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'[EE] Heatsinking 1N400x diodes.. .'
2006\03\18@115905 by Russell McMahon

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Has anyone successfully heat sunk 1N400x diodes?

Filtering out the

   - add more copper
   - change the orientation/location/...
   - use larger diodes
   - use a bridge
   - use a fan
   - liquid cool / heat pipe / transcendental meditation ...
   - get a life ...

responses :-)

I'm actually interested in things done to get more heat out of 1N400x
diodes.
PCB copper is about at a maximum.
Lead lengths are small (which is meant to be best)
They are where they are at present.
They are operating within nominal spec but get far hotter than I'd
like them to.
(They handle under 1A mean but current is pulsed at rather more so
heating is disproportionately high

16 diodes are in two parallel rows of 8
I vaguely toyed with the idea of clamping a heatsink bar along a row.
Contact an issue - thermal goo or conductive washer.
Uneven mounting height an issue.
I can imagine that even a very modestly sized an L or inverse T of
aluminum in conduct with the diode bodies would offer far better
cooling than at present.

Coating in a thermally conductive compound that doesn't creep may
assist. And may not.

Thoughts? Experiences?


       Russell McMahon




2006\03\18@122057 by Peter Todd

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On Sun, Mar 19, 2006 at 04:55:33AM +1200, Russell McMahon wrote:
{Quote hidden}

My highly untested advice would be to take a nice big copper bottom heat
sink, and place it ontop of the diodes such that it doesn't short out
anything important. Fill the airspace with thermally conductive potting
compound and you should be set. Hopefully any uneven mounting heights
will be taken up by the compound.

I say copper heatsink because it'll conduct heat better than aluminum
heat sinks, though aluminum radiates heat better...

--
spam_OUTpeteTakeThisOuTspampetertodd.ca http://www.petertodd.ca

2006\03\18@124948 by Bob Axtell

face picon face
The simplest solution, assuming the reverse voltage rating can take it,
is to use Schottky devices, The drop will be much less, so heating will
be manageable.

Schottky diodes also switch faster, further reducing the heat losses.

--Bob

Russell McMahon wrote:

{Quote hidden}

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2006\03\18@125557 by Vasile Surducan

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On 3/18/06, Russell McMahon <apptechspamKILLspamparadise.net.nz> wrote:
> Has anyone successfully heat sunk 1N400x diodes?
>
> Filtering out the
>
>    - add more copper
>    - change the orientation/location/...
>    - use larger diodes
>    - use a bridge
>    - use a fan
>    - liquid cool / heat pipe / transcendental meditation ...
>    - get a life ...
>
> responses :-)
>
> I'm actually interested in things done to get more heat out of 1N400x
> diodes.
> PCB copper is about at a maximum.
> Lead lengths are small (which is meant to be best)


On old TV receivers, switching diodes are heated using a copper
heatsink connected on anode (anyway on the terminal where silicium
chip is directly soldered -without any thin wire-, broke a diode and
see which is)
However using 1N400x in parallel is a curious thing for an old  capitalist...
:)
cheers,
Vasile


{Quote hidden}

> -

2006\03\18@125859 by Lars Bloch Gravengaard

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----- Original Message -----
From: "Russell McMahon" <.....apptechKILLspamspam.....paradise.net.nz>
To: "PIC List" <EraseMEPICLISTspam_OUTspamTakeThisOuTMIT.EDU>
Sent: Saturday, March 18, 2006 5:55 PM
Subject: [EE] Heatsinking 1N400x diodes.. .


>
> I'm actually interested in things done to get more heat out of 1N400x
> diodes.

Why not change the 1N400x  to a 1N5407 ?

1N4007 = Thermal Resistance, Junction to Ambient 50 °C/W
1N5407 = Thermal Resistance, Junction to Ambient 20 °C/W

Lars

2006\03\18@131115 by Dwayne Reid

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At 09:55 AM 3/18/2006, Russell McMahon wrote:
>Has anyone successfully heat sunk 1N400x diodes?

I have.  Stand the diodes up on end.  One end goes into the PCB.  The
other end goes into a strip of 16 gauge copper punched or drilled
with the correct size holes at the correct spacing.  Solder quickly
so as not to destroy the diodes - I used to use my old Weller
soldering gun or a 100W Weller soldering iron with large tip.

I've done it 2 ways: 1) the strip of copper (1/2" wide or so) is
parallel to the PCB or 2) the strip of copper is bent into an "L"
shape.  The short part of the "L" is bolted to the PCB, the long part
is right next to the diodes.  The diodes are inserted vertically into
the PCB and soldered.  The free end of the diode leads are folded
over the copper strip and soldered.

I see the same thing done in modern switch-mode power supplies.

dwayne

--
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2006\03\18@153957 by Wouter van Ooijen

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> I'm actually interested in things done to get more heat out of 1N400x
> diodes.

What I often see in SMPSes is a diode that is vertical to the PCB, with
the high side connected to an L-shaped slab of metal (other side of this
slab is connected to the PCB). Heatsinking with the top wire as heat
conductor. I think the housing itself is not designed to conduct heat
very well, so the wire might be the best way out for the heat. Probably
one wire is better than the other.

Wouter van Ooijen

-- -------------------------------------------
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consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\03\18@173120 by Peter Todd

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On Sat, Mar 18, 2006 at 11:11:10AM -0700, Dwayne Reid wrote:
> At 09:55 AM 3/18/2006, Russell McMahon wrote:
> >Has anyone successfully heat sunk 1N400x diodes?
>
> I have.  Stand the diodes up on end.  One end goes into the PCB.  The
> other end goes into a strip of 16 gauge copper punched or drilled
> with the correct size holes at the correct spacing.  Solder quickly
> so as not to destroy the diodes - I used to use my old Weller
> soldering gun or a 100W Weller soldering iron with large tip.

If you are going to do something like that, could you heat up the whole
assembly in a toaster oven with solder paste like they do for SMT
devices? Would save you having to mess around with 100W irons I think,
maybe even cause less thermal stress as the whole assembly, rather than
little points, would be heated.

Depends if the diodes can take a reflow cycle of course.

--
@spam@peteKILLspamspampetertodd.ca http://www.petertodd.ca

2006\03\19@192422 by Robert Ammerman

picon face
Cut a hole in the PCB directly below them.

Physically mount them elevated from the PCB.

Make small heatsinks out of a piece of AL extrusion normally used to make
window screens. The diode snaps into the place where the screen bead
normally goes.

Bob Ammerman
RAm Systems


{Original Message removed}

2006\03\19@194030 by Russell McMahon

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> However using 1N400x in parallel is a curious thing for an old
> capitalist...
> :)

The diodes are in 2 rows of 8 but are not electrically parallel.
They form 4 full wave bridges.

Others:

Peak DC in is approaching 200 volts. Schottkys tend to get rare and
dear as voltage rises.

Larger diodes (eg 1N540x) would be happier. But they take more room
and cost (slightly) more - and are not already there ;-)

As all 4 bridges feed a common rail the suggested heatsinks at one end
can be retrofitted to the existing design and may be worthwhile.



       RM

2006\03\20@082939 by Alan B. Pearce

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>16 diodes are in two parallel rows of 8
>I vaguely toyed with the idea of clamping a
>heatsink bar along a row. Contact an issue -
>thermal goo or conductive washer. Uneven
>mounting height an issue. I can imagine that
>even a very modestly sized an L or inverse T
>of aluminum in conduct with the diode bodies
>would offer far better cooling than at present.
>
>Coating in a thermally conductive compound
>that doesn't creep may assist. And may not.

My initial reaction would be to see if using the 3A version (1N54xx?) would
give cooler operation, based on the larger die area producing a lower
current per square, hence lower voltage drop. Also larger body to help
radiate the heat.

As an alternative I would look at using the little finned heatsinks that
were made for use on ECL chips, glued on with thermal conducting epoxy. Use
the epoxy as a filler to deal with the uneven heights.

2006\03\20@100151 by Peiserma

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> > Coating in a thermally conductive compound that doesn't creep may
> > assist. And may not.
>
> My highly untested advice would be to take a nice big copper
> bottom heat sink, and place it ontop of the diodes such that
> it doesn't short out anything important. Fill the airspace
> with thermally conductive potting compound and you should be
> set. Hopefully any uneven mounting heights will be taken up
> by the compound.

The problem you may run into is coefficient of expansion.

According to a colleage, glass-passivated diodes seemed to be the most
fragile in this respect (Although you're probably using regular silicon
diodes). You would want to test several compounds to determine which is
suitable, which is the approach this division (used to be Marconi) took.
Some compounds caused the junction of the diode to separate with
repeated cycling.

2006\03\20@105348 by David VanHorn

picon face
Interesting thought..

Glass encapsulated diodes were presumably once heated to nearly the
temperature of molten glass.
You'd think they would tolerate high temperatures pretty well, although that
initial event was not done with concurrent electrical stresses.

2006\03\20@133704 by Peiserma

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> Glass encapsulated diodes were presumably once heated to
> nearly the temperature of molten glass.
> You'd think they would tolerate high temperatures pretty
> well, although that initial event was not done with
> concurrent electrical stresses.

But in the case of encapsulating them with potting compound, it was the
mechanical stress due to different coefficients of thermal expansion
that led to their demise.

2006\03\20@144328 by David VanHorn

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>
> But in the case of encapsulating them with potting compound, it was the
> mechanical stress due to different coefficients of thermal expansion
> that led to their demise.


That's what I was wondering, wether the pulse heating would lead to
mechanical stresses that would crack the die.  The semi and glass have to
have pretty well matched coefficients, but if one heats up significantly
before the other, then that might not be enough to save you.

2006\03\20@154404 by Peter Todd

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On Mon, Mar 20, 2006 at 10:53:46AM -0500, David VanHorn wrote:
> Interesting thought..
>
> Glass encapsulated diodes were presumably once heated to nearly the
> temperature of molten glass.
> You'd think they would tolerate high temperatures pretty well, although that
> initial event was not done with concurrent electrical stresses.

That's a very good point... Anyone got any sure info how are glass
encapsulated diodes encapsulated? I'm very curious.

--
KILLspampeteKILLspamspampetertodd.ca http://www.petertodd.ca

2006\03\21@144024 by Peter

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On Mon, 20 Mar 2006, Peter Todd wrote:

{Quote hidden}

They use low temperature glass. You can melt it in a lighter's flame.
Melts at about 350-450 deg. C or so afaik. Some soldering irons can get
that hot.

Peter

2006\03\21@204424 by Peter Todd

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On Tue, Mar 21, 2006 at 09:40:23PM +0200, Peter wrote:
> > That's a very good point... Anyone got any sure info how are glass
> > encapsulated diodes encapsulated? I'm very curious.
>
> They use low temperature glass. You can melt it in a lighter's flame.
> Melts at about 350-450 deg. C or so afaik. Some soldering irons can get
> that hot.

Are there any thing about this glass that are different than normal
glass? Especially weak?

See, I'm thinking you could easilly make Nixie tubes with this stuff...
The fabrication would be fairly easy at low temperature, and aparently
the requierments for Nixie tubes in terms of gasses and purity are very
similar to neon tubes. It'd be nice to be able to assemble a stack of
glass with the electrodes in it, and then seal it at the edges.

A souped-up toaster oven could reach 450C I think...

--
RemoveMEpeteTakeThisOuTspampetertodd.ca http://www.petertodd.ca

2006\03\21@215646 by Jinx

face picon face

> A souped-up toaster oven could reach 450C I think...

I'm sure you could knock up a mini-kiln with a few fire bricks
and an old bar heater. Something I'd thought of but never got
around to for making decorative ceramics

Is there any reason you couldn't use acrylic or polycarbonate
for nixie-tube type things ? As long as they didn't get too hot....
A pluggable LED nixie tube ?

2006\03\21@224245 by Peter Todd

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On Wed, Mar 22, 2006 at 02:56:28PM +1200, Jinx wrote:
>
> > A souped-up toaster oven could reach 450C I think...
>
> I'm sure you could knock up a mini-kiln with a few fire bricks
> and an old bar heater. Something I'd thought of but never got
> around to for making decorative ceramics
>
> Is there any reason you couldn't use acrylic or polycarbonate
> for nixie-tube type things ? As long as they didn't get too hot....
> A pluggable LED nixie tube ?

Heat wouldn't be an issue with proper spacing. However my understanding
is that the gas inside the tube needs to be very pure neon, I'm assuming
that most plastics would outgas too much to achieve that. Aparently one
of the manufacturing steps to make neon tubes is to heat the tube to
just under the melting point for glass to vapourize any contaminents,
which are they pumped out.

Looking at google results for out-gassing polycarbonate though... Looks
like I may be wrong. Found a research paper essentially saying that
polycarbonate itself outgasses very little, but does pick up deeply held
impurities from the atmosphere. Multiple vacume baking cycles could
clean it enough to be used however.


--
spamBeGonepetespamBeGonespampetertodd.ca http://www.petertodd.ca

2006\03\21@231235 by Jinx

face picon face
> > Is there any reason you couldn't use acrylic or polycarbonate
> > for nixie-tube type things ? As long as they didn't get too hot....
> > A pluggable LED nixie tube ?
>
> Heat wouldn't be an issue with proper spacing

I haven't played with Nixie tubes for a long time - just wondered
about the heat generated by the filaments (Mike Harrison would
know - he's got a Nixie tube page)

> Looking at google results for out-gassing polycarbonate though...

I'd imagine that acrylic would probably give off free monomer at
temperature. You can certainly smell MMA if you saw it. Not sure
about polycarbonate though. Have the perception (with absolutely
no evidence to back that up) that it's more stable and/or more fully
polymerised

Still, if you were able to enclose LEDs in any plastic heat wouldn't
generally be a problem. Potting in clear resin might be a little tricky
if you used Luxeons, but the silvering could be a "feature" ;-) A tip
I learned a long time ago when woodworking. If you make a mistake,
make a deliberate one just like and turn them into a "feature", just as
if you'd planned it all along

2006\03\21@233455 by Russell McMahon

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> I'd imagine that acrylic would probably give off free monomer at
> temperature. You can certainly smell MMA if you saw it.

But, can you see it if you smelt it?

For that matter, if you smelt it what temperature does it melt at?
Which brings us back to the original point.



       RM

2006\03\21@235158 by Richard Prosser

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Jinx,
The nixie tubes I have don't have filaments IIRC. They're just shaped
Neon electodes.. I keep meaning to use them for something. (probably a
clock)

RP

On 22/03/06, Jinx <TakeThisOuTjoecolquittEraseMEspamspam_OUTclear.net.nz> wrote:
{Quote hidden}

> -

2006\03\22@005341 by Jinx

face picon face
> The nixie tubes I have don't have filaments IIRC

True

http://en.wikipedia.org/wiki/Nixie_tube

2006\03\22@005803 by Jinx

face picon face
> But, can you see it if you smelt it?

If you have synesthesia maybe

> For that matter, if you smelt it what temperature does it melt at?
> Which brings us back to the original point.

http://www.machinist-materials.com/comparison_table_for_plastics.htm

2006\03\22@010852 by David VanHorn

picon face
On 3/22/06, Jinx <RemoveMEjoecolquittspamTakeThisOuTclear.net.nz> wrote:
>
> > But, can you see it if you smelt it?
>
> If you have synesthesia maybe


He who smelt it, felt it.

2006\03\22@022014 by Jinx

face picon face

> > > But, can you see it if you smelt it?
> >
> > If you have synesthesia maybe
>
>
> He who smelt it, felt it.

OMG, I must be a synesthyte - I do that all the time. And
when I hear certain people I see red or green. Wow, I really
am special, just like mum says

2006\03\22@040517 by Peter Todd

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On Wed, Mar 22, 2006 at 04:12:00PM +1200, Jinx wrote:
> > Looking at google results for out-gassing polycarbonate though...
>
> I'd imagine that acrylic would probably give off free monomer at
> temperature. You can certainly smell MMA if you saw it. Not sure
> about polycarbonate though. Have the perception (with absolutely
> no evidence to back that up) that it's more stable and/or more fully
> polymerised

According to the comparison table that another poster mentioned
polycarbonate has a max temperature of 250C that it can handle, acrylic,
85C!

> Still, if you were able to enclose LEDs in any plastic heat wouldn't
> generally be a problem. Potting in clear resin might be a little tricky
> if you used Luxeons, but the silvering could be a "feature" ;-) A tip
> I learned a long time ago when woodworking. If you make a mistake,
> make a deliberate one just like and turn them into a "feature", just as
> if you'd planned it all along

Something on my todo list is to try embedding electronics in acrylic...
See, you make acrylic set by applying 150C and something like 200psi for
a few hours. That's within lots of electronics thermal envelope. LEDs
would be very neat as if you used clear ones the shell would vanish,
making it look like they are little spots of light eminating from metal
cups.

One of my friends embedded a vacume tube in acrylic using that process.
He said it worked fine, and you couldn't see the glass envelope at all.
Make a nice nightlight for his dad.

--
peteEraseMEspam.....petertodd.ca http://www.petertodd.ca

2006\03\22@051901 by Jinx

face picon face
> LEDs would be very neat as if you used clear ones the shell would
> vanish, making it look like they are little spots of light eminating from
> metal cups

The closer the refractive indices the more the two materials will
appear to be one. I used to be a resin chemist and we did a lot
(A LOT !!) of lunchtime experiments with clear polyester. I've
got a bag of PVA chunks that one day I want to make into giant
bubbles. For no particualr reason or for a reason I can no longer
remember

> One of my friends embedded a vacume tube in acrylic using that
> process. He said it worked fine, and you couldn't see the glass
> envelope at all. Make a nice nightlight for his dad

I've potted the innards of valves in polyester and they make good
ornaments. So do bugs, chips and all kinds of things. If I had the
time I'd like to get back into coasters. Particularly as nW PICs
now make it feasible to include displays. Heat is a problem as it
causes the plastic (polyester anyway) to expand away from the
object, which causes "silvering", which doesn't look professional.
The same also happens if the object has any liquid (eg moisture) in
it, as the exothermy of the curing causes a vapour layer if you don't
pre-coat

OTOH, using heat, including a sensor could make the coaster light
up and even change colour (RGB LEDs) as the temperature changes.
Might be too rough on small cells

Good hobby, bit smelly and messy though

2006\03\22@174507 by Peter

picon face


On Wed, 22 Mar 2006, Jinx wrote:

>>> Is there any reason you couldn't use acrylic or polycarbonate
>>> for nixie-tube type things ? As long as they didn't get too hot....
>>> A pluggable LED nixie tube ?
>>
>> Heat wouldn't be an issue with proper spacing
>
> I haven't played with Nixie tubes for a long time - just wondered
> about the heat generated by the filaments (Mike Harrison would
> know - he's got a Nixie tube page)

There are no filaments in a Nixie ? I think that you mean VFD. VFD is
much harder than Nixie, it requires 'electronic' vacuum. The Nixies use
something between 1 and 10 Torr. You can make Nixie-alikes with air or
welding gas (= blue-white discharge).

Peter

2006\03\22@174509 by Peter

picon face


On Tue, 21 Mar 2006, Peter Todd wrote:

{Quote hidden}

'weak' and 'low melting temperature' are not necessarily related. At
normal temperature they are as hard as ... glass. But you can take a
1N4148 and hold it into the gas flame of a lighter for a couple of
seconds and see the glass melt.

> See, I'm thinking you could easilly make Nixie tubes with this stuff...
> The fabrication would be fairly easy at low temperature, and aparently
> the requierments for Nixie tubes in terms of gasses and purity are very
> similar to neon tubes. It'd be nice to be able to assemble a stack of
> glass with the electrodes in it, and then seal it at the edges.

You have to study things like outgassing and adsorbtion and Invar (to
make the glass passthroughs) and getting the process under control
because the pressure at sealing time will be higher than when the object
cools off, and it may take some special magic to stabilize the
conditions in the tube enough to make it work reliably. I am not sure
whether the seal on diodes is hermetic. I do not think it is.

Peter

2006\03\25@020038 by Peter Todd

picon face
On Thu, Mar 23, 2006 at 12:11:54AM +0200, Peter wrote:
> > Are there any thing about this glass that are different than normal
> > glass? Especially weak?
>
> 'weak' and 'low melting temperature' are not necessarily related. At
> normal temperature they are as hard as ... glass. But you can take a
> 1N4148 and hold it into the gas flame of a lighter for a couple of
> seconds and see the glass melt.

Thanks for the info, and my new party trick. :)

{Quote hidden}

I may be a step ahead of your... Invar isn't used for the passthroughs,
because glass too has a co-efficient of expansion that isn't zero. There
are other methods, like Dumet seals, described very well in:

http://www.teralab.co.uk/Glass_Blowing/Glass_Metal_Seals/Glass_Metal_Seals_Page1.htm

Seriously, that website is amazing! Lots of info on how to do your own
scientific glass blowing.

Looks like some burners and glass stock are all you need for the basics,
after that it's a matter of getting a vacuum pump and other equipment. I
think I've got some space in my studio... Can probably setup some
ventilation, and summer is coming up soon.

--
EraseMEpetespampetertodd.ca http://www.petertodd.ca

2006\03\25@020437 by Peter Todd

picon face
On Thu, Mar 23, 2006 at 12:14:52AM +0200, Peter wrote:
> > I haven't played with Nixie tubes for a long time - just wondered
> > about the heat generated by the filaments (Mike Harrison would
> > know - he's got a Nixie tube page)
>
> There are no filaments in a Nixie ? I think that you mean VFD. VFD is
> much harder than Nixie, it requires 'electronic' vacuum. The Nixies use
> something between 1 and 10 Torr. You can make Nixie-alikes with air or
> welding gas (= blue-white discharge).

Welding gas? Like argon? I hope you don't mean acetylene...

One of my teachers, who I've found out spent all of last year on a
sabatical studying tubes, said that aparently some types of vacuum
diodes can be made to have a blue-white discharge if driven correctly,
he said it's due to the trace gasses added to them, so I think what you
describe may be the same mechanism.


The same teacher was also very impressed when I rigged up two tube
diodes to rectify AC and power... a pic chip. Next on my list is a
switching power supply, with a tube as the switching element.

--
RemoveMEpeteEraseMEspamEraseMEpetertodd.ca http://www.petertodd.ca

2006\03\25@021251 by Peter Todd

picon face
On Wed, Mar 22, 2006 at 10:15:49PM +1200, Jinx wrote:
> > LEDs would be very neat as if you used clear ones the shell would
> > vanish, making it look like they are little spots of light eminating from
> > metal cups
>
> The closer the refractive indices the more the two materials will
> appear to be one. I used to be a resin chemist and we did a lot
> (A LOT !!) of lunchtime experiments with clear polyester. I've
> got a bag of PVA chunks that one day I want to make into giant
> bubbles. For no particualr reason or for a reason I can no longer
> remember

Didn't think of that one... Now I am correct in saying that refractive
indices don't apply for solid objects right? Where the light hits the
object and heads directly back the way it came?

{Quote hidden}

Ahh thanks, I'll keep that in mind then. I recently embedded a watch
along with 6 batteries in parallel in polyester resin, I didn't have any
problems with silvering, but the plastics studio at school tends to be
really hot and dry.

A minute or two with a heat gun set on low should be enough to prevent
that right? At least for the surface moisture?

> OTOH, using heat, including a sensor could make the coaster light
> up and even change colour (RGB LEDs) as the temperature changes.
> Might be too rough on small cells

Do you mean that the cells, as in batteries, would be permenently
installed?

I've got a project on the backburner that would involve a flat disk with
embedded murcury tilt-sensors and solar-cells to run everything. I'd
throw in a bunch of super-capacitors for night operation. Just gotta
find a way to get sufficient power, it'd need a radio link to
communicate with a similar module inside, and super-capacitors just
don't store much energy.

> Good hobby, bit smelly and messy though

Not to mention the wonders of what methel-ethel ketone does in your
body...

--
RemoveMEpetespam_OUTspamKILLspampetertodd.ca http://www.petertodd.ca

2006\03\25@024719 by Russell McMahon

face
flavicon
face
> I've got a project on the backburner that would involve a flat disk
> with
> embedded murcury tilt-sensors and solar-cells to run everything. I'd
> throw in a bunch of super-capacitors for night operation. Just gotta
> find a way to get sufficient power, it'd need a radio link to
> communicate with a similar module inside, and super-capacitors just
> don't store much energy.

Inductive power transfer.
Essentially two transformer halves.
Resonating the receiving side allows quite magical separations.

Photocells (as you've noted).
You could cheat and drive them with IR at night.

Mechanical movement to drive an internal alternator (eg rock it to and
fro or shake it :-)  )

Ultrasonics.

...


       RM


2006\03\25@042154 by Peter Todd

picon face
On Sat, Mar 25, 2006 at 02:17:08AM -0500, Peter Todd wrote:
> On Thu, Mar 23, 2006 at 12:11:54AM +0200, Peter wrote:
> > > Are there any thing about this glass that are different than normal
> > > glass? Especially weak?
> >
> > 'weak' and 'low melting temperature' are not necessarily related. At
> > normal temperature they are as hard as ... glass. But you can take a
> > 1N4148 and hold it into the gas flame of a lighter for a couple of
> > seconds and see the glass melt.
>
> Thanks for the info, and my new party trick. :)

Hmm... Looks like the keyword here is "solder glass frit" According to
http://www.techneglas.com/products/solder.htm you can solder glass
together at 450C using this stuff, rather like soldering electronics
parts, heck, the temperatures aren't even that much higher. Other
manufactures offer the stuff with working temperatures as low as 325C,
pretty close to reflow soldering if I'm not mistaken.

It looks annoying to work with, for instance it's best if the part is
assembled with the frit, and then everything is heated to reduce thermal
stresses, but that's what modded toaster ovens are for...

On other interesting notes... Turns out there is such thing as a
"nanogetter", same idea as the getter in a vacuum tube, but for MEM
devices!

--
RemoveMEpeteTakeThisOuTspamspampetertodd.ca http://www.petertodd.ca

2006\03\25@042656 by Peter Todd

picon face
On Sat, Mar 25, 2006 at 07:39:32PM +1200, Russell McMahon wrote:
> > I've got a project on the backburner that would involve a flat disk
> > with
> > embedded murcury tilt-sensors and solar-cells to run everything. I'd
> > throw in a bunch of super-capacitors for night operation. Just gotta
> > find a way to get sufficient power, it'd need a radio link to
> > communicate with a similar module inside, and super-capacitors just
> > don't store much energy.
>
> Inductive power transfer.
> Essentially two transformer halves.
> Resonating the receiving side allows quite magical separations.
>
> Photocells (as you've noted).
> You could cheat and drive them with IR at night.
>
> Mechanical movement to drive an internal alternator (eg rock it to and
> fro or shake it :-)  )

Well they are designed to be outdoors and exposed to the wind! The whole
point, is that the tilt switches are arranged in a circle on the outside
module, and the inside module exactly reproduces the pattern of on and
off with LEDs.

If I can make a transmitter that can operate off the power of a single
slight tilt I'm set, and propably eligable for some sort of prestigious
award...

Use the switches to switch inductors/capacitors in and out of a resonate
circuit? IE I'd transmit RF at it, and listen to what the otherwise
passive device produces in response? Like those little silver anti-theft
devices, but longer range. I seem to remember hearing about a soviet bug
that worked that way...

> Ultrasonics.

Combine the outside part with a squirrel feeder, and use the rocking of
the squirrels and their ultrasonic noises to generate power?

Heck, eat the squirrels for power?

--
EraseMEpetespamspamspamBeGonepetertodd.ca http://www.petertodd.ca

2006\03\25@055302 by Jinx

face picon face
> Didn't think of that one... Now I am correct in saying that refractive
> indices don't apply for solid objects right? Where the light hits the
> object and heads directly back the way it came?

Well, say you pot things made of various resins in polyester. A piece
of cured, clear polyester, made from the same polyester as that you're
potting with, will largely disappear. It won't completely because the
bonding on the surfaces will be imperfect. For example, if you want
to "float" an object in an encapsulation, you'd put down a layer of
clear, then place the object on that layer when it's gelled. But gelled
only enough to hold the object up. Then fill the remaining space with
clear. Pouring one layer onto a softly gelled layer will make the boundary
of the pours virtually invisible

LEDs are made from epoxy, AIUI. The epoxy they are made from
is water-clear. Polyester potting resin is not water-clear, so the body
of the LED will be observed as clearer. Coloured LEDs of course you
wouldn't worry about. Other plastics, like acrylic, are water-clear. The
problem with polyester is that it has coloured additives. Generally this
would be the promoter, which an be anything from straw to purple.
Uncured clear encapsulating polyester is often pale blue

Mentioning epoxy - one thing I found with coaster experimenting is
that polyester doesn't like improperly cured epoxy or anything that
releases something. For example, objects glued together with the 5
minute or 24 hour epoxy you'd use on the bench stops polyester curing.
There's probably an excess of one of reagents, amine or acid, that
interferes with the catalyst or cross-linking. The one plastic polyester
doesn't mind is laminating sheet. Just won't stick to it. Or glass/metal
if you use release wax (sparingly). All are good for making a hard
smooth surface. Air inhibits polyester curing and any exposed surface
will be the last bit to cure and will not be smooth, and may be sticky
for quite some time. Polyester also doesn't like going on things like
paint (styrene is quite a strong solvent), polystyrene, the glue on
adhesive tape etc

> > The same also happens if the object has any liquid (eg moisture) in
> > it, as the exothermy of the curing causes a vapour layer if you don't
> > pre-coat
>
> Ahh thanks, I'll keep that in mind then. I recently embedded a watch
> along with 6 batteries in parallel in polyester resin, I didn't have any
> problems with silvering, but the plastics studio at school tends to be
> really hot and dry.

The main factors are temperature, catalyst and bulk. The higher the
resin temperature or higher the catalyst, the faster the resin will
gel/cure. And the faster it gels/cures, the higher the temperature of
the resin will get through exothermy. This is also influenced by the bulk
of the resin. For example, you can have a fairly high catalyst level
when fibreglassing because there's a large surface area and heat can
escape. The same catalyst level in a 1kg block might probably cause
it to split. It'll easily boil water. In the lab we even had the rare case
of polyester igniting

Our cavalier sales rep learned a valuable lesson. We warned him
about the dangers of naphthenates and peroxides. But would he listen ?
Would he heck. Then one day he threw a couple of litres each of MEKP
and cobalt naphthenate promoter into a box in the boot of his car. Maybe
the bottles had reagent on the outside or one or the other leaked. By the
time he'd popped in the office and come back out, the wall had well and
truly been written on. The fire brigade were hopelessly late. I'll say this
for a Toyota Corolla - it don't half burn well, even with a sales rep
shouting at it. And us lads thinking "told you so" but deciding this was
probably an inappropriate time to utter that out loud

During winter I'd have to warm all the ingredients up in a drier cabinet or
I'd be waiting all day for it to gel. In the summer you'd have to pop them
in the fridge for a while. Summer heat is a real pain for storage too. The
styrene in polyester self-polymerises very easily in summer and a can on
the shelf might last a couple of months

One thing to watch for in relation to curing heat is post-cure shrinkage.
In extreme cases this will cause cracking, but managing the temperature
and gel time properly (as above) should result in the resin just shrinking
away from the mould. You might expect 0.5 - 1%. Odd-shaped
encapsulations might go a bit funny, because of the heat distribution. In
that case you'd use a lower level of catalyst so the gel time is longer and
heat has time to escape and distribute more evenly. The other advantage
with a longer gel time is that air bubbles have longer to rise. You can go
too low, resulting in a soft cure because of incomplete immediate
polymerisation (would still hurt if someone threw it at you !!)

> A minute or two with a heat gun set on low should be enough to
> prevent that right? At least for the surface moisture?

You can also clean it in meths or acetone, as both are miscible with
water and will dry it. If you wanted to pot something like a leaf, you'd
pre-coat it with resin, using a fairly high (5% ?) peroxide level because
of the air exposure and rapid heat loss. That will trap the moisture, then
you can pot this when gelled

> > OTOH, using heat, including a sensor could make the coaster
> > light up and even change colour (RGB LEDs) as the temperature
> > changes. Might be too rough on small cells

> Do you mean that the cells, as in batteries, would be permenently
> installed?

I'm sure you could mould a coin-cell (eg 2032) holder into a coaster,
or even use adhesive aluminium foil as the contacts, with wires going
to the device from a battery compartment. You can use self-adhesive
felt for the bottom

> I've got a project on the backburner that would involve a flat disk
> with embedded murcury tilt-sensors and solar-cells to run everything.
> I'd throw in a bunch of super-capacitors for night operation. Just
> gotta find a way to get sufficient power, it'd need a radio link to
> communicate with a similar module inside, and super-capacitors
> just don't store much energy.

Watch the styrene-as-sovent issue, especially with thermo-setting
plastics. The el cheapo solar cells I've seen look to have what might
be polystyrene covers/lenses, which free styrene will attack before
polymerising

> > Good hobby, bit smelly and messy though
>
> Not to mention the wonders of what methel-ethel ketone does in
> your body...

Yeah, you have to watch most organic chemicals as they're fat-soluble
and can be absorbed through the skin. I well remember making my first
batch of polyurethane and getting a minute splash of toluene di-isocyanate
on my hand. Even before that, just looking at that big brown bottle gave
my sphincter plenty of exercise. So actually getting a drop on me was....

It was hysterical and wasted agonising is what it was. Just 2 seconds to
get to the tap and rinse it off. The time I got a drop of chromic acid on
my finger was something real though. Such a powerful oxidiser (it's
potassium dichromate dissolved in hot conc sulphuric acid - nasty) that
in just 2 seconds tapward bound I got burned and still have a 3mm
round scar


2006\03\25@094841 by olin piclist

face picon face
Peter Todd wrote:
> Now I am correct in saying that refractive
> indices don't apply for solid objects right?

Refraction is a property of any transparent substance, whether solid or not.
Glass, water, and air all refract light and this can be easily observed with
bare eyes and no special equipment.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\03\26@042914 by Peter

picon face


On Sat, 25 Mar 2006, Peter Todd wrote:

{Quote hidden}

P-10 etc

Peter


'[EE] Heatsinking 1N400x diodes.. .'
2006\04\15@083942 by Peter Todd
picon face
On Sat, Mar 25, 2006 at 10:44:26PM +1200, Jinx wrote:
> LEDs are made from epoxy, AIUI. The epoxy they are made from
> is water-clear. Polyester potting resin is not water-clear, so the body
> of the LED will be observed as clearer. Coloured LEDs of course you
> wouldn't worry about. Other plastics, like acrylic, are water-clear. The
> problem with polyester is that it has coloured additives. Generally this
> would be the promoter, which an be anything from straw to purple.
> Uncured clear encapsulating polyester is often pale blue

One of my friends just tried putting some LEDs in clear polyester resin.
I saw the results, the epoxy is completely invisible, you just can't see
it at all. The LED also effectively becomes a point source, the indexes
of refraction between the epoxy and the polyester must be close enough
that the curve stops acting like a lense. Looks just like a very small
SMD led.

> Mentioning epoxy - one thing I found with coaster experimenting is
> that polyester doesn't like improperly cured epoxy or anything that
> releases something. For example, objects glued together with the 5
> minute or 24 hour epoxy you'd use on the bench stops polyester curing.
> There's probably an excess of one of reagents, amine or acid, that
> interferes with the catalyst or cross-linking. The one plastic polyester
> doesn't mind is laminating sheet. Just won't stick to it. Or glass/metal
> if you use release wax (sparingly). All are good for making a hard

What exactly is release wax?

> smooth surface. Air inhibits polyester curing and any exposed surface
> will be the last bit to cure and will not be smooth, and may be sticky

Ahh, I'm definetely noticing that in the castings I've been doing, takes
as much as a week for the air exposed bits to go hard.

> for quite some time. Polyester also doesn't like going on things like
> paint (styrene is quite a strong solvent), polystyrene, the glue on
> adhesive tape etc

Styrene sure does make for a good solvent... I had project where I
needed to embed some text in the middle of a polyester block. So
basically, pour one layer, place text, pour the other. I tried pretty
much every method I could think of for printing the text, from standard
pens, to stamps, to laser prints on acetate to raw carbon to metalic
inks. The only stuff not dissolved was the metalic inks, gold and
silver, and raw carbon. Every thing else was dissolved to some extent.
Ink from pens or inkpads completely disappeared. Fortunately the laser
printed inks didn't move very much so as long as I didn't touch them
they were visible.

{Quote hidden}

Well I sure can't blame the techs at the plastic department for asking
me to keep my big container of polyester resin in the fire-proof
cabinets rather than my locker!

{Quote hidden}

Hmm... Can you speed of curing though application of heat? Basically,
put less than the needed amount of catelyst in, mix thoughly, and then
artifically bring the temperature up evenly.

{Quote hidden}

Hmm... Wonder how conductive the aluminum will end up? I'd be worried
about trying to make a long-lasted connection to it with the wires,
tough stuff to solder I'm sure.

Speaking of, I just did a run of 6 watches embedded in resin connected
to multiple batteries... I soldered thin wirewrap wire to connect the
batteries (standard silver oxide button cells) in parallel. For the
solder I used solder paste for SMD assembly. I found the large amounts
of flux in the paste worked very well to make a decent connection with
whatever those batteries are made of... I think stainless steel. The
joints seemed surprisingly well wetted. Hopefully the excess of liquid
water kept the batteries from getting too hot.

I've gotta build a mini-spot welder all the same though...

> Watch the styrene-as-sovent issue, especially with thermo-setting
> plastics. The el cheapo solar cells I've seen look to have what might
> be polystyrene covers/lenses, which free styrene will attack before
> polymerising

Hmm... Any sort of easy to apply coatings that styrene can't attack?

{Quote hidden}

Geeze... Well the other day I made the mistake of doing some polyester
resin casts in a less than veltilated room... Normally I'd do it in the
special plastics lab at school, which has enough ventilation that the
doorframes can literally buckle and make it impossible to get out...
Instead I wanted to avoid transporting 6 very fragile watch assemblies
downstairs so I did my pour in the electronics lab. Bad idea... Smelled
very strongly, even after I put lids on everything and moved it to the
seperately ventilated storage room. Lots of people complained about that
one.

Do that three times a week and I'm sure I could kill some brain cells.

> It was hysterical and wasted agonising is what it was. Just 2 seconds to
> get to the tap and rinse it off. The time I got a drop of chromic acid on
> my finger was something real though. Such a powerful oxidiser (it's
> potassium dichromate dissolved in hot conc sulphuric acid - nasty) that
> in just 2 seconds tapward bound I got burned and still have a 3mm
> round scar

You know I think I'll stick to things like, say, high-voltage
electronics and rock climbing. At least I won't have to ever worry about
what my mistakes are going to do to me in the long run...

--
RemoveMEpeteKILLspamspampetertodd.ca http://www.petertodd.ca

2006\04\15@093327 by Jinx

face picon face
> One of my friends just tried putting some LEDs in clear polyester resin.
> I saw the results, the epoxy is completely invisible, you just can't see
> it at all

Cool. The level of catalyst affects the final polymerised colour. As I
mentioned, the promoters / inhibitors in polyester can be quite strongly
coloured and getting the stoichiometry (reagent ratios) right can be a
little trial and error. Sounds like he/she was spot on, colour-wise

> What exactly is release wax?

In a pinch you can use waxy furniture/car polish, although it may
contain perfumes/solvents, but carnauba is the preferred one. Not
expensive and a little bit goes a long way

http://www.iasco-tesco.com/cat55/pg_0078.htm

The trick is to put it on and polish it off. Essential if you're using a
mold,
and especially if you want to use that mold again. For example a boat
shell

We'd do lunch-time encapsulations in 100ml Pyrex lab beakers and
although resin shrinkage separates it from the glass, without wax that
separation isn't always uniform and you get ridges. They can be
polished out with wet/dry paper, brass polish and silver polish but it's
a darn sight easier to wax the glass in the first place

> > smooth surface. Air inhibits polyester curing and any exposed surface
> > will be the last bit to cure and will not be smooth, and may be sticky
>
> Ahh, I'm definetely noticing that in the castings I've been doing, takes
> as much as a week for the air exposed bits to go hard.

When I make coasters I have circles of laminating plastic that I put
on the "bottoms" (they're in upside-down molds) to keep air out. A
sheet on the workbench too

Works a treat. I'm sure any copy shop that does laminating will
have scraps

My friend gets her film from  http://www.jenrite.co.nz/  I forget
the exact composition but I think it's a polyethylene/polyester mix.
Quite standard laminating film anyway

> Hmm... Can you speed of curing though application of heat?
> Basically, put less than the needed amount of catelyst in, mix
> thoughly, and then artifically bring the temperature up evenly

You can't be too stingey with catalyst as it's needed to initiate the
cross-linking. Some experimenting might be called for. It depends
on the volume : surface area ratio. It would be better to heat the
resin before adding catalyst. But don't go too crazy with the heat
if you want the bubbles out

I've got a block of polyester that was shot with a nail gun before it
cured, and it shattered inside. Looks brilliant when hit with a laser
pointer

> Hmm... Wonder how conductive the aluminum will end up? I'd be
> worried about trying to make a long-lasted connection to it with the
> wires, tough stuff to solder I'm sure

You'd wrap it around the wire and use a pen or something to rub
it smooth to make contact

> I've gotta build a mini-spot welder all the same though...

When trying the zapper technique (a big capacitor charged to about
20V IIRC) for revitalising NiCds the zapper wire often got welded to
the terminal

> Hmm... Any sort of easy to apply coatings that styrene can't attack?

Nitro-cellulose lacquer is good. I've used it for printed material like
photographs and newspaper. A quick first spray dries very quickly
and then you can build on that. Well-cured epoxy too for porous
materials, but not anything soluble like inks

2006\04\15@094213 by Jinx

face picon face
> Hmm... Any sort of easy to apply coatings that styrene can't attack?

BTW, nitro-cellulose lacquer is often used by car painters and
woodworkers. My brother is in the furniture caper so I have
access to a spray booth. Also anyone who repairs wooden
instruments (guitars, violins etc) might have a small spray set

2006\04\18@080917 by Alan B. Pearce

face picon face
>> I've gotta build a mini-spot welder all the same though...
>
>When trying the zapper technique (a big capacitor charged
>to about 20V IIRC) for revitalising NiCds the zapper wire
>often got welded to the terminal

Is that not why carbon electrodes get used? The centre electrodes out of the
original D cells always seemed about the right size for this.

2006\04\18@090437 by Jinx

face picon face

> Is that not why carbon electrodes get used? The centre electrodes
> out of the original D cells always seemed about the right size for this

Anything else you can do with those ? On the way home from the
supermarket the other night I found a box of a dozen D cells on the
pavement, and thought, ace, free score. But found out when I got
home that they were all dead ;-((( Someone had obviously thrown
them away. So, I've got a dozen batteries that are inching slowly
towards the bin........

2006\04\18@092637 by Alan B. Pearce

face picon face
>> Is that not why carbon electrodes get used? The centre electrodes
>> out of the original D cells always seemed about the right size for this
>
>Anything else you can do with those ? On the way home
>from the supermarket the other night I found a box of
>a dozen D cells on the pavement, and thought, ace, free
>score. But found out when I got home that they were all
>dead ;-((( Someone had obviously thrown them away. So,
>I've got a dozen batteries that are inching slowly
>towards the bin........

Grief I thought even dead ones are valuable out your way ;)))

maybe making a microphone by balancing a carbon on a couple of razor blade
edges. Always good for amusing small kids.

High power low value resistors for current measurement ??

electrodes for plating etc??

Seem to remember these were all uses for the carbon out of old Lechanche
type D cells when I was lad ...

2006\04\18@093552 by Russell McMahon

face
flavicon
face
>> Is that not why carbon electrodes get used? The centre electrodes
>> out of the original D cells always seemed about the right size for
>> this

> Anything else you can do with those ?


Water electrolysis

Don't try this at home arc lamp.

...

       RM



2006\04\18@100026 by Alan B. Pearce

face picon face
>Don't try this at home arc lamp.

Oh, I don't know - have a transformer rated at some amps with very low
volts, current is changed by changing primary taps ;)))

Now where are those welding glasses, could do with lighting up the garden at
night.

2006\04\18@132511 by Peter

picon face

On Tue, 18 Apr 2006, Alan B. Pearce wrote:

>> Don't try this at home arc lamp.
>
> Oh, I don't know - have a transformer rated at some amps with very low
> volts, current is changed by changing primary taps ;)))

You need between 12 and 50V to run an arc in air and there must be less
painful ways to commit suicide than breathing the chemical fumes and
thick smoke from Leclanche carbon sticks. Arc sticks are made of special
graphite or coke and baked out previously to prevent them from exploding
or catching fire too soon. They also have un-healthy additives in them.

Peter

2006\04\18@193213 by Jinx

face picon face
>> Is that not why carbon electrodes get used? The centre electrodes
>> out of the original D cells always seemed about the right size for this

> Grief I thought even dead ones are valuable out your way ;)))

They are indeed. Even though the magic power of the battery has
gone to the ether and is back with the spirits, by rubbing two together
we can make the fire to ward off marauding possums and wetas from
our meagre villages. As we rummage the detritus of the kings and
queens of the Eastern Lands, hoping to stumble upon any nutritious
food scraps or maybe even some soiled timber to repair our shacks,
the dead battery is a praise-worthy weapon against rats. And with the
god's luck, a kill provides sustenance for a family of ten for many days,
and the skin is another step closer to a complete mitten. All hail the
battery !!

Now, if you'll excuse me, a traveller has thrown a pizza box out their
mysterious roaring chariot (I believe they are called a "suv") and I see
some cheese on the lid. I can trade that for three C batteries and a left
shoe

2006\04\18@200032 by Marcel duchamp

picon face
Jinx wrote:
{Quote hidden}

Would you really trade your supper away for just three C batteries and a
left shoe?

And to think that we got here from "[EE] Heatsinking 1N400x diodes"...

2006\04\18@210900 by Russell McMahon

face
flavicon
face
>> Grief I thought even dead ones are valuable out your way ;)))

> ... and the skin is another step closer to a complete mitten.
>     All hail the battery !!

Battery skins make terrible mittens. The outer skins are either
inflexible and crack or are porous and with low wear resistance. The
inner skins are more useful. With care they may be beaten together to
form a thin somewhat flexible sheet which may be fashioned with
suitable dark knowledge into a cooking pot. These have little strength
and must never be used on a fire without liquid inside them. A special
curse and an especially bright fire sometimes awaits those who ignore
this warning.

When choosing such skins its best to use batteries that have only
recently died or even, if possible, to kill one yourself while it
still has a little life in it. Skins which are long dead tend to be
thin and pitted and may even have holes right through them. They can
be salvaged with much rebeating but with much greater effort and the
stones tend to erode them.

Weta skins are probably more useful.


               RM

2006\04\18@215427 by Bob Axtell

face picon face
Russell McMahon wrote:
{Quote hidden}

Sounds like the pair of "Lobster Claws" my wife ordered. When they got
here, I found out they
were just some silicone gloves for holding hot stuff.

Ya know, if ya don't watch out, ya could really get burned  buyin' stuff
on the web.

--Bob

>                 RM
>
>  

2006\04\18@233614 by Russell McMahon

face
flavicon
face
> Sounds like the pair of "Lobster Claws" my wife ordered. When they
> got
> here, I found out they
> were just some silicone gloves for holding hot stuff.

> Ya know, if ya don't watch out, ya could really get burned  buyin'
> stuff
> on the web.


Not if you are wearing lobster claws.



       RM

2006\04\19@111853 by Peter Todd

picon face
On Tue, Apr 18, 2006 at 05:00:28PM -0700, Marcel duchamp wrote:
> > Now, if you'll excuse me, a traveller has thrown a pizza box out their
> > mysterious roaring chariot (I believe they are called a "suv") and I see
> > some cheese on the lid. I can trade that for three C batteries and a left
> > shoe
> >
> Would you really trade your supper away for just three C batteries and a
> left shoe?
>
> And to think that we got here from "[EE] Heatsinking 1N400x diodes"...

Hmm, we'll lets bring this conversation a little more back to something
that involves electrons... Like scooters!

http://gw.petertodd.ca/~pete/pict0498.avi

Yeah... That's me in the yellow hat, and that scooter's running at 24V
rather than the usual boring 12V...

--
peteSTOPspamspamspam_OUTpetertodd.ca http://www.petertodd.ca

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