LEDs at Elevated Temperature

[Visitor]

Anybody here have any experience with LEDs at elevated temperatures?

I'm working on a temperature data logger to be used inside of a "Instant Pot" (pressure cooker) to evaluate a canning process that will reach a maximum of 122°C (boiling water under pressure) for less than 4 hours.

The micro, eeprom and temperature sensor are rated for operation at 125°C. I don't expect to get many operating cycles out of this, but these components should survive.

LEDs are another story. 80° – 90°C look like the typical rating. "High temperature" LEDs are rated at 100°C. I know elevated temperature will result in LEDs becoming dim. Any experience for operating a few hours at high temperature with LEDs flashing for short periods? Current towards the low end of the spec rather than higher (for more brigbtness)?

Just to cut off any helpful suggestions... the Instant Pot pressure vessel is metal with a tight seal to hold steam pressure and may not be penetrated. Temperature measurements on the wall of the pressure vessel to not reflect what's happening with the product inside, so that's not helpful.

 

[gophert]

The newer flat packs are getting higher and higher temp. The Osram Flat Black can handle 125°C

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[Reloadron]

Just to cut off any helpful suggestions... the Instant Pot pressure vessel is metal with a tight seal to hold steam pressure and may not be penetrated. Temperature measurements on the wall of the pressure vessel to not reflect what's happening with the product inside, so that's not helpful.

Beats me as I used thermocouples with compression fittings on autoclaves heating Grade A water to 600 F. I really do not see why the same can't be applied to a pressure cooker. Our vessels were pressurized to 3,000 PSI and thermocouples 1/8" OD Stainless sheath in a 3/8 compression fitting did fine. At 15 PSI above atmosphere the boiling point of water at sea level increases from 212 F to about 250 F so it's not like major pressure. Believe me compression fitting thermocouples do not leak or fail. You may want to read the specifications. Your 122 C is about par for a standard pressure cooker. Larger compression fittings are useable up to about 10,000 PSIG.

I seriously doubt you will find a solution which goes into the pot but good luck looking.





Ron

 

[JimB]

Why do the LEDs need to be inside the "Instant Pot"?
The pot is sealed when in operation, so the LEDs cannot be observed.

You are making a data logger, so presumably the data is recovered from the logger once the cooking process is over.
Why do you need the LEDs to be inside the pot?
If you just need a couple of LEDs for status indication at start and stop time, why not use simple "grain of wheat" incandescent lamps? No temperature problems with those.

JimB

 

[Visitor]

Interesting that lighting LEDs are capable of ever-higher temperatures. In this case though, I just would like a couple indicator LEDs, and have limited space available.

Pressure glands aren't practical in this case. I want to make a few measurements inside a jar of food product, inside a commercial Instant Pot. Permanently modifying the lid for a possibly one-time experiment is undesirable and penetrating the thin metal canning lid might invalidate the experiment.

I guess I'll try it, and if the LEDs survive a couple runs, great. If not, it makes the experiments a little more difficult.

 

[Mickster]

What's the purpose of the LEDs?
To report conditions/status at an end-of-cycle test, rather than have to read EEPROM?
EDIT:
Scratch that.......answered in the post above.

 

[Visitor]

There are a few reasons I may want some LEDs:

Setting up data acquisition interval.

Indicating when readings are being made, to verify operation. Not visible during the actual cooking process of course.

An indication that the desired time–temperature parameters have been met. The kill process for bacteria is a function of time at a certain temperature.

I can't design a microcontroller circuit without an LED to flash!


At this point, I don't know exactly what direction this project may take. There is a lot of interest in using Instant Pots for home canning with little quality information on the safety of doing so.

 

[gophert]

Use an ESP32 or ESP8266 and you can send WiFi or Bluetooth signals instead of flash an LED.
Easiest if you make the ESP a web server in Station/Access Point mode and each time you ping it with your phone/tablet or laptop, it sends current temp/pressure. It won't transmit through the steel installation well but, hey, same problem with LEDs. It would be interesting to hear if the ESP survives the 122°c for a few minutes.

 

[Mickster]

A kinda drop-in-and-leave data-logging 'egg', with a go/no-go result at the end?

 

[Visitor]

Use an ESP32 or ESP8266 and you can send WiFi or Bluetooth signals instead.....

I don't know that RF would get out of the pressure vessel. There is a silicon gasket, so it's not a total metal-metal seal, but the lid overlaps the gasket.

I suspect the temperature rating of an ESP32 doesn't approach 125°C. Have to look that up.

 

[gophert]

I don't know that RF would get out of the pressure vessel. There is a silicon gasket, so it's not a total metal-metal seal, but the lid overlaps the gasket.

I suspect the temperature rating of an ESP32 doesn't approach 125°C. Have to look that up.

 

[Visitor]

Might be worth a try.....

 

[schmitt trigger]

An acquaintance of mine used to work for a company which built bore hole probes used in the oil industry.
Those have to survive, for a period of time, the enormous temperatures and pressures found there.
Let me see if he can suggest something.

 

[gophert]

I can confirm LEDs can survive some amazing temps and pressures. Color may shift if you get too hot but it is more difficult than you think to kill a 5mm indicator LED - especially the red ones.

 

[Visitor]

I can confirm LEDs can survive some amazing temps and pressures. Color may shift if you get too hot but it is more difficult than you think to kill a 5mm indicator LED - especially the red ones.

I'm using suface mount 0603s, in yellow and red (green is marginal on my battery voltage). I'm adding patterns for through-hole LEDs if the surface mount ones don't survive.

 

[gophert]

I'm using suface mount 0603s, in yellow and red (green is marginal on my battery voltage). I'm adding patterns for through-hole LEDs if the surface mount ones don't survive.

Some modern (smd) green and most blue LEDs have silicone lens covers and don't survive pressure very well. The blue and "True Green" LEDs emit a small amount of UV so they turn the "normal" plastic yellowish which would shift the emitted color. The silicone is fairly soft and bond wires break under pressure.

 

[Nigel Goodwin]

I can't design a microcontroller circuit without an LED to flash!

Like bombs in films and TV programmes - you can always tell it's a bomb, as it has a flashing LED

But i know what you mean, it's always useful to have an LED stuck on an I/O pin, handy for debugging and all kinds of purposes.

 

[Reloadron]

I want to make a few measurements inside a jar of food product, inside a commercial Instant Pot. Permanently modifying the lid for a possibly one-time experiment is undesirable and penetrating the thin metal canning lid might invalidate the experiment.

Maybe all of this would go better if you defined in detail exactly what you are intending to do? You failed to mention a Mason Jar (or similar) in your initial post. Since this apparently becomes works in a jar how much space do you plan to displace and what food products will be in the jar? Why not fabricate a custom lid with feed through? These jars including lids are pretty inexpensive. What do you have in mind for a data logger? I assume whatever you bundle will need power within the bundle?

Ron

 

[Visitor]

Not that I don't appreciate the help and guidance, but my question was and remains to be how indicator LEDs will perform at elevated temperatures. That they are in a pressure cooker water bath is useful information because it means that the temperature cannot go beyond the specified temperature even for an instant.

The specific question was intentional. Too often I see people ask questions here, and rather than the question being addressed, their idea is torn apart, redesigned to be the way "I would do it", their motives questioned, etc. People may want to "do their own thing their way" even though it's not necessarily the best or easiest way to accomplish something.

All of that being said, here's what I am researching. In years past, "county extension agents", often working in conjunction with state universities, had programs to advice people on cooking techniques and food safety, gardening issues and other "home ec" areas. With changing lifestyles, changes in government funding and etc, these programs have been less active.

One of their large areas of expertise was in home canning – it's in the government interest to prevent people dying from botulism due to improper canning techniques and home canning of inappropriate foods. Depending on what's being canned (where the can is actually a glass jar), canning has been done in an open boiling water bath or a pressure cooker if a higher temperature is needed for the "kill step", which depends on time and temperature. For different foods and the types of bacteria that will grow in them, certain temperatures must be reached and maintained for certain time periods. If a higher temperature can be achieved, the food can be held at that temperature for a shorter period of time. Time and temperature charts have been developed for canning in pressure cookers, as their behavior is well understood and documented. Apply enough heat and maintain a pressure of X and the temperature will be Y. This is simple physics and is always true.

"Instant Pots" are the latest cooking craze – crock pot and pressure cooker all-in-one. But there is an unknown about these, resulting in extension services making the recommendation that they not be used for canning. It is unknown if the "smart" control system actually maintains a constant temperature during pressure cooking. Does the control system try to use as little energy as possible and keep the heat input to the minimum level necessary to maintain the pressure, and possibly cycle above and below the required temperature as it does so? If the 110°C temperature required to maintain a particular pressure cycles cycles around 110°C instead of always being 110°C as guaranteed by an adequate thermal input, the safety of the kill step is lost. This is the kind of research extension services used to do, but since nobody is doing it, the recommendation is that Instant Pots are unsafe for canning.

So the question is documenting the temperature over a period of time. The particular question – is it safe to home can tuna in an Instant Pot. What is the temperature profile in the center of a pint jar filled with tuna over a processing time of about 4 hours? Data should be logged often enough to provide a detailed temperature profile over a 4 hour span. Because a sample size of one doesn't provide proof of anything, the test needs to be repeated in different brands and types of Instant Pots to verify results. My partner is a foodie in a community of foodies, so the knowledge and interest to research the problem thoroughly exists.

Designing a data long for 125°C isn't too difficult, aside from a few issues:

¤ Power: Panasonic BR2450A lithium coin cell is spec'd to 125°C, and provides 550mAH at 3 volts.

¤ Crystal: Crystals rated for high temperature are available.

¤ LEDs: If run of the mill LEDs last though a few processing cycles, great. If not, it's just a little less certain that data logging is actually occurring during a given run.

I'm planning to have these assembled at JLCPCB. Micros in their parts assortment in the industrial temperature range are limited, but fortunately, the selection includes the PIC28F24/226F1K22-E/SS. For the temperature sensor, I'm using Microchip's MCP9808. A EEPROM rated at 125°C completes the circuit.

 

[Nigel Goodwin]

Not that I don't appreciate the help and guidance, but my question was and remains to be how indicator LEDs will perform at elevated temperatures. That they are in a pressure cooker water bath is useful information because it means that the temperature cannot go beyond the specified temperature even for an instant.

The specific question was intentional. Too often I see people ask questions here, and rather than the question being addressed, their idea is torn apart, redesigned to be the way "I would do it", their motives questioned, etc. People may want to "do their own thing their way" even though it's not necessarily the best or easiest way to accomplish something.

All of that being said, here's what I am researching. In years past, "county extension agents", often working in conjunction with state universities, had programs to advice people on cooking techniques and food safety, gardening issues and other "home ec" areas. With changing lifestyles, changes in government funding and etc, these programs have been less active.

One of their large areas of expertise was in home canning – it's in the government interest to prevent people dying from botulism due to improper canning techniques and home canning of inappropriate foods. Depending on what's being canned (where the can is actually a glass jar), canning has been done in an open boiling water bath or a pressure cooker if a higher temperature is needed for the "kill step", which depends on time and temperature. For different foods and the types of bacteria that will grow in them, certain temperatures must be reached and maintained for certain time periods. If a higher temperature can be achieved, the food can be held at that temperature for a shorter period of time. Time and temperature charts have been developed for canning in pressure cookers, as their behavior is well understood and documented. Apply enough heat and maintain a pressure of X and the temperature will be Y. This is simple physics and is always true.

"Instant Pots" are the latest cooking craze – crock pot and pressure cooker all-in-one. But there is an unknown about these, resulting in extension services making the recommendation that they not be used for canning. It is unknown if the "smart" control system actually maintains a constant temperature during pressure cooking. Does the control system try to use as little energy as possible and keep the heat input to the minimum level necessary to maintain the pressure, and possibly cycle above and below the required temperature as it does so? If the 110°C temperature required to maintain a particular pressure cycles cycles around 110°C instead of always being 110°C as guaranteed by an adequate thermal input, the safety of the kill step is lost. This is the kind of research extension services used to do, but since nobody is doing it, the recommendation is that Instant Pots are unsafe for canning.

So the question is documenting the temperature over a period of time. The particular question – is it safe to home can tuna in an Instant Pot. What is the temperature profile in the center of a pint jar filled with tuna over a processing time of about 4 hours? Data should be logged often enough to provide a detailed temperature profile over a 4 hour span. Because a sample size of one doesn't provide proof of anything, the test needs to be repeated in different brands and types of Instant Pots to verify results. My partner is a foodie in a community of foodies, so the knowledge and interest to research the problem thoroughly exists.

Designing a data long for 125°C isn't too difficult, aside from a few issues:

¤ Power: Panasonic BR2450A lithium coin cell is spec'd to 125°C, and provides 550mAH at 3 volts.

¤ Crystal: Crystals rated for high temperature are available.

¤ LEDs: If run of the mill LEDs last though a few processing cycles, great. If not, it's just a little less certain that data logging is actually occurring during a given run.

I'm planning to have these assembled at JLCPCB. Micros in their parts assortment in the industrial temperature range are limited, but fortunately, the selection includes the PIC28F24/226F1K22-E/SS. For the temperature sensor, I'm using Microchip's MCP9808. A EEPROM rated at 125°C completes the circuit.

It sounds an interesting project, I would suggest putting one together and giving it a test to see how it performs/survives - it sounds unlikely that anyone here has done something similar, so it's pretty well all guesswork.

You could even try just an LED or two and a battery, different types and makes, and see how they hold up - without bothering with the rest of the electronics for now.