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I am not from an electrical background and this might sound silly. What I am trying to do is create a hot wire cutter to cut thermocol(Styrofoam). The sugestions from internet is to use Nichrome but I cannot find one.

I have bunch of copper wire though. Can I heat the wire good enough to cut Styrofoam by shorting with 3 AA batteries ?

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    \$\begingroup\$ Unless you need really perfect cuts I'd suggest using a saw with fine teeth - that's much, much faster. \$\endgroup\$ – sharptooth Nov 13 '14 at 12:28
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    \$\begingroup\$ Find an old hair dryer. Those have nichrome or wire similar to it. Guitar wire as well. \$\endgroup\$ – Passerby Nov 13 '14 at 13:23
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    \$\begingroup\$ @Passerby Actually a nice way to tell whether one is more into electronics than into music, when one says guitar wire :-) \$\endgroup\$ – Pavel Nov 14 '14 at 9:58
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    \$\begingroup\$ @Passerby Guitarists call them strings. For the cutter I would still prefer the term wire, though. \$\endgroup\$ – Pavel Nov 15 '14 at 17:40
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    \$\begingroup\$ I made one of these. Here are a few things I learned: 1. Nichrome is cheap on eBay. 2. Buy a few different gauges; I needed to go thicker because the wire snapped when heated. 3. I used a 12V DC wall wart, safe and easy. 4. You can tune the heat by adjusting the wire length (varying the resistance). 5. I found the best heat for Styrofoam was when the wire was just about to glow. 6. Styrofoam fumes are really really bad for you! Do the cutting outside, if possible. 7. Be steady when cutting; varying your speed will vary the thickness of the cut. 8. Enjoy! It's fun cutting foam :) \$\endgroup\$ – bitsmack Jan 8 '15 at 16:47
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Not really, it does not self heat very well and when hot it anneals and gets soft.

Nichrome is good, steel or stainless steel should also work ok and may be preferred if you need less heat and more strength. Sources of resisting wire would include fishing leaders (or other fine wire rope), piano wire, guitar strings (music wire), salvaged heating element wires (brittle if previously heated), florists wire, and pretty much anything except copper and aluminium.

Using 3 AA cells to heat wire will be disappointing. They made some gimmick bag sealers that heated a short 10mm length of nichrome wire with 2 AA cells but I doubt it would have got hot enough to cut Styrofoam cleanly.

If you should find some very fine filament that will get hot enough to melt Styrofoam with the 3 cells you may find that it will cool down in air and on contact that your cutting speed will be measured in frustration. Transformers supplying 6 to 24V are often suggested for the wire heating and this for lengths of about 300mm (12 inches). The current may be a few amps so would drain small cells fast. Note that you need an isolating transformer for your scenario - using an autotransformer may have dire consequences (including electrocution).

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    \$\begingroup\$ Ordinary fuse wire is usually copper! \$\endgroup\$ – Leon Heller Nov 13 '14 at 10:33
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    \$\begingroup\$ I'd add that he needs an isolating transformer, not an auto-transformer. This is not too obvious. \$\endgroup\$ – sharptooth Nov 13 '14 at 12:25
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    \$\begingroup\$ I've got a wire heater made with Stainless (I think) and a 6V filament transformer. I run that off a variac to set a reasonable current. One thing to be aware of is the the wire gets longer as it gets hotter. \$\endgroup\$ – George Herold Nov 13 '14 at 15:14
  • \$\begingroup\$ @LeonHeller Thanks, I removed the Fuse wire, it was not based on experience just a gut feel but it is likely a wire better suited to carrying power than resisting current even if not pure (tinned) copper. \$\endgroup\$ – KalleMP Nov 20 '14 at 12:37
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Copper wire will quickly deform even when not heated as you apply pressure. Further, as a very low resistance, it will not heat well given most power supplies, and particularly using batteries.

The internal resistance of the power supply will dominate the circuit, and most of the heating energy will be lost in the batteries or power supply, rather than the wire.

You might be tempted to choose a thinner wire to increase its resistance, but you will only be frustrated by the lack of mechanical strength in the copper wire.

You can still make this work if you support the wire. Adhering it to a thin support, such as glass, will allow you to heat the wire significantly without worrying too much about breaking it while using it.

Unfortunately you then run into another problem - oxidation and uneven heating leading to fusing. Even if you find wire that is perfectly conductive throughout and has no change in resistance along its length, over time it will oxidize unevenly, causing hotspots and cold spots, and in order to get the whole thing up to temperature you will likely find one spot get hot enough to turn into a fuse, and cause a break in the wire.

This isn't going to happen immediately though, so if copper is your only choice and you've solved the power supply internal resistance problem, then you can simply replace the wire whenever it stops cutting well.

However, there are many other metals with superior mechanical and electrical attributes that would better fit your needs.

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I don't think it's silly. Copper wire that is strong enough will require a fairly low voltage, but it may work out for you.

According to NIST data, copper has about 3 times the resistivity at 800K compared to 300K. If we pick a reasonably sturdy wire such as an AWG 20, the resistivity of 6" (150mm) will be about 15m\$\Omega\$, so for a current 50% of fusing (about 30A), we'd need about 0.5V. That's about the current that six fresh Alkaline AA cells in parallel can supply at 0.5V terminal voltage- easy enough to try. Of course you need to use thicker wire to connect the calls (maybe AWG 8). Don't expect the batteries to last long, and the batteries will get very hot so keep them separated from each other and shielded physically in case they burst.

Longer term maybe procure some Nichrome wire (eg. eBay) and use a repurposed PC supply. Unfortunately Nichrome gets a bit brittle after use so it's difficult to scavenge from, say, a hair dryer.

Edit: see KalleMP's suggestion in the comment to consider music wire (steel) which could be used with a PC supply.

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  • \$\begingroup\$ I think you should do a test and see how long the batteries last across a shortcircuit. Some workable options include piano, guitar, fishing leader, heater element and fuse wire. To heat copper wire you need club.cycom.co.uk/hotwire/… \$\endgroup\$ – KalleMP Nov 13 '14 at 9:30
  • \$\begingroup\$ @KalleMP yes, that's probably about the right voltage- and those soldering guns will overheat if left on for very long. Music wire and a PC power supply is prolly a good option. +1, you should add the music wire option to your answer. \$\endgroup\$ – Spehro Pefhany Nov 13 '14 at 9:34
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Copper wire will stretch and deform quite quickly, jump onto ebay and purchase a small pack of nichrome wire, it's the most appropriate material for the task

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Model R/Cer's having been cutting styrofoam wings for decades with ni-cr wire and a variable power supply. (A model RR transformers can serve as a variable power supply and they're cheap on EBay.) Steel piano wire also works but will need a little more voltage. Search videos on "cutting foam wings". Use the lowest power that cuts and CUT SLOWLY.

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