Today's Message Index:
----------------------
1. 06:11 AM - Re: Alternator B Lead protection (Robert L. Nuckolls, III)
2. 06:43 AM - Re: oh no! OV again (Robert L. Nuckolls, III)
3. 06:45 AM - Flaky BNC Connection Repairable? (DAVID REEL)
4. 07:32 AM - Re: LED power....... (Peter Laurence)
5. 07:34 AM - Re: Flaky BNC Connection Repairable? (Brian Lloyd)
6. 10:10 AM - Re: Flaky BNC Connection Repairable? (Dale Ensing)
7. 11:43 AM - Remove from list (Leo Corbalis)
8. 12:44 PM - Wire length vs. fuse size (Jerry Grimmonpre)
9. 01:52 PM - right angle BNC (rd2@evenlink.com)
10. 01:59 PM - Re: right angle BNC (Gilles Thesee)
11. 02:13 PM - Re: LED power....... (Richard Tasker)
12. 03:59 PM - Re: Flaky BNC Connection Repairable? (Ken)
13. 03:59 PM - Re: Wire length vs. fuse size (LarryRobertHelming)
14. 04:41 PM - Re: LED power....... (Bill Dube)
15. 05:14 PM - Re: right angle BNC (Bob C.)
16. 05:14 PM - Re: Wire length vs. fuse size (Bob C.)
17. 06:52 PM - Rotax Charging (Guy Buchanan)
Message 1
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| Subject: | Re: Alternator B Lead protection |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 12:25 AM 4/17/2006 -0400, you wrote:
>--> AeroElectric-List message posted by: "DEAN PSIROPOULOS"
><dean.psiropoulos@verizon.net>
>
>
>Lectric Bob:
>
>I'm using a version of your Z-12 architecture modified for a single 60 AMP
>alternator (no backup YET, after the airplane flies I'll add an SD-8). My
>question has to do with alternator B lead fusing and I'll get right to the
>point.....
>
>Is it really necessary to put a fuse, breaker or ANL in this circuit?
Cars don't do it . . . and if you're comfortable with that in your
airplane too . . . you don't need to do it there either. But I believe
there was a recent case where a car caught fire in a parking lot . . .
don't recall the extent of the damage but I think the story cited
some form of failure in the alternator. Now, in all fairness, that
might have been a soft fault wherein b-lead protection would not
have opened and stopped progress of the event. Without detailed
analysis we're left with best hypothesis supported by what we hope
is good common sense and lots of experience. Unfortunately, it doesn't
take too many fertilizations of myth and bad science to turn
a perfectly understandable event into Scary Story version 1456.3
useful only for hangar flying over a pitcher of suds.
>My thinking on this goes as follows:
>1) The B lead would be routed from the alternator to the contactor on the
>engine side of the firewall only (no heavy wire inside the cockpit).
>2) I'm using an 8 gauge Tefzel wire provided in Van's wiring kit.
>3) An 8 gauge Tefzel wire will experience appx 30 degree (C) temperature
>rise at the 60 amps provided by the alternator at maximum output.
>4) Even sitting next to a 200 degree (F) engine crankcase the temperature
>rise on the wire should be within the capability of the wire insulation.
>5) Even under extreme charging circumstances the full 60 amps of the
>alternator will not be flowing in the wire for long periods, limiting the
>duration of the temperature rise and insulation stress
>6) B&C 60 amp externally regulated alternator with LR-3 reg/OV protect
>
>The only condition that I can think of that might cause trouble and where a
>fuse/breaker/ANL would mitigate a possible hazard is:
>
>An alternator fault that allows a dead short between the battery positive
>and crankcase ground through the alternator windings and the B lead. This
>could burn up the windings in the alternator and possibly melt the B lead.
>
>Is this the scenario that the ANL on the B lead is designed to mitigate?
That's it. Rare and in fact, I've not heard of one in many moons
with our customers. But the folks at Kelly see them come in from
time to time.
>What are the probabilities that such a scenario would occur in the field?
>Any experience with this type of fault in 40 years of working on spam cans?
>Would you advise against leaving this ANL out or is it just "extra
>insurance" for some other scenario I'm missing? Thanks.
I prefer not to deal in probability slicing. If the risks are not
zero -AND- potential for hazard under the fault condition is high,
then I prefer to design in plan-b hazard mitigation.
It's your airplane and I would not propose to dictate design
philosophies to you.
Bob . . .
Message 2
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| Subject: | Re: oh no! OV again |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 03:25 PM 4/16/2006 -0500, you wrote:
>--> AeroElectric-List message posted by: "gary" <gkrysztopik@satx.rr.com>
>
>
>I recently had what I suspect is a regulator failure with an EA-81 and
>Suzuki Samuri alternator. I'm not quite sure exactly what happened but many
>many thanks to Bob and the list for helping out when I was wiring my plane
>four or five years ago. My backup battery and backup ignition saved me and
>got me to the nearest airport (twice).
>
>I have a glass VFR panel but didn't want the complexity and weight of a
>bigger aux bus. My simple little 5AH aux battery is only wired to the
>backup ignition, second electric fuel pump, and tiny LCD voltmeter. It's
>just enough to keep the engine running while I get my handheld radio out
>(with VOR for backup nav). I wired it thru a completely different area of
>the panel and firewall for complete redundancy. It is connected to the main
>bus via a diode for charging. I check every preflight that the backup
>battery and ignition are working. That's the good part - it worked as
>intended.
>I was a long time reader on the list but went thru three big moves over the
>last couple years and I wasn't able to keep up with all my lists and missed
>a large part of the Paul vs Bob OV discussion as well as anything that took
>place since. I'm not sure whether to retain my OV module and solenoid but
>I'll be reading up on things. One of my mistakes was to have a partial OV
>circuit and the other was not to have sufficient and active engine
>monitoring. I'm here to learn so feel free to point out any other mistakes
>that we can learn from.
The figure Z-24 ov system is not inherently evil. It does offer
risks to the alternator's regulator IF the system is turned OFF
while the alternator is under load. On the other hand, the system
has performed as intended and taken runaway alternators off line
on several occasions reported to us. There's a replacement for
Z-24 in the design phases and some testing has been done which sent
us back to the drawing board. But it's a low priority concern. If
you have Z-24 in place, just operate it as you would any other
airplane and it will be fine in interim.
>- OV circuit problem last year - I noticed my battery was run down because
>the alternator was not charging it. I found that the alternator contactor
>was not closing (used in OV circuit for internally regulated alternators per
>aeroelectric schematic). I attributed the failure to a poor mounting
>location - I tried to keep it simple so I put it right between the alt and
>starter which was on the subaru cylinder head where there were spare
>mounting holes already tapped in the head. I'm guessing excessive heat and
>vibration caused the failure. I bypassed the contactor but left the OV
>module in there intending to relocate the contactor. I should have
>disconnected the circuit - either all in or all out.
I think your analysis has merit. The contactor would not live
happily mounted on the engine.
>- gnd strap problem last fall - while starting the plane, the power
>fluctuated then dropped out. I traced it to a loose ground strap. Funny, I
>made all my big cables per Bob's 12 ga wire wedge solder method and all held
>up great. For some reason I wanted a nice braided steel ground strap so I
>bought two custom length from an aircraft place for battery to firewall and
>engine block to firewall. These are the ones that failed - the crimp was
>loose and the strap pulled right out. Lesson - make redundant ground
>straps.
Or solder with confidence in your skill and powers of observation
to know that the join integrity is good . . .
> Another lesson - I gently tug on all bat and gnd straps preflight
>but the two gnd straps were neatly tie wrapped together so when I checked
>them, the good one was supporting the bad one. That's both good and bad I
>guess. I mention this because the incident blew some fuses and must have
>sent some spikes thru the system, possibly reducing the life of the
>regulator?
It's anybody's guess. Normally I would not expect the condition
you describe to chip away at the service life of a regulator.
>- in-flight failure #1 - the other week on the way to SNF, radio blinks,
>popping in headset, then panel goes black and engine gets quiet. Backup
>switch on, engine comes back up and land at nearest. Probe around and find
>battery contactor chattering, not able to keep bat and alt on main bus.
>Probe around engine and panel for a couple hours, everything else looks ok
>except alt OV breaker was popped (missed hint?). I assumed the main bus
>disconnect sent a spike thru the system and popped the breaker. I had a
>contactor fail before, made sense so I called around for one. No luck, so I
>move cables to one side of contactor to bypass. Only one hour flight to SNF
>so I'll find one there. Very long runup, everything looks good - off I go.
>
>- in-flight failure #2 - 15 minutes into flight, radio starts blinking and I
>start cursing. I notice aux bat volts fluctuating between 15.x and 16.x
>(this is after diode drop from main bus). This is normally at 13.8 volts.
>Aha! The regulator is bad! Everything goes out again. "golly, gosh darn
>it" (ya right) Backup switch on, engine comes on again (whew!). Land at
>nearest. Bad place to land but that's another story. I pull the alt and
>get a ride to town. I went to an auto parts store and they tested it. It
>failed on the tester "when the switch was on alternator but passed when it
>was set to generator". They had no idea what that meant but it sounded like
>a bad regulator to me. They didn't have a Suzuki Samuri alternator in stock
>but said a guy up the road fixes them. Off to the guy up the road and he
>tested it. "Nothing wrong with this alternator" he said. I asked to keep
>testing, and he got it really hot under full load and it still worked.
>Maybe under vibration or higher rpm? Dunno. Went to another auto parts
>store and they ordered one - "be here in two hours". They tested it and it
>passed on a third type of test stand, this one fully automated. I wanted
>new anyway.
This is not an unusual story. It's not uncommon for folks who
sell and even overhaul things to know exactly HOW the product
OR their test equipment works. They provide a very useful function
with their ability to fix common ailments (one doesn't have too
many choices as to repairable items in alternators) but in spite
of their extensive knowledge, it's not uncommon to find that
they understand little about the alternator and even less about
any unique features of your application.
>Got the new alt, went back and installed it, but the battery wouldn't come
>up after charging so it was toast. I found the same size and replaced it.
>I also removed the overvoltage circuit and removed a diode to ground on the
>field line from the contactor. It's normally not good to make more than one
>change at a time but I wanted to remove all in doubt and try to recreate the
>problem later at home. I ran it up for a long time not feeling good that I
>didn't understand exactly what happened or find and fix a hard failure.
>Told the tower that I was going to keep climbing and circling for a while,
>and everything seemed ok.
>
>Made it Lakeland (after doing several laps around Lake Parker #$%@&
>!),
>couldn't find a contactor and never found anything else wrong. So it made
>it to my new home after another 10 hours as-is. Everything seems fine with
>the new alt, new bat and contactor bypassed (I already ordered a new master
>contactor).
>
>- is it likely for the regulator to go bad but test ok?
>- would the regulator shut itself down? (someone said they do that)
>- would the OV ciruit have pulled the "field" line down and caused screwy
>operation because the OV contactor was not there?
>- would an overvoltage toast the master contactor?
>- the first main bus failure makes sense if the master contactor removed all
>power, but the second time they were hard wired (stupid, yes). Would the OV
>toast an RG battery that quick?
Yes. See:
http://www.aeroelectric.com/Pictures/Battery/Odyssey_OV/
> Battery goes high temp and shorts?
Shorts under normal operating conditions are rare in RG batteries.
The failure mode that precipitated shorts in flooded batteries does
not exist for RG batteries. However, under duress, all bets are off.
Here a real $high$ battery that shorted internally and caught fire
internally:
http://www.aeroelectric.com/Pictures/Battery/Internal_Fire
. . in this case, all damage was contained within the battery
except for a tiny hole in the case. We're not sure what precipitated
the event. Too much damage to burned cell to deduce and the other
cells did not show signs of overcharge. We're thinking this was
a one-of, exceedingly rare event . . . but who knows? We may get
a surprise one day.
>- do I replace the OV circuit and contactor? I had about 150 hours on it
>with no problems using the OV circuit.
I'd recommend you leave it in but move the hardware off the engine.
Had it been in place and functioning you should never have seen
the high voltage readings you cited. The ov event should have
be corralled in milliseconds after onset. Now, having the
Z-24 contactor open COULD be antagonistic to your alternator's
regulator . . . but since it has already wandered off into
the weeds, you might as well put it out of it's misery and
save the rest of the airplane.
At first blush, it sounds as if you might have multiple issues
of craftsmanship in installation and wiring of components. It's
a certainty that 'loose' connections in a system under load can
mimic the load-dump stresses known to be antagonistic to alternator
regulators.
>Happy to share my stupidity so nobody else does that, and highly recommend
>simple redundant circuits that will get you home. Also happy to provide
>real-world data for discussion here. In my feeble defense, this
>cross-country move came up quickly with a fixed timeframe so I scrambled to
>clean up details on the plane but didn't get to replacing or removing OV
>stuff. The plane flew great from RI to FL after 10 hours and when it failed
>I was 1000 miles from anyone I knew. If I was near home I don't think I
>would have continued until it was 100% but I'm also not sure that I would
>have found anything more than I did. I saved the old alt so I can try to
>get it to fail (Bob - you want it?).
Sure. I have access to an automotive guy who knows a great deal
and wants to understand as much as he can about what he knows.
We'd be pleased to take a look at it with due diligence to
understanding and respect for the repeatable experiment.
> It would be nice to know what happened
>and improve my design. I'm 90% done with a homemade engine monitor. I have
>three hall-effect current sensors in place and audio warning with data
>recording. Would have been nice but I still have 90% to go on it. I think
>I'll sell that project and buy a new one soon.
>Gary Krysztopik
>Pelican/Stratus - 175 hours
>San Antonio, TX
You're not real far from Wichita. It might be useful for you
to fly up some weekend and we could help you comb over the system
for any potential 'gotchas' that might still be lurking. It's
exceedingly difficult to pinpoint root cause purely from
un-quantified observations. Do you have a schematic of your
system you could send?
Bob . . .
Message 3
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| Subject: | Flaky BNC Connection Repairable? |
--> AeroElectric-List message posted by: "DAVID REEL" <dreel@cox.net>
I've noticed the satellite signal strength indicators on my GPS90 vary when I rotate
or wiggle the antenna cable where it goes into the BNC connection on the
GPS. So far, this hasn't seemed to affect operation in the air, but, since I
rely heavily on this mode of navigation, I'm wondering if there is something
I could do, short of replacing the unit, to give me a better connection. Some
sort of conductive grease or spray? The antenna cable is new but the GPS is
8 years old. I'll soon be going out on tiedown & the unit is mounted to the panel
& uses ship's power, so it's environment is about to become more hostile
too.
Dave Reel - RV8A
Message 4
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| Subject: | Re: LED power....... |
--> AeroElectric-List message posted by: " Peter Laurence" <Dr.Laurence@mbdi.org>
Dick
Nice explanation.
Would you give us a scenarion using a voltage regulator in a current
limiting mode?
Peter Laurence
> Essentially all LEDs require some sort of current limiter. That is,
> LEDs are current driven devices (rather than voltage driven like a
> normal incandescent lights) and putting a voltage higher than required
> to light them will cause almost instant self destruction. But it looks
> like you already knew that...
>
> That said, the LED assemblies offered on the referenced site may very
> well have internal limiters, especially where they come attached to a
> threaded plug that is designed to thread into an incandescent lamp socket.
>
> Most single (unassembled) LEDs do NOT have an internal limiter and are
> designed to work with something between 10-30 mA through them. This can
> be accomplished in a number of ways, but the simplest is just to wire a
> resistor in series with the LED. When you purchase an LED it should
> come with specifications that tell you what the operating voltage is
> (the voltage that it lights at) and the rated maximum current. Let's
> take a sample red LED with an operating voltage of 1.7V and a maximum
> current of 30 mA. Let's further assume that you want to operate this at
> something less than the maximum current to allow for high temperatures
> in the cockpit and choose 20 mA (a little less than maximum brightness,
> but probably still very bright). If we are operating this from the
> alternator/battery voltage we can assume about 14V available (actually
> 12-14.5V - see below). If we just hooked this to the LED it would be
> very bright (for a millisecond or two), then very dark :-) . We need
> to limit the current to the aforementioned 20 mA.
>
> So... We take the available voltage (14V) and subtract what the LED
> needs (1.7V) to get the voltage we need to "discard" (12.3V). We then
> calculate the resistor we need to allow 20 mA with this voltage
> (12.3V). Using Ohm's law (V=I*R) and rearranging (R=V/I) we plug the
> numbers into the equation to get 12.3V/0.02A=615 ohms. That is not one
> of the standard available values of resistor so we choose a value that
> is close (620 ohms for 5% resistors or 619 ohms for 1% resistors). Now
> we have a value but we still have to calculate the power "discarded" in
> the resistor so we can get one that will not burn up as soon as we turn
> things on. Power in watts is (W=V*I). Plugging the numbers in we get
> 12.3V * 0.02A = 0.246 W or 246 mW. Resistors come is various power
> ratings and we have to choose one that is at least what we just
> calculated. That means we should use 1/4W at absolute minimum.
> However, if we choose the 1/4W resistor it will run very hot to
> dissipate 0.246W of power - potentially shortening it's life and
> reliability. So we really want to choose at least a 1/2W resistor.
> That will give it some "elbow room" especially important if it will be
> operating in a warm environment.
>
> Use the same idea for any LED you may buy (different colors have
> different operating voltages). Additionally, you can connect two LEDs
> in series for whatever reason (lighting, etc.) and just do the same
> calculations but use 3.4V (in this case 1.7V times the two LEDs) instead
> of 1.7V. You can do this with several LEDs but you must allow some
> series voltage to drop across the resistor (remembering that the voltage
> on the aircraft bus varies from about 14.5V max. to about 12V min.). As
> the voltage varies the LEDs will vary in brightness. If you have one
> LED the "leftover" voltage will vary between 12.8V to 10.3V - a change
> of approximately 20-25%. If you series several LEDs (say four for a
> drop of 6.8V), the voltage will vary between 7.7V to 5.2V - a change of
> 30-50%. So do not add too many in series that you have too low a
> voltage across the resistor.
>
> Do not connect LEDs in parallel!!! If you do, the one that has a
> slightly lower operating voltage will "hog" all the current - causing it
> to use too much current (overheat) and be much brighter than the
> other(s). If you want to wire them in parallel for some reason, use a
> series resistor for each LED.
>
> If you have more questions, please ask. :-)
>
> Dick Tasker
>
> Sid Hausding wrote:
>
>>--> AeroElectric-List message posted by: Sid Hausding <avidsid@yahoo.com>
>>
>>Yes, nice site with lots of lighting ideas...........but, no tech ideas
>>for powering up the little buggers.....
>> anyone done this for their panels or other electric/electronic devices
>> and can tell me the needed requirements to keep the LED's from burning
>> out......?
>> Sid
>> -----------------------
>>
>>Sid Hausding <avidsid@yahoo.com> wrote:
>> --> AeroElectric-List message posted by: Sid Hausding
>>
>>Wondering if all LED's come with a built in current limiting device or if
>>most will need to have a resistor wired in line to keep the small power
>>requirements they use from burning out.........any info posted somewhere
>>on wiring in a 15mamp, 12dcv device to show power to the system out there?
>>Sid
>>--------------------
>>
>>"Alan K. Adamson" wrote:
>>--> AeroElectric-List message posted by: "Alan K. Adamson"
>>
>>Opps, helps if you post the link...
>>
>>http://www.ledtronics.com/
>>
>>
>>
>>Don't know if this has been posted before or not, but this place has just
>>about every LED imaginable and then some.
>>
>>
>>
>>
>>
>>
>>
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>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>"Why can't we all just get along?"
>>
>>---------------------------------
>>
>>
>>
>>
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>>
>>
>>
>>"Why can't we all just get along?"
>>
>>---------------------------------
>>
>>
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>>
>
> --
> Please Note:
> No trees were destroyed in the sending of this message. We do concede,
> however,
> that a significant number of electrons may have been temporarily
> inconvenienced.
> --
>
>
>
Message 5
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| Subject: | Re: Flaky BNC Connection Repairable? |
--> AeroElectric-List message posted by: Brian Lloyd <brian-yak@lloyd.com>
DAVID REEL wrote:
> --> AeroElectric-List message posted by: "DAVID REEL" <dreel@cox.net>
>
> I've noticed the satellite signal strength indicators on my GPS90 vary when I
rotate or wiggle the antenna cable where it goes into the BNC connection on the
GPS. So far, this hasn't seemed to affect operation in the air, but, since
I rely heavily on this mode of navigation, I'm wondering if there is something
I could do, short of replacing the unit, to give me a better connection. Some
sort of conductive grease or spray? The antenna cable is new but the GPS is
8 years old. I'll soon be going out on tiedown & the unit is mounted to the
panel & uses ship's power, so it's environment is about to become more hostile
too.
One should pull all panel mounted radios about once per year anyway in
order to clean them, blow out the dust, and clean the connectors. You
may find that solves any problems you may have.
Given that almost all BNC connectors use gold pins, corrosion and
contact resistance are usually not a problem. If you are having problems
with the antenna connector then you need to troubleshoot this before you
have an in-flight failure. Remember, most GPS antennas have their own
amplifier built-in that is powered by DC power going up the antenna coax
cable. It is more likely that it is DC resistance changing the voltage
arriving at the GPS antenna that is causing your problem.
--
Brian Lloyd 361 Catterline Way
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery
Message 6
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| Subject: | Re: Flaky BNC Connection Repairable? |
--> AeroElectric-List message posted by: "Dale Ensing" <densing@carolina.rr.com>
Dave,
I recently discovered the ring nut that holds the BNC connector was loose in
my Garmin 295 allowing it to turn in the housing. You might check that on
yours.
Dale Ensing
do not archive
Message 7
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| Subject: | Remove from list |
--> AeroElectric-List message posted by: "Leo Corbalis" <leocorbalis@sbcglobal.net>
Please remove this account from your list. Recipient is deceased.
Thank you.
Message 8
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| Subject: | Wire length vs. fuse size |
--> AeroElectric-List message posted by: "Jerry Grimmonpre" <jerry@mc.net>
Bob ...
If a load of 15A is fed with a 12 foot length of wire, is an inline fuse
used in this situation? Is the fuse size increased to accommodate the wire
length? What size fuse would be needed? This wire will feed the endurance
bus from the aft battery lug (bypassing the aft contactor) as a continuous
backup source of power.
Thanks ...
Jerry Grimmonpre'
Message 9
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--> AeroElectric-List message posted by: rd2@evenlink.com
I am about to install a right angle crimp type 2 piece solderless BNC but
am not sure what holds the coax center to assure good contact. Can anyone
enlighten me?
Rumen
Message 10
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| Subject: | Re: right angle BNC |
--> AeroElectric-List message posted by: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
rd2@evenlink.com a crit :
> --> AeroElectric-List message posted by: rd2@evenlink.com
>
> I am about to install a right angle crimp type 2 piece solderless BNC but
> am not sure what holds the coax center to assure good contact. Can anyone
> enlighten me?
>
In some models, once you've crimped the center conductor, you push the
center contact in place. In other models, you have to solder the core to
the center pin, then press in the small cover. Works well too.
Hope this helps,
Regards,
Gilles Thesee
Grenoble, France
http://contrails.free.fr
Message 11
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| Subject: | Re: LED power....... |
--> AeroElectric-List message posted by: Richard Tasker <retasker@optonline.net>
In concept it is really simple :-) .
The quickest way (since you can probably get the parts at Radshack) is
to use a three terminal regulator (in, out, ground) like the LM7805
series, although any voltage regulator will work. Connect a resistor
between the output of the regulator and the ground pin of the regulator
(do NOT connect the regulator ground pin to aircraft ground). Connect
the LED and the regulator assembly in series between +14V and ground -
it doesn't matter if you have the regulator connected to +14V to the LED
and then to ground or vice versa. For example, connect the input of the
regulator to +14V, the ground pin of the regulator/resistor to the
positive terminal of the LED and the negative terminal of the LED to
aircraft ground. You also must add appropriate capacitors per the
manufacturers datasheet recommendation - I really can't make any
recommendations here as each regulator is different.
Choose the resistor value based on how much current you want as
follows: Let's assume you want 20 mA and you have chosen a 5V
regulator. Calculate the resistor value (using ohms law) R = 5V / 0.2
mA = 250 ohms. The power dissipated in the resistor is P = 5V * 0.02mA
= 0.1W. In this case a 1/4 W resistor is fine.
Depending on how much current you choose and how many LEDs you use you
may have to add a heat sink to the regulator (unlikely). Bur just in
case, you calculate the power dissipated in the regulator like so
(assuming use of a 5V regulator): Find the maximum voltage across the
regulator +14.5V- 5V - 1.7V = 7.8V. Multiply that by the current, which
is essentially whatever you chose earlier (20 mA in this case) 7.8V *
0.02mA = 0.156W - a number that all but the smallest regulators can
handle without a heatsink.
As with a resistor limiter, you can use more than one LED in series.
You have to have enough voltage when you add all the voltage drops to
still be lower than the minimum expected aircraft supply voltage
(typically about 12V). The voltages that you must add together are: the
5V due to the regulator, the LED drop * the number of LEDs and the
minimum voltage required across the regulator itself (not the 5V, but a
voltage called the dropout voltage which is anywhere from several volts
to less than a volt - depending on the actual regulator used). As an
example, using a LM7805 with 2V dropout, you would have 12V - 5V - 2V =
5V, meaning you could drive three red LEDs down to about the 12V. You
can also find regulators that allow a smaller output voltage (than 5V)
which means that you have more for the LEDs - for instance, the LP2950
is available in a 3V version and this also has a lower dropout voltage
of about 0.5V.
The advantage of using an active regulator is that the current (and
therefore brightness) is essentially constant over the full aircraft
supply voltage (12V to 14.5V). The disadvantage is that it is a little
more complicated than a simple series resistor.
Dick Tasker
Peter Laurence wrote:
>--> AeroElectric-List message posted by: " Peter Laurence" <Dr.Laurence@mbdi.org>
>
>Dick
>
>Nice explanation.
>
>Would you give us a scenarion using a voltage regulator in a current
>limiting mode?
>
>
>Peter Laurence
>
>
>
>
>>Essentially all LEDs require some sort of current limiter. That is,
>>LEDs are current driven devices (rather than voltage driven like a
>>normal incandescent lights) and putting a voltage higher than required
>>to light them will cause almost instant self destruction. But it looks
>>like you already knew that...
>>
>>That said, the LED assemblies offered on the referenced site may very
>>well have internal limiters, especially where they come attached to a
>>threaded plug that is designed to thread into an incandescent lamp socket.
>>
>>Most single (unassembled) LEDs do NOT have an internal limiter and are
>>designed to work with something between 10-30 mA through them. This can
>>be accomplished in a number of ways, but the simplest is just to wire a
>>resistor in series with the LED. When you purchase an LED it should
>>come with specifications that tell you what the operating voltage is
>>(the voltage that it lights at) and the rated maximum current. Let's
>>take a sample red LED with an operating voltage of 1.7V and a maximum
>>current of 30 mA. Let's further assume that you want to operate this at
>>something less than the maximum current to allow for high temperatures
>>in the cockpit and choose 20 mA (a little less than maximum brightness,
>>but probably still very bright). If we are operating this from the
>>alternator/battery voltage we can assume about 14V available (actually
>>12-14.5V - see below). If we just hooked this to the LED it would be
>>very bright (for a millisecond or two), then very dark :-) . We need
>>to limit the current to the aforementioned 20 mA.
>>
>>So... We take the available voltage (14V) and subtract what the LED
>>needs (1.7V) to get the voltage we need to "discard" (12.3V). We then
>>calculate the resistor we need to allow 20 mA with this voltage
>>(12.3V). Using Ohm's law (V=I*R) and rearranging (R=V/I) we plug the
>>numbers into the equation to get 12.3V/0.02A=615 ohms. That is not one
>>of the standard available values of resistor so we choose a value that
>>is close (620 ohms for 5% resistors or 619 ohms for 1% resistors). Now
>>we have a value but we still have to calculate the power "discarded" in
>>the resistor so we can get one that will not burn up as soon as we turn
>>things on. Power in watts is (W=V*I). Plugging the numbers in we get
>>12.3V * 0.02A = 0.246 W or 246 mW. Resistors come is various power
>>ratings and we have to choose one that is at least what we just
>>calculated. That means we should use 1/4W at absolute minimum.
>>However, if we choose the 1/4W resistor it will run very hot to
>>dissipate 0.246W of power - potentially shortening it's life and
>>reliability. So we really want to choose at least a 1/2W resistor.
>>That will give it some "elbow room" especially important if it will be
>>operating in a warm environment.
>>
>>Use the same idea for any LED you may buy (different colors have
>>different operating voltages). Additionally, you can connect two LEDs
>>in series for whatever reason (lighting, etc.) and just do the same
>>calculations but use 3.4V (in this case 1.7V times the two LEDs) instead
>>of 1.7V. You can do this with several LEDs but you must allow some
>>series voltage to drop across the resistor (remembering that the voltage
>>on the aircraft bus varies from about 14.5V max. to about 12V min.). As
>>the voltage varies the LEDs will vary in brightness. If you have one
>>LED the "leftover" voltage will vary between 12.8V to 10.3V - a change
>>of approximately 20-25%. If you series several LEDs (say four for a
>>drop of 6.8V), the voltage will vary between 7.7V to 5.2V - a change of
>>30-50%. So do not add too many in series that you have too low a
>>voltage across the resistor.
>>
>>Do not connect LEDs in parallel!!! If you do, the one that has a
>>slightly lower operating voltage will "hog" all the current - causing it
>>to use too much current (overheat) and be much brighter than the
>>other(s). If you want to wire them in parallel for some reason, use a
>>series resistor for each LED.
>>
>>If you have more questions, please ask. :-)
>>
>>Dick Tasker
>>
>>Sid Hausding wrote:
>>
>>
>>
>>>--> AeroElectric-List message posted by: Sid Hausding <avidsid@yahoo.com>
>>>
>>>Yes, nice site with lots of lighting ideas...........but, no tech ideas
>>>for powering up the little buggers.....
>>> anyone done this for their panels or other electric/electronic devices
>>>and can tell me the needed requirements to keep the LED's from burning
>>>out......?
>>> Sid
>>> -----------------------
>>>
>>>Sid Hausding <avidsid@yahoo.com> wrote:
>>> --> AeroElectric-List message posted by: Sid Hausding
>>>
>>>Wondering if all LED's come with a built in current limiting device or if
>>>most will need to have a resistor wired in line to keep the small power
>>>requirements they use from burning out.........any info posted somewhere
>>>on wiring in a 15mamp, 12dcv device to show power to the system out there?
>>>Sid
>>>--------------------
>>>
>>>"Alan K. Adamson" wrote:
>>>--> AeroElectric-List message posted by: "Alan K. Adamson"
>>>
>>>Opps, helps if you post the link...
>>>
>>>http://www.ledtronics.com/
>>>
>>>
>>>
>>>Don't know if this has been posted before or not, but this place has just
>>>about every LED imaginable and then some.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>"Why can't we all just get along?"
>>>
>>>---------------------------------
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>"Why can't we all just get along?"
>>>
>>>---------------------------------
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>--
>>Please Note:
>>No trees were destroyed in the sending of this message. We do concede,
>>however,
>>that a significant number of electrons may have been temporarily
>>inconvenienced.
>>--
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
>
>
>
>
>
>
Message 12
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| Subject: | Re: Flaky BNC Connection Repairable? |
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
Hi David
If certain there is not a real correctable cause (there usually is) -ypu
could try Stabilant 22a. I have not tried it on antenna connections but
it supposedly pretty much removes the need to periodically clean
connectors and seems to help with intermittent connections. Or maybe it
just makes me feel better ;) .... I haven't noticed it advertised
lately although I seldom go to the places that used to advertise it
anymore.
Ken
DAVID REEL wrote:
>--> AeroElectric-List message posted by: "DAVID REEL" <dreel@cox.net>
>
>I've noticed the satellite signal strength indicators on my GPS90 vary when I
rotate or wiggle the antenna cable where it goes into the BNC connection on the
GPS. So far, this hasn't seemed to affect operation in the air, but, since
I rely heavily on this mode of navigation, I'm wondering if there is something
I could do, short of replacing the unit, to give me a better connection. Some
sort of conductive grease or spray? The antenna cable is new but the GPS is
8 years old. I'll soon be going out on tiedown & the unit is mounted to the
panel & uses ship's power, so it's environment is about to become more hostile
too.
>
>Dave Reel - RV8A
>
>
>
Message 13
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| Subject: | Re: Wire length vs. fuse size |
--> AeroElectric-List message posted by: "LarryRobertHelming" <lhelming@sigecom.net>
----- Original Message -----
> --> AeroElectric-List message posted by: "Jerry Grimmonpre" <jerry@mc.net>
>
> Bob ...
> If a load of 15A is fed with a 12 foot length of wire, is an inline fuse
> used in this situation? Is the fuse size increased to accommodate the
> wire
> length? What size fuse would be needed? This wire will feed the
> endurance
> bus from the aft battery lug (bypassing the aft contactor) as a continuous
> backup source of power.
> Thanks ...
> Jerry Grimmonpre'
>
>
Jerry, you first need to figure the size wire you need for pushing 15A 12
feet. There is a chart in Bob's book on this. You can always use a larger
wire for added protection but that increases your weight.
Next, you want to protect the wire you select by using the right size fuse.
The wire will handle the 15A with a bit of safety built in. You are pushing
15A maximum. So you should use a 20A fuse since a 15A fuse might give you
blown fuse when it is just working normally.
Indiana Larry
>
Message 14
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| Subject: | Re: LED power....... |
--> AeroElectric-List message posted by: Bill Dube <william.p.dube@noaa.gov>
If you are going to go through the effort to use a regulator, use an
LM317 instead. You can easily set it up as a current regulator and it
will put exactly 20 mA (or whatever you choose) through the LED.
Attached is a wiring diagram.
Here is a nice web page that gives all the basic "how to" for
running LEDs.
http://www.trainweb.org/girr/tips/tips7/white_led_tips.html
Use a 60 ohm resistor with the lm317 to get exactly 20 mA. A 62 ohm
will give slightly less, but you will never notice and it is a standard
value.
Here is the digikey order page for the style you would want to get.
Notice that thy cost less than $0.50.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=357151&Row=74749&Site=US
Get the TO-92 package as you don't need the large current that the
larger package will supply. You also don't want surface mount.
Bill Dube'
Message 15
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| Subject: | Re: right angle BNC |
--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
You crimp the center conductor or solder it?
Good Luck,
Bob is SE Iowa
On 4/17/06, Gilles Thesee <Gilles.Thesee@ac-grenoble.fr> wrote:
> --> AeroElectric-List message posted by: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
>
> rd2@evenlink.com a crit :
> > --> AeroElectric-List message posted by: rd2@evenlink.com
> >
> > I am about to install a right angle crimp type 2 piece solderless BNC but
> > am not sure what holds the coax center to assure good contact. Can anyone
> > enlighten me?
> >
> In some models, once you've crimped the center conductor, you push the
> center contact in place. In other models, you have to solder the core to
> the center pin, then press in the small cover. Works well too.
>
> Hope this helps,
> Regards,
> Gilles Thesee
> Grenoble, France
> http://contrails.free.fr
>
>
Message 16
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| Subject: | Re: Wire length vs. fuse size |
--> AeroElectric-List message posted by: "Bob C. " <flyboy.bob@gmail.com>
Jerry.
It seems to me that if you are going to fuse it for 20A you need to
size the wire for 20A also what you are protecting is an overload on
the wire! . . . 12 ft isn't going to be a huge deal . . . if you are
concerned go up one size.
Good Luck,
Bob in SE Iowa
On 4/17/06, LarryRobertHelming <lhelming@sigecom.net> wrote:
> --> AeroElectric-List message posted by: "LarryRobertHelming" <lhelming@sigecom.net>
>
>
> ----- Original Message -----
>
> > --> AeroElectric-List message posted by: "Jerry Grimmonpre" <jerry@mc.net>
> >
> > Bob ...
> > If a load of 15A is fed with a 12 foot length of wire, is an inline fuse
> > used in this situation? Is the fuse size increased to accommodate the
> > wire
> > length? What size fuse would be needed? This wire will feed the
> > endurance
> > bus from the aft battery lug (bypassing the aft contactor) as a continuous
> > backup source of power.
> > Thanks ...
> > Jerry Grimmonpre'
> >
> >
> Jerry, you first need to figure the size wire you need for pushing 15A 12
> feet. There is a chart in Bob's book on this. You can always use a larger
> wire for added protection but that increases your weight.
>
> Next, you want to protect the wire you select by using the right size fuse.
> The wire will handle the 15A with a bit of safety built in. You are pushing
> 15A maximum. So you should use a 20A fuse since a 15A fuse might give you
> blown fuse when it is just working normally.
>
> Indiana Larry
> >
>
>
Message 17
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--> AeroElectric-List message posted by: Guy Buchanan <bnn@nethere.com>
All,
I started the Rotax 582 for the first time today, and everything
was fine but the tachometer and the charging. I'd like some help
de-bugging, if I may.
Configuration: Rotax 582 grey head w/ 3-phase regulator wired per Z-17. GRT
EIS tach wire connected to yellow alternator output wire.
First start: Tachometer reads 0. No variation in voltage switching
alternator in or out, regardless of RPM. Voltage about 12.9V.
Disconnect regulator from alternator. Measure ACV across alternator and get
Rotax spec values. (~14 - 55 VAC depending on RPM.)
Re-connect regulator input wires and disconnect output wire and measure
voltage between it and ground: ~5 VDC invariant with RPM. Note that the EIS
RPM is now working.
Re-connect the output wire and clip DC volt meter between the regulator
output and ground: ~ 14.1 VDC at idle, decreasing to about 5 VDC at higher
RPM. EIS RPM is 0 again.
Basically I'm clueless as to how to diagnose whether the charging
system is working beyond the alternator output. Any help would be
appreciated. I think whatever's influencing the charging is probably
inhibiting the EIS RPM input, as well.
Thanks,
Guy Buchanan
K-IV 1200 / 582 / 99.9% done, thanks mostly to Bob Ducar.
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