# Is it safe for a CR2032 coin cell to be in an oven?

I'm designing a portable temperature logger that I would like to be able to measure temperature within my home oven. I plan on designing a mechanical enclosure to hopefully protect the design from 'frying'. Essentially I will be insulating it and I don't intend on keeping it in there any longer than it has to be.

I was looking at small coin cells to power my design (it's very important that this design be very flat, only a few mm's tall). I was looking at a couple CR2032 coin cells that assumed to be appropriate for my current draw and required capacity. However, I have noticed that they are only rated to 70C.

Now my oven will likely be getting up to 250C, so obviously it will be important to have good insulation because the battery will be outside of its rated temperature.

But I'm curious, is this safe? Assuming my design isn't exposed to an open flame, could the battery explode? I've been hearing a lot in the news of exploding batteries. I assume the battery would eventually stop working if it got too hot, but could the battery explode? Or would it likely just stop working? Again, I'm looking at a small CR2032 coin cell. I'm primarily curious in the case my insulation fails.

• Your insulation is only giving you a time delay - it will not ever prevent the inside of your enclosure from reaching the same temperature as the outside. The more effective your insulation, the longer it will give you. But if I read between the lines of your question it seems to me that what you're proposing would not be practical. – brhans Oct 24 '16 at 16:48
• It is NOT a good idea to put any kind of electronics inside food-preparation equipment. Batteries can leak noxious chemicals (eg. gasses) even without any visible evidence of having done so. This will contaminate any food and present a serious health hazard. – user98663 Oct 24 '16 at 17:41
• I think you need to take a step back and think about what you are trying to achieve, not how you think you want to achieve it. – Majenko Oct 24 '16 at 18:15
• It's very easy to run a thermocouple wire out through an oven door. Do that. – Spehro Pefhany Oct 24 '16 at 19:32
• Use a thermocouple inside the oven and keep the sensor and electronics outside. I don't know the answer to your question, but it seems incredibly ill advised. If you decide to go forward anyway, you could consider adding a large thermal ballast inside the insulated compartment where the electronics are. I am sure I would not try to do what you are doing. – mkeith Oct 24 '16 at 22:37

So, first of all, CR2032 is a Lithium Battery type, so, yes, overheat it and it has a good chance of exploding/combusting.

I'd really just go and use some cable to get the sensor into your oven, and keep the battery on the outside. Less trouble, more reliability, less isolation that could fail.

• Seconded on the idea of using cable to get the sensor in the oven. Me and my labmates rigged up a solder reflow oven with a standard toaster oven, and we ran wire from an outside box into the oven to get the thermistor inside. I would suggest something similar for this project. – justinrjy Oct 24 '16 at 21:43

The highest temperature range I've seen documented by a manufacturer are the Panasonic BR-A series (carbon monofluoride type) lithium. The maximum temperature is $125\:^\circ\textrm{C}$. You should probably consider using something like that and then also calculate the expected duration before the interior of your enclosure reaches that temperature. (Corners and edges will have different behavior than broad surfaces, too.) Don't assume. Develop an accurate model, because you are the only person who has enough data to make such estimates. In general, semiconductor-based devices will probably be in better position to operate at those temperatures and higher, but you should also do some estimations of temperature drift in their behavior, as well.

I don't think manufacturers specify the behavior of their batteries when operated beyond their absolute maximum specification limits. So whether or not it will explode? You'd probably have to contact a manufacturer and ask, or else do the experiment yourself.

Given what little you've written and what I can find on such battery types, it's probably not safe. (You asked. That's my answer.) But if you provide more information, create some modeling to demonstrate results, and discuss them here, then it may be possible to convince me (or others) that it may be safe to try. But with what little you've provided, it's almost certainly not safe.

You might try using sensors that run leads to the outside of the oven. Isn't that the usual way? Why aren't you doing that, instead? I've even used fiber optics for this purpose, before (both in regular ovens as well as in commercial microwave oven units.) I'm not sure why you aren't approaching the problem's solution from that angle.

• DO NOT undertake experimentally subjecting any cells to high temperatures inside your oven if you are also using it for food preparation. You could contaminate any food subsequently prepared if the cells either do explode or leak toxic microparticles into the oven. – deed02392 Oct 26 '16 at 14:01
• @deed02392 I didn't assume food was present at $250\:^\circ\textrm{C}$. Others did. I've actually set up a data logger system in a rotating platform in a home oven operating at $150\:^\circ\textrm{C}$, which also exceeded battery specs and where testing was required to validate the operational time. In fact, I've set up a small FAB at home, with wafer temps nearing $1500\:^\circ\textrm{C}$ and ramps of $200\:\frac{^\circ\textrm{C}}{s}$, with nickel reflectrs, N2 backfill, and water cooled quartz walls. Of course I agree food shouldn't be present. But I doubt there is at those temps. – jonk Oct 26 '16 at 15:45
• @jonk I think deed's point is that if the device sprays (or even might have sprayed) toxic crap all over your oven, you'd better decontaminate that oven before you use it for food again. – David Richerby Oct 26 '16 at 20:13
• @DavidRicherby Yeah. There's that. But heck. Those are the risks. The battery can be contained while heating it to mitigate such risks. I guess it boils (no pun) down to this: One may caveat their answers like some commercial companies do with their products, saying, "Do not stick this brand X carving knife in your eye." But I tend not to assume the OP is an idiot unless they demonstrate it in their question. I gave them the benefit of the doubt and not going off half-cocked assuming they are insane. I've done this kind of thing myself, so perhaps this is optimistic of me. But there it is. – jonk Oct 26 '16 at 20:43
• @jpaugh I have such experiences. That doesn't make either of us wrong. It just means that we made different reasonable conclusions from the same (lack of) information from the OP. I found the assumptions made by others to be misguided. I looked at the temperature being suggested in coming to that conclusion. I did question myself here and tried to see what the totality of facts suggested. I also then read the OP's writing and felt the OP would know better than to test a battery unenclosed. (He specifically said he planned an enclosure, I noted.) So you and I saw it differently. – jonk Oct 27 '16 at 20:30

No, a battery exposed to the temperatures inside the chamber would mean violations of food safety and machine safety, no matter how good you shield it. Solder will also melt at temperatures well below 250°C. Capacitors will also be a problem.

1. Infrared

According to this article, this would be one of the use cases infrared thermometers are designed for:

Checking heater or oven temperature, for calibration and control

However, this answer https://cooking.stackexchange.com/questions/21655/infrared-thermometer-for-oven-temperatures suggests, that you cannot just use it to "look through the glass", which makes it impractical.

2. Probe

Commercially available high temperature loggers are battery-powered and well shielded, but they all come with a probe (http://www.deltatrak.com/products/high-temp-data-logger) and the battery/electronics part is always meant to be positioned well away from the heat source.

3. Outside the box

You could attach a sealed circuit without a battery to the inside of the oven window, and power it by induction, if you can get it close enough (in the way wireless chargers work). But still the challenge to get the other components heat-proof remains.

A decent oven would be IoT integrated and should have temperature, humidity, and the blood type of the turkey readily available on a static IP.

• but does it support HTCPCP? – user2813274 Oct 25 '16 at 1:45
• Be aware that the turkey may be able to initiate a DDOS attack on your home network, though. – alephzero Oct 25 '16 at 4:57
• @alephzero All you need to prevent that is a proper firewall. – a CVn Oct 25 '16 at 11:06
• @alephzero, Distributed Denial of Stuffing? – user98663 Oct 25 '16 at 11:58
• Unfortunately that oven model had to be delayed due to concerns about "shielding of emissions". Specifically, it kept catching fire and burning down the test room as the the sensors insisted the turkey was still frozen. – Kaithar Oct 26 '16 at 17:38

I worked for a major battery company developing lithium coin cells like the CR2032, so I will answer simply: because of the extreme thermal abuse you are thinking about, you will vaporize the liquid electolyte inside, which will rupture the cell. Popping the cell will also expose the lithium metal inside--not a good idea. Please employ one of the work-arounds people have suggested that doesn't involve putting a battery into the oven.

They use 1/2" thick Silicone molds for DAQ profilers with battery LiPo battery power use for reflow oven thermal profiles on bare boards to get the thermal recipe right then do a run a few with populated boards. But then the entire reflow profile is completed in 5 minutes MAX.

I suggest you use external DAQ board and battery or invest in hotplates.

and as others have said , it may rupture with nasty chemicals inside the oven and your Mom/gf/wife wont like it. It may add an odd carcinogenic flavour to your cooking.

The only safe way to put sensitive electronics in hot environment is to use an active thermal control system. The simplest example would be a thermally insulated container filled with a liquid with low boiling point (like alcohol), which in turn hosts your electronic component in a sealed package. The insulation slows down the heat transfer, and the boiling liquid cools down the interior, keeping your device at a stable temperature.

ATCS are used in real life, e.g. on space telescopes (e.g. using liquid Helium to cool down the infrared sensors), but I'm certainly not suggesting to implement this in your oven. Keeping everything except the temperature sensor outside the oven is by far the simplest solution.

In general, there is a whole engineering discipline of high temperature electronics; for an introduction, do a web search about so called downhole electronics, these are used in the oil business where exposure to a temperature range similar to a food oven is an unavoidable fact.

Use evaporative cooling, it'll prevent (part of) your device from going above 100 °C.

A recent Kickstarter, the Meater, used wireless thermometers that you could put inside an oven, grill, smoker. I'm not sure why it's so great over a wired thermistor/thermocouple, but I liked their idea to bury the battery and more sensitive electronics down in the tip of the device that you'd stab into something wet. As the wet thing cooked, its temperature wasn't going to exceed the boiling point (100 °C or so) until it completely dried out, in which case it would probably be inedible.

Designing for 100 °C ambient is infinitely easier than 250 °C.

Is it safe for a CR2032 coin cell to be in an oven?

it is safe alright for the coin cell.

it may not be as safe for the oven or people around the oven.