Today's Message Index:
----------------------
1. 06:56 AM - Re: Fuse links (Robert L. Nuckolls, III)
2. 07:10 AM - Re: paranormal resistance (Robert L. Nuckolls, III)
3. 07:13 AM - Re: Wing wiring grounds (Robert L. Nuckolls, III)
4. 07:43 AM - Re: Toggle switch - both master/battery and (Robert L. Nuckolls, III)
5. 07:45 AM - Re: mag switches (Robert L. Nuckolls, III)
6. 07:48 AM - Re: Re: COM static on 123.05 (Robert L. Nuckolls, III)
7. 08:01 AM - Re: Toggle switch - both master/battery and starter (Mickey Coggins)
8. 08:24 AM - Re: Re: How do you carry the braid from a shielded (N1deltawhiskey@aol.com)
9. 09:58 AM - LED Bias Resistors (John Schroeder)
10. 10:25 AM - Re: Toggle switch - both master/battery and (Robert L. Nuckolls, III)
11. 10:48 AM - Re: LED Bias Resistors (Richard Tasker)
12. 12:10 PM - Re: LED Bias Resistors (Matt Prather)
13. 12:38 PM - Re: Advice about 24V systems (Nigel Harrison)
14. 12:51 PM - Re: Advice about 24V systems (Nigel Harrison)
15. 05:05 PM - Re: LED Bias Resistors (John Schroeder)
16. 05:58 PM - Re: LED Bias Resistors (Richard E. Tasker)
17. 05:58 PM - Re: LED Bias Resistors (Matt Prather)
18. 06:09 PM - Stereo vs. Mono Headphone Jacks (Dennis Johnson)
19. 09:53 PM - Re: Stereo vs. Mono Headphone Jacks (James E. Clark)
20. 10:33 PM - Re: LED Bias Resistors (Robert L. Nuckolls, III)
Message 1
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--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 12:59 AM 2/14/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: TimRhod@aol.com
>
>Bob: I am using duel light speed electronic ignitions. One I am running
>off of a battery fuse block with a 5 amp fuse. The second I want to run
>off a
>second battery using a fuse llnk as described in your book. The wire run is
>a 20AWG which I understand would normally be linked with a 24AWG. This is
>rated for only 3 amps though.
Recall the recent discussions we've had about current ratings
on wire. The 24AWG fusible link is a VERY robust, but weak
link in a wire that's rated for approximately twice the current
rating for the same voltage drop and temperature rise. The
24AWG fusible link upstream of a 20AWG power conductor would
would be fine. The current rating of 24AWG wire in a wire bundle
has no practical bearing on the performance of 24AWG wire in
a fusible link. It will be VERY robust . . . not unlike the ANL
current limiters that will CARRY 200% of rated current indefinitely.
>I need a 5 amp protection. Can I fuselink a
>20AWG with a 22AWG? I dont really want to change the wire run to 18AWG
>which
>you recomend in your book to fuse link with 22AWG If not what about an in
>line fuse of 5Amp? Thanks Tim
An inline fuse would be fine too but have lower reliability numbers
due to increased connections. I'd go with 20AWG feeder and 24AWG
fusible link . . . or you could build a Battery Bus for the second
battery using one of the fuseblocks. The ignition system might run
from one of the fuse-block taps while offering opportunities for
other duties to be assigned to that battery.
Bob . . .
Message 2
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| Subject: | Re: paranormal resistance |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:04 PM 2/13/2005 -0700, you wrote:
>--> AeroElectric-List message posted by: sarg314 <sarg314@comcast.net>
>
>Here's one for electric Bob: This is not really relevant to building a
>plane, but I observed something when making my battery cable that I
>cannot explain. I used Bob's method for soldering lugs onto a #02 cable
>using a propane torch. The soldering went as expected. Maybe 20
>seconds after I was finished, with the cable still pretty hot, I used my
>multi-meter to measure the resistance of the cable. I have no sensible
>reason for doing this. The odd thing is that the resistance showed as 3
>ohms. As the minutes went by the indicated resistance dropped
>steadily. The meter is a Fluke model 11 and seems to have an accuracy
>of about 0.1 ohm at the low end of the scale. After the cable was just
>warm to the touch - probably 80 or 90 deg. F - it still showed 1 ohm,
>which is 1000 times too much. The resistance continued to drop over the
>next 5 or 10 minutes until it got down to 0.1 ohm which, I think is as
>good as 0 with this meter. That's what it usually shows when you short
>its leads together.
>
>Elevated temperature will increase the resistance of a wire, but the
>resistance was significantly different from 0 when the cable appeared to
>be nearly at room temperature. Further, I made 2 cables and they both
>showed the same effect.
>
>Could it be some thermocouple effect that is confusing the resistance
>measuring circuit in the meter?
Bingo!
> I did noticed that it demonstrated
>polarity, which points to something like that. That is, if it was
>indicating 0.8 ohms and I reversed the leads, it would then indicate
>-0.8 ohms. Negative resistance indicates the meter was pretty
>confused. Any ideas what was going on here?
Your understanding an retention of simple ideas (in this
case the Seebeck effect) has served you well and you have
properly deduced root cause for the effects you observed.
EVERY connection we make between non-identical conductors
will exhibit this phenomenon and except for an observation
at elevated temperatures they go largely unnoticed.
Modern ohmmeters run very low bias currents and therefore
must be sensitive to small voltage changes. My ol' Simpson
260 in the x1 ohms scale might barely display the effect
you observed . . . your digital instrument turns out to
be quite sensitive to the point of making ohmmeter readings
meaningless.
I was working in an airplane last week where a crew
was working on tail de-ice system that draws a lot of power.
I was doing some continuity tests with an ohmmeter on another
system and while checking some ground circuits, I could SEE
the ohmmeter responding to switching cycles of the de-ice
system . . . a real world example of the effects of ground loops.
Thanks for sharing this with us.
Bob . . .
Message 3
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| Subject: | Re: Wing wiring grounds |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:55 PM 2/12/2005 -0600, you wrote:
>--> AeroElectric-List message posted by: "Dean" <dvanwinkle@royell.net>
>
>John and Jay
>
>The best way to insure a good structural ground is by use of abrasive
>bonding brushes to remove the primer and any anodize coating. I obtained
>mine from The Yard in Wichita. A 4 piece set, P/N 14706, is $3.95 in the
>current catalog. They have a 1/4 inch shaft and 3/32, 1/8, 5/32, and 3/16
>pilots. They have a much more expensive set that is more suited to avionics
>shop or production line use. Try 1-800-888-8991 or www.yardstore.com.
>Finish with an appropriate ring terminal, bolt, and locknut.
Excellent point that illustrates common practice in most
vehicular ground systems. When I went to work at Boeing
in 1961, the first suit of expendables from the toolcrib
to my toolbox was a couple of sizes of bonding brushes.
Bob . . .
Message 4
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| Subject: | Re: Toggle switch - both master/battery and |
starter
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
starter
At 10:51 AM 2/11/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Mitch Faatz" <mitchf@skybound.com>
>
>With the goal of reducing my switch count, I'm wondering if it's possible
>to double up the Master/Battery toggle and Starter switch but not sure
>it's possible toggle-switch-wise. At first I thought if I could find a
>DPDT switch that is Off-On-(On), I could do it. I've found a red toggle
>switchguard that returns a toggle that is in the top position back to
>center (which would drop starter back to master on) and leave a toggle
>that is in the bottom position alone (master off stays master off).
>
>Useability sounds good, switch guard up, switch to master on, momentary
>full up for starter, returns to master on. With a DPDT switch I could
>have one pole control starter, but I'm worried about the master/battery
>pole. If it goes from middle position (on) to up position (momentary on
>for starter), will there be a brief interruption and if so will that cause
>a problem?
Don't recommend combining battery master and starter functions but
the 'Connection chapter offers a variety of ways to utilize progressive
transfer, two pole switches to combine functions. E.G.
2-10 on-on-on works nicely for battery master combined with alternator
like the infamous split rocker.
2-50 on-on-(on) or 2-5 on-off-(on) can be used as combination magneto
and starter functions.
2-10 is suggested for an OFF-TAXI-LND+TAXI function
2-10 could do an OFF-STROBE-STROBE+NAV function.
2-50 works well for OFF-BOOST-BOOST+PRIME
2-10 has been suggested in wig-wag systems for OFF-ON-WIGWAG function
Just keep in mind that combining functions into one
control forms a single point of failure for both functions
but the risk of problems is very low.
Bob . . .
Message 5
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| Subject: | Re: mag switches |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 12:47 PM 2/7/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "Jones, Michael" <MJones@hatch.ca>
>
>hi all
>
>is see in my aeroelectric book on z-11 generic system that 2-5 switches are
>used for mag control, in the section under switches pg 11-18 however 2-3
>switches are described for use on the mag controls, which is correct or are
>both correct
either works. 2-5's allow combining mag switch operation with
starter function. 2-3's work fine too but you need a starter
pushbutton.
>if using the 2-5 switches i see there is no push button for a start, is this
>because of the spring loaded 2-5 switches, so what happens at each switch
>when starting the engine
Right mag OFF, left mag ON and lift switch to START
>right mag, position 1 off, position 2 ??. spring position 3 ???
>left mag, position 1 off, position 2 on, spring position 3 start then back
>to position 2 on
>
>guess what i need is what does off-start/on refer to on the 3 switch
>position
The right mag must be OFF for the starter to work. This is because
most right mags do not have impulse couplers and should be disabled
during cranking.
Bob . . .
Message 6
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| Subject: | Re: COM static on 123.05 |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:43 PM 2/2/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: xl <xl@prosody.org>
>
>
>No COM noise until about 125 hours.
>Then it was very annoying at certain frequencies.
>
>I inspected all of the connections shields and grounds.
>I tried filters on some power leads - no help with radiated noise.
>
>I noticed that there was some play in the distributor caps.
>I shimmed the clamps - and the noise went away.
>
>Problem solved.
Joe, thanks for sharing this with us!
Bob . . .
Message 7
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| Subject: | Re: Toggle switch - both master/battery and starter |
--> AeroElectric-List message posted by: Mickey Coggins <mick-matronics@rv8.ch>
> Just keep in mind that combining functions into one
> control forms a single point of failure for both functions
> but the risk of problems is very low.
>
My first panel design was full of combined switches - it was
very cool. Then I priced those 2-10 switches and decided
that having one switch per function was more cool! :-)
--
Mickey Coggins
http://www.rv8.ch/
#82007 Wiring
Message 8
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| Subject: | Re: How do you carry the braid from a shielded |
--> AeroElectric-List message posted by: N1deltawhiskey@aol.com
Comments below
In a message dated 13-Feb-05 13:14:01 Pacific Standard Time,
emjones@charter.net writes:
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: N1deltawhiskey@aol.com
>Your comments for coax makes sense when it comes to low energy RF signals.
>And coax connectors are designed to do just as you suggest.
>Not as quiet as concentric pass-throughs, but a lot better than unshielded.
>On the other hand, I have trouble imagining a pass-through using D-sub
>connectors that would be concentric. What you seem to suggest is that all
shielded
>wires be connected using some other kind of connector. What do you have in
>mind that would allow us to do what you suggest?
>Regards, Doug Windhorn
Hi Doug,
The issue of what power levels and what frequencies require proper
connections is fraught with peril. You might think that audio frequencies
are easy, but a square wave is made up of ALL frequencies. (Fourier Series:
Signals can be composed by a superposition of an infinite number of sine and
cosine functions. The coefficients of the superposition depend on the signal
being represented and are equivalent to knowing the function itself.....I
bet you already knew that!)
Ya, I did, a long time ago; a little reminding brings back the memories. Of
course, that is the reason that switching DC currents may produce a pop in the
audio system. And probably the reason that a lot of digital devices create
RF havoc with some installations.
All D-sub connectors have matching covers to which the shield may be
grounded.
I have some that don't. The benefit of this discussion is that I will be
looking into getting some that do. One concern that I have though; perhaps you
can answer: If a shielded wire is grounded to the D-sub, I assume the ground
is carried through by the terminal frames to a similar ground shield on the
other side. Now if the terminal frames are mounted to aluminum mounting panels
as are mine, either those panels must be electrically isolated from the
airframe somehow, or we may get into dealing with a ground loop condition. Plausible?
I would not be going very far out on the limb to say that all
coaxial and common shielded cables have matching connectors.
Agreed.
There are of
course ungrounded shields--but you can get pretty much anything--so there's
no accounting for taste. My description of how coaxial cable and shielded
cable should be terminated would be helped by illustrations--none of which I
have. But I assure you that this has been the standard technique since the
1980's.
Don't doubt the efficacy of your recommendations. Only question whether they
are needed in all cases.
I expect many builders to say, "Well...it's good enough." This is my second
favorite invitation to disaster right after, "Watch this...Hold my beer."
If simple methods work, why do something more difficult/costly? If whatever
noise gets into the system is not objectionable, so what. However, if it does
get into the system, your comments should certainly give people a places to
start looking.
Thanks for pointing this issue out.
Regards, Doug
Message 9
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| Subject: | LED Bias Resistors |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
Bob -
In the diagram published on your website that shows the circuitry for
converting the incandescent low voltage light to an LED, you show power
coming off a fuse directly to the LED then thru a 220 ohm resistor then to
terminal 5 of the LR3 voltage regulator. There is also a 220 ohm resistor
bypass around the LED. Several Questions:
1. Shouldn't the first resistor described above be before the LED not
after?
2. With an LED that has a 1.9v forward, 20 milliamps of current and a
buss voltage of 13.8v, I get 595 ohms for the resistor. Radio Shack has a
560 ohm and a 680. Is the 560 ohm OK?
3. Would the bypass resistor also be 560 or some other value?
I looked in the archives and read an explanation of the need for a bypass
resistor, but could not find the explanation for where to put the bias
resistor. Most LED diagrams have it on the + battery side, thence to the
LED. Many thanks for the help.
John Schroeder
--
Message 10
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| Subject: | Re: Toggle switch - both master/battery and |
starter
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
starter
At 05:00 PM 2/14/2005 +0100, you wrote:
>--> AeroElectric-List message posted by: Mickey Coggins
><mick-matronics@rv8.ch>
>
> > Just keep in mind that combining functions into one
> > control forms a single point of failure for both functions
> > but the risk of problems is very low.
> >
>
>My first panel design was full of combined switches - it was
>very cool. Then I priced those 2-10 switches and decided
>that having one switch per function was more cool! :-)
If you have the room, single switches is the way to go
EXCEPT very specific functions like DC PWR MASTER switch
that schedules battery/alternator operations.
There's quite a number of tandem cockpit airplanes
under construction wherein panel real estate is
more precious. If you're trying to make room for
some accessory that helps you fly the airplane
better, closing up ranks on switches is at least
one way to do that.
Bob . . .
Message 11
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: Richard Tasker <retasker@optonline.net>
In a series circuit (components connected one after another from +12V to
ground) it makes no difference which comes first. The order "+12V, LED,
resistor, ground" works the same as "+12V, resistor, LED, ground". Put
the parts where it is most convenient
Dick Tasker.
John Schroeder wrote:
>--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
>
>Bob -
>
>In the diagram published on your website that shows the circuitry for
>converting the incandescent low voltage light to an LED, you show power
>coming off a fuse directly to the LED then thru a 220 ohm resistor then to
>terminal 5 of the LR3 voltage regulator. There is also a 220 ohm resistor
>bypass around the LED. Several Questions:
>
>1. Shouldn't the first resistor described above be before the LED not
>after?
>
>2. With an LED that has a 1.9v forward, 20 milliamps of current and a
>buss voltage of 13.8v, I get 595 ohms for the resistor. Radio Shack has a
>560 ohm and a 680. Is the 560 ohm OK?
>
>3. Would the bypass resistor also be 560 or some other value?
>
>I looked in the archives and read an explanation of the need for a bypass
>resistor, but could not find the explanation for where to put the bias
>resistor. Most LED diagrams have it on the + battery side, thence to the
>LED. Many thanks for the help.
>
>John Schroeder
>
>
>
Message 12
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
560ohm overdrives that LED by about 6%. Probably okay, but it may
run a little bit warm. Probably not.
560ohm bypass is probably okay too, though the LED may turn on
very dimly all of the time, even when there isn't any OV/LV event.
Regards,
Matt-
> --> AeroElectric-List message posted by: "John Schroeder"
> <jschroeder@perigee.net>
>
> Bob -
>
> In the diagram published on your website that shows the circuitry for
> converting the incandescent low voltage light to an LED, you show power
> coming off a fuse directly to the LED then thru a 220 ohm resistor then
> to terminal 5 of the LR3 voltage regulator. There is also a 220 ohm
> resistor bypass around the LED. Several Questions:
>
> 1. Shouldn't the first resistor described above be before the LED not
> after?
>
> 2. With an LED that has a 1.9v forward, 20 milliamps of current and a
> buss voltage of 13.8v, I get 595 ohms for the resistor. Radio Shack has
> a 560 ohm and a 680. Is the 560 ohm OK?
>
> 3. Would the bypass resistor also be 560 or some other value?
>
> I looked in the archives and read an explanation of the need for a
> bypass resistor, but could not find the explanation for where to put
> the bias resistor. Most LED diagrams have it on the + battery side,
> thence to the LED. Many thanks for the help.
>
> John Schroeder
>
> --
>
>
Message 13
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| Subject: | Advice about 24V systems |
--> AeroElectric-List message posted by: "Nigel Harrison" <naharrison@manx.net>
Thanks for your input. I'm coming round to the idea that 12V may work out
fine.
Regards
Nigel
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Ken
Subject: Re: AeroElectric-List: Advice about 24V systems
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
If I may be so bold -
A pound of battery is a pound of battery and it is silly to suggest that
there is more energy or safety margin in arranging it into 24 volts
rather than 12 volts. Your 12 volt accessories will drain just as much
energy as 24 volt accessories for all practical purposes. IMO there is
however a real safety margin advantage to sticking with tried and proven
12 volt components such as supplied for use with the stock 912S. THere
is more discussion on this in the archives.
Ken
Nigel Harrison wrote:
>--> AeroElectric-List message posted by: "Nigel Harrison"
<naharrison@manx.net>
>
>
>Dear All,
>I am a Europa builder and am planning to install an all-electric set up
with
>a Grand Rapids EFIS etc. Reading Greg Richter's artlcle on Aircraft wiring,
>he is of the opinion that a 24V electrical system will provide much more
>safety margin tha a 12V system in the event of generator failure. My
>aircraft will have a Rotax 912S. The engine manufacturers have advised me
>that "Unfortunately the Rotax electrical system is only 12 V DC.The
internal
>alternator gives an AC voltage above 24 V at a speed of about 3000 rpm,
>which may possibly be suitable, but you would have to design or procure a
>rectifier/regulator for 24 V." Can someone advise me whether this
alternator
>would be suffiiciently powerful to charge 2 x 12V 16Ah batteries in series.
>Rotax also mention a rectifier/regulator. Advice on this too would be
>useful.
>
>I have little in the way of electrical knowledge/knowhow, so simple
>explanations would be most helpful.
>
>Thanks
>
>Nigel Harrison
>
>
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Message 14
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| Subject: | Advice about 24V systems |
--> AeroElectric-List message posted by: "Nigel Harrison" <naharrison@manx.net>
Thanks for your help.
What I'm fitting is as follows: Grand Rapids Horizon 1 EFIS with EIS, Skymap
111c, Trutrak digitrak autopilot, SL40 comm, Garmin transponder (model yet
to be decided upon), and back up ASI, ALT, Compass and electric T/C. In
addition there are the usual nav lights & strobes.
Regards
Nigel
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Robert
L. Nuckolls, III
Subject: RE: AeroElectric-List: Advice about 24V systems
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
At 09:49 AM 2/13/2005 +0000, you wrote:
>--> AeroElectric-List message posted by: "Nigel Harrison"
><naharrison@manx.net>
>
>
>Thank you Bob for your thoughts and recommendations. I will stay with
>aeroelectric. I've ordered the aeroelectric book too. It looks as if I
would
>be best to go for 12 V with the addition of a second battery as a back up.
What is it that you want to "back up"? Most aircraft with
a 912 engine are relatively simple. What systems do you plan
to carry and what flight operations do you anticipate that
demand extra-ordinary power supply reliability?
>Am I correct in thinking that if they were connected in parallel this would
>allow the generator to charge both? Some sort of switching mechanism could
>then allow the back up to be used once the main battery power was used up.
You can have as many batteries as you wish and run them in
parallel for all normal operations. Active notification
of low voltage heralds failure of an alternator whereupon
the pilot separates each battery from the others to accomplish
their respective tasks. Let's talk about the equipment you
plan to carry, how much energy each system requires and how
you plan to us the airplane.
Bob . . .
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Message 15
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
Richard -
Thanks for the clarification. I'll put the resistor first (before the
LED). What effect does the resistor of the same ohms have on the circuit
when it taps in on the plus side of the LED and ends on the negative
terminal of the LED. This looks a bit like a voltage divider.
Thanks,
John
On Mon, 14 Feb 2005 13:46:32 -0500, Richard Tasker
<retasker@optonline.net> wrote:
> --> AeroElectric-List message posted by: Richard Tasker
> <retasker@optonline.net>
>
> In a series circuit (components connected one after another from +12V to
> ground) it makes no difference which comes first. The order "+12V, LED,
> resistor, ground" works the same as "+12V, resistor, LED, ground". Put
> the parts where it is most convenient
>
> Dick Tasker.
>
> John Schroeder wrote:
>
>> --> AeroElectric-List message posted by: "John Schroeder"
>> <jschroeder@perigee.net>
>>
>> Bob -
>>
>> In the diagram published on your website that shows the circuitry for
>> converting the incandescent low voltage light to an LED, you show power
>> coming off a fuse directly to the LED then thru a 220 ohm resistor then
>> to
>> terminal 5 of the LR3 voltage regulator. There is also a 220 ohm
>> resistor
>> bypass around the LED. Several Questions:
>>
>> 1. Shouldn't the first resistor described above be before the LED not
>> after?
>>
>> 2. With an LED that has a 1.9v forward, 20 milliamps of current and a
>> buss voltage of 13.8v, I get 595 ohms for the resistor. Radio Shack
>> has a
>> 560 ohm and a 680. Is the 560 ohm OK?
>>
>> 3. Would the bypass resistor also be 560 or some other value?
>>
>> I looked in the archives and read an explanation of the need for a
>> bypass
>> resistor, but could not find the explanation for where to put the bias
>> resistor. Most LED diagrams have it on the + battery side, thence to
>> the
>> LED. Many thanks for the help.
>>
>> John Schroeder
>>
>>
>>
>
>
--
Message 16
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: "Richard E. Tasker" <retasker@optonline.net>
Yes, it is a voltage divider of sorts, although since the LED functions
with a semi-constant voltage across it, it really works more like a
current divider.
In other words, the LED really controls what the voltage across the LED
and parallel resistor is. The series resistor controls the current
through the LED and parallel resistor. The parallel resistor "steals"
some current from the LED and causes it to stop lighting at a slightly
higher voltage than it would otherwise do. Specifically, (assuming that
your LED has approximately 1.9V drop across it when it is lighting) the
case with just the series 560 ohm resistor the LED will become too dim
to see somewhere around 2 to 3V. If one adds the parallel resistor, the
same LED will become just as dim at 4 to 5V.
Add a smaller value in parallel and the difference becomes even more.
All this mainly serves to make the LED brightness follow more closely an
incandescent lamp when both are adjusted with a dimmer circuit.
By the way, adding the parallel resistor reduces the current through the
LED and in your case puts the maximum current down below 20 mA - so your
LED is not "overdriven" as you expected!
Dick Tasker
John Schroeder wrote:
>--> AeroElectric-List message posted by: "John Schroeder" <jschroeder@perigee.net>
>
>Richard -
>
>Thanks for the clarification. I'll put the resistor first (before the
>LED). What effect does the resistor of the same ohms have on the circuit
>when it taps in on the plus side of the LED and ends on the negative
>terminal of the LED. This looks a bit like a voltage divider.
>
>Thanks,
>
>John
>
>
>On Mon, 14 Feb 2005 13:46:32 -0500, Richard Tasker
><retasker@optonline.net> wrote:
>
>
>
>>--> AeroElectric-List message posted by: Richard Tasker
>><retasker@optonline.net>
>>
>>In a series circuit (components connected one after another from +12V to
>>ground) it makes no difference which comes first. The order "+12V, LED,
>>resistor, ground" works the same as "+12V, resistor, LED, ground". Put
>>the parts where it is most convenient
>>
>>Dick Tasker.
>>
>>John Schroeder wrote:
>>
>>
>>
>>>--> AeroElectric-List message posted by: "John Schroeder"
>>><jschroeder@perigee.net>
>>>
>>>Bob -
>>>
>>>In the diagram published on your website that shows the circuitry for
>>>converting the incandescent low voltage light to an LED, you show power
>>>coming off a fuse directly to the LED then thru a 220 ohm resistor then
>>>to
>>>terminal 5 of the LR3 voltage regulator. There is also a 220 ohm
>>>resistor
>>>bypass around the LED. Several Questions:
>>>
>>>1. Shouldn't the first resistor described above be before the LED not
>>>after?
>>>
>>>2. With an LED that has a 1.9v forward, 20 milliamps of current and a
>>>buss voltage of 13.8v, I get 595 ohms for the resistor. Radio Shack
>>>has a
>>>560 ohm and a 680. Is the 560 ohm OK?
>>>
>>>3. Would the bypass resistor also be 560 or some other value?
>>>
>>>I looked in the archives and read an explanation of the need for a
>>>bypass
>>>resistor, but could not find the explanation for where to put the bias
>>>resistor. Most LED diagrams have it on the + battery side, thence to
>>>the
>>>LED. Many thanks for the help.
>>>
>>>John Schroeder
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>
>
>
Message 17
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: "Matt Prather" <mprather@spro.net>
Hi John,
LED's have, by their nature, extremely non-linear relationship between
voltage and current - unlike the textbook resistor. So, when you start to
pump current through a diode, the voltage across it goes up and up until
you get to a voltage where it biases on. Then the voltage rise slows down
a bunch for the same change in current. The effect in the circuit is that
you
have a resistor operating where R = V/I = 1.9V/.02A = 95ohm. Remember,
this is not a real resistor, but something that we're just modeling as one
for
the moment. Back to your question... When you put a 95ohm resistor in
parallel with a 560ohm resistor (the one making the voltage divider), the
lower resistance gets the most current...
Req = 1 / (1/R1 + 1/R2) = 1 / (1 / 95 + 1 / 560) = 81ohm. So adding the
560 ohm resistor made the equivalent resistance drop from 95 ohm to 81
ohm. We'll ignore that the LED is now operating at a different IV point;
this is
close enough. If we were still dropping 1.9V across the diode and hence
also across the parallel resistor, I = V/R = 1.9V/560ohm = 3mA. Not a big
deal. Close to 20mA is still going through the diode.
To figure the precise size of the bypass resistor, we'd need to know what
the output characteristics of the circuit driving it (what's the keepwarm
voltage),
and more precise data about the IV curve for the LED. You could measure
the output characteristics of the module, and the IV curve for the diode.
Then
we could figure out how much bypass was required to keep the LED dark. In
practice, I am going to guess that the keepwarm voltage is low enough that
any
resistor in the 100ohm to 1kohm range will probably do the trick, - keep from
forward biasing the diode enough to produce light. An easy way to check it
out is wire it up in the hangar some night using a pot instead of a fixed
resistor.
Twiddle with the resistance of the pot to get what you want, measure the
resistance value you get and then pick a resistor that gets you close.
Regards,
Matt-
> --> AeroElectric-List message posted by: "John Schroeder"
> <jschroeder@perigee.net>
>
> Richard -
>
> Thanks for the clarification. I'll put the resistor first (before the
> LED). What effect does the resistor of the same ohms have on the circuit
> when it taps in on the plus side of the LED and ends on the negative
> terminal of the LED. This looks a bit like a voltage divider.
>
> Thanks,
>
> John
>
>
> On Mon, 14 Feb 2005 13:46:32 -0500, Richard Tasker
> <retasker@optonline.net> wrote:
>
>> --> AeroElectric-List message posted by: Richard Tasker
>> <retasker@optonline.net>
>>
>> In a series circuit (components connected one after another from +12V
>> to ground) it makes no difference which comes first. The order "+12V,
>> LED, resistor, ground" works the same as "+12V, resistor, LED,
>> ground". Put the parts where it is most convenient
>>
>> Dick Tasker.
>>
>> John Schroeder wrote:
>>
>>> --> AeroElectric-List message posted by: "John Schroeder"
>>> <jschroeder@perigee.net>
>>>
>>> Bob -
>>>
>>> In the diagram published on your website that shows the circuitry for
>>> converting the incandescent low voltage light to an LED, you show
>>> power coming off a fuse directly to the LED then thru a 220 ohm
>>> resistor then to
>>> terminal 5 of the LR3 voltage regulator. There is also a 220 ohm
>>> resistor
>>> bypass around the LED. Several Questions:
>>>
>>> 1. Shouldn't the first resistor described above be before the LED
>>> not after?
>>>
>>> 2. With an LED that has a 1.9v forward, 20 milliamps of current and
>>> a buss voltage of 13.8v, I get 595 ohms for the resistor. Radio
>>> Shack has a
>>> 560 ohm and a 680. Is the 560 ohm OK?
>>>
>>> 3. Would the bypass resistor also be 560 or some other value?
>>>
>>> I looked in the archives and read an explanation of the need for a
>>> bypass
>>> resistor, but could not find the explanation for where to put the
>>> bias resistor. Most LED diagrams have it on the + battery side,
>>> thence to the
>>> LED. Many thanks for the help.
>>>
>>> John Schroeder
>>>
>>>
>>>
>>
>>
>
>
> --
>
>
Message 18
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|
| Subject: | Stereo vs. Mono Headphone Jacks |
--> AeroElectric-List message posted by: "Dennis Johnson" <pinetownd@volcano.net>
Greetings,
I'm starting the electrical planning for my Lancair Legacy and wonder about the
advantages and disadvantages of stereo vs. mono headphone jacks. At this point,
I don't see any need for stereo headphones, but if there aren't any significant
disadvantages, I wonder if it would be wise to wire for stereo in case my
plans change in the future. What happens if I plug mono headphones into a stereo
jack and vice versa? Any other thoughts?
Thanks,
Dennis Johnson
Lancair Legacy
Message 19
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|
| Subject: | Stereo vs. Mono Headphone Jacks |
--> AeroElectric-List message posted by: "James E. Clark" <james@nextupventures.com>
Go STEREO.
In that Legacy on those LONG cross country trips, either you or your
passenger will just LOVE to listen to you Ipod or other MP3 player while
enroute. You will want to do it in STEREO. I see NO downside to stereo but
if you wire it mono and want it later it will be a pain to do.
Many stereo headsets have a stereo/mono switch so if you plugged them into a
mono system and heard stuff in just one ear, slide the switch and you've got
"mono both".
James
| -----Original Message-----
| From: owner-aeroelectric-list-server@matronics.com [mailto:owner-
| aeroelectric-list-server@matronics.com] On Behalf Of Dennis Johnson
| Sent: Monday, February 14, 2005 9:08 PM
| To: aeroelectric-list@matronics.com
| Subject: AeroElectric-List: Stereo vs. Mono Headphone Jacks
|
| --> AeroElectric-List message posted by: "Dennis Johnson"
| <pinetownd@volcano.net>
|
| Greetings,
|
| I'm starting the electrical planning for my Lancair Legacy and wonder
| about the advantages and disadvantages of stereo vs. mono headphone
| jacks. At this point, I don't see any need for stereo headphones, but if
| there aren't any significant disadvantages, I wonder if it would be wise
| to wire for stereo in case my plans change in the future. What happens
| if I plug mono headphones into a stereo jack and vice versa? Any other
| thoughts?
|
| Thanks,
| Dennis Johnson
| Lancair Legacy
|
|
|
|
|
Message 20
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| Subject: | Re: LED Bias Resistors |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 12:57 PM 2/14/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "John Schroeder"
><jschroeder@perigee.net>
>
>Bob -
>
>In the diagram published on your website that shows the circuitry for
>converting the incandescent low voltage light to an LED, you show power
>coming off a fuse directly to the LED then thru a 220 ohm resistor then to
>terminal 5 of the LR3 voltage regulator. There is also a 220 ohm resistor
>bypass around the LED. Several Questions:
>
>1. Shouldn't the first resistor described above be before the LED not
>after?
You can wire it several ways with lots of different resistors.
The reason I provided the schematic shown is to take advantage
of resistors sold in PAIRS from Radio Shack. The shunt resistor
is necessary because of some light-off bias current that flows
in the output lamp driver for the LR-3. This design was
developed so that the warning light will still illuminate
even when all power is removed from the LR-3. The residual
bias won't light the incandescent lamp but causes a noticeable
output from an LED if not swamped out by the parallel resistor.
A pair of 220 ohm resistors wired as suggested provides
about 35 mA of drive to an LED when the LR-3 is flashing the lamp.
220 was picked because it's a commonly stocked value at
Radio Shack and comes in a blister-pak of 2. Other configurations
will obviously work too . . . but may optimize with values not
so easily obtained and you may have to buy two pairs if different
values meaning that you throw away the extras.
Folks are making this into a much larger issue than it needs
to be. The schematic shown was well considered, tried on the
bench and is recommended as published. Works good and lasts
a long time.
Bob . . .
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