I tried shrink wrap; special plastic film that you wave a heat gun over and it shrinks up… in theory it works as advertised, but when you think about it, there is almost always a teeny gap somewhere. I imagine large-scale industrial strength shrink wrap works much better, but I only had some I bought off eBay, and a heat gun for drying e.g. paint. To me, it’s one of those things that sounds good in theory but when you get right down to exactly how much you put where, and how it’s going to shrink (without heating it so much it bursts), I just couldn’t get a complete seal relative to an immersion test.
I can always try it with plastic film / cling film / Saran Wrap … it’s very easy to wrap it around some little thing that’s covered in toilet paper… Then hold it under water a half hour, and see if any of the tissue paper gets the least bit wet.
Andy, it’s not that I totally disagree with you. Obviously plastic wrap or shrink wrap is much better than nothing, and probably more than good enough in many situations. I’m just asking, what ideas do people have? and how good do they work. It is good to hear film works great for you.
John, I am thinking silicone is still in the lead here. It might be slightly gunky but it otherwise ticks every check mark you want. I guess I will give plastic wrap a spin first, to see how well it does. Easy to test.
Batteries outgas, and consequently unless the Device is specifically designed to operate in an airtight container, it’s not a good idea to weatherproof it to that extent.
In addition, there’s an issue of heat dispersion. The casings are almost always designed to be part of the heat dispersion method, and blocking or sealing any part of it may greatly reduce the life of the radio inside.
So rather than trying to weatherproof the sensor itself, unless there is a manufacturer – approved method, just put it in an electronics “project box” approved for your location with the air gap on the bottom (that’s how they’re designed generally anyway). It will be firesafe, it will be easy to change the batteries when needed, it won’t void the warranty, and it will preserve the expected life of the device.
If it’s a PIR motion sensor, you will need to leave a gap over the lens for detection.
Just don’t put a battery operated device in a Ziploc bag, or cling film, or try to seal it with silicon, or anything else which will change the heat dispersion or prevent the battery gases from escaping.
Your local electronics warehouse should have lots of project boxes to choose from.
I appreciate what you’re saying JD, but does your argument about battery gas mean that a sealed device would explode from pressure eventually? I am pretty sure a number of people seal with silicone, and I can’t recall hearing of anything like that. Is there a thread on it?
Also, seeing as how these devices have never once been hot to the touch or even warm, I’m sorry but I can’t agree with a heat dispersion problem. Something like the SmartThings Multipurpose or Motion Sensor are, for all practical purposes, sealed against air movement through them, so the designers expect no appreciable heat. (That’s not the same as being completely moisture sealed, though.) Nor would one expect a tiny button battery to last long at all if a device was using energy so fast that it was constantly hot.
Let me ask folks reading this thread: What’s the longest you’ve had something sealed? What kind of sensor was it? Have you seen problems like JD describes?
We’re all just sharing thoughts and experiences here. Thanks, JD!
Some of us are also sharing professional experience.
Designing for heat dispersion is a huge issue in battery-operated devices, and even more so in networked devices. it doesn’t mean it’s hot enough for you to feel a difference when you touch the device.
By the way, have you had a chance to read any of the threads in the forum on using PIR motion sensors outdoors? That’s an entirely separate issue, but it’s something you should probably be aware of.
Anyway, by all means, write the manufacturer of the specific device you’re considering and ask them if it’s OK to weatherproof it with silicone or anything else.
And for those interested in technical details:
with shrinking form factor and increasing functionality and performance, portable battery power equipment is demanding more power than ever before with a limited board space, making thermal management One of the most critical design challenges today.
Unfortunately, sometimes system design engineers fall into the trap of assuming that the IC components they use in their equipment designs are also “plug and play.” It is easy to assume that if you just “connect the dots” in the same way that is shown in the application diagram from the IC’s data sheet, you won’t have to do any additional analysis or validation of your design. But while the guidelines and suggestions provided in modern IC data sheets might simplify system design, they don’t entirely eliminate the work that needs to be done by the product design engineer.
Designing the power system for battery-operated equipment consists of two major sections. First, we have to choose the right type of battery technology and pack design. Second, we have to develop the electronic circuitry to charge that battery pack and convert the battery’s unregulated “raw” voltage into the regulated output rails needed to operate the actual system electronics. Last month, we talked about the importance of choosing the right type of battery technology as the first step. Once we do this, then the “real work” begins.
A very common oversight is the lack of thermal analysis. In particular, for very low-power battery-operated equipment, it’s easy to think that the power levels are not high enough to worry about thermal management. However, remember that the power density of these handheld systems can actually be quite high.
Table 1 shows us that even devices with low absolute power consumption need to be carefully designed, keeping thermal management in mind.
Remember, we are cramming that low power consumption into a very tiny space. For higher power devices such as ultrabooks, notebooks and computers, heat dissipation is quite noticeable. The device actually feels warm to the touch.
For lower power devices, with only milliwatts of internal dissipation, the end-user may not feel the unit case getting hot. However, if the dissipation in the low-power circuitry is localized to a small “hot spot” inside the unit, there may be concerns associated with device reliability or usability. This is especially true if the semiconductor components are being operated closer to (or above) the recommended thermal limits.
When you seal it, you inevitably raise the internal temperature of the device. But beyond that, I can pretty much guarantee you that the engineering process for designing that device looked at how heat would dissipate through that specific case. Weatherproofing materials can change the thermal patterns, creating the hot spots mentioned in the article. That’s the main reason that that kind of process almost always voids the warranty on the device.
But again, the best thing is probably to talk to the manufacturer of the specific device you’re intending to modify. They’ll know best what impact, if any, you can expect.
Hey wow, that sounds like a truly simple alternative, cuboy! A little less hassle than silicone… not that silicone is a huge hassle, but jars of vaseline sit there for years… silicone is a tube that dries up, doesn’t wash off with water, etc.
What @JDRoberts says about batteries & outgassing is very important. There are boxes specifically made to “breathe” without letting water in.
That being said, the vents usually point downward. Other parts of the box are sealed, often with O-rings or similar gasket material. Someone earlier asked for alternatives to common silicone sealant. There used to be a silicone product for sealing around an automotive windshield that was “runnier” than common sealers. Perhaps you could check auto supply stores for that?
Do all batteries outgas? I ask because I have several waterproof flashlights using everything from lithium 123 (same as many sensors) to small button battery powered ones. Since a flashlight would have a much higher draw wouldn’t outgassing be even higher?
electronics failures are not a yes or no thing. Excess heat degrades transistors within electronics over time and causes them to fail sooner than they are designed. Even if it doesn’t feel hot or you don’t notice a problem, that doesn’t mean there isn’t one. Electronics in RF components are vary sensitive and require dissipation and free air movement.
Yeah, what do I know. I just have a Masters in electrical engineering and design semiconductors.
You both misinterpreted me. Heat has to go somewhere. When electronics are enclosed in a box they have to dissipate through the package. The outside of that package needs air flow for the heat to dissipate, hence putting another sealed box around it was not intended by the design team.
Will it work? Sure, you just risk the reliability lifetime of the sensor. The main EFR of semiconductors is related to heat. It’s yours to do with what you want.
According to this the ecolink motion sensor can operate in ambient temps up to 120 F. So, battery gassing aside, if this was sealed and in a 80 F, would the dissipation be suitable for a motion event 20 times a day causing a radio signal? Now I doubt anyone can be that specifc, but you get the idea. Still very interested in how all these waterproof devices I have with 18650s and CR123s are humming along… flashlights are just the start of it… lots of diving equipment as well, etc.
I have a Masters in electronics I perfectly agree with your logic, but it’s all about scale. How much heat are we trying to radiate out of the box? And if the second box directly touches the first box (cling wrap), without any insulating air stratum, then what is the heat transfer factor between the two “boxes”? Definitely not 1, but much better than air’s. I was trying to make a point, I have a contact sensor working at 130 degrees Fahrenheit in a shed. Was it designed for that amount of external heat? Heat flows TO it - it has to, it’s a thermometer by design. I don’t know that answer. Will it affect its lifespan? Sure will. Will the lifespan be 3 years instead of 5 years? Maybe. Can I afford $20/3 years in order to have a contact sensor on my shed door to know if anyone opens it? I Think so. It’s all about risk assesment. Yeah, theory is right, practice follows suit, but how much is too much? I can get that sensor and put it in a controlled Faraday cage, forcing all radio transmission into heat, and I bet you the temperature of the inside sensor would not got much higher than a contol just outside the cage. Will it be higher, assuming a 25C controlled environmental temperature?! Maybe, but how much? 0.1 degrees? And then, keeping my home at 79 instead of 80 would be safe to assume would affect the lifespan of all my sensors within it, right? So then should I set my thermostat to 79 to “save” lifespan on all those devices? It’s all relative and it comes down to costs, in both hardware and time to maintain them.
Not to divert too much from the subject, but in the same vien of where the conversation has gone…
Decades of wisdom taught us to supercool our datacenters. Intel, Dell and others have recently proven they can maintain hardware at open air temperatures without cooling and will even warranty their devices in those circumstances. Will the hardware last AS long under the circumstances? No sure, need imperical data, but the data we have so far shows it will last the expected life enterprises have so it matters not.
I have several sensors outside now and not had a problem with a single one. I used the rubberized spray paint. I saw the commercial on tv with some watermelon drop or something but you can get it at Lowes and home depot. they have white so it looks normal. I also like that I can scratch it off with my nails when I need to change batteries. The tv brand is called flex seal, but just ask for the rubberized spray paint as they all make a version now.
I was JUST thinking about the same thing, well actually Plastisol - like kids spray their wheels and cars with, but that sounds better.
(Jason "The Enabler" as deemed so by @Smart)
I’m, I’ve got to throw my 2 drachma in here too. I’ve got no master’s degrees, I’ve got no doctorate, or any of that fancy learning crap…
But I did have 20 plus years experience working in aviation electronics, specifically in the high power RF generation and amplification for electronic countermeasures. What I worked on was liquid cooled.
So, now that I’ve said a bunch of useless crap…
Like Adrian said, it’s about risk assessment. Will you get at least a year out of that 20.00 sensor for the peace of mind of having that shed monitored? If the risk is too high, I certainly hope the shed is empty.
Yes, heat affects electronics in many different ways, especially lifespan.
But we are talking about a sensor that stays on for a couple of milliseconds at most, to read the temp and send a quick data pulse. How much heat is being generated? I’m going to guess, very very little.
The part that really affects the electrons is simple, there are two issues…
First - prolonged power consumption without proper cooling, think CPU.
Second - the fluctuating temp of a device turning on and off. Changing from 75° to 120° does more damage than anything.
Ok, I’m getting off my soapbox and going back to mopping the bathroom at Kmart.
But just remember, if you can’t afford to replace it in a year, you should probably not buy it in the first place.