high temperatur covering system for battery and PCB

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
Hi everyone;

I'm doing a reverse engineering for thermocouple system that works in specifique condition (temperature=300°C), knowing that the originaly systeme use the material below in the figure for covring the battery and the pcb.

Battery.jpg

I have already finished the electronique parts and the pcb and is wright.
My question is: what's kind of the green material is in the picture??
Or an equivalent material for isolate the battery and electronic part from the temperature ??

thank you in advance for any help
have best day
 
Last edited by a moderator:

LesJones

Joined Jan 8, 2017
2,840
The picture looks like polyolefin heatshrink sleeving. I do not think this will tolerate 300 degrees C and it will not protect the batteries from that temperature.

Les.
 

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
The picture looks like polyolefin heatshrink sleeving. I do not think this will tolerate 300 degrees C and it will not protect the batteries from that temperature.

Les.
thanks alot for your response,
1- the PCB is encapsulated by the same way.
2- I managed to decender from 300 ° C up to 120 ° C by an isothermal box, but 120 ° C it 'to hot, I'm searching now a good material to encapsulate my system (battery lithium + PCB) to decender less than 120 ° C.
thank you
 

AlbertHall

Joined Jun 4, 2014
10,780
If you have a 'something' in an environment then whatevr you wrap the 'something' in it will reach the same temperature as the environment unless it has some active refrigeration system. All the wrapping around 'something' can do is to reduce the speed of the temperature equalisation.
 

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
If you have a 'something' in an environment then whatevr you wrap the 'something' in it will reach the same temperature as the environment unless it has some active refrigeration system. All the wrapping around 'something' can do is to reduce the speed of the temperature equalisation.
thank you su mutch for your response, it's verry importante remarque and that what i'm trying to do.
the passage of my syteme under the oven is 7 min, on this periode i was able to rediuse the temperateur under the isotherme box to 120°C and it's still to hot for the system
 

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
Why not put the thermocouple in the oven and have the electronics outside? That's the usual way.
Thank for your response, it was my first idea, but the specifications given by the client contain this condition (the passage of all the system inside the oven),
the length of the oven is 10 meters it's to hard to find a temperature sensor by this length.
 

LesJones

Joined Jan 8, 2017
2,840
Surround it with a water jacket with a vent to the outside for steam to escape. That would limit the temperature to 100 degrees C. provided all the water did not boil off.

Les.
 

jpanhalt

Joined Jan 18, 2008
10,963
Put it in an insulated, battery powered refrigerator.

1) You mention 300°C. Is that the temperature of the oven?
2) What is the source of the heat? For example, IR radiant or hot air?
3) Is air circulating in the oven?
4) How long is the exposure?
5) If the oven is at 300°C, temperature is constant, and travel time is constant, why does your client need to "monitor" the temperature? There are very inexpensive indicators that show whether a particular temperature is reached.
 

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
Put it in an insulated, battery powered refrigerator.

1) You mention 300°C. Is that the temperature of the oven?
2) What is the source of the heat? For example, IR radiant or hot air?
3) Is air circulating in the oven?
4) How long is the exposure?
5) If the oven is at 300°C, temperature is constant, and travel time is constant, why does your client need to "monitor" the temperature? There are very inexpensive indicators that show whether a particular temperature is reached.
thank you su much for your response,
1) No 300 ° C is the peak value, the oven contains 10 chambers, the temperature is adjustable for each chamber and the highest value is 300 ° C.
2) the source of the heat is hot air
3) yes;
4) the exposue through the oven is 7min
5) 300° C is not a constant temperature (as i said in response number 1), my goal is not determine the oven temperature but the pieces send through the oven.
 

Darkstar

Joined Sep 3, 2010
177
Hi everyone;

I'm doing a reverse engineering for thermocouple system that works in specifique condition (temperature=300°C), knowing that the originaly systeme use the material below in the figure for covring the battery and the pcb.

View attachment 225599

I have already finished the electronique parts and the pcb and is wright.
My question is: what's kind of the green material is in the picture??
Or an equivalent material for isolate the battery and electronic part from the temperature ??

thank you in advance for any help
have best day
Ordinary clear GE silicone glue can take temperatures of 400*F. "Red RTV", another silicone, can go to 450*F. I heard they have one called "Grey RTV" which can go up to 500*F. They're easy to use. Just spread it out over the item you want to encapsulate & let it cure for a day. Some types release acetic acid, vinegar, so can corrode sensitive parts if they are exposed.
GE has a new formula that doesn't release acid fumes.
Note: I'm talking about the glue. Many people see silicone caulk and think it's the same thing. It's not.
 

LesJones

Joined Jan 8, 2017
2,840
Could you mount your device inside a stainless steel vacuum flask ? A metal lid would have to be made to replace the original plastic one. Also glass fiber (Or similar.) insulation would have to be on the inside of the metal lid. The temperature probe could stick out from the lid.

Les.
 

andrewmm

Joined Feb 25, 2011
909
Your first problem is that you are using a battery,
Standard batteries do not work at 120 degrees C,
in-fact most of them will go with a very big BANG at anything above 90 degrees.
So you are into either very specialised batteries a thermal battery such as sodium comes to mind,
or some thermal sink and insulation.

If you can get sufficient insulation around the items, were talking may be a thermos flask type system,
then its internal power thats the concern,
obviously design the system to dissipate uWatts is the first step,
if all you have to do is monitor temperature, then a small uP that wakes up every second, takes reading and sleeps should be down the sort of power levels you want.

Even if you wake say 10 times per second, and the processor takes a few micor seconds to take a reading then you have significant power saving.

So we have minimised heat getting in, minimised heat being generated, now the head sinking.
you obviously can not dissipate the heat, as the environment is to hot.
You could use things like a Cu block, that is cooled to say zero before the run, then sealed in to the thermos,

A phase change material could also be used, Ice is a great one, but can be messy.
others like slats are available, that can absorb amazing amounts of heat by changing states between crystal and liquid.

BTW: thermocouple leads of 10 m are far from unusual.
 

Darkstar

Joined Sep 3, 2010
177
Thank for your response, it was my first idea, but the specifications given by the client contain this condition (the passage of all the system inside the oven),
the length of the oven is 10 meters it's to hard to find a temperature sensor by this length.
Maybe you don't need a 10 meter temp sensor. Buy some extension thermocouple wire to reach the length of the oven and connect it to a small sensing tip. This is like the wire inside the steel sheath of the tip, only it's exposed. It is coated for protection to about 500*. The resistance of the extra wire would cause a slightly lower voltage readout but the wire resistance is known so you can compensate for the extra resistance and correct the sensor voltages.
 

Thread Starter

Mohamedimad

Joined Dec 22, 2020
15
Could you mount your device inside a stainless steel vacuum flask ? A metal lid would have to be made to replace the original plastic one. Also glass fiber (Or similar.) insulation would have to be on the inside of the metal lid. The temperature probe could stick out from the lid.

Les.
I made an isothermal box in metal, inside this box I put a layer of silicone rubber in the as you see in the image,
by this method i could arrive to 120 ° C
is ther a way to reduce the temperature less than 120° C
 

AlbertHall

Joined Jun 4, 2014
10,780
Maybe you could use a gel pack, frozen before the trip through the oven, which could keep the temperature of the battery and electronics down.
 

LesJones

Joined Jan 8, 2017
2,840
I don't think silicone rubber is a particularly good thermal insulator. Glass fiber or mineral fiber insulation would be better. Perlite or vermiculite are other possible alternatives but I think a vacuum flask would be the best. (Assuming that it's size would not be a problem.) How much time does the device have to cool down between the times it passes through the oven ?
A point about andrewmm's suggestion of using copper as a thermal sink. Although copper is a very good thermal conductor it has quite a low specific heat. Water has a specific heat more than 10 times that of copper.

Les.
 
Last edited:

jpanhalt

Joined Jan 18, 2008
10,963
@Mohamedimad

Just curious... As I understand it, your design must use a thermocouple and the entire amplifier+battery must be in the oven.

What will you use for your reference temperature (aka cold junction)? Where will it be placed? How will you connect to it?
 

LesJones

Joined Jan 8, 2017
2,840
I think I have seen a thermocouple amplifier chip with built in cold junction compensation. I think it is a MAX31856.
Edit. I have found the datasheet and attached it .

Les.
 

Attachments

Last edited:
Top