cant get my foam cutter to work.

ok im building a foam cutter, kind of following the instructions from

aaand it doesent work. i have a 10v 5 w transformer attached to a metal frame that holds the wires. and the transformer is attached to this stainless steal wire. i was thinking that maybe because i have it attached to a metal frame it sucks all the current but technically shouldent it try to "find" the thinnest place to short circuit and heat up? When I touch the wires to the frame it sparks up, so there is a current going through. And also if I just hold a piece of wire on my hands and connect it to the transformer, it doesn’t heat up either.

sorry no pics, i might have some in a couple of days.

helps! or suggestions as to what the reason might be for it not working. i am trying to build model for school, alas i think the foam cutter itself is more of a project then what im building

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motley (author) 10 years ago
hm, you maybe right. here is a diagram of it though(hope it works, im not quite sure how the uploading thing works either. in flywoodkb s tutorial he doesent use a resistor at all. then again it is a wooden frame. the part that confuses me ( and that is an easy task some times) is why it doesent work like a battery, when i hold a piece of wire between + - it doesent heat up :(. is it because the transformer shuts itself off? as in read a short? so if the wire was long enough between +- it would heat up right?
LasVegas motley10 years ago
in flywoodkb's tutorial, he's not using a current-limited power supply. Your supply is limited to a maximum of half an amp (5W). He's controlling the current with the Dimmer switch. You don't have that luxury. He also noted that he improperly is not using a fuse in the circuit. This could prove very dangerous.

A battery's current is limited by the internal resistance of the battery itself. While it would heat a short wire, you'll also note that the battery itself will get very hot.

Your power supply is not a battery. It has a stated limit of 5 Watts. 5W/10V = 0.5A. This is why I suggested that you add a 20ohm/5Watt resistor (10V/0.5A = 20ohm) This would allow your power supply to put out it's maximum current. I can't say it would be enough to heat the wire though.

It would be best to duplicate flywood's design. The transformer isn't too expensive.

BTW: I don't know what format your document is in.
motley (author)  LasVegas10 years ago
aa things started to get a bit more clear now! thanks!! i tried ading rezistors to the contraption but i forgot about the 5w thing when i was buying them, so i got 5 10ohm 1/4w rezistors... and now my room smells like burnt plastic yay! i will try ading a dimmer and proper rezistors to the equasion tomorow. i also have a nother smaller transformer that is 4.5 v, 400ma. do you think that would be a better option then the biggre transformer? here is my setup
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LasVegas motley10 years ago
You cannot have a metal frame! The wire must be totally insulated from the frame.

400mA = 0.4A @ 4.5V would give you 1.8W. Quite a bit less. No. It won't work.

Get a 25V, 2A transformer (That's up to 50Watts!) from RadioShack. I know it's more expensive, but it's necessary. So is the Dimmer!

Do not do anything with your contraption until you get rid of the metal frame!
motley (author)  LasVegas10 years ago
ok, will do now i am all excited about this. i hope it works this time. 25v 2a and a dimmer it is. do you think that my 10v would do the trick as well with just a dimmer? my wire currently isnt longer then 1', and i dont see it getting any longer.
LasVegas motley10 years ago
A 1" wire might get hot enough with the 10v supply, but the 20ohm/5w resistor is absolutely necessary. No substitutions! If you used 2 10ohm resistors they would still have to be 5 watt resistors. These will look like a ceramic brick about 1.5" long and 1/4" square or brown ceramic tube about the same size. You cannot use the dimmer with the 10v supply since that supply is already using an internal regulator. If you use the dimmer/transformer setup with that tiny wire, start with the dimmer full down and turn it up just until the wire appears to smoke a tiny bit. It won't take much. Again... Don't use that metal frame!
motley (author)  LasVegas10 years ago
awesome! thanks a lot! i truly appreciate it. im using the metal frame but im replacing the attachment parts with dowels, so there wont be current going through it. i like the metal frame cos i can tension the wire really easily. oh and the wire is 1 foot long :) here is my final shopping list then: dowels for insulating, 25v 2a trans, dimmer. and i will attach them just like in flywoodkb's tutorial, wall outlet ->dimmer ->transformer -> wire. no resistors. thanks again for being patient.
I'm using the metal frame but I'm replacing the attachment parts with dowels, so there wont be current going through it. I like the metal frame because I can tension the wire really easily.

I don't think LasVegas stressed it enough..... for safety, you need a frame that will not conduct. That is, should something go wrong... and eventually something will go wrong (guaranteed) - you need to be isolated completely.

Wood frames can be just as easy to tension ;) It's up to the designer (you) on how easy it is to build and adjust ;)
If you keep the metal frame with the dowels, pick up a roll of black electrical tape (This is real cheap!) and cover the frame with the tape. You don't want any metal exposed around the filiment.
motley (author)  LasVegas10 years ago
ok got me some tape the transformer and a dimmer! tonight i shall construct the deamon. hm im going to try to isolate it as much as i can but what would happen in case of the 24 v toucing the frame? i imagine if the 110 touched it it would be a bit different. my faulty highschool physics tells me that not much would happen because the metal frame has a higher rezistance and the current will prefer the thiner cutting end... tell me it is so and i wont blow a fuse or my house.
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