Design details for a butter knife warmer

[Shay10825]

Yeah I threw it away. Yeah I can buy more. Should I still do the battery test with the copper wire I have and if so should I only use one strand or the number of strands that were in the wire?

 

[Gokul43201]

Use all the strands. And yes, do the test with what you have. Right now, your current will be small, so the wire is most probably just fine.

How do you connect the wire to the battery terminals and the resistor leads ?

 

[Gokul43201]

So I let the metal touch the whole resistor that's covered in tape (the wires too) or should I only let the metal touch the part of the resistor with the different color lines?

Do the basic test before trying aluminum foil.

The foil should not touch any of the metallic parts of the circuit - the resistor leads, the wire, the battery terminal. If the leads and wires are all taped up, it's okay for the foil to cover them too. To get a more realistic idea, I would double up the foil, to make it twice thick.

And use the heat sink paste over the ceramic part of the resistor (the part with the color code), and make sure the foil is making contact with the paste, or even the ceramic itself.

 

[Shay10825]

I tape the wire to the battery and wrap it around the resistor wires.

 

[Gokul43201]

I tape the wire to the battery and wrap it around the resistor wires.

Okay, just to make sure the wire is making good contact to the battery terminals, you might want to press down with your fingers. Make sure you only put your finger over the tape, and not the metal. Not that it will harm you...

 

[Ivan Seeking]

I'm thinking (since Ivan says that 1 amp is safe)

Keeping in mind that this was for the Energizer e2 and intermittent use only.

 

[Gokul43201]

Yay, you're here !

Hope that didn't sound like I was going to point my finger at you if something went wrong ?

Okay, I've independently verified that the Eveready A95 (D-cell) can be used with 1.5 ohms (drawing 1 amp) for 4mins out of every 15 mintes, and will have a life of 15 hours of usage at this current.

So I too would say that 1 amp draw should be okay, as long as you don't run it for more than 4 minutes at a time, with at least 10 minute breaks.

 

[Ivan Seeking]

I think you're doing a great job! I just wanted to add a word of caution.

 

[Shay10825]

I probably can't experiment and post anything tonight because I have a really important Physics test to study for (what I get on this determines my grade ), and a ton of Physics homework. I might be able to start back testing tomorrow.

 

[Shay10825]

I just tried connecting the resistor to the battery and it does not get hot. I wrapped the copper wire around the resistor wire then taped it to the end of the battery. I did this for both sides of the resistor and battery. Why is it not getting hot? Could it have something to do with the way I'm wrapping the copper around the resistor?

 

[Shay10825]

And use the heat sink paste over the ceramic part of the resistor (the part with the color code), and make sure the foil is making contact with the paste, or even the ceramic itself.

I did not use the heat sink paste over the ceramic part of the resistor. Could this be the reason why the resistor does not get hot?

 

[Ivan Seeking]

First, which resistor are you using - the 1/4 watt or 1/2 watt resistor? Ten ohms right?

The heat sink paste only serves to transfer the heat from the resistor to the metal.

Do you understand how to measure voltage and current?

You should measure about 150 milliamps of current flowing with the circuit made Check that you have current flow. Be patient. We are starting slowly but things will pick up quickly once we're all set in just a few more steps.

 

[Ivan Seeking]

Did you find out what the deadline is for your report and project?

How did you do on your physics test?

 

[Shay10825]

First, which resistor are you using - the 1/4 watt or 1/2 watt resistor? Ten ohms right?

Do you understand how to measure voltage and current?

Both the .25 and .5 watt to see which works best.

Do I understand how to measure voltage and current with the multimeter? No. What should the wires and needles be touching?

Did you find out what the deadline is for your report and project?

How did you do on your physics test?

Yeah the report and the project is due November 18.

Not so good . I got a 72 . But it does not determine my grade anymore because the school board extended the quarter. So we will have 1 or 2 more tests.

 

[Ivan Seeking]

Read this
http://www.ehow.com/how_16767_voltmeter.html
the section about measuring with a voltmeter here
http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/Basic/Basic3v.html#Measuring
and pages 1,2 and 6, here
http://hibp.ecse.rpi.edu/~connor/education/IEE/labs/Lab_1_Current_Voltage_and_Resistance.pdf

There should also be some instructions with the meter. Make sure that you read those as well.

Do you have a Radio Shack nearby?

Not so good . I got a 72

...better next time.

 

[Shay10825]

Do you have a Radio Shack nearby?

Yeah there is a radio shack nearby. why?

 

[Ivan Seeking]

They have some really nice, very short books that introduce the basics with pictures for clarity. They are small pamphlets - thin paperbacks and hand written! You will usually find them in the electronic's sections with the resistors and transistors. It would be worth a stop to take a look and see what they have. In fact, there is a thin, full sized (8.5" X 11") book, green I think, that covers much of the basics... In fact I just checked and I have my 1983 version. It is called "Getting Started in Electronics"; Cat no. 62-5003. It is a handy, practical reference.

 

[Gokul43201]

Shay, with just one 10-ohm resistor, your not generating enough power to get it hot. You will need either a higher power, lower resistance resistor, or a bunch (say 5 to 7) of .5 watt, 10-ohm resistors to generate enough heat.

You may also not be making proper contact between wires. The right way to maximize contact (short of soldering or using wire nuts) is to hold the wires side-by-side and twist them together, several times. Then tape over this, tightly.

To check if your circuit is okay, test it with the multimeter. First connect the probes of the meter to the socets corresponding to voltage measurement. The black (negative) lead goes into the ground socket, and the red (positive) lead goes into the socket labeled V (not the one labeled I, for current).

Now the dial on the meter has different settings. Find the positions for DC voltage measurement, and set it to the value that is just above the expected voltage of 1.5V (so, if there's a 5V or 10V position, use that). Check the voltage across the battery and across the resistor. They should be nearly the same. Similarly, by changing the dial position to read resistance (ohms), you can check the resistance across one or more resistors. The current can be found using Ohm's Law.

 

[Shay10825]

When I'm titling this invention for the science fair does it need to be a question?

 

[Ivan Seeking]

Did the rules for the fair indicate this?

 

[Shay10825]

Yeah never mind I found it. It has to be something catchy. Any ideas ?

 

[Cliff_J]

You might borrow from the old "...building a better mousetrap..."

Maybe two words or word fragments like many other products so maybe a combo of thermo and knife or slicer or something

Or visit places that sponsor inventions like Hammacher Schlemmer, they have tons of gadgets.
http://www.hammacher.com/
http://www.hammacher.com/sfi/sfimain.asp

Hope all is progressing well.

Cliff

 

[Shay10825]

The Better Butter Cutter (BBC)

 

[Cliff_J]

Hey I own a "Butter Butler", its handy for the few times I use butter. My dad has a coffee mug with a adapter to plug in the cigarette lighter to keep the coffee warm while driving, also handy. Who knows what people might like?

http://www.krbctv.com/Does It Work/DIW Archive/diw_archive_cooking_butter butler.htm

 

[Ivan Seeking]

Shay,
I wanted to try this before saying too much. Once you know how to use your meter you are safe to go ahead as follows: Using your 1/2 watt resistor and two D-Cell batteries connected in series [end to end like in a flashlight], go ahead and apply 3 volts across the resistor for ten or fifteen seconds. The resistor will get hot. If you leave the circuit connected long enough, eventually the resistor should burn up.

Potential [V]= 1.5 volts + 1.5 volts = 3 volts
Resistance [R]= 10 ohms
Current = 3 Volts / 10 ohms = 0.3 Amps
Power [P]= VI = 3 volts X 0.3 Amps = 0.9 watts

Since the resistor is rated for 0.5 watts and you are running it at 0.9 watts, you are running the resistor beyond its design limit. This is why it starts to get too hot.

Next, use 4 D-Cells, a 1.0 watt -10 ohm - resistor [available at Radio Shack], a piece of metal about the size of a knife blade, and your heat sinking compound.

By running the batteries in series we get:

1.5 volts X 4 = 6 volts
I = 6/10 = 0.6 amps
P = 6 volts X 0.6 amps = 3.6 watts

Again, I used a 1.0 watt resistor, so I was running the resistor at 360% of the design limit.

I did this using a fairly heavy piece of brass sheet metal - about 1/2" X 2" in size. First, a good layer of heat sinking compound was applied to the metal. Then a toothpaste sized blob was applied and the resistor was secured to the metal using only the cohesiveness of the compound. Pull the resistor's leads back so they don't short out on the metal and wiggle the resistor around a little to ensure a good bond. Also make sure that it's buried in the heat sink blob. This will pull heat away from the resistor and transfer it to the metal; thus preventing the resistor from burning up.

After applying power I that found that an area of about 1/2" X 1/2" got hot very quickly - in less than 30 seconds. Afer five minutes the entire piece of brass was very warm, with half of it too hot to hold. The batteries did not get hot and the resistor was hot but it seemed fine. So it appears that we can safely heat sink the resistors and overdrive them. This seems to work pretty well.

 

[Arctic Fox]

You may not have seen the original thread in GD where some similar suggestions were made. Shay10825 is hooked on a heated blade for now.

Hooked, huh?

No chance in a heated wire on a cheese cutter?

http://www.twinsupply.com/fdick_cutlery/81055-00.jpg

 

[Gokul43201]

After applying power I that found that an area of about 1/2" X 1/2" got hot very quickly - in less than 30 seconds. Afer five minutes the entire piece of brass was very warm, with half of it too hot to hold. The batteries did not get hot and the resistor was hot but it seemed fine. So it appears that we can safely heat sink the resistors and overdrive them. This seems to work pretty well.

There, now if you can only convince Ivan to ship over his stuff to you.

I'm not sure how long the resistors will last if you overload them repeatedly. You could consider using a couple or more resistors in parallel, to divide the power.

 

[Ivan Seeking]

The advantage is the significantly reduced mass and volume of the resistor. To a point she should be okay but I agree that this is unconventional.

Is this just our project now or is Shay coming back?

 

[Gokul43201]

The advantage is the significantly reduced mass and volume of the resistor.

In my approximation, the mass of the blade dominates the mass of the resistor.

Shay's got a couple weeks to go and seems to have fallen prey to the powerful yet illusory bliss afforded by procrastination. Haven't we all bitten on that, sometime or the other ?

 

[Shay10825]

Ok I'm back. I'm sorry. I've just been so busy with a ton of homework and tests these last couple weeks. It's been crazy at my school. The 9-weeks just ended so I'm working all weekend on this project. Ivan Seeking I'm going to try what you said right now.

Sould I use a 20 gauge wire?

 

[Shay10825]

Would this work?
http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=270-396

or do the batteries have to be on top of each other?

 

[Shay10825]

When I connected the .5 watt 10 ohm to the resistor it seemed hot when I touched it. It was weird (or maybe I'm just weird and it's suppose to feel like this). Are the lines on the resistor the only thing that's suppose to get hot? It did not get the metal hot. Is this because I did not put and heat sink on the metal? Is it suppose to be like this?

 

[Ivan Seeking]

20 gauge is perfect.

If you look at the connections on the battery case that you linked, you will see that they are wired in series - as if end to end, or on top of each other. So this should work fine. This means that you will have about 6 volts to work with = 4 X 1.5 volts per battery.

On your last question I'm a little confused. The entire body of the resistor will get hot. The lines are your color code - which you are supposed to know by now.

How many batteries are you using? Two? Then yes, the resistor should get hot. Again, this is producing 0.9 watts of heat in a 0.5 watt resistor. In principle, the resistor should eventually burn up or fail from excessive heat.

When you talk about the metal, do you mean the leads on the resistor or did you get a separate piece of metal? The metal leads on the resistor cannot touch your metal knife blade; or any other conductor for that matter. And you will need to use the heat sink compound to transfer the heat from the resistor's body to the knife blade. This compound will not short out the resistor leads; so it can touch the leads.

Make sure that you learn how to measure the voltage and current as you do this. check that the values measured agree with what you calculate.

 

[Shay10825]

What would happen if I used a 22 gague wire?

 

[Shay10825]

Which one is better?

http://www.radioshack.com/product.a...name=CTLG_011_010_006_000&product_id=278-1388

http://www.radioshack.com/product.a...name=CTLG_011_010_003_000&product_id=278-1222