Not electronics but who knows where to ask: anti-fog, anti-frost clear material? - Page 1
Forum section: electronics / general

author: mortrek
author_rank: Contributor
timestamp: December 02, 2020, 09:14:19 pm
content: I have an outdoor camera that does not have access to AC power and is enclosed in a box with a viewport. It's a project I've worked on for a couple years and it runs entirely off of a limited battery supply. I need to have a polycarbonate or glass window viewport on the front, and it needs to last for a year without fogging or frosting up in varying environments. I know this is asking a lot...I used an "anti-fog" treated piece of polycarbonate but the problem this time of year is that the hydrophilic surface attracts water, which then freezes and becomes largely opaque. Untreated polycarbonate would have a similar issue. Would hydrophobic treatment work better in low temperatures? I can apply different coatings for different times of year, but preferably I'd get 1+ years without any significant fog or frost, and without any intervention.Any ideas I'm missing, other than hydrophobic coatings? I don't think I have the battery capacity to blow warm air on it. The viewport will be mostly in shade, to avoid glare. It's possible to redesign the setup a bit to add a little battery capacity, but I'm unsure of how much energy it would really take to warm a thin piece of plastic covered in a layer of frost enough to melt the frost. It's probably more energy than I can justify.The plastic window is about 3mm thick, 6x6" in size (although the actual used viewport area is much smaller) and the battery bank is meant to last for 1 year, but I've built in an extra 50-100% or so battery overhead, so I may have about 2700mah at 9V to spare, or 24WH. It's likely to be below freezing for 15-20 days a year. That leaves at most 1WH to warm ice per day or ~3600J . Ice heat of fusion is ~334 J/g. I am unsure of the thickness of the water on the hydrophilic material, but a small window of melted ice would be maybe 2x2inches and .5mm water thickness would make just over 1g, so only ~400J in theory, but much more in practice... and again, I could add batteries.So if no treatment works, should I look in to some sort of targeted heating system that points at the focal area of the window for the camera and heats it for X seconds before taking photos? And then only have it trigger when temperatures are below 0C? it takes probably 8-10 photos per day during the winter... but temps often go over 0C during mid-day. Ugh, I've worked on this project for a while and this was a major concern that was never fully resolved. I'd be fairly happy with it getting a single good photo during freezing periods, rather than multiple blurry iced-over photos, so maybe when the temperature gets low it should heat the viewport and take fewer photos?Of course, ideally there would be a passive solution that allows all the photos to be crystal clear...If anyone has any suggestions I'd love to hear them. I'm so close to done with this project, except for the frost issue...

author: Domagoj T
author_rank: Frequent Contributor
timestamp: December 02, 2020, 09:18:51 pm
content: Before contact lenses, when I wore glasses I had this anti fog substance that worked miracles. It was decades ago, so I don't remember what it was, but it may be a start for your search.Can you purge the atmosphere inside the enclosure with nitrogen? Throw in a pack of desiccant for a good measure.

author: mortrek
author_rank: Contributor
timestamp: December 02, 2020, 09:35:23 pm
content: I've done this. The inside is fine, it's the fog/frost on the exterior that is the problem unfortunately.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 02, 2020, 09:48:34 pm
content: There are some anti-fog/anti-frost gels, some are used for car windshields, too.Use hermetic cases and add silicagel granules inside the enclosure to absorb any moisture. If it's very exposed to ice/snow, use a defrosting/heating band.

author: mortrek
author_rank: Contributor
timestamp: December 02, 2020, 10:19:01 pm
content: It's an IP67 case with an anti-fog coated polycarbonate viewport. I have lots of silica gel packets in the case. The problem is the exterior.Does anyone know of any extremely small low-draw (probably <2A) 5-12V heat guns that I could direct onto the viewport area? I have been looking for hours now and cannot find anything even close to what I'd need.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 02, 2020, 11:01:04 pm
content: Maybe whipers + antifreeze sprinklers then, like the cars use?

author: themadhippy
author_rank: Super Contributor
timestamp: December 02, 2020, 11:59:58 pm
content: washing up liquid or liquid soap,, used to stop the visor on my skid lid fogging up

author: coppercone2
author_rank: Super Contributor
timestamp: December 03, 2020, 01:19:52 am
content: the problem is that with hydrophobic surfaces you get beading, so if you have dust on it, then water gets on it, and dirt, it makes a little drop on the surface which tends to concentrate the crap in a small dot and it evaporates to form a point that is aggressively contaminated when compared to a surface tension surface that evaporates it on a broad area (the drop do not form as big they are more like puddles).This is a car problem, you have great ceramic coats that have the potential to replace wax, but as soon as anything but clean rain water dries up on the car it ends up looking like garbage, because it bonds to the coating and the differential contraction ends up destroying it when the stuff crystallizes etc.It's not really a solved problem. Rain-x is good but you need to hose off and dry you car after winter salt roads or it makes your windshield really bad.Heated glass is a good option if you have the power budget but you don't solve the dirt and dust problem without mechanical action of some sort. That is a common aerospace product, but they still have some guy with a squeegee clean it up once in a while.The hydrophobic coatings for cars are considered a double edge sword and basically require cleaning to stay good.In a nutshell : hydrophobic requires cleaning in certain conditions or it has the potential to get really bad.

author: helius
author_rank: Super Contributor
timestamp: December 03, 2020, 02:06:14 am
content: A product called "ceramic hybrid wax" leaves a durable hydrophobic coating. That coating is thick and not optically clear, but after scrubbing with Windex it becomes clear and still hydrophobic. The warning about dirt above is true: if water beads up, it concentrates contamination.

author: coppercone2
author_rank: Super Contributor
timestamp: December 03, 2020, 06:10:16 am
content: for glass rain-x cleaning and protecting spray might be a better bet if you do maintenance but for durability a paste wax will last the longestNot sure I would paste my windshield but maybe it works. I use mcguires hybrid spray wax on my car (procedure is to wet car, spray a little wax, then hose it to distribute it then wipe it off. When I reapply it on the roof (once a month ideally) I don't notice problems with my windshield but its not paste. It must run down on the windows.Not actually sure what paste wax will do to optical clarity?

author: mortrek
author_rank: Contributor
timestamp: December 03, 2020, 06:19:59 pm
content: I think there is genuinely no amount of current, accessible materials science that will solve my problem. Hydrophilic surface is great for fog, but terrible for frost. Hydrophobic is great in theory, but in practice just makes the viewport area filthy and doesn't really eliminate fog that well anyway.I think my only choice is to use the hydrophilic coated viewport, and use some sort of heating to melt off frost.I have two options (that I can come up with, anyway). First, use batteries to heat a focused part of the viewport, where I melt just enough for the lens view angle. I have DS3231 connected to the uC, so I could probably just use the thermal data from that to tell if it's close to or below freezing. Then, whenever needed (possibly just once per day) I trigger a mosfet or relay or whatever to turn on a heating element that blows air onto the window. I would need to figure out how long this is necessary to melt the unknown thickness of ice on the window.I do not have a heater that is compact enough to do this. It needs to be very small, have a fan, only consume maybe 1A, and run from 9V. Since I can't find this, I will try building my own from a fan and some power resistors w/heatsinks or nichrome or something. Probably the resistors, since they would be safer. So maybe a 10W heater with a fan. Hopefully this would not take too long to clear out a little frost.Another option, which limits placement of the entire system, bulks it up and costs more, would be a solar cell connected to a mechanical thermostat that just runs a heating element inside the main rig as long as it receives power, possibly with a battery backup. It would likely stay above freezing much of the time, but that introduces not only the problems I already mentioned, but then the solar system becomes a whole issue to deal with in addition to everything else. I would like to be able to put my project in a wooded area, so solar dependency is not ideal.So, for now, I'll experiment with the battery-based air heating system.** What I could really use from someone is a source for a very small ~10w forced air low voltage (5-9V) heater. If such a thing doesn't just exist to buy, is there some sort of product that exists that I could cannibalize for parts? Like even cheapo heat guns are usually AC or, if low-voltage DC, are very high current devices. It needs to be very compact, the smaller the better. It's hard to specify an exact size, but something like less than 4cm cubed would be great, or even a form factor like a thick permanent marker would work.

author: themadhippy
author_rank: Super Contributor
timestamp: December 03, 2020, 06:27:49 pm
content: wot about a usb soldering iron as the heat source,might finally find something useful to do with them,and a small fan

author: nali
author_rank: Frequent Contributor
timestamp: December 03, 2020, 06:35:11 pm
content: Is this a still or video camera? If still, could a mechanical wiper or shutter work?Note that you'll also probably need to consider dew as well as frost depending on environmenthttps://en.wikipedia.org/wiki/Dew_point

author: mortrek
author_rank: Contributor
timestamp: December 04, 2020, 07:34:54 pm
content: I'm using a still camera. A mechanical wiper would probably not work because the ice would form regardless. A mechanical shutter is an interesting idea but I have no idea how to implement it. It would likely lock up from ice exposure, for example. The interior needs to be kept sealed from the outdoors for the equipment inside to have any chance of surviving a year outside, so a shutter would have to be exterior, and my head starts spinning a bit from the challenges introduced by it.Not to keep bumping this topic... but I've got some ideas/a loose plan.I ordered a 20W 12V infrared halogen 35-degree angle flood bulb originally meant for saunas. I will see if that is an efficient way to melt the ice. I will likely add at least one additional parallel bank of batteries, as well. It will detect freezing conditions with the DS3231, turn on the bulb for some time that will need to be figured out, and hopefully focus the energy effectively enough to clear the ice. Once the ice melts, presumably the hydrophilic surface will spread it out and the viewport area will be optically clear enough for a photo.Of course, one or many of these things may not work out. I may just have to implement solar heating or something, which makes my project much less flexible.I'll also need some sort of test environment, since it won't be freezing at night forever where I live. Maybe I'll just toss the thing in the freezer...

author: Kleinstein
author_rank: Super Contributor
timestamp: December 04, 2020, 09:25:10 pm
content: I mechanical shutter (on the outside) may still be a good option. Even if it would not stop the icing all the way, it could reduce the ice and could help reducing the heat needed to clear the rest, as less heat is lost. For the shutter one could consider a rotating disk with a hole - possibly transparent, so that failure would not block the sight totally.Already having a kind of tube for shade can help, as there would be less air movement and less dirt. Chances are the window would not be the coldest part and ice would form at the tube instead of the glass. A colder part can catch the water before it reaches the window.Icing is often bad on parts that get especially cold in the night - e.g. the roof of the car that looses radiative heat to the sky.For the heater it could help to check if there is actually ice. There can be quite some days below zero without icing.Depending on the lens and distance, some local spots may not be so bad, if the window is rather close to the lens. The dirt that is way out of focus (e.g. on the cameras front lens) with no light from behind does not show up very much. So not sure if the hydrophobic surface is actually so bad.

author: eliocor
author_rank: Unknown
timestamp: December 04, 2020, 11:06:55 pm
content: ever heard ofTransparent Heater Windows?Just some examples:https://tfdinc.com/products/transparent-heaters/http://www.visionteksystems.co.uk/transparent_heater_window.htmhttps://diamondcoatings.com/ito-heater-windows/https://abrisatechnologies.com/tech-notes/what-is-a-transparent-window-heater/

author: cdev
author_rank: Super Contributor
timestamp: December 04, 2020, 11:13:29 pm
content: Its my understanding from discussions here about OCXOs that most devices that need to generate heat in a very controllable and optimally energy efficient wayuse transistors to do it, not resistors.There was one thread about a Bliley OCXO teardown where I think the use of transistors was discussed, perhaps in the thread about Lars Wallenius's simple GPSDO build.Sorry that I could not provide more info.Quote from: mortrek on December 03, 2020, 06:19:59 pm