Post by thread:[OT] Preventing Condensation on Outdoor Equipment

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

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

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

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 ==================================================================

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

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_OUTrsmithTakeThisOuTbitworks.com 501.521.3908 Sr. Design Engineer http://www.bitworks.com

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 ==================================================================

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. .....rsmithKILLspam@spam@bitworks.com 501.521.3908 Sr. Design Engineer http://www.bitworks.com

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 <listsKILLspamHOME.COM> To: .....PICLISTKILLspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.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}>>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

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}> > 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 <listsspam_OUTHOME.COM> > To: @spam@PICLISTKILLspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamMITVMA.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 > >>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

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.