# Producing a constant 37 degree celsius temperature using 3.5 to 9 volts

Discussion in 'The Projects Forum' started by Pi Chi, Jul 17, 2015.

1. ### Pi Chi Thread Starter New Member

Jun 10, 2015
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0
Good Day!

My team's working on a fermenting device.
It's supposed to produce a constant temperature but it's not necessary to stay like that all the time.
The device must be able to produce 37 degree Celsius using 3.5 to 9 volts.
After reaching the desired temperature, an allowance of maybe 2 to 3 degree Celsius is allowed then the source will automatically "Turn-off".
Once it reached 2 to 3 degrees less than 37, the device will automatically turn on again.
We're thinking of using a nichrome wire to produce the desired heat but we're still looking for other materials.
The heating material will be placed inside a vaccum.
I understand that this kind of project would need a thermostat but I still don't know where to start.
I tried comparing it with the operations of rice cookers but those need water in order to maintain constant temperature.
So, 1.) How can one maintain a constant 37 degree celsius using 3.5 to 9 volts? (minimal temperature discrepancy/tolerance is allowed)
2.) What kind of heating material is best for such project?
3.) Are there any other approaches that could yield the same function?

My english isn't very good but I hope I was able to state my case as simple and as precise as possible.

2. ### crutschow Expert

Mar 14, 2008
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3,362
What is the form of the physical device are you trying to heat in a vacuum?
Power resistors may work well as heating elements in your application.

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Apr 5, 2008
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Hello,

What level of vacuum do you intend to use?
You might want to know that vacuum is often used as thermal isolation.

Bertus

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4. ### AnalogKid Distinguished Member

Aug 1, 2013
4,685
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What is the material you are measuring?
Is the heating element immersed in the fermenting material?

What you have described is a hysteretic or bang-bang controller, the most basic kind. This can be done with something as simple as a snap-disc thermostat device immersed in the material, or with a thermistor temperature sensor and a small electronic circuit to turn the heater on and off. There is a time delay between when the heater comes on and when the material starts to warm up. This might cause a problem for the temperature controller.

ak

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5. ### #12 Expert

Nov 30, 2010
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There is still missing information. For instance, (I believe) you can't ferment in a vacuum, so where and what are you going to measure? I did a nice thermostat that can be set for about a tenth of a degree C difference, but it needs 9.5 volts minimum. Is 9.0 volts your limit for the heater or for all the parts? If so, you can fake the LM723 design with a modern low voltage, single supply, operational amplifier.

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6. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0

Good Day!

Actually I didn't know about vacuum levels until now. Thank you for that.
From what I read it's the difference between the atmospheric pressure and the pressure in the evacuated system.
I still don't understand it fully. Our initial idea of "vacuum" is just that no air can get inside the container.
The container that we're actually gonna use is just a big casserole.
Is that already "vacuum"? Thank you!

7. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0

Hello!

Actually we're trying to ferment a solid matter inside the "vacuum" (Which is a big casserole btw.)
Our first option was to use a filament wire (Probably nichrome) as a heating element to be placed inside the container, surrounding its inside perimeter.
A "strainer" or a metallic net (wherein the shape is the same with the container) will also be placed inside in a suspended manner.
We're supposed to put the solid matter there. It's actually a mixture so the only thing we need is heat and no other catalysts for fermentation are required.
Thank you for suggesting power resistors. We'll see what we can use if we're going to choose this option.

8. ### DickCappels Moderator

Aug 21, 2008
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9. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0

Hi!

The heating element is not actually immersed, I guess, since we're not going to ferment a liquid material.
It's actually a solid matter. We are told that "ferment" is the right term but in layman's term we're just trying to speed up the process of making that solid matter create white molds.
For the thermostat, thank you for the information. I know very little about thermostats. I did some research but I think I still have to read more. How is the delay gonna cause problem with the controller? Thank you!

10. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0
Good day!

We're just told that "ferment" is the right term. But we're just trying to speed-up the process of creating white molds.
Actually we're trying to ferment a solid matter inside the "vacuum" (Which is a big casserole btw.)
Our first option was to use a filament wire (Probably nichrome) as a heating element to be placed inside the container, surrounding its inside perimeter.
A "strainer" or a metallic net (wherein the shape is the same with the container) will also be placed inside in a suspended manner.
We're supposed to put the solid matter there. It's actually a mixture so the only thing we need is heat and no other catalysts for fermentation are required.
And no, 3.5 to 9 is just our ideal target. But I think we could still push it up to 12 volts.
Thank you for suggesting LM723, we'll check it!

11. ### cmartinez AAC Fanatic!

Jan 17, 2007
3,698
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Maybe by "vacuum" you mean an oxigen-free atmosphere? If so, what would the pressure be inside your vessel?

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12. ### #12 Expert

Nov 30, 2010
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I think that in this case, vacuum does not mean vacuum. It means hermetically sealed.
I would also like to point out that water is not necessary to heat a substance in a closed container. Anything inside the container will eventually arrive at the temperature it is surrounded by. When you pick up a bag of popcorn in a supermarket, all the popcorn is the same temperature as the store, regardless of the container being sealed and there being no liquid water at all in the container.

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13. ### Alec_t AAC Fanatic!

Sep 17, 2013
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This sounds like a school assignment?
Since fermentation/mould growth may be a lengthy process, which do you think would be the preferred power source ? :-
1) a mains-powered converter to give 9V (or so),
2) a battery.

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14. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0

Good day!

Yes sir, it is a commercial product.
I'll take note of the custom constant temp. ceramic heater.
Thank you for suggesting it!
It's really good that we're learning different approaches here.
We just have to plan a design that bests suit our objective
(And one that wouldn't cost too much since it will blow up the whole purpose of making the device)
Again thank you for the response!

15. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0
Hi!

Yes! It's supposed to be an Anaerobic set-up.
About the pressure.. we're not really sure about how are we going to do that..
That one question that we do have to address but we really have no idea.

16. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0
Thank you for that clarification sir!
We got a little confused after learning about how a rice cooker works and how it regulates temperature.
Again, with the container, if it's just hermetically sealed, what factor should we consider if we really have to turn it into vacuum?
I'm not really sure how will I know the pressure inside or how to control it.
If it's not vacuum then is it still necessary to know the pressure inside the container?
Again thank you for answering again.
I'm sorry if I ask too many questions.

17. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
0

Hello!

Yes! It's a school stuff but it's not just an assignment. It's actually a research project.
As for the power source. It's supposed to run on renewable energy. Either solar powered or powered via wastewater.
That's why we need low voltage only. And the prices of materials are also one of our top concerns. The cheaper the better! since we'll loose one of our main objectives. But we haven't proceeded to that part yet because we still haven't finished the design for the heat controller.
The heat controller will be tested first with a battery temporarily

Apr 5, 2008
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19. ### Pi Chi Thread Starter New Member

Jun 10, 2015
21
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Good evening!

We're trying to speed up fermentation for commercial bokashi (balls)
According to the information we have gathered, the mixture is already complete with all the catalysts it would need.
Thus "heat", is the only one missing, aside from the fact that the balls should be contained in a dry, cold place.
Usually, people put them in cartons between layers of sack so it's not really "vacuum".
But in order to speed up it's fermentation from weeks to days, or at best, to hours, the best conditions to grow the white mold for the balls must be acquired.
Thank you very much for the links! I'm checking them now.

Last edited: Jul 18, 2015
20. ### wayneh Expert

Sep 9, 2010
12,374
3,226
I'd place your entire "fermentor" inside an incubator, which is little more than a moderately insulated enclosure with a light bulb as a heat source, like people use for hatching eggs. A small fan would be nice but is probably not necessary. Fungi are very forgiving as long as you don't cook them.

Sunlight on a sunny day would be more than enough energy to hit 37°C, so if you expect to use passive solar, you'll need a shade to prevent cooking your ferment. Put the whole thing inside a regulated greenhouse.

If the thing cools off a little at night, but resumes 37°C operation during the day, is that bad?

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