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'[ee]: Enclosed outdoor circuitry, moisture prevent'
2002\01\20@144140 by Jim

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Please keep us posted on this.

I would think that there are a lot of people that would
be interested in any unseen "gotcha's" that crop up.

I, for one, would not opt for a 'sealed' system with a
gel-cell within the 'sealed' area. Perhaps it can be
vented (anyone recall the tubes used on motorcycle
batteries that vent any 'fumes' down and away?).

I also have a question. Will the 'box' be subject
to radiative cooling?

That is, will it be outside and subject to exposure
to the night sky? I believe this is your *worst case*
with regards to condensation. Any 'heat' genned by the
components can be used to keep the temp above the
dew point and avoid condensation.

Jim


{Original Message removed}

2002\01\21@050036 by Alan B. Pearce

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>I suppose it might - if I can find a source for those packets, I could just
>stuff it in the available space. Is this the same substance that is
"recharged"
>by placing in the oven?

>>I'd say some silica gel would probably do wonders.

Yes, and you would need to put in a dry one every time you opened the box. I
would also go for spray coating the boards, even if you just used a clear
lacquer spray can from the local paint shop.

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2002\01\21@052745 by Jinx

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Been trying to remember something I meant to try in a
greenhouse once (but never did). The idea was that you
filled black tubes with a compound that has a high latent
heat (higher than water). During the day they heated up
and then released the heat during the night to stop frosts.
I thought it was a super-saturated solution, but these guys
are using the solid

http://www.kellysearch-extension.co.uk/Science0704.htm

They've got slightly different goals than just avoiding
condensation, but it should work to some degree in a
simple form

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2002\01\21@054632 by Alan B. Pearce

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>Been trying to remember something I meant to try in a
>greenhouse once (but never did). The idea was that you
>filled black tubes with a compound that has a high latent
>heat (higher than water). During the day they heated up
>and then released the heat during the night to stop frosts.

I seem to remember something like this called a "nightstor heater" 'cept it
was 12 hours out of phase ;)

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2002\01\21@102239 by Don Hyde

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On another list devoted to light airplane electrical systems, there's been a
lot of discussion of "gel-cell" batteries.  It seems that although they are
still widely called gel cells, those have mostly been replaced by
recombinant gas technology.  These cells have a vent, but it is a safety
vent only, and doesn't emit anything unless the battery fails
catastrophically or is in a fire, in which case it releases pressure so the
case doesn't explode.

Check with the battery manufacturer, but it is probably sealed and won't
release any sort of gases unless it's failed, in which case you're going to
have to open the case and service the thing anyway.

I'd go with a little pack of silica gel unless I could ensure that it wasn't
being opened in the field, and I could assemble them in a known low-humidity
environment.

> {Original Message removed}

2002\01\22@003009 by Russell McMahon

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> >Been trying to remember something I meant to try in a
> >greenhouse once (but never did). The idea was that you
> >filled black tubes with a compound that has a high latent
> >heat (higher than water).

Water has a rarther high heat capacity compared to most other common
materials.
Where you can win is if you can get a phase change somewhere in your
temperature range.
You can store 10 or 20 times more energy in a solid-liquid or liquid-gas
phase change than in the whole temperature swing between  0 & 100 degrees C.

>>During the day they heated up
> >and then released the heat during the night to stop frosts.

A reasonable alternative is SAID to be softdrink bottles filled with water
which is blackened just enough that you can't see sunlight through it when
in the bottle.

> I seem to remember something like this called a "nightstor heater" 'cept
it
> was 12 hours out of phase ;)

Nightstore uses the fact that from SOME power boards you can get a rate for
power offpeak that is MUCH cheaper than on peak. Not all power boards offer
this. (Mine offer a $NZ0.065 / kWh night rate (11pm - 7am on) compared with
typically $0.096 to $0.115 / kWh daytime rates depending on other factors)

The original nightstores used wax as an energy storage medium. This did have
a phase change (the wax melted during heating) so had very good capacity.
However, there were a number of fires with these for reasons I'm not aware
of (ie I would have thought  that it SHOULD be possible to achieve proper
control - maybe they got massive temperature buildups near the elements and
inadequate circulation) and AFAIK they recalled them and changed to bricks
as the storage medium. Bricks are not known to exhibit phase changes across
the temperature range of interest :-) so the thermal capacity is much worse.



       RM

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2002\01\22@034410 by Jinx

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> Where you can win is if you can get a phase change somewhere
> in your temperature range. You can store 10 or 20 times more
> energy in a solid-liquid or liquid-gas phase change than in the
> whole temperature swing between  0 & 100 degrees C.

At the link I provided they are using solid Sodium Sulphate. This
melts during the day and releases its heat at night

The story with the greenhouse heater was that you'd use the fully
hydrated Sodium Sulphate (Na2SO4.10H20 - not an uncommon
salt), not the anhydrous form. This has obviously been looked into
by whover it was I got the suggestion from, and shown to give
better results.

For such a small box, I think some chemical heat storage is
worth a crack. If the circuit is also giving off some heat that
will help

What's the possibility of using a one-way mirror to collect
heat through that will act as a (mediocre) insulator by internal
reflection at night, like a Thermos flask ?

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2002\01\22@065455 by Russell McMahon

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> What's the possibility of using a one-way mirror to collect
> heat through that will act as a (mediocre) insulator by internal
> reflection at night, like a Thermos flask ?

The equivalent of one way mirrors feature on the front of most solar
water/air heaters you see - they just don't look like that to us.
Ordinary "clear" glass is transparent to shorter wavelength light including
visible light (which is why we think it is clear) and near infrared. It is
generally opaque to longer wavelength IR. Incoming IR from the Sun is
shorter wavelength due to its high source temperature. Once it is absorbed
in the blackened collector it is immediately re-radiated but due to the
lower temperature the wavelength is longer and the glass is opaque to the
radiation, trapping it in the collector. Relying on this for night storage
may be a bit of an ask but one can add a shutter of some sort for this
(often called curtains :-) ).

Blown polystyrene beads inside a double glazed frame is used by some people
to make an unusual automated blind - beads are blown to and from storage and
window frame as required. .


       RM

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2002\01\22@093757 by JB

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FYI: I set this thing outside last night. The temperature was about 13 degrees
F this morning when I cracked it open, and I found the insides to be slightly
warm, no condensation. I had sealed it the day before when it was about 40F.

This is the actual installation:

 http://www.rof.net/yp/alphaone/activities/electronics/sowap/

Once I obtain some silica gel, I should be fine, at least until summer. I'll re-
evaluate the situation when the weather warms up some.

I like this phase-change suggestion, and I should explore it later on as the
temperature swings become more pronounced. Will let you know how it works out.

JB

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2002\01\22@105314 by Roman Black

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Jinx wrote:
{Quote hidden}

Maybe aluminium foil, a few hand packed layers
would only be a few mm thick but have trapped
air layers. I don't know how good it would be,
but it's easy to try, at least, just stick the
3W resistor in the box put the box in the freezer.
:o)
-Roman

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2002\01\22@105324 by Roman Black

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JB wrote:
>
> FYI: I set this thing outside last night. The temperature was about 13 degrees
> F this morning when I cracked it open, and I found the insides to be slightly
> warm, no condensation. I had sealed it the day before when it was about 40F.
>
> This is the actual installation:
>
>   http://www.rof.net/yp/alphaone/activities/electronics/sowap/
>
> Once I obtain some silica gel, I should be fine, at least until summer. I'll re-
> evaluate the situation when the weather warms up some.
>
> I like this phase-change suggestion, and I should explore it later on as the
> temperature swings become more pronounced. Will let you know how it works out.


Hi JB, nice app! :o) Having seen the inside
of the box, have you considered just stuffing
all the crevices with styrofoam packing chips?

One thing i've always wanted to build is a PIC
MPPT (max power point tracker), using a simple
buck circuit, but switched by a PIC and the
current drawn from the solar panel is adusted
in real time to maintain max power output from
the panel. Many types are available, but I haven't
seen a PIC one. A 16F873 with A/D inputs, a
transistor, diode, inductor would be a low cost
alternative to your LM317, and may give 20% or
more total power from the panel.
-Roman

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2002\01\22@114851 by Michael Vinson

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Russell McMahon wrote, in part:
>[About using phase change for heat storage]
>The original nightstores used wax as an energy storage medium. This did
>have
>a phase change (the wax melted during heating) so had very good capacity.

Another example of the same principle was the cooling system used
on the Apollo Lunar Rover's communication relay electronics. Wax
was allowed to melt during operation on EVAs, thus absorbing heat.
Between EVAs (while the crew rested in the LM), mirrors were used
to provide shade, and the wax would radiate its heat and resolidify.
This worked well over the course of three missions (Apollos 15, 16,
and 17), with three seven-hour EVAs each.

To bring this posting just a little closer to topic, imagine how
PICs could be used on a modern lunar mission. The Apollo command
module and lunar module computers were considerably less powerful
than a 16F877, I think (I haven't done a point-by-point comparison,
but if I do I'll report back).

Michael V

Thank you for reading my little posting.


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2002\01\22@140201 by Jinx

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> I like this phase-change suggestion

Just a thought - what does NASA do to protect circuits that
are in environments (eg Moon, Mars) that experience huge
day/night temperature swings ? Obviously no problems
with condensation, but surely the effects from that sort of
thermal cycling must be detrimental. Do they do anything
that you could use in a smaller way ?

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2002\01\22@142506 by Jinx

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> I like this phase-change suggestion, and I should explore it later
> on as the temperature swings become more pronounced. Will
> let you know how it works out

> > Apollo Lunar Rover's communication relay electronics. Wax

Ah, so NASA did do something. What might be helpful is to do
or get a temperature max/min log for the installation site, and then
pick a wax that will best service an optimum range. Your problem
with condensation might not necessarily be in the season with the
largest min-max differential, so perhaps a little research into
seasonal humidity variations too. For instance, when those trees
leaf up there'll be a different local micro-climate. Looking at the
pics, you should be able to put the night heater amongst the boxes,
rather than inside one. This assumes that you'll have dependable
solar heat during the day. You might consider those times when
it rains for a few days and the area is continually damp. Plan A B
& C ?

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2002\01\23@091223 by Roman Black

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Russell McMahon wrote:
>
> > >Been trying to remember something I meant to try in a
> > >greenhouse once (but never did). The idea was that you
> > >filled black tubes with a compound that has a high latent
> > >heat (higher than water).
>
> Water has a rarther high heat capacity compared to most other common
> materials.
> Where you can win is if you can get a phase change somewhere in your
> temperature range.
> You can store 10 or 20 times more energy in a solid-liquid or liquid-gas
> phase change than in the whole temperature swing between  0 & 100 degrees C.


What about a heap of 2 foot fluoro tubes glued
with silastic to form a "box" about 2 tubes thick?
Some electrical wholesalers have a recycle bin for
old tubes, you might be able to get the 20 or so
you need for almost nothing.
-Roman

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2002\01\23@232536 by Josh Koffman

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I don't get the flourescent tube thing...enlighten me?

Josh
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Roman Black wrote:

> What about a heap of 2 foot fluoro tubes glued
> with silastic to form a "box" about 2 tubes thick?
> Some electrical wholesalers have a recycle bin for
> old tubes, you might be able to get the 20 or so
> you need for almost nothing.
> -Roman
>
>

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2002\01\24@064053 by Roman Black

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Nothing serious, just people were discussing
insulating the control box from the high and low
desert temperatures. I added a couple of suggestions
for basically zero cost and very low time, like
aluminium foil layers and using old fluoro tubes
to buld a "vacuum walled" box.
Not as effective as the solid/liquid wax but somtimes
a cheap+quick solution can be a good one. :o)
-Roman

Josh Koffman wrote:
{Quote hidden}

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2002\01\24@092009 by Vasile Surducan

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Nothing serious ? It's a damn serious topic here...
I had also a dead application running outdoor.
I was trying to thermostate a small portion from PCB
at 50C using a power bipolar transistor. It worked but
no more than one or two years...
From -40c to +70C and moisture up to 90% is not easy.
regards, Vasile


On Thu, 24 Jan 2002, Roman Black wrote:

{Quote hidden}

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