nichrome

[Pyromarty]

hey all, just recived 10' of 40GA nichrome and 48GA from P and J resources. i can fire 40GA at 50' with a 9V battery. i can't even handle the 48 without tweezers using cat 5 for leads. just thought i would share this info.

[Dewey]

I have experienced the same results.
This is were I have been buying 40 awg nichrome:
http://cgi.ebay.com/40-AWG-Nichrome-...QQcmdZViewItem

The nichrome comes on a nice spool... 75ft shipped to the door for $3.99.

[shooter]

Marty how are you attaching the wire?

[yeagerb]

I have 38 gauge wire and I thought that was small!!! 40 gauge, WOW!!!

[johnny_boomboom]

Dude, Get yourself a wirewrap tool ... they are the bomb... There was a post here a while back that suggested it and I bought one... Although I have gone almost exclusively to chip igniters, the wire wrap tool works great...

[JoeRatman]

PyroMarty - what gage was the 50' wire? If I knew that, then I could figure out how much amperage was running through the circuit.

Here is a Radio Shack's wire wrap tool.

http://www.radioshack.com/product/in...ductId=2103243

I would have to agree, I thought 38 gage was hard to work with. Here is a post from another thread that gives tables of how much amperage it takes to heat up or break different gages of nichrome wire. The thinner the nichrome wire (higher gage), the less amps it takes to heat and break it.

Here are two useful tables to help you make nichrome wire igniters. They show how much amperage is required to heat certain sized nichrome wire to a particular temperature.

Note, most nichrome wire has a break or melt point around 2300-2500F. You want the wire to break in an igniter so it will have to have more amperage than the 2000F column.

Both of these tables assume quiet air (no wind). If it is windy, it will take more amperage to heat to the specified temperature. Also, if the nichrome is wrapped, then the heat can not disipate as fast and it should heat up faster with less amperage.

The first assumes a straight piece of wire.
http://www.wiretron.com/nicrdat.html

The second assumes the nichrome forms a spiral coil. This spiral coil is generally used for wire wrapped fuse. Though, if you wire wrap your fuse, the coil will have a larger diameter than those in the table because most fuse is 3/32" nominal diameter. That means you the amperages need to be higher than what is in the table because of the larger diameter.
http://www.resistancewire.com/Html/T...urrentTemp.php

Note, if a wire needs less amperage to break, then there will be less of a spark. For instance, commercial ematches generally use around 52 gage wire. Commercial ematches have a safe no-fire of 0.200 amps and a fire of 0.500 amps. But they have some sort of pyrogen that the small spark ignites. This pyrogen then causes a much larger flame.

[PyroZ]

http://cgi.ebay.com/40-AWG-Nichrome-...QQcmdZViewItem

The nichrome comes on a nice spool... 75ft shipped to the door for $3.99.

This is the same place I get my nichrome. A great deal with quick delivery. I can't imagine handling anything finer than 40 AWG.

What I do is use a sewing needle to diagonally pierce through the core of the visco. I then connect to the nichrome with smooth aligator clips (available at Radio Shack) on the end of 24 gauge telephone wire. I am able to virtually instantly ignite the fuse over 100 feet of wire with just 12 volts.

[Don F]

Ive got a 8 oz spool of 48 guage nichrome somewhere around three miles worth.
the stuff will break with a aa battery under 1/4 inch .
when using extremely fine wire you need a pyrogen that takes and gives fire very easily ( which also means its friction sensitive)

[Pyromarty]

sorry i didn't post more specs. i have 24GA Cat 5. at 50'. i'm wraping the wire and then soldering. i'm thinking about a little micro press that will fold the cat 5 in half and crip it onto the nichrom. kinda like they make filliments for lightbulbs. using about 1.5" per match.

[JoeRatman]

24 gage copper is 25.67 ohms per 1000'.

A 50' run of wire is really 100' (out and back) which gives you 2.567 ohms.

Assuming you used standard nichrome wire, 40 gage is 60.8 ohms per foot or 5.066 ohms per inch. 1.5" of nichrome would be 7.6 ohms.

Thats 10.167 ohms total.

amps = 9 volts / 10.167 ohms

amps = 0.8852 available for this circuit.

I have a table here that says a straight piece of 40 gage nichrome wire requires 0.79 amps to hit 2000F. It needs to get about 2500F to break. Theoretically, you were running real close to the what is possible. I think if you has used thicker nichrome wire or more nichrome or more copper wire, it would probably not have worked.

I am curious did the nichrome break? Was there still continuity on the circuit after the igniter fired or not?

[Pyromarty]

On a fresh 9V battery the nichrome will break. it's only good for about 6-8 shots though. i havn't tested my system with a 12v Optima Gel cell yet. couple weeks still.