Today's Message Index:
----------------------
1. 06:58 AM - Oregon seminar date set (Robert L. Nuckolls, III)
2. 07:00 AM - Re: Fat/thin wire routing (Robert L. Nuckolls, III)
3. 07:37 AM - Re: PowerSchottky (Paul Messinger)
4. 10:13 AM - radio rack width (Ken)
5. 10:45 AM - Re: radio rack width clamav-milter version 0.80j on juliet... (BobsV35B@aol.com)
6. 10:58 AM - coil-and-distributor ignition (The Minearts)
7. 05:15 PM - Re: PowerSchottky (glaesers)
8. 05:54 PM - Re: radio rack width (Ken)
9. 08:07 PM - Re: coil-and-distributor ignition (Robert L. Nuckolls, III)
10. 08:21 PM - Re: PowerSchottky (Robert L. Nuckolls, III)
11. 08:31 PM - Re: Re: PowerSchottky (Robert L. Nuckolls, III)
12. 10:45 PM - starter contactor unnecessary? (thomas a. sargent)
13. 11:05 PM - Private Pilot (Tom Brusehaver)
Message 1
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| Subject: | Oregon seminar date set |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
EAA Chapter 292 has graciously offered to host a weekend
seminar next April 2/3. Since my brother lives in Portland
Oregon, we're always pleased when folks in that neck of the
woods are interested in spending a weekend talking "airplane-speak".
Looking forward to meeting many of you face to face next spring.
See:
http://aeroelectric.com/seminars/Independence_OR.html
Bob . . .
--------------------------------------------------------
< Throughout history, poverty is the normal condition >
< of man. Advances which permit this norm to be >
< exceeded -- here and there, now and then -- are the >
< work of an extremely small minority, frequently >
< despised, often condemned, and almost always opposed >
< by all right-thinking people. Whenever this tiny >
< minority is kept from creating, or (as sometimes >
< happens) is driven out of a society, the people >
< then slip back into abject poverty. >
< >
< This is known as "bad luck". >
< -Lazarus Long- >
<------------------------------------------------------>
http://www.aeroelectric.com
Message 2
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| Subject: | Re: Fat/thin wire routing |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 05:17 PM 11/20/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: Jerry2DT@aol.com
>
>Bob and all,
>
>IIRC, you say not to run fat and thin wires together. Does this hold true
>for the #8 power wire and #18 field wire to the alternator? Or does "fat"
>just
>mean the #2 & #4's?
Sorry for the confusion. That was a tongue-in-cheek suggestion
that it's a good idea to separate especially noisy wires (usually
fat ones) from especially vulnerable wires (usually small ones).
This is generally easy to do since the strong noise wires are
usually limited to electrical system and potential victims
are avionics and audio wires. They're generally easy to segregate
in the airplane.
However, with proper grounding/shielding techniques, it is quite possible
to intermix ALL technologies into the same wire bundles with
no adverse results. Without spending a lot of time crafting
the "ideal" system, it's generally easier to fabricate and install
wiring such that physical separation (anything greater than a few
inches) is maintained.
Bob . . .
Message 3
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| Subject: | Re: PowerSchottky |
--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
Bob you sort of missed Eric's main point.
That is a forward V fwd drop of 0.2V. Otherwise there is no need for use of
anything other than the diode bridge you often suggest. Great if you can
allow the higher forward voltage drop (0.7-1.1)which most applications can.
Getting 0.2V drop takes a high junction temp (125 C at 7 amps). If you
design a heat sink for that condition (where you force the Junction temp
high for the low forward drop then the heat sink is too small for higher
currents and visa versa :-) ) then the Tj can get over spec (150 C) at 10.5
amps. (just from reading figure 5 and ignoring the thermal design details).
My point is its a good device but not a practical one to consider if you
want the stated 0.2 forward drop.
Also its not isolated so there is the need for special mounting.
I question the practical application of this specific device as well as the
real need for such a low forward drop and the apparent limit of just over 10
amps for the stated 0.2V.
I have been suggesting a different device for years and have had many happy
users with the IR 160CMQ045. Its in an isolated package and can be bolted
down and wired to with lugs (all #10//AN3) size. Not quite the low voltage
drop but still impressive ( there is a 30v unit also with lower V drop). ST
also has hi current, low drop, diodes that are isolated and bolt style. No
heat sink thermal isolation etc. 0.3V forward drops are possible at low
currents and these IR and ST parts are so much more usable mechanically.
I also question the usability of 30V rating devices as my testing has
demonstrated spiking above that level and the time delay of most OVP devices
is far too long to prevent potential damage to the device. These high power
devices often are made up of a large number of smaller diodes in parallel
integrated into the larger die. One failure mode is gradual short/open of
individual dies and eventually failure of enough so the entire device fails.
Use of the Transorb type of OV protection (extremely fast OV clipping) is
one solution to the use of very low voltage rated parts in an otherwise
noisy environment.
Even 15 V units are used in 12V battery applications but they have extra
external protection from any noise spikes.
Paul
----- Original Message -----
From: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Subject: Re: AeroElectric-List: PowerSchottky
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
>
> At 07:22 PM 11/21/2004 -0500, you wrote:
> >--> AeroElectric-List message posted by: "Eric M. Jones"
<emjones@charter.net>
> >
> > >> ...Schottky diodes, ....and found 20L15T diodes on Digikey for
> >$1.31USD..... The
> > >>specs look good to me (20V, 15A, less than .5V forward drop).
> >
> > >>Any suggestions from the list??
> >
> >Be careful! When the vendor say a Schottky is good for 15A, he means 15A
at
> >50% duty cycle. That's 7.5A for you and me. And 20V is really on the
ragged
> >edge of the requirement. Most assuredly the Schottky 20L15T diode WILL
NOT
> >DO.
>
> ??? I'm looking at the data sheet on the 20L15T at:
> http://www.irf.com/product-info/datasheets/data/20l15t.pdf
> I find that it's a 20 AMP (not 15A) device, and 15 VOLT (not 20V)
device.
>
> Most rectifiers are used in power supplies where they conduct
> on every other half-cycle or 50% duty cycle. This means that
> peak and average currents through the device are different. Voltage
> drop is a function of peak current while thermal considerations are
> based on average values.
>
> The "50% duty cycle" notation is simply a recognition of the
> way that power supply rectifiers work and is not a suggestion
> that the part be de-rated to 1/2 it's average current for use
> in applications where DC power is being routed around.
>
>
> >No mystery. The Schottky I sell is International Rectifier p/n 122NQ030R.
> >This is a beefy package with a wide die that makes for very very low Vf
of
> >under 0.2 V, and will carry 60 Amps in a pinch.
>
>
> This part will carry a whole lot more than 60A and you don't even
> have to pinch it . . . but you DO need to maintain the device's
> case at some relatively low temperature. For example, looking at
> figure 6 of the data sheet . . .
>
> http://www.irf.com/product-info/datasheets/data/122nq030.pdf
>
> we find a curve for DC applications telling us that the device will
> carry 120A DC while dissipating about 48W without exceeding
> the RMS dissipation limits also depicted on this graph.
>
> Thermal resistance of this part from junction to case is 0.4
> degrees-C/Watt so the junction will rise about 20 degrees
> C at 48W dissipation. This means that the case must be
> limited to 130 degrees C or less.
>
> With a 50C ambient, the thermal resistance from case to
> ambient is (130-50)/48 or 1.7 degrees C/W maximum for the
> device to carry 120A.
>
> Note that Figure 5 supports this analysis where it shows
> us that the device's case temperature must be held at or
> below 130C for a DC forward current of 120A.
>
> Bob . . .
>
>
Message 4
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| Subject: | radio rack width |
clamav-milter version 0.80j
on juliet.albedo.net
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
Will provision for a 6 1/4 inch wide panel opening fit most radio trays?
I'd like to install side rails for future avionics before I install the
panel.
thanks
Ken
Message 5
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| Subject: | Re: radio rack width clamav-milter version 0.80j on |
juliet...
--> AeroElectric-List message posted by: BobsV35B@aol.com
In a message dated 11/23/2004 12:15:33 P.M. Central Standard Time,
klehman@albedo.net writes:
Will provision for a 6 1/4 inch wide panel opening fit most radio trays?
I'd like to install side rails for future avionics before I install the
panel.
thanks
Ken
Good Afternoon Ken,
I would suggest that you make them a little wider than six and a quarter.
That is the nominal distance of almost all GA sleeves, but there are
differences in ho the various manufacturers build the boxes. There are even
differences between the boxes used by the same manufacturer. It may say they
are the
same in the brochures, but some are as much as fifty thousandths bigger.
It is fairly easy to add a shim to accommodate a narrow box, but getting a
slightly over size box mounted in rails that are the bare minimum distance
apart can be a bear.
I recently mounted a set of RadioRax RK 1020 (_www.radiorax.com_
(http://www.radiorax.com) ) support beams instead of aluminum angles. They recommend a
spacing of 6.3 inches. I used that spacing and found that a couple of my
sleeves were still a bit tight. I think if I were doing another, I would add
another twenty thousandths of an inch. Six and five sixteenths might be adequate.
For what it is worth, I like the RadioRax product. They are expensive, but
they make it very easy to change things around and they eliminate the need
for any aft supports on the boxes.
If you think you will ever make any changes in your radio rack, they should
really make the next time a snap.
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
Message 6
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| Subject: | coil-and-distributor ignition |
--> AeroElectric-List message posted by: "The Minearts" <smineart@kdsi.net>
OK, here's a novice question: in a system with coil and distibutor, where does
the power supply come from? The closest thing on the Z-diagrams is the electronic
ignition systems, where power comes off the main bus. Or would the coil,
or 2 coils via a coil switcher, get power through a fat wire direct from the
battery contactor?
Steve Mineart
CH601/Wynn Corvair
Message 7
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| Subject: | Re: PowerSchottky |
--> AeroElectric-List message posted by: "glaesers" <glaesers@wideopenwest.com>
Do we really need devices rated for 160A for our applications - or is it
that those devices are the ones with the really low Vf? They are rather
pricey! I'm willing to live with a somewhat higher loss across the diode
for a better price.
If you only need one - for the Primary bus to Endurance bus, it's not so
bad. But I'm looking at 5 (+2 for the dual feeds for ECM power, and +2 for
dual alternate feeds from the Main & Aux hot busses to the Endurance Bus).
If I use regular diodes I can get them all for the price of one of those
Schottkys - but with about a volt loss.
What about something like a 50HQ...?
http://www.irf.com/product-info/datasheets/data/50hq.pdf
(If=60A, Vrrm=35V or 40V or 45V) That package looks easy to mount. At a
10A this has a Vf of less than 0.5 volt (still about half that of a
'regular' diode). And the price is <$10 each - Digikey page 675.
For me, these things need to handle 14V at 10A continuously forward, and
stop the same in the reverse direction. So the 40V device (20V for us due
to the 50% duty cycle) seems like it would work. I blew it last time - am I
getting closer?
Thanks,
Dennis Glaeser
Message 8
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| Subject: | Re: radio rack width |
clamav-milter version 0.80j
on juliet.albedo.net
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
Thank you Bob.
That was exactly what I needed. I failed to find that information in the
Book, the archives, Ferrara's Book, or Bingelis.
Ken
BobsV35B@aol.com wrote:
>--> snip
>
Message 9
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| Subject: | Re: coil-and-distributor ignition |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 12:57 PM 11/23/2004 -0600, you wrote:
>--> AeroElectric-List message posted by: "The Minearts" <smineart@kdsi.net>
>
>OK, here's a novice question: in a system with coil and distibutor, where
>does the power supply come from?
Doesn't matter what electrically dependent ignition system you
run, I'd recommend you run from the battery bus. If you have
smoke in the cockpit, you can shut off EVERYTHING else and
not have the engine stop.
> The closest thing on the Z-diagrams is the electronic ignition systems,
> where power comes off the main bus. Or would the coil, or 2 coils via a
> coil switcher, get power through a fat wire direct from the battery contactor?
Dual coils and dual points?
Bob . . .
Message 10
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| Subject: | Re: PowerSchottky |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 07:35 AM 11/23/2004 -0800, you wrote:
>--> AeroElectric-List message posted by: "Paul Messinger" <paulm@olypen.com>
>
>Bob you sort of missed Eric's main point.
>
>That is a forward V fwd drop of 0.2V. Otherwise there is no need for use of
>anything other than the diode bridge you often suggest. Great if you can
>allow the higher forward voltage drop (0.7-1.1)which most applications can.
>
>Getting 0.2V drop takes a high junction temp (125 C at 7 amps). If you
>design a heat sink for that condition (where you force the Junction temp
>high for the low forward drop then the heat sink is too small for higher
>currents and visa versa :-) ) then the Tj can get over spec (150 C) at 10.5
>amps. (just from reading figure 5 and ignoring the thermal design details).
>My point is its a good device but not a practical one to consider if you
>want the stated 0.2 forward drop.
??? Eric cited a 50% de-rating of a device's spec-sheet rating
based on mis-interpretation of an operating characteristic.
You seem to be talking about a technique for driving
down the already low Vf by under-cooling the device . . .
different discussion.
>Also its not isolated so there is the need for special mounting.
Yup . . . one of several reasons for choosing the lowly bridge
rectifier . . .
>I question the practical application of this specific device as well as the
>real need for such a low forward drop and the apparent limit of just over 10
>amps for the stated 0.2V.
>
>I have been suggesting a different device for years and have had many happy
>users with the IR 160CMQ045. Its in an isolated package and can be bolted
>down and wired to with lugs (all #10//AN3) size. Not quite the low voltage
>drop but still impressive ( there is a 30v unit also with lower V drop). ST
>also has hi current, low drop, diodes that are isolated and bolt style. No
>heat sink thermal isolation etc. 0.3V forward drops are possible at low
>currents and these IR and ST parts are so much more usable mechanically.
>
>I also question the usability of 30V rating devices as my testing has
>demonstrated spiking above that level and the time delay of most OVP devices
>is far too long to prevent potential damage to the device. These high power
>devices often are made up of a large number of smaller diodes in parallel
>integrated into the larger die. One failure mode is gradual short/open of
>individual dies and eventually failure of enough so the entire device fails.
>Use of the Transorb type of OV protection (extremely fast OV clipping) is
>one solution to the use of very low voltage rated parts in an otherwise
>noisy environment.
>Even 15 V units are used in 12V battery applications but they have extra
>external protection from any noise spikes.
Yeah, but if the system sees a load dump transient, it's positive . . .
meaning that it drives any system power steering diodes into
conduction. It's the reverse voltage transient that puts the
diode at risk.
Bob . . .
Message 11
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| Subject: | Re: PowerSchottky |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 08:13 PM 11/23/2004 -0500, you wrote:
>--> AeroElectric-List message posted by: "glaesers"
><glaesers@wideopenwest.com>
>
>Do we really need devices rated for 160A for our applications - or is it
>that those devices are the ones with the really low Vf? They are rather
>pricey! I'm willing to live with a somewhat higher loss across the diode
>for a better price.
>
>If you only need one - for the Primary bus to Endurance bus, it's not so
>bad. But I'm looking at 5 (+2 for the dual feeds for ECM power, and +2 for
>dual alternate feeds from the Main & Aux hot busses to the Endurance Bus).
>If I use regular diodes I can get them all for the price of one of those
>Schottkys - but with about a volt loss.
>
>What about something like a 50HQ...?
>http://www.irf.com/product-info/datasheets/data/50hq.pdf
>(If=60A, Vrrm=35V or 40V or 45V) That package looks easy to mount. At a
>10A this has a Vf of less than 0.5 volt (still about half that of a
>'regular' diode). And the price is <$10 each - Digikey page 675.
>
>For me, these things need to handle 14V at 10A continuously forward, and
>stop the same in the reverse direction. So the 40V device (20V for us due
>to the 50% duty cycle) seems like it would work. I blew it last time - am I
>getting closer?
The 50% duty cycle cited in the data sheets has no significance
for the way we use diodes to steer DC power. As to 'need', I'm
still mystified by the quest for lower voltage drop diodes
at more expense and less convenience than the plain vanilla silicon
bridge rectifier. The only time one needs to consider diode
losses is during normal alternator operations where available
energy is greatest and surplus. There's no reason to run any
accessory through diodes during battery-only operations so agonizing
over a few tenths of a volt difference is like chrome plating one's prop
spinner for more speed. But each to his own. My only reason
for joining this conversation . . . again . . . was due to
gross mis-interpretation of the data sheets for the Schottky
devices. Use whatever parts floats your boat but please understand
how the part works and what the specs mean so that your decision
is based on good use of simple-ideas.
Bob . . .
Message 12
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| Subject: | starter contactor unnecessary? |
--> AeroElectric-List message posted by: "thomas a. sargent" <sarg314@comcast.net>
I talked to a fellow at Skytec about wiring up my starter (149-12LSX).
He told me that since I intend not to have an ignition key switch, I can
dispense with my starter contactor. Apparently the Skytec starter has a
contactor solenoid built into it which also engages the drive gear. My
start push button is stout enough to handle the current (about 1 amp I
think) that the solenoid requires to engage. Key switches evidently are
a little too light to handle the load directly, so in those cases he
recommends the starter contactor.
Eliminating a part always sounds like a good idea. But, I don't recall
anyone mentioning this configuration on the list before. Is everybody
using a key switch, or is there some downside to this approach that he
didn't tell me?
--
Tom Sargent
RV-6A
Message 13
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--> AeroElectric-List message posted by: "Tom Brusehaver" <cozytom@mn.rr.com>
There is an article in the current Private Pilot magazine,
well kind of a question about avionics master stitches. The
author of the article not only says it is a good idea, he
even suggests putting in a relay.
I tried to straighten him out, but he believes, or won't
consider any other position. Pretty weird.
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