nichrome wire..anyone familiar with it and its properties?

[strokedmaro]

Ive started a project using nichrome wire and found it has some strange properties. I purchased several different gauges but I will use one as an example. The wire is called "nikrothal 60" and its 38awg..its supposed to measure 43.29 ohms per foot which is about 3.6 ohms per inch. I made a coil for a heating element out of a one inch piece of this wire and when the coil is stretched or contracted the readings are anywhere from 5 to 20 ohms. Why are the readings affected by the shape?

 

[Sceadwian]

Is your multimeter solidly attached to the ends, simple bad or variable contact will provide that much variation. By the way, who is your supplier for that wire, and what is it's power handling capacity listed at? I'm going to assume it's rated to dissipate X watts per inch or foot or what not, or does it just have an upper temperature limit?

 

[Dean Huster]

That's some pretty thin wire for a heating element (unless it's a crystal oven or something like that. Out of curiosity, what's your application?

 

[HarveyH42]

Probably perfect for lighting fuses from a 9 volt battery (which seems popular with the kids these days). That's some thin wire, about the same as a hair, I'd guess. Is there a web site source for this, or a little thicker.

 

[chemelec]

Ive started a project using nichrome wire and found it has some strange properties. I purchased several different gauges but I will use one as an example. The wire is called "nikrothal 60" and its 38awg..its supposed to measure 43.29 ohms per foot which is about 3.6 ohms per inch. I made a coil for a heating element out of a one inch piece of this wire and when the coil is stretched or contracted the readings are anywhere from 5 to 20 ohms. Why are the readings affected by the shape?

That Sounds Strange?
My various sizes of nichrome wires don't do that!

 

[Sceadwian]

I severely doubt the resistance was actually changing that much, it was more than likely issues with the probe contacting the wire. For wire that small you almost have to solder something to it to get enough of a surface area for good contact. I could be wrong though, flexing metal does cause it to heat locally, not sure how much nichrome wire changes it's resistance when it's heated.

 

[elMickotanko]

Hi,

They shouldnt be affected noticably by the shape. Is it maybe the individual coils are touching when contracted so shorting out thereby reducing resistance?

The resistance goes up by about 0.5-1% when hot i think.

Ive been trying to do the same thing recently. I bought some 28gauge off ebay, that was the thinnest i could find. Its 10.7ohm/m

Im trying to use it as a fireworks fuse lighter. Been playing around with it but struggling to light anything reliably.

Anyone got ideas about the best shape / way to do it?
Something that allows easy reuse for lighting fireworks?

Ive can use any length (resistance) up to 2m(21ohms) and can use 3-12V up to 1.2A.

Cheers,
Mick.

 

[Sceadwian]

Try to draw it out, heat some up with a modest current or a small torch and then carefully pull the two ends of the wire, it will stretch, getting thinner and longer, and it's resistance per unit of length should drop pretty fast.

 

[MrAl]

Hi,

A coil of the wire should not change resistance when the coil itself is stretched.
If the wire itself however is stretched making it thinner than the resistance
goes down proportional to the cross sectional area. i doubt it is doing this though.

The wire can increase in resistance by 10 times or more when it gets red hot.
Depends a lot on the actual temperature.