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Forums
4hv.org :: Forums :: General Science and Electronics
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glow wire

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rp181
Tue Dec 04 2007, 02:46AM Print
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
 		for a glow wire at 3A, 12V am i correct that 4ohms resistace is required?
if not, how do i find out how much resistance?
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EDY19
Tue Dec 04 2007, 03:40AM
EDY19 Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408
 		Google ohms law. However, with temperature change, materials will change resistance, so it depends on your glow wire material.
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Hazmatt_(The Underdog)
Tue Dec 04 2007, 06:18AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		Nichrome wire is what you're talking about and depending on what gauge you want to use the current differs quite a bit. Smaller gauges will require hardly any current and larger gauges much more, but that depends if you're intent is resistors or glow plugs and what kind of energy you plan on dissipating in the wire.
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rp181
Tue Dec 04 2007, 02:05PM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529
 		ya, i searched ohms law and got 4 ohms, im using .5mm graphite piece.
so the hotter it gets, more or less resistance?
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Mates
Tue Dec 04 2007, 02:15PM
Mates Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
rp181 wrote ...

ya, i searched ohms law and got 4 ohms, im using .5mm graphite piece.
so the hotter it gets, more or less resistance?

Only the gasses are lowering their resistance when are getting hot...The graphite and other solid conductors do the oposite.
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rp181
Wed Dec 05 2007, 12:55AM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529
 		so i did about 3 inches of .7 lead from a 3ah 12v lead acid battery, it got really bright orange. After some time, a black skin would peel away, almost like shedding. After a little more time, it got bright white, then extreemly bright white and broke. While it was still orange, it could immediatly melt solder. how can i make the lead piece last longer?
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Shaun
Wed Dec 05 2007, 01:21AM
Shaun Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
 		thats loosely bonded carbon you are using, which will not hold together under even a small amount of stress. Plus, I don't know what use it would be as a glow wire, being so fragile it would break when used.

You may want to try a few strands of steel wool twisted together. I know you can make a simple glow wire cutter with a single strand of this across a 9V battery. This will glow a bright orange. You said your graphite became bright white; this is a lot more heat than you need.
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rp181
Wed Dec 05 2007, 03:45AM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
 		ok, i know that was way more then i need, was just having fun =). I think ile stick with lead from wooden pencils, i can heat that to bright orange and have it last. About how much heat to ignite hydrogen? dull orange, bright orange?
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Shaun
Wed Dec 05 2007, 05:34AM
Shaun Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
 		If you are looking for a way to easily+reliably ignite H2, i would suggest a piezo ignitor from an old grill (or they can be found new at hardware stores). A platinum wire is also a good idea, though harder to control exactly when it ignites.

And if you want some of the nichrome wire hazmatt mentioned to play around with, toasters use several feet of it as their heating elements. So if you have an old toaster or can pick one up at a yard sale, go for it.
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EDY19
Wed Dec 05 2007, 08:27AM
EDY19 Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
 		Hair Dryers are also a great source of nichrome wire, and a little fan for what its worth tongue
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