Hi Guys,
Ive been given an electrical project to do at college. I want to make an ice cream scoop which heats up so the ice cream scoops out of the container easier. I need to make a really rough prototype of this circuit. So all i want is a heating pad which is run off batteries which stays at a constant temperature of 50 degrees C. Can anybody give me any advice on how to build this circuit? Which type of temperature sensor i need? Can i buy a thermostat or thermocouple which will shut off my circuit at a specific temperature? Do i buy these ready set or do I have to set this myself?
Thanks in advance Meg x

 

Welcome.
Many ways to do it; I would heat water in a cup the scoop is kept dipped in before use. The water heater element can be a simple low voltage light bulb, submerged, and electrically isolated with silicone or similar.
Or wrap the cup with the heating pad, if you have it already.
Batteries will not last much if implemented with such.
A thermocouple and controller for a heating element would be too much of an elaborated approach for the task. But good for learning from such.
The scoop will not care much if 50C or 40C or 30C; will work equally well.

 

Hi Guys,
Ive been given an electrical project to do at college. I want to make an ice cream scoop which heats up so the ice cream scoops out of the container easier. I need to make a really rough prototype of this circuit. So all i want is a heating pad which is run off batteries which stays at a constant temperature of 50 degrees C. Can anybody give me any advice on how to build this circuit? Which type of temperature sensor i need? Can i buy a thermostat or thermocouple which will shut off my circuit at a specific temperature? Do i buy these ready set or do I have to set this myself?
Thanks in advance Meg x

Welcome to AAC


" I want to make an ice cream scoop which heats up so the ice cream scoops out of the container easier."
There are more of these on the market than I thought - https://www.amazon.com/s/ref=nb_sb_...x=heated+ice+cream,aps,120&crid=37KSM6XGCBRUE

This one is pretty slick (well, at least the movie that they made for it)

But, of course, you are not there yet.

"So all i want is a heating pad which is run off batteries which stays at a constant temperature of 50 degrees C"

Well, you need a heating pad that can run off of a battery - maybe one designed for pet reptiles and the like...maybe one like this but the battery-operated part could be a bit of an issue since even small ones take a lot of current for any small battery.

"...which stays at a constant temperature of 50 degrees C."

So, temperature control circuit in Google and maybe Wikipedia to learn about PID and thermostats- no?

"Can i buy a thermostat or thermocouple which will shut off my circuit at a specific temperature? Do i buy these ready set or do I have to set this myself?"

A thermocouple is a heat sensor and alone would not turn anything on - no? But, yes, you can buy either. You might have to actually set it yourself - I know, outrageous. Then again, you could build a circuit that was calibrated for the temperature you wanted - even one that was programmable.

Also, would you want it to reach 50 C and then just shut off, like you said or do you want it to keep the temperature at around 50 C.

"Ive been given an electrical project to do at college."

Do you mean that you paid to take a course in exchange for some degree of learning experience?

So, I have a question? What is the name of the class, prerequisites and college year you are in?

OK, you get some degree of sarcasm, but honestly, wouldn't it be a good idea to first do at least an hour of background reading and thinking to come up with an approach? Too harsh? Sorry, but I did 10 min of background research and all I got was a hankering for a couple of scoops of Cherry Garcia (do they still have that?).

Stick with it and let us know what you come up with.

 

Minco makes flex circuit heaters. I don't know what their smallest standard size is, but it might be small enough to be bonded to the back side of a large ice cream scoop. For a typical closed-loop system there would be a temperature sensor embedded in the scoop to sense the temperature drop on contact with the ice cream. The sensor drives a comparator that drives power to the heater.

An alternative is a positive temperature coefficient resistor heating element bonded to the back of the scoop. With the right element material it will modulate its own power, acting as both heater and sensor. This is how incandescent light bulbs work.

ak

 

Hi! Thanks for your answer!
Ive had a look at those minco pads and if im understanding it properly it looks like what i need! It seems like they are preset pads which have a temperature control built in so i wouldnt need a therosat or anything because it heats itself up when it senses cold temperatures. Do you have experinace with these pads and is this the case? So i could simply hook it up to a power supply and attach to the scoop? Thanks again, meg xx

 

Thanks for answering my question, I think!

Im doing my HNC for electrical engineering and for one of the units i need to build and design and product. My background is in electrical marine installation so i really stuggle in my lesson to do with electronic circuits as i work with more the partical side of things rather then the theory.
Ive spoke to my tutor today and he gave me some guidance. He said to attach a thermistor to the scoop which is being heated and when it hits the temperature i want it will shut off. But i need to work out what resistors i need, he also said i need an inst. Amp in the circuit amd measure voltage. He drew me a rough diagram.
I understand to people on this forum it may seem really basic electronics but i wrote on here for help because im strugging and wanted some guidance. Im researching my hardest but theres so many electrical components which i have no idea about. I just wanted to hear from peoples experience what they would advise. Without fishing for sympathy im trying to juggle college with working an awkward shift pattern at work haha

 

Thats what a tutor used to try explain to me haha still went over my head

 

Thats what a tutor used to try explain to me haha still went over my head

Yeah, so he is drawing this on the whiteboard and you are not following any of it and that must be frustrating, but at least you took a picture.

You have to design a product - but do you have to use any particular design elements. If so (and I suspect as much), then I suggest that you need to divide and conquer. So, if you need to use an instrumentation amplifier and a thermistor and that is "really" the assignment, focus on those components.

You said the tutor told you that you have to use a thermistor. So, figure out how a simple resistor divider works. Then, what a thermistor is and how the resistance of a thermistor changes with temperature. Then put that thermistor in the voltage divider as one of the resistors. Then look into what a Wheatstone bridge is and see if you can put a thermistor in that and understand what is going on.

That's only one part, but it is a start. The instrumentation amplifier is another matter - but if you can get to the Wheatstone bridge part and understand it, you will be on your way.

I still want ice cream.

 

Yeah, so he is drawing this on the whiteboard and you are not following any of it and that must be frustrating, but at least you took a picture.

You have to design a project - but do you have to use any particular design elements. If so (and I suspect as much), then I suggest that you need to divide and conquer. So, if you need to use an instrumentation amplifier and a thermistor and that is "really" the assignment, focus on those components.

You said the tutor told you that you have to use a thermistor. So, figure out how a simple resistor divider works. Then, what a thermistor is and how the resistance of a thermistor changes with temperature. Then put that thermistor in the voltage divider as one of the resistors. Then look into what a Wheatstone bridge is and see if you can put a thermistor in that and understand what is going on.

That's only one part, but it is a start. The instrumentation amplifier is another matter - but if you can get to the Wheatstone bridge part and understand it, you will be on your way.

I still want ice cream.

Sorry, just to give you an idea of background, this is a project specific to me. So I stayed behind to ask the tutor what he could advise me. Its not like im in a lesson and not listening, I just dont understand to get started with my circuit. I havent been told i need to use a thermistor, thats just what he said he would personally use. Ive only just been told to use the thermistor and op amp hence why i havent researched them yet. What is the purpose of a op amp in the circuit? Im sorry I understand is frustrating trying to explain to someone who doesnt get it but im only asking for some guidance, is that not the purpose of a forum?

 

Sorry, just to give you an idea of background, this is a project specific to me. So I stayed behind to ask the tutor what he could advise me. Its not like im in a lesson and not listening, I just dont understand to get started with my circuit. I havent been told i need to use a thermistor, thats just what he said he would personally use. Ive only just been told to use the thermistor and op amp hence why i havent researched them yet. What is the purpose of a op amp in the circuit? Im sorry I understand is frustrating trying to explain to someone who doesnt get it but im only asking for some guidance, is that not the purpose of a forum?

No problem at all - I admire your enthusiasm and hope you persevere and get it all worked out.

One of the problems with "assignments" is understanding what the instructor is trying to teach specifically. My feeling and "help" was intended to basically say - look, find out what the instructor really wants and attack it in pieces.

Sometimes, it may be just as they say - meaning do it any which way you like. Other times (most other times I think), they have some particular ideas or concepts in mind. From what you had said so far and specifically that diagram, my thinking is that this is not a free-for-all but rather a guided instruction. That's my interpretation of the assignment and I could be wrong.

Sorry, if I am being too abrupt or curmudgeonly. There are many, many on here that can help.

 

No problem at all - I admire your enthusiasm and hope you persevere and get it all worked out.

One of the problems with "assignments" is understanding what the instructor is trying to teach specifically. My feeling and "help" was intended to basically say - look, find out what the instructor really wants and attack it in pieces.

Sometimes, it may be just as they say - meaning do it any which way you like. Other times (most other times I think), they have some particular ideas or concepts in mind. From what you had said so far and specifically that diagram, my thinking is that this is not a free-for-all but rather a guided instruction. That's my interpretation of the assignment and I could be wrong.

Sorry, if I am being too abrupt or curmudgeonly. There are many, many on here that can help.

Its okay I probably havent explained myself properly. The assignment is basically a free for all haha. Everyone in the class was asked to choose their own project idea, for example some people are making alarmed threshold mats, lights for DJ decks which flash to the beat and bike brake lights which are powered by the wheels. On top of all this the tutor who takes us for the subject doesnt even have an electrical back ground haha. The diagram I took a photo of was actually drawn for me by a tutor who takes me for a linear control lesson and I stayed behind to ask if he could give me some advice. I suppose where I need to go from here is to reseach what thermistor i need for this type of circuit, theres so many though haha im just gonna have to look at all the data sheets for the resistance/temp graphs. And i'm assuming thats what resistors i use for the other 3 resistors in the wheatstone bridge?

 

Minco makes flex circuit heaters. I don't know what their smallest standard size is, but it might be small enough to be bonded to the back side of a large ice cream scoop. For a typical closed-loop system there would be a temperature sensor embedded in the scoop to sense the temperature drop on contact with the ice cream. The sensor drives a comparator that drives power to the heater.

An alternative is a positive temperature coefficient resistor heating element bonded to the back of the scoop. With the right element material it will modulate its own power, acting as both heater and sensor. This is how incandescent light bulbs work.

ak

I love positive temperature coefficient resistive heaters. The idea of a self-regulating component that's so incredibly simple is just awesome in my eyes.

This seems like a good application too - despite what the thread starter said, I think you could get away with a fair bit of temperature variation and still be effective, so the not-quite-perfect results from a PTC heater would probably suffice.

EDIT:
Despite what I just said, the PTC element may not be the best solution for this assignment. The teacher may want a more complicated circuit than what the PTC element would require.

If I just needed to keep an ice cream scoop warm, I'd use the PTC element (or a warm water bath,) but if I wanted a project idea to strut my stuff and try to get a good grade, I'd probably go with something more challenging!

 

This right here is all you need it came out of a coffee cup the inside was aluminum with a cover over it the inside was kept nice and hot the controller you set the temp and it kept it there wrap it inside the handle it would heat the aluminum up Im sure .


The stuff looks like rubber but it can reach 150 c the limit on it was 120 c .
It's got a name on it Ill see if I can read it it was using 12 volt supply

 

A coffee cup heater ran at 250 degrees F???

 

Nope 120 degrees F that rubber looking wire said it's good for 150 c 304 degrees F,
The limit it had on it to shut off was 120 c

I would think it would melt But it can get hot I tested it. I got the coffee mug to get the heater out of.
It said it could heat and cool it can heat but it don't get cold it just keeps your drink cold if you had ice in it

But it can heat and it heats fast. I don't think it could get to 304 degrees F without something melting, but the wire has that on it every where and the name of it but that small print LOL.

http://www.ok630.com/en/ltd.asp?id=3651

 

I know it's lazy, but i'd just drill holes into the back of a metal scoop (with a heat resistant handle), bolt on a 10w aluminium clad power resistor of around 15 ohms and use a 12v 1.5A supply (a battery is going to struggle to work for any length of time and I don't think it's a great idea). I doubt it would need any temp control at all, 10w of heat sounds about right for something that size.
But with an external supply you can also have an external temp controller or even just use a thermal switch (like the KSD9700 series).