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'[OT]: Balloons and wires'
2000\08\10@215832 by Sean Breheny

face picon face
Hi all,

Ready for another one of my weird questions?! Yes, it has to do with my
recent rocket project (mentioned here about 1.5 months ago), and yes, that
is almost at completion.

I want to suspend some LEDs (high power IR LEDs) from a balloon(40 inch
diameter using helium) which will be tethered to the ground at about 100 to
150 feet altitude on a day with calm or no wind. Rather than try to make
the balloon carry the weight of batteries AND a tether, I was thinking of
using wires (2 of them, 22 AWG each) as the tether, and putting the
batteries on the ground. (It will be far away from any power lines).

A few safety issues come to mind and I'd like to see what you guys think.
this thing would probably be really dangerous if there was any lightning
near by, so I won't try it if the weather looks iffy. However, I am aware
that there is a considerable electric field in the atmosphere even in fair
weather. So, should I take any additional precautions besides grounding
both wires where they meet the ground? (I should be able to ground both
because the voltage will only be about 12 volts and can certainly tolerate
some leakage).

Thanks,

Sean

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
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2000\08\11@030931 by Michael Rigby-Jones

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{Quote hidden}

Depending on soil conditions you might get quite a bit of leakage.  Not to
mention your grounding posts getting icky through the electrolotyic action.
I would have thought grounding just one side would have been fine, the
battery does have a pretty low impedance so the non-grounded side shouldn't
be able to be raised to a very high potential at all.

Mike

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2000\08\11@072027 by Peter L. Peres

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>40" He ballon

What is the net lifting power of that ?

Static over 100 feet is not so terrible, but you should ground the wires
using a large tent nail driven into the ground imho.

On nice dry days with no wind static could be significant but I have never
heard of anything bad happening.

Peter

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2000\08\11@072644 by Andrew Kunz

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NO SEAN NO!!

Definitely fly the power supply.  It isn't that heavy!  It takes a long time to
discharge some NiMH or Li cells!

Even if there's NO "iffy" weather, you are creating a big potential by doing
this!!  _Any_ wind will create a potential across your setup.

Andy









Sean Breheny <.....shb7KILLspamspam.....CORNELL.EDU> on 08/10/2000 09:58:01 PM

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Subject: [OT]: Balloons and wires








Hi all,

Ready for another one of my weird questions?! Yes, it has to do with my
recent rocket project (mentioned here about 1.5 months ago), and yes, that
is almost at completion.

I want to suspend some LEDs (high power IR LEDs) from a balloon(40 inch
diameter using helium) which will be tethered to the ground at about 100 to
150 feet altitude on a day with calm or no wind. Rather than try to make
the balloon carry the weight of batteries AND a tether, I was thinking of
using wires (2 of them, 22 AWG each) as the tether, and putting the
batteries on the ground. (It will be far away from any power lines).

A few safety issues come to mind and I'd like to see what you guys think.
this thing would probably be really dangerous if there was any lightning
near by, so I won't try it if the weather looks iffy. However, I am aware
that there is a considerable electric field in the atmosphere even in fair
weather. So, should I take any additional precautions besides grounding
both wires where they meet the ground? (I should be able to ground both
because the voltage will only be about 12 volts and can certainly tolerate
some leakage).

Thanks,

Sean

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
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2000\08\11@081216 by Andy Howard

picon face
----- Original Message -----
From: "Sean Breheny" <KILLspamshb7KILLspamspamCORNELL.EDU>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Friday, August 11, 2000 2:58 AM
Subject: [OT]: Balloons and wires


> Hi all,
>
> Ready for another one of my weird questions?! Yes, it has to do with my
> recent rocket project (mentioned here about 1.5 months ago), and yes, that
> is almost at completion.
>
> I want to suspend some LEDs (high power IR LEDs) from a balloon(40 inch
> diameter using helium) which will be tethered to the ground at about 100
to
{Quote hidden}

I'd still be inclined to hoist the power source instead. If you use an Li
rechargeable (mobile phone battery for example) the weight won't very
different to several hundred feet of wire anyway. And as you say, even
without lightning there will be a significant buildup, and even on a still
day there is wind at higher altitudes.

If the battery life with Li still won't be enough then maybe you can change
the duty cycle of the LEDs to extend it. Another point to consider is the
resistive losses in your long, thin wires.

P.S. If you do go for using wires don't rely on them to secure the balloon,
use some kite line to take the mechanical strain, it's very light and
designed to do the job and means you won't lose your target in the event of
an unexpected breeze.

Good luck with the flight.

Cheers,

Andy.








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2000\08\11@085818 by M. Adam Davis

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LEDs don't need much power.  If a battery is too expensive (weight wise) then
you can get solar cells which will work well (unless doing this at night, which
I half suspect)

-Adam

Sean Breheny wrote:
{Quote hidden}

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2000\08\11@090101 by Andy Howard

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----- Original Message -----
From: "Andrew Kunz" <TakeThisOuTakunzEraseMEspamspam_OUTTDIPOWER.COM>
To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Friday, August 11, 2000 12:26 PM
Subject: Re: [OT]: Balloons and wires


> NO SEAN NO!!
>
> Definitely fly the power supply.  It isn't that heavy!  It takes a long
time to
> discharge some NiMH or Li cells!


Agreed.

E.g. the battery from my cellphone gives 4.1V offload, 3.8V nominal, and is
rated at 850mAH. It weighs 25 grams (less than an ounce) according to my
kitchen scales.
From a chart I found online 22 AWG wire weighs in at 1.9 lb/1000ft, i.e. you
could loft some 8 of those batteries (6.8 AmpHours) for the weight of the
wire required.

Another point to consider is the resistance of 22 AWG stranded copper wire
(around 5-6 ohms for the distance mentioned if my calculations are correct).












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2000\08\11@091142 by Graham North

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What about solar power!

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2000\08\11@103156 by stouchton

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I actually have experience here!!!!!!!!! :)

Been flying a blimp that is 52" long and about 30" wide.  Amazing lifting
capability.  3 electric motors, lithium battery, plastic gondola, propellers
and mounting arrangement and about 30 pennies to get to neutral bouyancy.

So... I don't see the problem with lifting the LED's and the battery.  The
tether will add weight but I can't see it as being as much as 30 pennies.

Been thinking about hydrogen also... apparantly has 4 times the lifting
capability of helium.

{Original Message removed}

2000\08\11@180826 by Sean Breheny

face picon face
Thanks to everyone for the responses.

As for the LED power, they are REALLY power hungry (this thing puts out
pulses of nearly a watt of 880 nm IR! - it's an array of 15 24 mW IR
emitters, each being pulsed at a 50% duty cycle at a little more than
200mA, which gives about 48mW out each), it draws an average current of
about a half an amp(the LEDs are in groups of three, so there are only 5
200mA paths at 50% duty). I suppose flying the power supply is possible,
but it will probably require two balloons, instead of one. Solar power is
not an option, even though it will be during the day.

Pulsing at a lower duty cycle probably wouldn't work either because it
would require increasing the bandwidth of the receiver (and hence the
background noise).

I thought that a conductive path to ground would actually make something
like this SAFER, because the static charge wouldn't have a chance to build
up. If I use kite line (as someone suggested), wouldn't I have to worry
about touching the balloon after taking it down?!

I would prefer not to use NiCds for this because it is a one-time
application. However, I might have to (due to their lower internal R)
because I found that even a pack of 8 D-cells (in series) drops by about
1.5 volt when drawing the kind of current this needs.

Any other suggestions?

Thanks again,

Sean



At 10:21 AM 8/11/00 -0400, Stouchton wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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Personal page: http://www.people.cornell.edu/pages/shb7
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2000\08\11@192338 by David Duley

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On Fri, 11 Aug 2000 18:07:06 -0400, you wrote:

{Quote hidden}

Hi Sean,

Don't use a direct path to ground.  Use a spark gap.  There are
several companies that make devices for this purpose.  Look for "spark
gap" or "Gas discharge tubes"  The look like overgrown diodes.  They
are very high resistance except when the threshold voltage is reached.
Then they conduct and they conduct very fast.

Check out http://www.lumex.com

Look under products and then gas discharge tubes.

Best regards

David Duley

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2000\08\11@225946 by Bob Ammerman

picon face
Um, Is this really any different than a 100' to 150' long antenna?

I see lots of those.

I don't really think there is too much trouble here.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
sofftware)

> Sean Breheny wrote:
> >
> > Hi all,
> >
> > Ready for another one of my weird questions?! Yes, it has to do with my
> > recent rocket project (mentioned here about 1.5 months ago), and yes,
that
> > is almost at completion.
> >
> > I want to suspend some LEDs (high power IR LEDs) from a balloon(40 inch
> > diameter using helium) which will be tethered to the ground at about 100
to
> > 150 feet altitude on a day with calm or no wind. Rather than try to make
> > the balloon carry the weight of batteries AND a tether, I was thinking
of
> > using wires (2 of them, 22 AWG each) as the tether, and putting the
> > batteries on the ground. (It will be far away from any power lines).
> >
> > A few safety issues come to mind and I'd like to see what you guys
think.
> > this thing would probably be really dangerous if there was any lightning
> > near by, so I won't try it if the weather looks iffy. However, I am
aware
> > that there is a considerable electric field in the atmosphere even in
fair
> > weather. So, should I take any additional precautions besides grounding
> > both wires where they meet the ground? (I should be able to ground both
> > because the voltage will only be about 12 volts and can certainly
tolerate
{Quote hidden}

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2000\08\11@231010 by mjb

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Sean Breheny wrote:
>
> Any other suggestions?
>
> Thanks again,
>
> Sean
>

A few years ago I went on a job interview at a research lab- one of the
guys there was a high voltage (AC) power supply designer, specifically
to power very power hungry equipment in aerostats.  If my memory serves-
he just had one conductor- hence the AC, and I guess his return path was
just free space capacitance.  That may be a bit extreme for you, but
consider going to higher voltage, then the resistive losses from the
wire won't matter as much, so you can go to a thinner diameter wire.  If
you can handle putting possibly dangerous voltages on your wire with a
buck converter up high- this can be pretty efficient.

Also,think about this: instead of putting them in groups of three- wire
them all in series, and use a current source on the ground to pulse
them. You will have to live with some capacitance (twisted pair 30 ga
wire is 1pf/in, I think) from the wire, but it will probably be small
with respect to the LEDs.

Matt Bennett
RemoveMEmjbEraseMEspamEraseMEhazmat.com

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2000\08\12@004642 by Sean Breheny

face picon face
Hi Bob,

Possibly not, but I thought maybe there was a difference because AFAIK, the
E field vector in the atmosphere usually points perpendicular to the
ground, so you would have a potential difference between 0 and 100 feet up,
however, going horizontally, you wouldn't.

Sean

At 10:22 PM 8/11/00 -0400, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
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2000\08\12@104029 by Thomas McGahee

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Sean,

You can lessen the effects due to the internal resistance of the
batteries if you place a large value electrolytic cap in parallel
with the battery. This increases the weight, of course, but
experiment and find out what is the smallest value that does the
trick. The newer capacitors pack a lot of capacitance into a
fairly small size. Choose a voltage rating that is very close
to the maximum voltage coming from your battery pack.

Fr. Tom McGahee

{Original Message removed}

2000\08\12@234644 by Donald L Burdette

picon face
I was going to suggest (as Matt Bennett already did) putting the LED's in
series and pulsing them with higher V, lower I.  If you did this you
could use #36 magnet wire, which has a resistance of about 0.4 ohms/foot,
for a total of 120 ohms.  It makes a nice little current limiting
resistor!  If you use such fine wire, definitely use a kite string for
tethering the baloon!

As to using Hydrogen - Helium should have a density about 1/8 that of
air.  That means that even a complete vacuum would have a lifting power
only about 14% greater than helium.  And I'm guessing that H2, with a
molecular weight of 2, would have about half the density of He, which has
a molecular (atomic) weight of 4, giving it around 7% more lifting power.
Hydrogen was used because it was more easily available, not because it
was better.

As for grounding vs. isolating the balloon, IIRC the atmospheric electric
field is normally in the range of several 100's of volts/meter.  Even if
it were 1000 V/m, then an object at the end of a 50 meter wire would
develop a static charge of 50 kV with respect to ground.  That's enough
to jump nearly 2 inches and give a painful shock, and plenty to fry your
electronics, but not really dangerous.  Spark gaps are used in things
like antennas and telephone wires because these must have high impedance
to ground under normal circumstances, and low impedance when the voltage
gets excessive - perfect application for a spark gap.

So - I'm for using helium balloons, batteries on the ground, grounded
(one side only), thin wires, and kite string.

P.S. I just looked up gas densities
(http://www.vcs.ethz.ch/chemglobe/ptoe/) and my guesses were pretty
close.
He -0.178 grams/liter at 273 degrees kelvin (0 degrees C)
H2 - 0.090 g/l
O2 - 1.43 g/l
N2 - 1.25 g/l
Air (calculated) 1.3 g/l


Don

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2000\08\12@235531 by David VanHorn

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>.
>  Hydrogen was used because it was more easily available, not because it
>was better.

Indeed. The US was pissed at Germany, and we have all the Helium mines.


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2000\08\13@122845 by Donald L Burdette

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>>  Hydrogen was used because it was more easily available, not because
it
>>was better.

>Indeed. The US was pissed at Germany, and we have all the Helium mines.

Actually, the site where I found the data says that most of the world's
helium comes from natural gas wells in the US and Poland.  So Germany
would have had access to Helium, though perhaps they didn't know it then.

Don

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2000\08\13@145718 by David VanHorn

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>
> >Indeed. The US was pissed at Germany, and we have all the Helium mines.
>
>Actually, the site where I found the data says that most of the world's
>helium comes from natural gas wells in the US and Poland.  So Germany
>would have had access to Helium, though perhaps they didn't know it then.

Natural gas well / helium mine. It's nice that you don't have to haul it
out though :)

Germany wouldn't have had a lot of luck getting anything with military
applications at that point in time from her neighbors.
Russia has a huge supply too, IIRC, the US and russia are nearly equal, and
have something like 80% of the supply.
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2000\08\13@161237 by Lance Allen

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On 13 Aug 2000, at 12:33, Donald L Burdette wrote:

> >>  Hydrogen was used because it was more easily available, not because
> it
> >>was better.
>
> >Indeed. The US was pissed at Germany, and we have all the Helium mines.
>
> Actually, the site where I found the data says that most of the world's
> helium comes from natural gas wells in the US and Poland.  So Germany
> would have had access to Helium, though perhaps they didn't know it then.
>
At risk of going off into the weeds.....
Recent research has revealed the Hindenberg's skin was
impregnated of some sort of Nitrate and a static discharge set if off,
the Hydrogen didnt catch until the whole thing was alight stem to
stern (note the airship was still floating and level when it was
burning, also hydrogen has a pretty much invisible flame).
BTW the Germans knew this around 1 week after the disaster, but
kept it quiet.


_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

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2000\08\13@174152 by Sean Breheny

face picon face
Thanks again to all who replied.

What I didn't make clear is that I will be doing this in a matter of days
and my LED pulsing setup is already designed and built(and works), so I
can't make major changes to it electronically. It already has a large
electrolytic right across the power supply on the same board as the
LEDs(thanks for the suggestion, Fr. Tom). It uses a 16F84 to pulse the LEDs
(via a TIP120) at an exact rate of 2907 Hz. The current being drawn by it
is fairly constant (about 15% ripple on it). Even so, it causes a volt or
so drop from a string of 8 D cells in series (they might not be the
absolute freshest D cells).

I think I am going to split the difference. I am going to try to fly the
supply (possibly a bunch of fresh A cells, and might add a few more than 8
to keep the voltage up), but also have a 10 foot or so copper wire dangling
down which will contact the ground first, to discharge the thing before I
touch it. I'll use kite string as suggested. I think I'll also use one more
balloon than is necessary, in case one gets popped. (a 40" He balloon can
lift about 1.2 pounds according to my calculations).

If I do end up using wires to the ground, I would either ground both or use
a switch which would ground the second one when not connected (I was
planning on having a switch to turn it off due to the high current drain).

Thanks again, and I will be sure to let you guys know how it goes. The
rocket is coming together nicely, and has TWO PICs in it :-) A 16F876 and a
16F84. The sensor works pretty well with the addition of a 38 mm lens. I
plan on having video of it, and might digitize it and put it on my web site
if it isn't too embarrassing (like a "lawn dart" maneuver right after
launch) <VBEG>!

Sean



At 11:51 PM 8/12/00 -0400, Donald L Burdette wrote:
>So - I'm for using helium balloons, batteries on the ground, grounded
>(one side only), thin wires, and kite string.
>

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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2000\08\13@194758 by Jinx

face picon face
> Natural gas well / helium mine. It's nice that you don't have to haul it
> out though :)

I read a book on helium once. Couldn't put it down

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2000\08\14@043348 by Alan B. Pearce

face picon face
>Recent research has revealed the Hindenberg's skin was
>impregnated of some sort of Nitrate and a static discharge set if off,
>the Hydrogen didnt catch until the whole thing was alight stem to
>stern (note the airship was still floating and level when it was
>burning, also hydrogen has a pretty much invisible flame).
>BTW the Germans knew this around 1 week after the disaster, but
>kept it quiet.

It sounds like you saw a documentary that was shown here in the UK about a year
ago, where a retired NASA scientist investigated the disaster. He found that the
outer skin was impregnated with a mix of bronze, iron oxide, and aluminium IIRC.
His response when he realized what this was, "I know that stuff, its solid
rocket propellant". He came to the conclusion this was set off by a static
discharge, and gave the flame its colour.

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2000\08\14@071216 by Andrew Kunz

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NiMH.  A 1200mAH NiMH cell is the size of a AA.

They have very low internal R (100A is possible!) so the dropout is nothing.

You said nothing about duration of flight.  If 2 hours is acceptable, a single
NiMH pack will do nicely.

Andy








Sean Breheny <EraseMEshb7spamEraseMECORNELL.EDU> on 08/11/2000 06:07:06 PM

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Subject: Re: [OT]: Balloons and wires








Thanks to everyone for the responses.

As for the LED power, they are REALLY power hungry (this thing puts out
pulses of nearly a watt of 880 nm IR! - it's an array of 15 24 mW IR
emitters, each being pulsed at a 50% duty cycle at a little more than
200mA, which gives about 48mW out each), it draws an average current of
about a half an amp(the LEDs are in groups of three, so there are only 5
200mA paths at 50% duty). I suppose flying the power supply is possible,
but it will probably require two balloons, instead of one. Solar power is
not an option, even though it will be during the day.

Pulsing at a lower duty cycle probably wouldn't work either because it
would require increasing the bandwidth of the receiver (and hence the
background noise).

I thought that a conductive path to ground would actually make something
like this SAFER, because the static charge wouldn't have a chance to build
up. If I use kite line (as someone suggested), wouldn't I have to worry
about touching the balloon after taking it down?!

I would prefer not to use NiCds for this because it is a one-time
application. However, I might have to (due to their lower internal R)
because I found that even a pack of 8 D-cells (in series) drops by about
1.5 volt when drawing the kind of current this needs.

Any other suggestions?

Thanks again,

Sean



At 10:21 AM 8/11/00 -0400, Stouchton wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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2000\08\14@071428 by Russell McMahon

picon face
>I read a book on helium once. Couldn't put it down


Was that a joke ? :-)
Books on Helium and Hydrogen are indeed liable to inspire levity.



RM

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2000\08\14@072634 by Jinx

face picon face
> >I read a book on helium once. Couldn't put it down
>
> Was that a joke ? :-)
> Books on Helium and Hydrogen are indeed liable to inspire levity.
>
> RM

You didn't think I'd pass up the chance to use the only helium joke
I know do you ? Might be years before I get another chance. Sorry
Paul

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2000\08\14@084646 by Jinx

face picon face
> >I read a book on helium once. Couldn't put it down
>
> Was that a joke ? :-)
>
> Books on Helium and Hydrogen are indeed liable to inspire levity.
>
> RM

Just a bit of light reading

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2000\08\14@085313 by D Lloyd

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part 1 1076 bytes content-type:text/plain; charset=us-ascii

These jokes are so good! They're a gas....



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 |14/08/2000 01:49 PM                                                     |
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Please respond to pic microcontroller discussion list <TakeThisOuTPICLISTKILLspamspamspamMITVMA.MIT.EDU>

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Subject:  Re: [OT]: Balloons and wires

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> >I read a book on helium once. Couldn't put it down
>
> Was that a joke ? :-)
>
> Books on Helium and Hydrogen are indeed liable to inspire levity.
>
> RM

Just a bit of light reading

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2000\08\14@092044 by Don Hyde

flavicon
face
I would suggest lithium primary cells that are used in digital cameras.  We
use them for battery-powered transmitters and they are fantastic.  2/3A
cells are available at the Walgreen's drugstore next door here, and are good
for something like an amp-hour at 3V.  They're expensive ($5-$6 at the
drugstore), but they're very light.  Their internal impedence is so low that
it is illegal to pack them densely in boxes for shipment lest they somehow
get shorted out and explode, though some of the engineers here tell me that
they now have internal fuses set at several amps for just that reason.

I know I've seen them running at 1.5A or more, and the voltage hardly sags
until they are empty.

> {Original Message removed}

2000\08\14@092644 by Jinx

face picon face
(: groan :)

> These jokes are so good! They're a gas....
>
> > >I read a book on helium once. Couldn't put it down
> >
> > Was that a joke ? :-)
> >
> > Books on Helium and Hydrogen are indeed liable to inspire levity.
> >
> > RM
>
> Just a bit of light reading

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2000\08\14@092655 by M. Adam Davis

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Donald L Burdette wrote:
> If you did this you
> could use #36 magnet wire...
> If you use such fine wire, definitely use a kite string for
> tethering the baloon!

Just note that most strings and ropes will stretch far more than wire, and the
wire will end up carrying a lot of the load.

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2000\08\14@093258 by D Lloyd

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part 1 1233 bytes content-type:text/plain; charset=us-ascii

That bad, huh?
I knew I heard a drum roll and a clash of cymballs with the punch line ;-)



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cc:    (bcc: Dan Lloyd/GBPTD/ABB)
Subject:  Re: [OT]: Balloons and wires

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(: groan :)

{Quote hidden}

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2000\08\14@093923 by M. Adam Davis

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To reduce the resistance in the battery cells, put smaller patteries in series.

Ideally the resistance of the load will match (or be higher) than the resistance
of the battery pack.  You would have better luck if you replaced each D cell
with four AA or AAA cells in parallel.

You may even be able to make up for some of the losses by building your cells
into a 6v pack and using a switching power supply to up it to your needed
voltage.

-Adam

Sean Breheny wrote:
> I would prefer not to use NiCds for this because it is a one-time
> application. However, I might have to (due to their lower internal R)
> because I found that even a pack of 8 D-cells (in series) drops by about
> 1.5 volt when drawing the kind of current this needs.
>
> Any other suggestions?

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