making a tiny heat element

[flamer]

Hi Guys,

What I am looking to do is, use something like a short length of toaster wire connected to a power source. The length of wire will be about 2cm long and bent into almost a complete circle.

What it will be used for, is a piece of nylon will be run through that loop, and using a remote control I can apply the power to the circuit, the wire will get hot and "cut" the nylon string. think of it as a anti-snag device.

the problem I think I may have is, I only have 12 volts DC power supply (7.2A/H SLA battery). Does anyone know if that will get toaster wire hot enough? I assume the average kitchen toaster is not transforming the voltage or stepping it down, can anyone give me some advice on this? I would of just tested it but I don't have any nichrome lying around.

 

[Gryd3]

Hi Guys,

What I am looking to do is, use something like a short length of toaster wire connected to a power source. The length of wire will be about 2cm long and bent into almost a complete circle.

What it will be used for, is a piece of nylon will be run through that loop, and using a remote control I can apply the power to the circuit, the wire will get hot and "cut" the nylon string. think of it as a anti-snag device.

the problem I think I may have is, I only have 12 volts DC power supply (7.2A/H SLA battery). Does anyone know if that will get toaster wire hot enough? I assume the average kitchen toaster is not transforming the voltage or stepping it down, can anyone give me some advice on this? I would of just tested it but I don't have any nichrome lying around.

This will work, but you may need to calculate the length of the wire a little more carefully.
As the wire gets shorter, it will also heat up more... It gets to a point where it will act as a fuse instead of a heating element. You could simply just add more loops to compensate... additionally, how fast do you need the wire to heat up?

 

[flamer]

That makes sense, yes maybe i could coil it like a spring and have the nylon run through the length of it. Is there a particular calculation for figuring it out? I assume it relates to the gauge of the wire?

The speed is not of importance, a slow heat is fine so long as it reaches hot enough to achieve the melt of the nylon.

thanks

 

[Gryd3]

That makes sense, yes maybe i could coil it like a spring and have the nylon run through the length of it. Is there a particular calculation for figuring it out? I assume it relates to the gauge of the wire?

The speed is not of importance, a slow heat is fine so long as it reaches hot enough to achieve the melt of the nylon.

thanks

Here's where my limited experience hinders me a little.
I know the total resistance of the wire will dictate the current flow when you apply a voltage.
I also know that larger diameter will have a lower resistance per foot.
I don't know the equations though :s
If it were me making it, I would probably end up measuring the resistance of the existing setup in a toaster setup for 120V, then cut the wire length in proportion to the new voltage I planned to use... This may not be the smartest way of doing it though.

 

[hevans1944]

You may want to consider using Kanthal wire instead of nichrome. This is popular among vapers who build their own heaters. It is readily available in small diameters. It operates on low voltages for reasonable lengths of wire and does not oxidize when heated to incandescence in open air. I would suggest winding about six turns on about a 2mm form to pass your nylon string through.To get you started, check out this web site.

 

[flamer]

You may want to consider using Kanthal wire instead of nichrome. This is popular among vapers who build their own heaters. It is readily available in small diameters. It operates on low voltages for reasonable lengths of wire and does not oxidize when heated to incandescence in open air. I would suggest winding about six turns on about a 2mm form to pass your nylon string through.To get you started, check out this web site.

Excellent post and thank you both. Sounds like a good plan i will try it out once I source some of this Kanthal wire!!

 

[Bluejets]

We used to use nichrome wire in small lengths (from 40 to 100mm) mounted to wooden blocks with two tabs hanging out. The wire was a gauge that would hold it's section while in use.
To this we would connect aligator clips ( as there were several profiles) connect via variable power supply (in our case it was a low voltage transformer with about 5A output) and to vary the power required we used a standard light dimmer (400Va) on the input primary (240V)
These tools were used to cut profile sections from white foam cores to epoxy in carbon fibre stringers on model aircraft wings etc.

All dimensions and power settings were found by trial and error and then a record kept for future use for each tool.

 

[duke37]

I made a cutter for model aircraft foam for a friend. We tried Nichrome wire and also stainless suture wire and violin string wire. Fishermen use wire also I believe. You do not need to have wire which will resist oxidation at very high temperatures. Constantan is another source, used in thermocouples.

I do not have the data here of the various wires but an amp or two will do the job with suitable wire which your battery should manage.

 

[Externet]

Just pass the nylon string a couple of millimeters in front of (or nearly rubbing) a plain automotive cigarette lighter. It works on the 12V you have, and you will not have the trouble of properly bonding (crimping) the heating element to the wires.

If you want to consider another option, a single pulse of power will do it intantaneously with :
----> http://www.ebay.com/sch/items/?_nkw=electric scissors&_sacat=&_ex_kw=&_mPrRngCbx=1&_udlo=&_udhi=&_sop=12&_fpos=&_fspt=1&_sadis=&LH_CAds=&rmvSB=true

 

[Bluejets]

Just pass the nylon string a couple of millimeters in front of (or nearly rubbing) a plain automotive cigarette lighter. It works on the 12V you have, and you will not have the trouble of properly bonding (crimping) the heating element to the wires.

Only problem with that is the heater section has to be fitted into a socket to heat up.

 

[Externet]

If you do not unscrew the heating element, the socket and the whole car dash is needed.
----> http://www.pelicanparts.com/catalog/images/new_images2/cigarette_element.JPG

 

[Bluejets]

My point is, the centre is one terminal and the outer case is the other for powering the heat coil.
As those coils pull quite an amount of current, quite a substancial set terminals would have to be provided to make sufficient contact.
With those in place, nowhere to pass the nylon.

 

[flamer]

The ciggie lighter is a good idea! hadnt thought of that. Will have a think about it, only issue is the shape of it doesnt really fit my purpose.

Also I need to figure out a way to attach my power cables to the kanthal wire. I guess I can use a hard plastic wiring block or something?

edit: also what gauge of kanthal should I be looking for?

 

[duke37]

You will want a thin wire, try a stainless violin E string or a steel wire from a geetah.
You could use a copper wire which would be easy to solder. Getting the size right would cut the nylon and then fuse to turn off the battery.

 

[flamer]

Hmm I don't really want/need it to fuse, I have control to turn the voltage off and on, I can tell when the nylon has been severed, I release the current then hopefully I can use it over again with new nylon, is that possible?

 

[duke37]

Hot copper will oxidise so will not be suitable for repeated use.

 

[Calmore]

You will want a thin wire, try a stainless violin E string or a steel wire from a geetah.
You could use a copper wire which would be easy to solder. Getting the size right would cut the nylon and then fuse to turn off the battery.

Some of the "home" built micro satellites use just this technique. A piece of steel tape measure is used as the antenna and is held coiled up by a piece of fishing line. At a pre-determined time a current is sent through a piece of copper wire, melts the nylon and the antenna stands to attention. In this case it doesn't matter if the copper fuses as it's only designed to be used once.

Ingenious, cheap, simple and lightweight.

 

[Rory Starkweather]

There aren't many places where you can find information on how much current a wire can stand, because there are so many different compositions of wire.

As a general guideline you can consider things like P = IE, but that actually tells you nothing that you need to know.

I suggest that you buy several segments of wire and test them to failure. Get a idea from that. only an IDEA, though. IRL wire doesn't act like it does in your mind.

On topic, three of my colleagues were sent to Iraq for Desert Storm. they were entrusted with a very expensive piece of DoD equipment. After a few days it blew a fuse. Having little else to do they decided to fix it.

Please keep in mind that these three had more than 2 years of 10 hour a day electronics, each.

So, after many calculations, they decided to replace the fuse with a wire. They even put the glass back in. (Make it look more like a fuse? IDK)

Maybe they had a meeting to celebrate.

So they powered it up, and things started popping and catching on fire immediately. They finally used a fire extinguisher to shut it off. Total write off.

Now what didn't they do right?

Moral of the story? Never trust wire. It has a mind of it's own. It is supposed to conduct electrons in an orderly fashion. It is up to you, the builder, to let it know where and how fast.

Ignore your responsibilities at your own risk.

 

[Gryd3]

I suggest that you buy several segments of wire and test them to failure. Get a idea from that. only an IDEA, though. IRL wire doesn't act like it does in your mind.

I've done this with 32 gauge wire to make a temporary hot-wire to cut Styrofoam balls in half.
Used the 5V rail on an old desktop computer power supply... If the wire was too short, it allowed too much current to pass through and got too hot and failed. If it was too long, it didn't heat up, or didn't heat up fast enough to actually make a cut in the styrofoam.
It took me 5 or 6 attempts to get a good length of wire to behave like I wanted, and even then there was a section of wire on the edge of the cutting area that would get hotter than the rest. (I had to blow on it to keep it cool enough not to break)

 

[Rory Starkweather]

I've done this with 32 gauge wire to make a temporary hot-wire to cut Styrofoam balls in half.
Used the 5V rail on an old desktop computer power supply... If the wire was too short, it allowed too much current to pass through and got too hot and failed. If it was too long, it didn't heat up, or didn't heat up fast enough to actually make a cut in the styrofoam.
It took me 5 or 6 attempts to get a good length of wire to behave like I wanted, and even then there was a section of wire on the edge of the cutting area that would get hotter than the rest. (I had to blow on it to keep it cool enough not to break)

As stated above, wire is wire. Every piece is different. Even if you have Stephen Hawkings as a consultant, results may vary.