This simple project uses several nichrome wires to cut and slice big chunks of styrofoam. More than that, you will be able to control the temperature of the cutting wires using a sort of dimmer circuit.
Why using multiple wires instead the traditional single one?
The original idea was to transform large pieces of styrofoam used in packaging into "pellets" used to protect fragile items inside cardboard boxes. So, instead of cutting the styrofoam pieces one by one, if I use several wires I would be able to reduce large styrofoam chunks into smaller parts much faster.
Why recycled parts?
Well... the dimmer circuit is not recycled... but is cheap. The other parts are recycled.
In my country most homes use electric showers. These pieces of equipment warm the water with powerful "resistors" of thick nichrome wires (that dissipate about 5,5kW). Sometimes these resistors break due to the high temperature, and, after some time you'll end up with several meters of spare nichrome wire. For sure you can buy them... they are also a very cheap item... .
Step 1: Materials Required:
For the wood frame and voltage divider:(detailed drawings can be dowloaded below)
2 pieces of wood 45 mm x 315 mm x 9 mm thick (for side boards).
1 piece of wood 56 mm x 220 mm x 9 mm thick (union board).
1 piece of wood 56 mm x 100 mm x 9 mm thick (suport board).
1 piece of wood 3" x 12" x 3/4" thick (for the voltage divider resistor).
2 pieces nichrome wire, 0.7mm diameter 6 meters long. (You can get it in electric showers).
1 piece of nichrome wire, 0.5 mm diameter 1 meter long.(you can get it in hardware store)
12 flat head screws 3/16" x 1" bsw thread.
2 flat head screws 3/16" x 2" bsw thread.
26 hexagonal nuts 3/16"
18 3/16" flat washers
3 Connector bar (cut three and remove the plastic cover)
For the High power Dimmer circuit
1 TRIAC BTA 41600
1 DIAC DB3
1 Capacitor polyester 100nF 630V
1 Capacitor polyester 47nF 400V
1 resistor 15k2 1/4" W
1 potentiometer with plastic axle 100K linear.
1 Perf-board 50 mm x 100 mm will do.
20 A copper wires
1 110V 20A plug
Step 2: Other Possible Versions:
It is possible to build this same project in two other different versions:
1) Without the tension divider: the dimmer can lower the voltage by itself but you will have to connect two other TRIACs in paralllel with the one I already used. It is very likely that only one TRIAC might not be able to handle the current when connecting the cutter nichrome.
2) Without dimmer (It was the original idea) in this case you'll have do add more resistance to lower the circuit current, you will need about another six meters of nichrome wire. Needless to say that this is the easy version to assemble but it is the less "intelligent" in terms of power consumption. (the original idea was to have it built completely with recycled parts despite of high energy consumptiom).
Step 3: How It Works:
Typically, nichrome is wound in coils to a certain electrical resistance, and current is passed through it to produce heat. it is widely used in electric heating elements, such as in appliances and tools.
Almost any conductive wire can be used for heating, but most metals will be rapidly oxidized when heated in air. When heated to red hot temperatures, nichrome wire develops an outer layer of chromium oxide, thermodynamically stable in air, mostly impervious to oxygen, and protects the heating element from further oxidation. (I got this text from Wikepedia).
I read that the temperature generally used in Styrofoam cutters is about 200º C degrees, so we have "control" the current in order to not to get a "too hot" wire. I must mention that in this cutter the wire does not get red... It starts to melt the styrofoam much before. Therefore, the role of dimmer and voltage divider do is hold the current until a value that can warm the wire enough only to cut the material.
Step 4: Build the Wood Frame
I have used the 3/16 screws to hold the assemble together. The drawings I posted here are just to give an idea and may be changed if you want to slice larger pieces of styrofoam. Tough, there is an important detail: If you make the holes for the screws that hold the nichrome wire too close, the washers will touch each other and short circuit the cutting nichrome. Leave them apart 15 mm, at least, if you use regular size flat washers.
Check the pictures for you to have an idea how it was put together.
Step 5: Wind the Thinest Nichome Wire to Set Up the Cutting Part
Wind up the 0.5 mm nichrome wire around the screws in a way that you get 4 parallel wires. After that, mount another nut on every screw to ensure that the wire won't fall down. After that connect a piece of wire on each end of the nichrome wire. These two ends will be wire in series with the power resistors. Please refer to the wiring diagram.
Step 6: Set Up the Voltage Divider
The voltage divider is made with the two lenghts of thicker nichrome wires serially mounted. I used the screws to hold the wires in a way to keep the heat far from the wood base (it will burn the wood). In order to connect the nichrome coils to the circuit I used brass connectors with the plastic cap removed (it will melt if you leave it).
Between the nichrome wires and wood base I left about 8 mm.
Step 7: Setting Up the Power Dimmer
I have used a circuit that I found online. Unfortunately I do not recall the original source...
I have used a perfboard to make things easier and, since there are only a few components I soldered them simply following the circuit diagram. Take extra care when soldering the BTA41600, I added the pinout for you to check what are the correct terminals. You will have to use a medium size heat dissipator attached to the DIAC.In my assembly I used a small piece of stainless steel size 90 mm x 35 mm x 0.3mm.
Dimmers are interesting circuits, you can do many thing with them. Some universal electric (blender for instance) motors can have their speed controlled with a help of a dimmer. Only the old filament lamps can be controlled with dimmers, the compact fluorescent cannot. After having mounted the dimmer you must connect it in series with the voltage divider and cutting nichrome.(check the main wiring diagram).
Step 8: Operation
First and the most important thing... SAFETY!
Differently from other popular styrofoam cutters this design does not use a transformer to lower the voltage. Here I use a powerful resistor to divide the voltage... also, I use the dimmer circuit to a better control. What I mean is that this is a HIGH VOLTAGE circuit! Please, take care not to touch any live parts. If you intend to build this project, please enclose the tension divider and dimmer circuit inside heat resistant boxes.
Please note that with the voltage divider and dimmer connected the voltages measured on the cutting nichrome and the voltage divider are about 8.9 V and 37.5 V. Anyway, avoid at all costs touching both wires (risk of burn your fingers and get electrical shock).
1- Fix the wood frame on a table in a way where you will get a open space to let the cut styrofoam fall.
2- Connect the circuit to the mains and turn the potentiometer to the minimum. Slowly, turn the potentiometer until you get a temperature on the thinner nichrome wire hot enough to cut the styrofoam.
3 - Force big chunks agaisnt the hot wire until it get sliced. Take the big slices and cut them again several times until
you reach the size desired.
(check the video for a better visualization).
If you have any doubt, please do not hesitate to contact me! Best regards and good luck on your projects!