using diodes
across the contactor coils . . . and the starter
contactor that B*C sells already has one installed.
Ditch the MOVs. Does this cover 'the rest of the story?'
Bob . . .
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