Today's Message Index:
----------------------
1. 05:16 AM - Re: The alternator drive stand . . . (Robert L. Nuckolls, III)
2. 06:13 AM - Re: in-rush limiters (Robert L. Nuckolls, III)
3. 08:49 AM - Turning a Brushless Motor into an Alternator (John W Livingston)
4. 09:01 AM - Dividing one voltage by another using an op amp? (John W Livingston)
5. 03:04 PM - AF-2500 installation question (auido (William Gill)
6. 05:29 PM - Re: The alternator drive stand . . . (Charlie England)
7. 07:13 PM - Re: The alternator drive stand . . . (Robert L. Nuckolls, III)
8. 07:41 PM - Re: The alternator drive stand . . . (Robert L. Nuckolls, III)
9. 08:23 PM - Debating on an alternator or two batteries? (Tony Gibson)
Message 1
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| Subject: | Re: The alternator drive stand . . . |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 11:32 PM 9/3/2006 -0400, you wrote:
>--> AeroElectric-List message posted by: "Richard E. Tasker"
><retasker@optonline.net>
>
>FYI.
>
>McMaster Carr has a 5HP 230V single phase for $350 and a 5HP three phase
>(if you want to set up a phase converter with a new motor) for $230.
>
>Dick Tasker
Thanks! I'll check it out. I'm shaft-size critical for this
task. Half of the speed changer mechanism mounts directly on
the motor shaft so that feature has bounded my choices to
some degree. Appreciate the heads-up!
Bob . . .
Message 2
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| Subject: | Re: in-rush limiters |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 07:56 AM 9/1/2006 -0400, you wrote:
>--> AeroElectric-List message posted by: FLYaDIVE@aol.com
>
> >Oh! When choosing the wire size, do NOT go by the Mil-Spec wire size
> used in
> >wiring the plane. I would DOUBLE that wire size.
>
> Don't understand why. The current ratings for choosing wire
> size from charts like those found in AC43-13 or chapter
> 8 of the 'Connection are already de-rated for 10C temperature
> rise. The 6A lamp cited in the original post would not
> seriously warm an inductor wound with 22AWG (5A rated) wire.
>
> Bob . . .
>==================================
>Hello Bob:
>
>You have me smiling ...
>Now how did I know you were going to question this part :-)
>
>Let me start off by asking a LOADED QUESTION:
>
>What determines the current handling capabilities of a wire?
>
>I should wait at this point for a responce, but concidering that the question
>is also put the site's reading public ... I will guess at their answer and
>maybe yours.
>That being: The diameter, cross-sectional area of the wire.
>
>Does that sound like the most given answer? And it is a logical answer. But
>not the whole story. I did say it was a LOADED QUESTION.
>
>So to unload the answer:
>The Determining factor is the INSULATION, the thickness and type.
Sure. Cross section controls resistance, but says nothing
about ability to reject heat energy due to I(squared)R heating
combined heat transfer physics of the assembly.
>Here is why. You have to ask the questions: What fails? And How?
>There are two failures. As the wire heats up, it heats up so much that it
>MELTS the insulation. FAILURE ... This exposes the wire to do any
>combination
>of events: Fire, short to ground - case - airframe or melt into and short to
>another wire.
Yup.
>The other failure is crystalization of the wire from the heat. Usually
>repeated heat and that leads to the wire failing in an OPEN. This is not
>the norm.
> The norm is the insulation FAILING.
Temperature rises that put COPPER at risk are so much
beyond temperatures that damage insulation that failure
of the conductor is exceedingly low on the list of concerns.
>Now, most builders do use Mil-Spec wire and the Mil-Spec wire does have a
>higher tempature rating and dialectric rating. So what determines the
>current
>handling capabilities of a wire? INSULATION - Told ya it was Loaded!
Yup, this is discussed in Chapter 8.
>Lets switch to the coil construction I mentioned. You said 30 Turns ... Only
>30 Turns? Way Much More than 30 turns can fit on a form that has a 1/2" ID
>and a 1" OD and 2" Long ... That gives you 1/4" of room to build up and
>about 1
>1/4" length to fill. I haven't worked out the Henry's (inductance) of the
>coil and quite honestly it does not matter. Too much engineering and not
>enough
>practicality. I know the size will work.
Define "work". The goal is to add a SIGNIFICANT reduction in area under the
inrush current curve without degrading system performance. I guess I don't
know about "too much engineering" . . . it's been said that if the only tool
you have is a hammer, lots of things begin to look more and more like a
nail.
I'm an engineer and my first thoughts for working a problem DO focus on
the physics.
> How do I know? A life of
>experimentation! I have been getting my ass shocked since I was 11 years
>old :-)
>As the commercial says: Try it you'll like it. As we say here in NJ: Don't
>worry about it!
Whether one chooses to worry or not to worry, the physics
doesn't change.
>O! For the size of the wire -- I would suggest 18 or 16 AWG enameled
>(Transformer) wire. It should handle the current and both circuit heat
>and engine
>heat. And even with this large size wire you should be able to get way more
>than 30 turns.
Inrush Limiting 101
Agreed. Taking your adjustments to my mis-perceptions of the
hypothesized single layer coil, let us assume as follows:
1/2" od core 2" long wound with 5 layers of #16AWG wire
(0.050" diameter) for a depth on the order of .25" for a total
diameter of 1". 050" wire will take 40T to cover 2" of
length for each layer so 5 layers is 200T total.
Goto:
http://www.captain.at/electronics/coils/
. . . and plug in 200T, 1" and .5" and 2" (be sure to select
units to "inches" and we get about 300 microhenries. Assuming a
ferrite core with permeability of 10, we might push this inductance up
to 3 millihenries.
Let us further consider 16AWG wire with a resistance of about 4 milliohms
per foot. The 200T will have an average circumference of .75 x 3.14 or
or 2.3 inches. 200T offers a total length of 460 inches or 38 feet
and a resistance of 150 milliohms.
>Try it you'll like it. We are the EAA, Experiment!
Good idea. Went to the bench and measured the cold-resistance
of a 65W, halogen head lamp bulb and got 0.150 ohms. 12v applied
directly to the terminals of this lamp will produce an in-rush
current of 12.0 /0.15 = 80 Amps! Okay, lets wire it up with some
clip leads and a 12v battery and plot this puppy. Here we get
a curve like . . .
http://www.aeroelectric.com/Pictures/Curves/Exemplar_Incandescent_Lamp_Inrush.gif
Note that the peak inrush current was not 80 amps, but just
about 38 amps. Okay, this means that circuit cold-resistance
was 12/38 or 315 milliohms. Understandable. Wire used to hook
the system up combined with about 15 milliohms of battery
resistance produces a new, higher cold-resistance.
Adding your hypothesized inductor of 3 millihenries and
150 milliohms would raise the total circuit cold resistance to
315 + 150 = 460 milliohms. Adding the inductor would produce
a drop in in-rush current to about 26 amps if it exhibited
no inductive characteristics at all!
Going back to the curve we see that the time constant (measured
to 37% of the delta between peak (38A) and static (5A) or
(38-5)*.37 + 5 = 17A. The trace crosses 17A at about 15
milliseconds. At this same time, total loop resistance is on the
order of 600 milliohms without the hypothesized inductor.
I do not doubt that you observed reductions in in-rush
current as a byproduct of the actions you suggested.
It's easy to see here that adding the hypothesized inductor
will indeed cause a significant drop in the inrush current,
NOT because it's an inductor, but because it adds a
significant resistance to the circuit. The L/R time constant
for the added inductance is still much shorter than the
15 millisecond time constant demonstrated on the bench
so that the benefits of adding the inductance are small
at best.
Inrush Limiting 102
If inrush limiting is a really big thing for the designer,
there are thermal devices offered by a several manufacturers.
Here's one example:
http://www.aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/GE_Sensors/CL_limiters.pdf
In this case, we're adding to the cold-resistance of the
circuit by means of a style of thermistor . . . a temperature
sensitive resistor chosen for its NEGATIVE temperature
characteristics. The hotter it gets, the lower the resistance.
Take a look at p/n CL-30. It has a cold-resistance on the order
of 2.5 ohms. Adding this resistance in series with the
hypothetical .315 ohms cited above raises the cold-resistance
of the system to about 2.8 ohms. This will reduce the in-rush
current observed to 12 / 2.8 = 4.3 amps! Nice reduction indeed.
Now, as the thermistor is allowed to heat up, we see that
when loaded to 50% of rated load (It's a an 8A device and
our 55w lamp will load it to about 4A) its operating resistance
drops to about 140 milliohms. The power tossed off under
normal operating conditions is .14 x 4 = .56 volts x 4A
2.25 Watts. This is about the same losses as for the
hypothesized inductor cited above but with a profound
effect on in-rush current.
Caveats: The CL-30 inrush limiter must be allowed to heat
up. One cannot clamp it down against a heat-sinking surface
for mechanical support lest you soak the heat energy out.
This can cause excessive dissipation internal to the device
and failure (been there, done that). On the other hand,
the critter is mounted on 18AWG solid copper leads and
not terribly resistant to breakage under vibration. On
the GP-180 program we wrapped the limiter in fiberglas
tubing before capturing it under an aluminum bracket.
In the final analysis, builder needs to decide what return
on investment is needed on an effort to mitigate in-rush.
The original goal was to increase lamp life. In the BH
era (before halogen) there was some benefit to lamp life
by considering some form of keep warm or inrush limiting.
Nowadays, I doubt that the return on investment is
positive. The bulbs are very long lived running "barefoot"
but they're still going to fail at some point in time -
in-rush limiting is not a reliability issue.
So unless your system is vulnerable to the effects of
a 40 amp, 20 millisecond transient (shame on you if it
is!), then there's no positive return on investment I
can perceived for adding special in-rush limiting
features to your landing light system.
Bob . . .
Message 3
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| Subject: | Turning a Brushless Motor into an Alternator |
--> AeroElectric-List message posted by: "John W Livingston" <livingjw@earthlink.net>
Bob, All,
I have a project coming up that needs a small, high speed (~10K RPM or
higher), light (as practically possible) alternator which will produce about
.5KW at 30-50 volts. I was thinking of converting one of the numerous
permanent spinning magnet brushless motors that are available for RC
aircraft. My thought was to introduce appropriate diodes and turn it into a
brushless alternator. Would this be a reasonably straight forward project or
is it just a crazy idea?
Message 4
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| Subject: | Dividing one voltage by another using an op amp? |
--> AeroElectric-List message posted by: "John W Livingston" <livingjw@earthlink.net>
Bob, All,
I seem to remember from my analog computer class (yeh, I'm that old) that
you can divide using an op amp. Can anyone point me a circuit which does
this? Thanks. One of my students built an AoA indicator a couple of years
ago with a cheap differential pressure chip, but he brought the signal out
and into a digital computer that we already had installed on the airplane
for storing flight data. He then divided it by the dynamic pressure using
software. It worked great. I thought it would be fun to see how simple it
could be done using analog circuits. These pressure measuring chips are just
a couple of dollars and you would need two of them. One differential for the
angle and one absolute pressure chip for the dynamic pressure.
Message 5
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| Subject: | AF-2500 installation question (auido |
I'm getting ready to connect the audio output (pin 5 & 9 from screen
port 2, DB-9 connector) to one of the unswitched inputs of the Garmin
GMA-347. Can anyone tell me the purpose of pins 2 & 3 from that same
DB-9 connector? I have a KLN 94 GPS. Thanks in advance for your
assistance.
Bill Gill
Lee's Summit, MO
RV-7 wiring & FWF
Message 6
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| Subject: | Re: The alternator drive stand . . . |
--> AeroElectric-List message posted by: Charlie England <ceengland@bellsouth.net>
Robert L. Nuckolls, III wrote:
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <nuckollsr@cox.net>
>
> I took a short trip yesterday in 'ol blue (a truck I inherited from
> Dad) to take a look at the alternator drive stand I spoke of last
> week. What a magnificent machine! Motor controlled variable speed
> drive, well instrumented, self contained system simulator with
> batteries, really beefy carbon pile load. Minimal barn-bird-crap
> and rust. Best yet, mounted on casters.
>
> Now the down side . . . it's fitted with a 10 hp, 440v three-phase
> motor. I've been digging through the catalogs for reasonable
> replacements that will run from the electron-pipe that comes into
> my house.
>
> I think I've identified a 5 hp, 240v single phase with the right
> shaft diameter . . . and it's only $400 plus another $100 shipping.
> When you're talking this size of motor, they start getting HEAVY!
>
> I've made an agreement with the current owner to take over his
> project with the proviso that he has access to it as needed and
> that if I decide to get rid of it, he has first crack at it at
> the "brother-in-law" price. Sounds like a deal to me.
>
> I may well have this puppy up and running in my shop before
> the end of the year.
>
>
> Bob . . .
New versions of 3phase converters ain't as expensive as the old days ( &
ship a lot cheaper):
http://www1.mscdirect.com/CGI/N2DRVSH
Should be a lot easier to install, too.
I wish I had known this before I had 3phase run to my house & hangar.
Charlie
Message 7
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| Subject: | Re: The alternator drive stand . . . |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>
>New versions of 3phase converters ain't as expensive as the old days ( &
>ship a lot cheaper):
>
>http://www1.mscdirect.com/CGI/N2DRVSH
>
>Should be a lot easier to install, too.
>
>I wish I had known this before I had 3phase run to my house & hangar.
>
>Charlie
Great data point! Thanks. I'll look into this technology.
Bob . . .
Message 8
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| Subject: | Re: The alternator drive stand . . . |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>
>New versions of 3phase converters ain't as expensive as the old days ( &
>ship a lot cheaper):
>
>http://www1.mscdirect.com/CGI/N2DRVSH
>
>Should be a lot easier to install, too.
>
>I wish I had known this before I had 3phase run to my house & hangar.
Good info Charlie. Did some surfing on the
static converter topic and picked up some
good information. Thanks for the heads-up!
Bob . . .
Message 9
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| Subject: | Debating on an alternator or two batteries? |
Hi Group, my name's Tony Gibson, I've been a lurker on the list for almost a year
now and am building a Sonerai 2L - read 550lb slightly underpowered two place!
:)
I'm trying to take as much weight out of the plane as I can by keeping it simple.
There's a lot of reasons I'm considering two batteries rather than a battery
and an alternator. But saving a bit of weight isn't the main reason, the
fact that I can move the weight of battery where ever I want in the plane is
a big bonus for servicing it nevermind balancing, and ....the last thing I will
do is put lead weight back into it!
I have an ignition system that draws ~1 amp and a single fuel pump that draws
another amp. I decided against the starter and the only other amp draws will
be two small Stratomaster instruments drawing less than half an amp together.
Total draw would be less than 2.5 Amps
With the right warning system to indicate a low primary battery I'm wondering
if something like a 3 - 5 Ah battery would be large enough for a backup? What
about the primary?
The downside of course is what would I do on a crosscountry trip? Argh! :)
Thanx a lot, appreciate any help and opinions!
Tony
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