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'[OT] Preventing Condensation on Outdoor Equipment'
1999\01\07@231358 by Mark Winters

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Hello All,

I've built some PIC-based circuits for use outdoors, where I expect them to
be used from the spring to fall, with them powered down in the winter. This
is currently a "hobby" project, but I may find a commercial use at some
point.

To protect the main circuit from snow and rain, for now I've placed it on a
small platform about a foot high, and covered the whole thing with an
upside-down 5-gallon paint bucket. During the summer and fall this worked
great. We also had a break in the snow recently so I plugged it in and
everything worked fine.

Now for the problem. When I removed the paint bucket recently to see if
everything was OK, I noticed some water had formed on the "wall-wart"
transformer I use to power the circuit (the wall-wart is under the bucket as
well, hooked up to an extension cord from the house). I didn't notice any
water on the circuit itself, however.

I don't know that much about the condensation process, but I'm guessing the
water has formed on the transformer because it has a high amount of "thermal
intertia," where it is colder than the surrounding air in the morning just
after the sun has come up and begun warming the air. Having everything close
to the wet ground may also be a factor.

Does anyone know of an inexpensive way of preventing the condesation? I know
I probably shouldn't be using an "indoor" wall-wart this way, but this is
still just a "hobby" project, so I'd like to keep the investment low  :-)  I
suppose I could keep the thing powered up all the time, and that may help
the transformer, but I'm also worried about some of the larger parts
(relays, etc.) having the same problem.

Any suggestions would be appreciated.

Thanks,
Mark Winters

1999\01\08@021420 by Gerhard Fiedler

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At 21:00 01/07/99 -0700, Mark Winters wrote:
>I don't know that much about the condensation process, but I'm guessing the
>water has formed on the transformer because it has a high amount of "thermal
>intertia," where it is colder than the surrounding air in the morning just
>after the sun has come up and begun warming the air. Having everything close
>to the wet ground may also be a factor.
>
>Does anyone know of an inexpensive way of preventing the condesation? I know
>I probably shouldn't be using an "indoor" wall-wart this way, but this is
>still just a "hobby" project, so I'd like to keep the investment low  :-)  I
>suppose I could keep the thing powered up all the time, and that may help
>the transformer, but I'm also worried about some of the larger parts
>(relays, etc.) having the same problem.

it seems to me that the best way to deal with this is some kind of coating
(eg. silicone) or encapsulation (eg. resine potting).

ge

1999\01\08@031641 by Steve Smith

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Fit anti-condensation heater........

Bathroom mirror princable if the mirror is cold water vapour from the air
condenses into water droplets and causes steam up (visability poor) Heat the
mirror to a tempreture above the ambient tempreture and condensation dosent
form same princable is used in industrial panels with pannel heaters........

Alternativly use a small box and seal with silicone rubber / potting compound
.....

Cheers Steve........:-)

1999\01\08@050714 by Nigel Orr

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At 21:00 07/01/99 -0700, you wrote:
>Does anyone know of an inexpensive way of preventing the condesation? I know
>I probably shouldn't be using an "indoor" wall-wart this way, but this is

Would it be possible to put the wall wart inside, and feed low voltage ac
out to the circuit?  It would be easy if the circuit isn't drawing A's of
current.  As for waterproofing, can you encapsulate the circuit, or put it
in a sealed box with some silica dessicant?

Nigel

1999\01\08@115443 by Reginald Neale

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Mark said:

>To protect the main circuit from snow and rain, for now I've placed it on a
>small platform about a foot high, and covered the whole thing with an
>upside-down 5-gallon paint bucket. During the summer and fall this worked
>great. We also had a break in the snow recently so I plugged it in and
>everything worked fine.
>

 If you just leave the power on all the time, the two or three watts
 of heat that the wall-wart develops will tend to be trapped by your
 inverted bucket. That'll help to keep the condensation down. Might
 be good to line the bucket with foil-faced foam and close it off to
 keep critters out.

 Reg Neale

1999\01\08@124633 by Andy Kunz

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At 04:53 PM 1/8/99 GMT, you wrote:
>Mark said:
>
>>To protect the main circuit from snow and rain, for now I've placed it on a
>>small platform about a foot high, and covered the whole thing with an
>>upside-down 5-gallon paint bucket. During the summer and fall this worked
>>great. We also had a break in the snow recently so I plugged it in and
>>everything worked fine.
>>
>
>  If you just leave the power on all the time, the two or three watts
>  of heat that the wall-wart develops will tend to be trapped by your
>  inverted bucket. That'll help to keep the condensation down. Might
>  be good to line the bucket with foil-faced foam and close it off to
>  keep critters out.

Also, if you can keep the lid on it that will help.  The expansion and
contraction of the air will bring crap in.  If you have the lid on, it acts
somewhat as a drum would.

Andy

==================================================================
 Andy Kunz - Montana Design - http://www.users.fast.net/~montana
==================================================================

1999\01\08@145002 by Peter L. Peres

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Hello,

 afaik there are only two ways to keep condensation out. One is, to put a
heater in your circuit so it never reaches the dewpoint. This method is
sometimes used with boom-mounted antenna amplifiers. The heater can be
a simple power resistor screwed to the circuit casing or directly on the
print at a suitable point. imho, for a hobby project, this is the way to
go.

 The other way is, to seal the circuit either in conformant sealing
compound (available as spray I think), or put it in a sealed container
(can be plastic) pressurized with dry air. Production facilities can do
this. This is the industrial way.

hope this helps,

       Peter

1999\01\10@121239 by Richard A. Smith

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On Fri, 8 Jan 1999 19:23:33 +0000, Peter L. Peres wrote:

>  The other way is, to seal the circuit either in conformant sealing
>compound (available as spray I think), or put it in a sealed container
>(can be plastic) pressurized with dry air. Production facilities can do
>this. This is the industrial way.

We conformal coat boards all the time.  Several of our
products go into Chicken/Turkey plants where condensation
is a fact of life.   I would suggest that you use the box
and a heater method as conformal coating is a real
pain-in-the arse.  To get a good solid waterproof coating
the board must be oil free,moisture free, the coating must
be applied correctly, and it can't be too hot or too cold
while drying.

When done right though conformal coating is great.  I have
boards that can run while held under a stream of tap water.

If you are interested in the details of conformal coating
let me know.

If you just want to get a can and see what happens you can
call:

Tech Spray
(806) 372 8523

AC TECH SOUTHEAST
800-763-7999

We use Conap-1170 from AC Tech Southeast.  I don't remember
if they will sell to the Hobbiest or not.


--
Richard A. Smith                         Bitworks, Inc.
spam_OUTrsmithTakeThisOuTspambitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

1999\01\10@155852 by Andy Kunz

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At 11:05 AM 1/10/99 -0600, you wrote:
>On Fri, 8 Jan 1999 19:23:33 +0000, Peter L. Peres wrote:
>
>>  The other way is, to seal the circuit either in conformant sealing
>>compound (available as spray I think), or put it in a sealed container
>>(can be plastic) pressurized with dry air. Production facilities can do
>>this. This is the industrial way.
>
>We conformal coat boards all the time.  Several of our
>products go into Chicken/Turkey plants where condensation
>is a fact of life.   I would suggest that you use the box
>and a heater method as conformal coating is a real
>pain-in-the arse.  To get a good solid waterproof coating
>the board must be oil free,moisture free, the coating must
>be applied correctly, and it can't be too hot or too cold
>while drying.
>
>When done right though conformal coating is great.  I have
>boards that can run while held under a stream of tap water.

I use 3M potting compound.  My devices are run under water all the time,
and work perfectly.  That's my selling point over the competition.

Andy


==================================================================
 Andy Kunz - Montana Design - http://www.users.fast.net/~montana
==================================================================

1999\01\11@104701 by Richard A. Smith

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On Sun, 10 Jan 1999 15:53:25 -0500, Andy Kunz wrote:

>At 11:05 AM 1/10/99 -0600, you wrote:
>>On Fri, 8 Jan 1999 19:23:33 +0000, Peter L. Peres wrote:
>>
>>When done right though conformal coating is great.  I have
>>boards that can run while held under a stream of tap water.
>
>I use 3M potting compound.  My devices are run under water all the time,
>and work perfectly.  That's my selling point over the competition.

I have though about potting... Never used any though...

What kind of prep requirements are needed for potting?

Do you have to make special adjustments for heat
dissipation?

How do you get it off for rework or failure analysis?

--
Richard A. Smith                         Bitworks, Inc.
.....rsmithKILLspamspam@spam@bitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

1999\01\16@102915 by Rich Graziano

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Perhaps you could put your circuit in a small plastic container with a
desicant and sealt it.  If you have a way to partially evacuate the
container it would also be helpful .

Richard

From: Gerhard Fiedler <listsspamKILLspamHOME.COM>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Date: Friday, January 08, 1999 2:13 AM
Subject: Re: [OT] Preventing Condensation on Outdoor Equipment


>At 21:00 01/07/99 -0700, Mark Winters wrote:
>>I don't know that much about the condensation process, but I'm guessing
the
>>water has formed on the transformer because it has a high amount of
"thermal
>>intertia," where it is colder than the surrounding air in the morning just
>>after the sun has come up and begun warming the air. Having everything
close
>>to the wet ground may also be a factor.
>>
>>Does anyone know of an inexpensive way of preventing the condesation? I
know
{Quote hidden}

1999\01\16@150939 by Mark Willis

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Sometimes people store food in carbon dioxide, come to think of it;  I
believe you could store electronics in CO2 as well, possibly.

 (CO2 is used because it is "heavier than air" and tends to displace
the air from the foodstuffs, nitrogen packing could be used also but
it's harder to do at home!)

 I would definitely suggest renting a CO2 cannister, not just throwing
a lump of dry ice in there <G>  (Perhaps melt the dry ice and pour the
resulting CO2 into the container?)

 Anyone used CO2 near electronics?  I'm a little concerned about
carbolic acid (I think that's what I mean) if any moisture DID get in
there <G>)

 With a heat source in there, shouldn't be a problem, though (Gun safes
use a ceramic rod heater to keep rust stopped.)

 (Also, am I remembering correctly that you can take a piece of gypsum
wallboard and "roast" it to give you fresh, cheap [free, if potentially
messy!] dessicant, or is my brain worn out today?  It's being a hard
weekend <G>)

 Mark

Rich Graziano wrote:
{Quote hidden}

1999\01\16@220552 by paulb

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Rich Graziano wrote:

>  Perhaps you could put your circuit in a small plastic container with
> a dessicant and seal it.  If you have a way to partially evacuate the
> container it would also be helpful.

 Nope.  Sorry, you got that the wrong way round!  Unless you use
"hermetic" sealing techniques (all terminations made through conductors
cast into glass seals, like electron valves), it *will* leak.  In
practice, you will wish to open it up for servicing anyway.

 *When* it leaks, if it is evacuated, it *sucks in* moisture-laden air.
Instead, you pressurise it with dry nitrogen (I would think wet carbon
dioxide may indeed be corrosive).  That may leak out, but it'll be
pushing contaminants *out* while it does so.

 And yes, if it is durable, pouring an amount of LN2 into the *cover*
rather than the electronics, and providing an over-pressure blow-off
would be a simple way to do that.

 ([OT]: I've yet to try the "LN2 in a soft-drink bottle" trick yet!)
--
 Cheers,
       Paul B.

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