Project Vape:DIY magic Flight Launch Box (commence tommorow)ALL HELP IS APPRECIATED

Well I think that the retail mflb gets to 380 degrees.( It's on their website FaQ.) but you could try using all your components, wire, battery, mesh, and connect them together and see if it heats up.

 

Degrees don't help when you have nothing to measure it with.

make the mesh 2.5cm tall, then about 3cm long, and wrap it around the wire (preserving the 2.5cm dimension). I found that copper wire conducts TOO well for this design. You should find some steel rod instead. A coathangar would work, or welding rod (with the flux cracked off if it's stick welding).

The copper will work, but the battery gets pretty hot. Too hot to touch after a while. Gotta be careful with it.

 

Subscribing to this thread. I was thinking about doing the same.

Nowarning - those plants don't look like weed plants. Plus he ain't got that camera hidden. If he was growing he would hide that camera better.

 

Trim the screen down a bit if it's not getting hot enough.

Also, you MUST use rechargable batteries (ie. Ni-MH or Ni-Cad). Non-rechargable batteries can't provide enough current, thus they can't get as hot.

 

I've read several attempts at making a LB, and a common failing is a lack of heat at the mesh, which indicates to me that proper materials are not being used. What we are talking about is a heating element based on Joule heating law or also known as resistance heating. The resistor, in this case wire mesh, heats up as current is applied, and more heat is generated as resistance increases or current increases.

The key as I see it is the resistance of the mesh material. Some have said that you need higher resistance in the rod that attaches to the mesh, but I'm doubtful of this.

The resistance ρ (nΩ m) of stainless steel, the common mesh material in copycat LB designs is 720, while nichrome wire, commonly used in heating elements is 1500. The higher resistance of nichrome wire is guaranteed to make more heat than stainless steel. Plus you can solder nichrome and it forms a protective coating when heated for the first time.

Just some food for thought.

P.S.

There is a good website that has a calculator. You input your desired temp, gauge of wire, length, and how much power you are applying. NichromeCalc

For example if I wanted 360 degrees, well a AA battery produces 1.5 volts, so I would need 6.12 inches of wire at 22 gauge. Now keep in mind if you form the wire into a mesh, I think you want the current to run the full length of the grid. So, I would think there would only be two connection points to the grid, meaning you don't wrap the mesh fully around the leads that carry the current.

 

subd

 

If you go to the wed site for Nichrome wire application calculator, it seems pretty simple to find the length of wire resistance to suit your needs - that is getting the temperature you want. But a problem arises when you form the straight wire into a mesh structure. By making a mesh, it seems to me that you are making a combination of resistors in parallel and resistors in series. This video may help.

[ame=http://www.youtube.com/watch?v=AoXvkr-sEAk]8-CET-Karnataka-2003-Trick-Question-Equivalent-Resistance-of-Mesh-Electrical-ckt-IIT-JEE-Phy.flv - YouTube[/ame]

 

Uncle Benny: Your first post is wrong. But it looks like you figured it out.

A lower resistance will make a higher current, and the high current flow is what makes the heat. Even though for the same current a less conductive material will create more heat, since current is not limited, a lower resistivity will give a much higher current.

A lot of people attempting to make the MFLB heating element likely ignore the fact that oxides on the metals they are using provide contact resistance. You need a solid, clean connection. Get some sand paper, and sand the mesh until it's shiny. Same thing with the wire/rod. Soldering/Welding them together creates a connection that will not oxidize and change the resistivity over time. The next best thing is to mash them together really well like in a vice or with a hammer on a steel surface.

 

thanks for the knowledge bro

 

Kurt, I have to disagree with you. It is the resistance that generates the heat in proportion to the current applied. Look at few schematics for toaster, dampers, bug zapperes, etc. The part that heats up is the resistor.

The current applied in this simple device, the L.B., is set and does not vary, the only way to vary the heat generated at the grid is vary the resistance of the grid. The highest potential current that you develop with no resistance would be a piece of copper wire between the positive and negative terminals of the battery, but if you do this, the only thing that heats up is the battery since you are basically shorting it out. What you need is a resistor which converts the current into heat.

I do agree with you that a major problem would be getting a good electrical connection between the rails and the stainless steel or nichrome mesh. Like you said you need to clean the two different materials really well and heat them to hell. Brazing with goodly amount of flux and silver based solder might get a really good connection.

P.S. I could not find a cheap source of Nichrome mesh material. I can find nichrome wire on ebay for really cheap, but forming that into a mesh would be a PIA.

Also according to this http://www.vaporpedia.com/wiki/Magic-Flight_Launch_Box they are shooting for 380 degrees as optimum temperature.

 

They also don't use solder. It is natural

 

Magic Flight seems to use a form of resistance welding to weld the screen to the rods. Silver solder's melting temperature is close to that of vapourization, but as of yet, I've not melted it during use.

Uncle Benny: You're right. But it still doesn't explain why the copper wires heat up faster when using copper wires with a stainless steel mesh.

NiChrome Thermal Conductivity: 11.3 W/m'C
Stainless Steel: 16 W/m'C
Tin (Silver Solder): 67 W/m'C
Copper: 401 W/m'C
Brass: 109 W/m'C
Wood: 0.1-0.2 W/m'C

Thermal conductivity is the quantity of heat transmitted through 1 metre of material due to a 1'C temperature gradient under steady state conditions.

So although a material with a higher resistivity heats up more, a higher thermal conductivity transmits more heat via conduction, right?

Thermal Conductivity of some common Materials and Gases

 

Your point is well taken. I think we are both right as heat generation per ohms law is a combination of current flow squared times resistance. The heat generation of the copper leads may be a case of too much current flowing through too small a diameter wire, sorta like the filament to a light bulb.

Hence the need for copper clad steel wire to prevent heat build up as the diameter of the wire looks small. I see welding rods and iron clad copper suggested as the leads, have you tried actual copper clad steel like this?
Antennacraft Copper-Clad Steel Grounding Wire (25-ft.) : Antennas | RadioShack.com
Also, what diameter wire are you using for the leads?

You are probably right, they are using some sort of resistance welder. I found some guy who actually made his own, WOW! hahahah

[ame="http://www.youtube.com/watch?v=FGrEN6TNLEM"]SOLID STATE CAPACITOR DISCHARGE WELDER - YouTube[/ame]

 

I wish I had an IR thermometer, it would be a simple matter to measure this and find out which type of wire gets hotter on the surface.

I don't think we can both be right. Wikipedia says "An electric heater is an electrical appliance that converts electrical energy into heat. The heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current through a resistor converts electrical energy into heat energy." So a higher resistivity means more heat is generated from current, but less current is flowing through. I mean, if you have a resistance of infinity, you have such small current that it won't get hot at all.

I believe to maximize heat, you must maximize the resistance of the screen (ie use stainless steel) while at the same time minimizing the overall resistance of the rest of the circuit. (ie use copper wire). Does that make sense?

The easiest solution, since as you stated magic flight already figured this out, is to just use what they did. My MFLB is new this year, and the steel wires are NOT copper-coated. They appear to be just mild steel. In fact, some flux and some soldering rusted the ends to hell, so it's not even stainless steel.


TLDR; Use stainless steel.

 

Do you have a digital multimeter? Some come with temperature probes - I've never used mine, but thinking of using mine for this project.

I think we are both right in the sense that you need both resistance and current in order to generate heat, but it needs to be balanced in order to get the temperature you want. High current with no resistance = no heat, but also resistance that cuts current to almost nothing would also = no heat. You initially said that current is important, and I said that you also need resistance - so we are both talking about the two components of resistance heating, right.

I'm just throwing this out there, but maybe the design is so simple that battery is just directly connecting to the resistor/heating element? Meaning that, what I was calling leads to the mesh, are really just an extension of the heating element. The heating element is then in effect U shaped with middle of the U (the mesh) is heated first. Think of a Weller Soldering tip. All you are doing is directly connecting a battery to the ends of the soldering tip.


Can you tell how thick the rods are?

But, I would agree with you that your leads to the heating element should have low resistance to allow maximum current.

 

Get this, in talking about the Weller soldering gun, Hubert Luckett of Popular Science magazine, said that “the instant-heat soldering gun is one of the rarities - a truly needed invention". Further it is reported:

"Weller improved on his soldering gun by making it lighter weight and using easily interchangeable tips to allow for multiple temperature levels to be used for whatever soldering challenges might be run into. The tips are a key factor in the design of the soldering gun, since the tip generally takes up a much smaller area than the rest of the circuit. The smaller the cross sectional area of a metal, the higher resistance it has. This is very important, since it allows most of the heat energy to go to the tip and not to the rest of the tool."

Interesting I think. Consider this, if the F.B. is based on the Weller principle of resistance through changing the cross sectional area of the circuit, and not by changing the resistance properties of the materials used, then it might be possible to used different materials. Further Kurt, it helps to explain why using a copper to attach to the steel mesh causes overheating.

In the Weller soldering tip design, it is made out of copper, and copper has very low resistance. Also the gun also uses very low voltage but high current (very similar to the L.B.). What happens in this design as I understand it, is that the copper allows a lot of current to flow through the tip, but at the point of the tip the cross sectional area of the copper becomes smaller and heat is formed at the point. You can think of a garden hose with water rushing through it, and then you put a kink in the hose. At the point of the kink, is where the heat is formed.

Now why is there overheating in the copper when attaching to the steel mesh? I think it's because the "kink" has shifted to the attachment point of the copper to the steel. Think about this, you are an electron flying out of the battery down this piece of copper, and then BAM you hit this new steel material that has much higher resistance, and this his were the heat is going to form.

Further think about this, could you just skip using steel in circuit completely? If it is only about just changing the cross sectional area of the material enough to cause sufficient resistance and heat, why not make it all out of copper? Benefits, higher current flow better and easier material to work with. If this is possible, then, why didn't M.F. do it? Maybe they were afraid of gassing of the copper, which is supposed to be bad for you. Or, maybe they knew if they used copper, it would be too easy to copy.


This is all just kinda thinking out loud...

 

MFLB seems to use ~1/8" rod. The hole drilled to insert it is 5mm. It appears they use the "reduction is cross sectional area" method to create heat primarily at the screen.

Copper is thermally conductive. The heat is being mostly generated by the screen, but I would think the copper wire, directly attached to the screen, would conduct heat away from the screen, acting like a heat sink. Here's a thought experiment. You have a rod made out of some material, with a constant-temperature heat source at one end. You measure the steady state temperature of the rod's surface. You repeat the experiment with a layer of insulation around the rod. You will find that when the rod is insulated, less energy is used by the heat source to heat the rod. So, ideally, you would want insulated copper wire connected to a highly resistive screen to maximize heat, as less heat will be conducted away from the screen.

Funny you should mention seeing what would happen if you made it all out of copper. I ordered some brass screen just for that purpose. I will make two identical screens of the same size using the same mesh size and same rod lengths but using brass for one screen and stainless steel for the other. We'll see which gets hottest.


Regarding thermocouples: They won't work well for measuring the temperature in this application. You have to touch the thermocouple against the screen, and the reading is not instantaneous. The thermocouple will act as a heat sink, drawing heat away from the screen. Thermocouples are designed to measure environmental temperatures moreso than something like this. You will get a steady state temperature that is lower than the actual steady state temperature of the screen. Heisenberg Uncertainty Principle at work, in a way.

IR thermometers are pretty cheap, you can get them off of ebay for ~$20 maybe. They will be able to measure the temperature of the screen without touching it, getting an instantaneous, more accurate reading.

 

So I did a simple experiment today. I had some copper number 4 AWG wire which is maybe about 1/4 thick, and I found some copper strand wire (very thin). I made a U shaped heating element by placing about 2 inches of the strand wire between two 4" pieces of the thick wire. Then I attached a AA battery to the other end of the thick wire, and BAM the strand wire heated up like a son of a bitch. It burned right through the towel that I had laid down on the table for protection. And the nice thing is the heat was concentrated right in the middle of the strand wire, and no heat to the thick wire nor to the battery.

Conclusion, it proves to me that a significant reduction in the cross sectional area of a circuit will produce instantaneous concentrated heat as Weller discovered years ago. Now the key question is determine proper amount of reduction to get the proper temperature range you want.

Kurt you mentioned the F.B. is using about a 4AWG wire going to the mesh and the 100 mesh you referenced to buy on ebay has a 37AWG. So I hope I can explain this right. The cross sectional area of the 4AWG wire is 16.8mm^2 compared with the 37AWG area of .01mm^2. Ok, so to have no resistance in the circuit you could lay the mesh along the length of the 4AWG wire so that the enough of the mesh area is in contact with the 4AWG wire to equal the cross sectional area of the 4AWG wire, if that even makes sense? Based on the diameter of the 37AWG wire, I calculate that 184.8mm of the mesh would have to be exposed to the 4AWG wire. But according to some drawings, it looks like only 23mm of the mesh is exposed to the wire (i.e. length of the trough). So that the kink in the hose from 184.8mm to only 23mm is providing the resistance necessary to produce the heat.

Somebody out there could probably actually calculate how much reduction is actually needed to produce X joule watts, based on 1.2 volt over X amount of wire at X gauge. But, even then some experimenting would be necessary to find perfect temperature you want.

So I took you advice and ordered an IR gun little for less than $20 bucks from China. I had wanted one before so I have other uses for it.

P.S. I may just go the copper route for my prototype heating element. The material is easier to work with and I think the hazardous gas claim is BS. Plus by using copper, I might be able to a few bells and whistles to project