Today's Message Index:
----------------------
1. 05:43 AM - Re: Search for Gremlins (Robert L. Nuckolls, III)
2. 07:13 AM - Re: Tachometer Noise (Michael Forhan)
3. 07:19 AM - Dry Cell Batteries? (Steve Stearns)
4. 08:06 AM - Re: Printed circuits (Steve Stearns)
5. 08:20 AM - Re: Re: Tachometer Noise (Robert L. Nuckolls, III)
6. 08:44 AM - Re: Dry Cell Batteries? (Robert L. Nuckolls, III)
7. 09:08 AM - Re: High resistance pops breaker? (Joe)
8. 10:36 AM - Re: Search for Gremlins (Dale Rogers)
9. 10:53 AM - measuring capacitance. (Peter Laurence)
10. 11:36 AM - Re: measuring capacitance. (Roger & Jean)
11. 01:34 PM - Re: measuring capacitance. (Terry Watson)
12. 02:05 PM - Re: measuring capacitance. (Peter Laurence)
13. 02:23 PM - Re: measuring capacitance. (Matt Prather)
14. 02:48 PM - Re: measuring capacitance. (Roger & Jean)
15. 03:32 PM - Re: measuring capacitance. (Terry Watson)
16. 03:41 PM - Re: measuring capacitance. (Ron Quillin)
17. 04:16 PM - Re: High resistance pops breaker? (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Search for Gremlins |
At 11:33 PM 8/24/2008 -0700, you wrote:
><ftyoder@yoderbuilt.com>
>
>With the success of the test of running a new ground wire from the oil
>pressure gauge to the engine case, that removed the wiggle when I activated
>the Alt., I did as you suggested and ran a new fat - ground wire (8 gauge)
>from the engine case to the ground block. I then removed the original engine
>to motor mount jumpers and temporary oil pressure ground wire. I started the
>engine and wiggle came back. DRATS!
8 AWG is small for the usual engine ground. I used
to fabricate custom case ground jumpers for builders
from three concentric conductors of copper braid
that added up to about an 0 AWG wire. But 8 AWG has
a resistance of just under a millohm/foot, it should
be okay. How long is the wire?
By the way, I'm not sure I recall what engine,
alternator and airplane combination we're talking about.
> I then removed all the ground wires from
>the ground block, cleaned the blocks and re installed the grounds. O/P
>needle still wiggles in the same way. The only part of the system I haven't
>checked is the battery which is located behind the baggage compartment, I
>planed to do that this week.
Where does the battery ground?
>If this report leads you to any other suggestions I will certainly
>appreciate them.
If push comes to shove, you can certainly leave the
oil pressure gage grounded to the engine. The stimulus
that upsets it is on the order of tens of millivolts.
Not enough to bother other accessories in your airplane -
only those instruments where sensors get grounded to
the crankcase. It would be interesting to see what
combination of 'fixes' makes the problem go away but
let's not spend a lot of $time$ on it . . . the
exercise at this point is more academic than practical.
Bob . . .
Message 2
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| Subject: | Re: Tachometer Noise |
Ralph & Bob-
Thanks much for your excellent advice. My motivation for asking came from the
fact that both Jabiru and VDO documentation discuss using the alternator as a
signal source. After experiencing the noise problem I surfed around the internet
and found comments to the effect that others had used a filter to stabilize
the system, but no one provided details of the filter configuration. Given
the number of Jabiru installations out there I expected to find a relatively easy,
ready-made solution.
Bob, in answer to your question, I am an electrical/electronics type and worked
in aerospace for many years, so on one hand I am intrigued by the problem and
am tempted to design a solution. But, at the end of the day, I think the best,
most reliable and most elegant solution is to just switch to a dedicated sensor
as you and Ralph suggest.
Thanks again,
Mike
Message 3
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| Subject: | Dry Cell Batteries? |
Bob and the group:
I did an aeroelectric search for "Dry Cell" and came up empty. A quick
(too quick, apparently) look at Concord's web-site comparing Dry Cells
to VRLA batteries indicated that for the same Amp-Hr rating, the Dry
Cells are a little heavier and significantly better in cold-cranking amps.
However, since I'm removing the starter as part of my LongEZ rebuild
that doesn't do much for me.
On the other hand, if Dry Cell batteries perform better than VRLA in
terms of durability (specifically shell-life, self-discharge and
tolerance of time spent sitting while discharged) I would be interested.
Any thoughts from the group on the advantages (if any) and disadvantages
(other than the obvious weight/cost. e.g. do they use the same charging
profile?) of a Dry Cell battery on a starterless airplane?
Best regards to all,
Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07): N45FC O235 Longeze Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D
Message 4
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| Subject: | Re: Printed circuits |
Since the interest level seems high, I'll add a little more info....
> ** Right on. My all time favorite solder is Kester Resin
> 44 that I've stockpiled to a lifetime supply. It flows
> well, fluxes well, and yes . . . it demands some attention
> to cleaning when you're all done.
> **
I also use and prefer Kester 44 for use in hand soldering. Most of my
work these days, however, is with surface mount parts which I reflow.
Here I use Kester R276 No-Clean solder paste. Invariably I end of with
a mix of both fluxes as, after re-flow, I'll have to hand-solder the
through-hole parts or do some rework (I haven't had good luck with
no-clean solder-wick so I stick to the rosin based fluxes on my solder
wick as well). This gets cleaned with Isopropyl (via cotton swabs) or
with a mixture from a flux-remover pen (I haven't checked the MDS but I
suspect it's Isopropyl with a little MEK, it's a bit more aggressive
than the Isopropyl alone). Which results in some white residue from the
no-clean flux. So then I add Kester #951 from a flux pen (which I
recommend - good stuff) and reheat with hot air.
This sounds more time-consuming than it is. In reality it goes pretty
fast and I don't have to get up from my bench. My lab does not have a
good facility for appropriate board-level cleaning operations so when I
have to clean a whole board I do it outside...
Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07): N45FC O235 Longeze Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D
Message 5
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| Subject: | Re: Tachometer Noise |
At 07:09 AM 8/25/2008 -0700, you wrote:
>
>Ralph & Bob-
>
>Thanks much for your excellent advice. My motivation for asking came from
>the fact that both Jabiru and VDO documentation discuss using the
>alternator as a signal source. After experiencing the noise problem I
>surfed around the internet and found comments to the effect that others
>had used a filter to stabilize the system, but no one provided details of
>the filter configuration. Given the number of Jabiru installations out
>there I expected to find a relatively easy, ready-made solution.
Agreed.
>Bob, in answer to your question, I am an electrical/electronics type and
>worked in aerospace for many years, so on one hand I am intrigued by the
>problem and am tempted to design a solution.
These things are always fun if not practical . . . but
then education was NEVER inexpensive. I presume this is
an analog tach . . . but without a cal-adjustment,
I'm mystified as to how calibration is accomplished.
If it's digital, then the HARD part is a multiply-by-
K-divide-by-N circuitry needed to scale the sensed
signal frequency to something that displays true
engine RPM. I'd be interested in seeing what folks
are using to make this happen.
In the analog world, we used to drive a transistor
with the distributor's ignition points signal
to get a pretty clean square wave at the collector.
A small capacitor and two diodes differentiate the
the edges of the square wave and depended on the
meter's inertia to integrate the frequency. A potentiometer
provided a means to calibrate the reading to display
RPM. I built a bucket full of these things for
the hot-rod guys using surplus meter movements.
>But, at the end of the day, I think the best, most reliable and most
>elegant solution is to just switch to a dedicated sensor as you and Ralph
>suggest.
Yeah, life IS that way sometimes. What does this
engine use for ignition triggering?
Bob . . .
Message 6
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| Subject: | Re: Dry Cell Batteries? |
At 08:14 AM 8/25/2008 -0600, you wrote:
>
>Bob and the group:
>
>I did an aeroelectric search for "Dry Cell" and came up empty. A quick
>(too quick, apparently) look at Concord's web-site comparing Dry Cells to
>VRLA batteries indicated that for the same Amp-Hr rating, the Dry Cells
>are a little heavier and significantly better in cold-cranking amps.
>
>However, since I'm removing the starter as part of my LongEZ rebuild that
>doesn't do much for me.
>
>On the other hand, if Dry Cell batteries perform better than VRLA in terms
>of durability (specifically shell-life, self-discharge and tolerance of
>time spent sitting while discharged) I would be interested.
>
>Any thoughts from the group on the advantages (if any) and disadvantages
>(other than the obvious weight/cost. e.g. do they use the same charging
>profile?) of a Dry Cell battery on a starterless airplane?
Don't know what's being called a "dry cell". I'm aware
of NO lead-acid technology that does not reside in
one of three categories (1) flooded - like on your
'65 chevy (2) gelled - like those on many wheelchairs
and other 'mess-sensitive' need for deep-cycle
batteries and (3) starved-electrolyte, valve-regulated
lead-acid, recombinant-gas, thin-film, glass-mat, etc. etc.
These are all names for essentially the same technology.
The reason you didn't find "dry cell" mentioned in the website
postings is because there's no such thing. ALL lead-acid
technologies use liquid water and sulfuric acid electrolyte.
The differences are whether the stuff is liquid and
(1) sorta contained but with vented caps, (2) immobililzed
by adding 'jello' or (3) immobilized by the wetting/
capillary action of a finely woven glass 'kleenex'.
Some folks like to call these "dry" . . . you CAN
drive a nail through the side of the battery and it
will not leak . . . but it is by no means dry.
http://www.aeroelectric.com/articles/bat_thd.pdf
http://www.aeroelectric.com/articles/battery.pdf
Battery selection should not take up much of your
time. What's your battery maintenance program?
How much do you plan to depend on a battery?
If you're day-vfr only, buy the cheapest battery
you can find, run it 'til it craps. Engine cranking
is the primary concern and any sealed lead-acid
battery with terminals for fat wires will get your
engine started. CAPACITY is another matter. If you
plan to design and maintain a known level of
battery-only endurance for en route operations
then your first task is an energy analysis of
your battery-only endurance, pick a battery that
meets that requirement at 80% of rated capacity
(don't forget to further de-rate for load!), and
decide what protocols (preventative maintenance)
you'll adopt as owner-operator to make sure that
capacity is available to you at all times.
This exercise can be successfully carried out
with ANY battery brand or technology.
Bob . . .
Message 7
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| Subject: | Re: High resistance pops breaker? |
DC motors have the greatest torque and current when they are standing
still and voltage is first applied. According to my old college book on
basic electricity, a DC motor (with shunt winding) starting current can
be up to 100 times greater than the full load running current. For
larger motors, a resistance type motor-starter is used to limit the
starting current to prevent damage to the motor and also to prevent
excessive acceleration that could damage the load. Adding resistance to
the circuit during starting slows the acceleration and prolongs the
time that it takes for a motor to attain normal running speed.
Getting back to that Sport Aviation article that claimed that "High
Resistance Pops Breaker". The circuit breaker in that landing light
circuit might have been sized to trip if the motor current was high due
to a jammed landing-light retract mechanism. But due to the time-delay
characteristics of circuit breakers, the breaker would not trip during
normal motor starting even though the starting current is above the
breaker trip point for a short time. Is it possible that there is some
value of resistance (due to bad connections) that, when added to the
circuit, could allow motor-starting current to flow that is still above
the circuit breaker trip point, but for a prolonged period of time?
Could the author of that Sport Aviation article be correct that bad
connections did cause the circuit breaker to trip, but for entirely
different reasons than he stated. He said that bad connections made the
current go up. Perhaps the resistance made the current go down (but not
below the circuit breaker trip point) and prolonged the motor-starting
time long enough for breaker to trip.
Joe Gores
Message 8
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| Subject: | Re: Search for Gremlins |
Robert L. Nuckolls, III wrote:
> Where does the battery ground?
>
>> If this report leads you to any other suggestions I will certainly
>> appreciate them.
May I expand on that? Look at the automotive world ...
The most difficult job the battery has is cranking the engine. All
modern automobiles - of which I am aware, anyway - run a large ground
cable (#4 - #00) straight from the battery to the engine. The starter
motor is grounded via the engine. Then the chassis is grounded to the
engine. Everything else is grounded to the engine, via the chassis or a
ground bus.
If you want a robust electrical system, that's a good starting point.
And yeah, I've been told before "that's cars; cars aren't airplanes".
Sorry - the physics works the same for both.
Dale R.
COZY MkIV #0497
Ch.12; Ch's 13, 16, 22 & 23 in-progress
Message 9
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| Subject: | measuring capacitance. |
Bob and others,
Can one determine the inherent capacitance of a container of water with two
metal plates? Formula?
Peter Laurence
Message 10
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| Subject: | measuring capacitance. |
Can one determine the inherent capacitance of a container of water with two
metal plates? Formula?
Peter Laurence
Peter,
What does this container of water and 2 metal plates have to do with my OBAM
aircraft???
Roger
Message 11
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| Subject: | measuring capacitance. |
Testing capacitance fuel tank gauges, perhaps?
A little broader focus beyond "..my OBAM aircraft" would be helpful.
Terry
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Roger &
Jean
Sent: Monday, August 25, 2008 11:39 AM
Subject: RE: AeroElectric-List: measuring capacitance.
<mrspudandcompany@verizon.net>
Can one determine the inherent capacitance of a container of water with two
metal plates? Formula?
Peter Laurence
Peter,
What does this container of water and 2 metal plates have to do with my OBAM
aircraft???
Roger
Message 12
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| Subject: | measuring capacitance. |
Roger,
H2 generation
Peter
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Roger &
Jean
Sent: Monday, August 25, 2008 2:39 PM
Subject: RE: AeroElectric-List: measuring capacitance.
<mrspudandcompany@verizon.net>
Can one determine the inherent capacitance of a container of water with two
metal plates? Formula?
Peter Laurence
Peter,
What does this container of water and 2 metal plates have to do with my OBAM
aircraft???
Roger
Message 13
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| Subject: | Re: measuring capacitance. |
A capacitor is a device which stores electrical energy by maintaining
separation between regions of differing charge - that is, two conductive
plates separated by an insulator.
Most real-world water is at least somewhat conductive (contaminated by
salts). The amount of contaminant which causes water to ionize and become
conductive is very low.
Coating the metal plates would allow a capacitive system to be built -
keeping there from being a short between the plates. Water between the
already insulated plates would further change the permittivity of the
system - changing it's capacitance.
So, is this question about a lab environment in which you can setup with
distilled water, and keep it clean? If so, then it is possible to
calculate the capacitance of system that has metal plates and water as the
dielectric.
If the concern is about how water effects the capacitive senders in a
modern fuel system, I think that's a different issue..
Regards,
Matt-
> <dr.laurence@mbdi.org>
>
>
> Bob and others,
>
> Can one determine the inherent capacitance of a container of water with
> two
> metal plates? Formula?
>
>
> Peter Laurence
>
>
Message 14
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| Subject: | measuring capacitance. |
Testing capacitance fuel tank gauges, perhaps?
Perhaps not?
A little broader focus beyond "..my OBAM aircraft" would be helpful.
I thought OBAM aircraft was what this forum was all about!
Roger
Message 15
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| Subject: | measuring capacitance. |
My RV-8A has capacitance fuel gauges. But then that's MY OBAM aircraft.
Terry
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Roger &
Jean
Sent: Monday, August 25, 2008 2:51 PM
Subject: RE: AeroElectric-List: measuring capacitance.
<mrspudandcompany@verizon.net>
Testing capacitance fuel tank gauges, perhaps?
Perhaps not?
A little broader focus beyond "..my OBAM aircraft" would be helpful.
I thought OBAM aircraft was what this forum was all about!
Roger
Message 16
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| Subject: | Re: measuring capacitance. |
At 10:52 8/25/2008, you wrote:
>Can one determine the inherent capacitance of a container of water with two
>metal plates? Formula?
http://www.pa.msu.edu/courses/2001spring/PHY232/lectures/capacitors/twoplates.html
For DC or low frequencies you can use e= 80 for water.
Look up values here:
http://www.asiinstruments.com/technical/Dielectric%20Constants.htm#Section%20W
Ron Q.
Message 17
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| Subject: | Re: High resistance pops breaker? |
At 12:06 PM 8/25/2008 -0400, you wrote:
>DC motors have the greatest torque and current when they are standing
>still and voltage is first applied.
Yes, zero velocity = zero counter emf. Therefore in the instant of time
were the armature is just spinning up, current draw is applied voltage
divided by internal resistance. That's the lower most end of the speed-
torque curve and is usually called "stall current".
> According to my old college book on basic electricity, a DC motor
> (with shunt winding) starting current can be up to 100 times greater than
> the full load running current.
Yes, a shunt winding has a great deal in common with
modern PM motors for starters. The magnets are so strong
that fewer turns are needed in the armature to achieve
desired performance . . . the speed torque curve is
flatter and the stall current VERY significant.
> For larger motors, a resistance type motor-starter is used to limit the
> starting current to prevent damage to the motor and also to prevent
> excessive acceleration that could damage the load. Adding resistance to
> the circuit during starting slows the acceleration and prolongs the time
> that it takes for a motor to attain normal running speed.
Correct . . . artificial increase in slope of speed-torque
curve. Torque AND inrush current are reduced.
>Getting back to that Sport Aviation article that claimed that "High
>Resistance Pops Breaker". The circuit breaker in that landing light
>circuit might have been sized to trip if the motor current was high due to
>a jammed landing-light retract mechanism. But due to the time-delay
>characteristics of circuit breakers, the breaker would not trip during
>normal motor starting even though the starting current is above the
>breaker trip point for a short time. Is it possible that there is some
>value of resistance (due to bad connections) that, when added to the
>circuit, could allow motor-starting current to flow that is still above
>the circuit breaker trip point, but for a prolonged period of time? Could
>the author of that Sport Aviation article be correct that bad connections
>did cause the circuit breaker to trip, but for entirely different reasons
>than he stated. He said that bad connections made the current go
>up. Perhaps the resistance made the current go down (but not below the
>circuit breaker trip point) and prolonged the motor-starting time long
>enough for breaker to trip.
I pondered that for a bit but I don't think so. Acceleration
of a motor to full speed takes but tens of milliseconds. The
only landing light motors I've seen were split series field
motors . . . apply (+) to one field to retract, the other
field to extend. The effect of series windings is to limit
stall current (although torque tends to get better due to
increased field flux - assuming the magnetics are not saturated).
Starting current on these relatively small mechanisms is
short in duration and not spectacular.
If the motor were jammed . . . yeah, I can see this generating
a trip but a simple cleaning/tightening of joints in the wiring
can't account for an increase of current to an I(squared)*T
value necessary to trip a breaker.
Bob . . .
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