Hi,
I’m going to make a hot wire cutter for foam to build house for a small robot. I have a 9v @ 1amp adapter to use. How to calculate the wire length please so to have the needed resistance? (I’m going to use guitar string wire).
Really?
Basic math eludes you?
Resistance per foot multiplied by total feet equals total resistance?
Really?
9v @ 1amp adapter. Show us a picture. Not nearly enough…
Sorry seems I didn’t put the question correctly, I’d try to improve:
I first used an ordinary atx power supply. When I connected the guitar wire (around 40cm) between two ordinary screw (5m dia. x 25mm length) and connected them to the 12v of the power supply, I didn’t get it that hot. I don’t have dimmer switch currently. So to get it hot, I cut the wire down to some 8cm and power supply stopped (not burned, just stopped and I every time could restart it). Then the main problem is that I don’t know how to calculate the correct length. Sure if I have the dimmer, then it is easy: just to turn it until getting the needed temperature. But then how the length is calculated for the known adapter - in this case my atx - to know if I want a 200deg/c heat, what must be the length of the wire please? where is the formula that I can’t find on the google? (perhaps not submitting the right keyword, but only ‘hot wire foam’).
Or…you could get a variable output power supply and do it “right”.
True, and didn’t write to forum to ask for formula.
Guitar string? I Guess that could work. I’ve always use nichrome wire for cutting foam. Then used the formula as mentioned above to set lenfth and power supply output.
If your ATX PS is shutting down then the wire’s resistance is too low which tries to draw too much current from the PS.
Also, a dimmer switch will not work with an ATX PS since this is a switching PS that will try to regulate its output Voltage.
A dimmer is only used for a step-down transformer.
http://www.instructables.com/id/Hot-wire-foam-cutter/
If the guitar wire is not getting hot enough or is shutting down your PS try using a thinner guitar wire. Thin means it will have more resistance per length (google wire resistance and calculate). Resistance times current equals power as heat (just simple equation again).
thank you very much!