Today's Message Index:
----------------------
1. 12:48 AM - EFIS brownout capacitor (user9253)
2. 06:59 AM - Re: EFIS brownout capacitor (Robert L. Nuckolls, III)
3. 09:41 AM - Re: EFIS brownout capacitor (user9253)
4. 09:43 AM - Knobs and Dials (Etienne Phillips)
5. 09:44 AM - Re: EFIS brownout capacitor (user9253)
6. 10:01 AM - Re: Knobs and Dials (Jeff Luckey)
7. 12:08 PM - Re: Re: EFIS brownout capacitor (Robert L. Nuckolls, III)
8. 01:19 PM - Re: 1 Wire vs. 3Wwire alternators (cdnch701builder)
9. 02:37 PM - Re: Re: EFIS brownout capacitor (Robert L. Nuckolls, III)
10. 06:22 PM - Re: 1 Wire vs. 3Wwire alternators (Robert L. Nuckolls, III)
11. 09:34 PM - Re: Knobs and Dials (Etienne Phillips)
Message 1
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Subject: | EFIS brownout capacitor |
Bob and all,
Is it feasible to provide brownout protection for an EFIS during engine cranking
with a large electrolytic capacitor? A capacitor would not have to be replaced
periodically and it might not weigh as much as a backup battery. Each brand
of EFIS might have a different supply voltage requirement. But for this discussion,
let's assume that 9 volts are required to prevent the EFIS from rebooting.
How long is the battery voltage below 9 volts when starting the engine?
The starter will draw the most current when it is first energized. Once the
starter is rotating, back EMF will reduce the current draw. So for the first
several milliseconds, the battery voltage will be at the lowest. If a large
capacitor could support the EFIS voltage for one second, would that be long
enough? If an EFIS draws 1 amp, what size capacitor would be required? Some
EFISs have dedicated terminals for a backup battery. I assume that those EFISs
have an internal diode to prevent discharge of the backup battery into the aircraft
electrical system. Otherwise an external diode is needed.
Could a capacitor provide brownout protection? Or would it have to be so large
as to make it impractical?
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=359987#359987
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Subject: | Re: EFIS brownout capacitor |
At 02:44 AM 12/1/2011, you wrote:
Bob and all,
Is it feasible to provide brownout protection for an EFIS during
engine cranking with a large electrolytic capacitor? A capacitor
would not have to be replaced periodically and it might not weigh as
much as a backup battery. Each brand of EFIS might have a different
supply voltage requirement. But for this discussion, let's assume
that 9 volts are required to prevent the EFIS from rebooting. How
long is the battery voltage below 9 volts when starting the
engine? The starter will draw the most current when it is first
energized. Once the starter is rotating, back EMF will reduce the
current draw. So for the first several milliseconds, the battery
voltage will be at the lowest. If a large capacitor could support
the EFIS voltage for one second, would that be long enough?
Probably. It might even be as short as 250 milliseconds. See:
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1_2.gif
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1.jpg
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_3.gif
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_1.gif
The traces above were taken from the two vehicles
we were driving at the time. The Saturn has a PM
starter motor, the Safari has a wound field. The
larger depression of battery voltage in the Saturn
trace can be partially attributed to the the
greater inrush current for the PM motor.
If an EFIS draws 1 amp, what size capacitor would be required? Some
EFISs have dedicated terminals for a backup battery. I assume that
those EFISs have an internal diode to prevent discharge of the backup
battery into the aircraft electrical system. Otherwise an external
diode is needed.
Could a capacitor provide brownout protection? Or would it have to
be so large as to make it impractical?
It's been done. Consider that the rate of change
across a capacitor is defined by V/S = A/F
1 Amp of charge (or discharge) on a 1 Farad
capacitor produces a voltage change rate
of 1 Volt per Second. Of course, few devices
draw a constant current as the voltage varies
so this relationship has a practical limitation
that falls apart for more than short durations.
Of course, that's what we're talking about.
Of the top of our head, we could estimate that
a capacitor charged to .7 volts below battery
voltage (12.5 - .7) = 11.8 volts. The goal is
to limit voltage drop to 2.8 volts over a .25
second interval
So, V/S = A/F
(V/S)F = A
F = AS/V = .25/2.8 = .09 Farads
There's an RC vs. V calculator at
http://www.bowdenshobbycircuits.info/rc.htm
which can be used to do the same math. In
this case, plug in some essentially constant
current combination, say 100 volts and 0.1K
ohms (1A). Then plug in time of 250mS and
voltage change of 2.8 volts. The tool calculates
88029.7978 microFarads or 0.088F.
Unfortunately, fat-caps don't come in the
range of incremental sizes as their smaller
cousins. Also, 16V ratings is in the realm
of high voltage for a super-cap. Here's a
device that would fit our hypothetical:
http://search.digikey.com/us/en/products/BZ12GA124ZAB/478-6281-ND/2506257
It's a 120 milliFarad device described in this
data sheet:
http://www.avx.com/docs/Catalogs/bestcap.pdf
This exercise suggests to the practicality of using
more 'active' forms of bus voltage regulation. If
I were writing specs for a modern EFIS system
where design goals called for improved immunity
to starter brownout, I'd call for the switchmode
power supply output to be stable down to 7 or 8
volts. Of course, input currents to the supply
would double during the brownout interval but
it's a short duration.
Bottom line is that its a lower cost of ownership
to design brown out protection into a device than
to paste it on outside.
I proposed a scheme to a customer some years
back where we explored the addition of a 3 volt,
DC to DC converter to be switched in as a bus
voltage booster during cranking times. The customer
tried it in the lab with positive results . . .
don't know if it ever went into production.
A 3v, 1A supply is an ittty-bitty critter compared
to a super-cap.
Bob . . .
Message 3
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Subject: | Re: EFIS brownout capacitor |
Bob,
Thank you very much for taking the time to reply.
Digikey has some other large capacitors that are not as expensive:
$16 http://search.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=ECE-T1EP104FA
$12 http://search.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=ECE-T1CP104FA
One of these capacitors might be a viable alternative to replacing an expensive
internal backup battery for someone who only needs brownout protection and not
a longer backup time.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=360010#360010
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Hi All
Not strictly aero-electric, but vaguely related...
I'm desperately looking for 2 knob assemblies for a 4mm shaft
>From this catalogue
http://docs-europe.electrocomponents.com/webdocs/002a/0900766b8002a402.pdfthe
parts numbers for the assembly are
S210 004 - Black knob
C210 Black 5 cap
D211 or D218 figure dial
I've tried RS Components, Mouser, Digikey, Mantech, Selco (who make them,
have a $50 minimum charge, but don't have the figure dials), and a horde of
others without success.
If I had one already, I'd consider making a mould and casting a new one!
Thanks, in desperation...
Etienne
Message 5
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Subject: | Re: EFIS brownout capacitor |
When the master switch is turned on, would the inrush current to a 0.1F capacitor
be a problem?
Thanks, Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=360011#360011
Message 6
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Just off the top of my head -
Could you get a more standard/easier-to-find knob for a 1/8 inch shaft
(isn't that about 3 mm?) and drill it out?
_____
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Etienne
Phillips
Sent: Thursday, December 01, 2011 09:40
Subject: AeroElectric-List: Knobs and Dials
Hi All
Not strictly aero-electric, but vaguely related...
I'm desperately looking for 2 knob assemblies for a 4mm shaft
>From this catalogue
http://docs-europe.electrocomponents.com/webdocs/002a/0900766b8002a402.pdf
the parts numbers for the assembly are
S210 004 - Black knob
C210 Black 5 cap
D211 or D218 figure dial
I've tried RS Components, Mouser, Digikey, Mantech, Selco (who make them,
have a $50 minimum charge, but don't have the figure dials), and a horde of
others without success.
If I had one already, I'd consider making a mould and casting a new one!
Thanks, in desperation...
Etienne
Message 7
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Subject: | Re: EFIS brownout capacitor |
At 11:41 AM 12/1/2011, you wrote:
>
>When the master switch is turned on, would the inrush current to a
>0.1F capacitor be a problem?
>Thanks, Joe
Good question. If the cap is fed with say,
4' of 22AWG (16 mOhm/ft) then there is
potential for a 150+ Amp inrush. You might
want to consider some ballasting resistance
or perhaps an inrush limiter sized to your
operating loads.
Bob . . .
Message 8
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Subject: | Re: 1 Wire vs. 3Wwire alternators |
Thanks bob...
I have a 3 wire internally regulated alternator... that I would like to convert
to external
regulator!
Is there any info online somewhere that provides instructions to do the conversion?
I have
been searching and I cannot find!
Ron
:--)> <nuckolls.bob@aeroelectric.com>
:--)>
:--)> At 11:43 AM 11/22/2011, you wrote:
:--)>:--)>
:--)>:--)> I need some help here with alternators! What is the difference
:--)>:--)> between a 1 wire and a 3 wire
:--)>:--)> system?
:--)>:--)>
:--)> I'm not sure there's a uniform convention for
:--)> 1 versus 2 versus 3 wire alternators. The
:--)> 1-wire alternators I see for boats, RVs and
:--)> utility vehicles have regulators built in. They
:--)> have ONE b-lead that connects to the system and
:--)> they automatically shut down internally when
:--)> the alterantor is not turning.
:--)>
:--)>:--)> Can a 1 wire setup be shut down with a switch as per over voltage protection
:--)>:--)>
:--)> No
:--)>
:--)>:--)> ... or does it have
:--)>:--)> to be a 3 wire?
:--)>:--)>
:--)>
:--)> It certainly needs to have more than one wire, the
:--)> second of which offers absolute control over field
:--)> excitation. Check out B&C or Plane Power. They've
:--)> provided for satisfaction of the legacy philosophy for
:--)> putting alternators on airplanes.
:--)>
:--)>
:--)> Bob . . .
:--)>
:--)>
http://www.matronics.com/Navigator?AeroElectric-List
Message 9
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Subject: | Re: EFIS brownout capacitor |
At 01:35 PM 12/1/2011, you wrote:
><nuckolls.bob@aeroelectric.com>
After some sifting through the gray matter archives, I retrieved
the core principals behind an active 'bus booster' that I
crafted some years back. Making this technology work for brown-out
protection would look something like this:
http://aeroelectric.com/Pictures/Schematics/Royer_Oscillator_Bus-Booster.pdf
I've used this style power oscillator in dozens of products.
It's designed around a saturable core transformer that operates
in the 1000-4000 Hz range. These are usually tape-wound toroidal
cores.
This particular implementation uses 'upside down PNP' power
transistors with grounded collectors. The assembly staff really
liked that . . . no insulating washers and grease!
This would be a DC-DC power supply that produces say 3.5 volts
for a 12 volt input. The instant the starter contactor is
energized, battery voltage applied to the protected device
is boosted to about 16.0 volts. When the starter inrush
hits, battery voltage drops to say 9 volts with a
proportional drop in boost level to about 2.4 volts
which is added to the 9 volts for a 'protected' output
of 11.4 or so.
When the starter is de-energized, the oscillator is
unpowered, boosting is replaced by normal bus power through
the upper, diode-isolated input. To handle a 1A load, output
power would be under 5 watts. This is a really small oscillator.
Bob . . .
Message 10
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Subject: | Re: 1 Wire vs. 3Wwire alternators |
At 03:13 PM 12/1/2011, you wrote:
>
>Thanks bob...
>
>I have a 3 wire internally regulated alternator... that I would like
>to convert to external
>regulator!
>
>Is there any info online somewhere that provides instructions to do
>the conversion? I have
>been searching and I cannot find!
It varies from one brand and model to the next. An
alternator repair shop could open it up and easily
identify the means by which the internal regulator
could be by-passed. I've seen some articles but don't
recall now where . . . Sorry.
Perhaps somebody here on the List will recall some
exemplar articles.
Bob . . .
Message 11
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Subject: | Re: Knobs and Dials |
On 01 Dec 2011, at 7:58 PM, Jeff Luckey wrote:
> Just off the top of my head '
>
> Could you get a more standard/easier-to-find knob for a 1/8 inch shaft
(isn=92t that about 3 mm?) and drill it out?
>
>
>
Hi Jeff
That is definitely an option, along with using a spacer sleeve to get
the shaft size to 6mm. However, the 21mm knob diameter and the figure
dials seem to be what makes this combination particularly hard to find.
Thanks for the input though :)
Etienne
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