Copper wire vs. nichrome

[rstaff3]

I need someone to refresh my memory....

I stumbled on some fine copper wire used in the winding of a contactor relay. I immediately though of igniters. It's awfully fine and is undoubtedly coated, but could it be made to work in a bridge wire igniter? Thoughts?

 

[ben]

I believe it has something to do with copper oxidizing.

Ben

 

[DaveHein]

According to wikipedia, copper has a resistivity of 1.8*10**(-8) and nichrome is 1.4*10**(-6). At the same gauge, a copper wire would have to be 100 times longer than a nichrome wire to have the same resistance. At the same length, the diameter of the copper wire would have to be one-tenth that of the nichrome wire.

I have seen cat 5 cables used for igniters. They do require a lot of current.

 

[Kaycee]

I need someone to refresh my memory....

I stumbled on some fine copper wire used in the winding of a contactor relay. I immediately though of igniters. It's awfully fine and is undoubtedly coated, but could it be made to work in a bridge wire igniter? Thoughts?

It should work fine provided you supply enough amps to the igniter. Also, you didn't specify how you'd make the bridge-wire, but I assume you will be coating these with pyrogen(?)

Interesting factoid---Maybe 10-12 or so years ago Estes supplied our club (as Beta testers) with some igniters that (I think) had a copper bridge-wire although I don't know what gauge. The interesting thing about these there that they had NO pyrogen. We used many of them and for the most part they worked well. The only failures were with those that were damaged while inserting the igniter plug.

Needless to say, these igniters never were marketed.

 

[davel]

Best answer is no. You need a resistance wire that will stay intact at high temperatures. Nichrome.

Copper wire is relatively low resistance and will not heat well. And when it does heat, it will fall apart before it gets very hot. It *may* work as an ignitor, but I wouldn't count on it being too reliable.

 

[bobkrech]

The coating is probably enamel or varnish insulation which you would have to remove for electrical contact. My guess is that the wire resistance will be too low but if the wire is thin enough so the bridge wire resistance is between 1 and 2 ohms it should work when coated with a pyrogen but the only way to know for sure is to try it.

Bob

 

[falingtrea]

Best answer is no. You need a resistance wire that will stay intact at high temperatures. Nichrome.

Copper wire is relatively low resistance and will not heat well. And when it does heat, it will fall apart before it gets very hot. It *may* work as an ignitor, but I wouldn't count on it being too reliable.

I would have to agree with Davel. NiChrome is a alloy of nickel and chromium which has a much higher tensile strength than copper.

 

[bobkrech]

I would have to agree with Davel. NiChrome is a alloy of nickel and chromium which has a much higher tensile strength than copper.

Tensile strength has nothing to do with how a material acts as an igniter bridge wire.

Copper melts at 1981 F or 1083 C where as Nichrome melts at 2550 F or 1316 C. Both temperatures are well above the typical pyrogen ignition temperature of ~600 F or 300 C so melting point is not an issue. The problem with copper is that the resistance is so low that you can only have a very small cross-section wire for a reasonable current draw. The small cross-section provides a smaller amout of heat capacity in the metal to heat the pyrogen so the ignition process is likey to take longer and the ingition delay time will be more variable. It can be used as an exploding bridgewire igniter, but this is beyond the hobby level of technology.

Bob

 

[shreadvector]

I think your memory is foggy. Estes sent out a load of pyrogen-less igniters to see how they would do in case they could not ship igniters or sell igniters with the pyrogen on them (may have been European issues or could have been USA as well they were preparing for). They encouraged use by beginners in clubs as well as with clusters to gather data. All used plugs.

A few years earlier they had coppery looking lead wires on the standard Estes igniters (aka ""Solar igniters").

With nichrome wire so cheap, why risk damage to your launch controller with a massive (50? 100? more) amp current flow to heat up a copper wire?

It should work fine provided you supply enough amps to the igniter. Also, you didn't specify how you'd make the bridge-wire, but I assume you will be coating these with pyrogen(?)

Interesting factoid---Maybe 10-12 or so years ago Estes supplied our club (as Beta testers) with some igniters that (I think) had a copper bridge-wire although I don't know what gauge. The interesting thing about these there that they had NO pyrogen. We used many of them and for the most part they worked well. The only failures were with those that were damaged while inserting the igniter plug.

Needless to say, these igniters never were marketed.

 

[rstaff3]

Thanks for refreshing my memory fellers. I had thought of most of this stuff but wanted to test the waters.

Bob, I had also heard tensile strength was an issue, thanks for clarifying this.

Well shux, since I have a bunch of nichrome anyway, I guess the contactor will go in the garbage.

 

[quickburst]

Thanks for refreshing my memory fellers. I had thought of most of this stuff but wanted to test the waters.

Bob, I had also heard tensile strength was an issue, thanks for clarifying this.

Well shux, since I have a bunch of nichrome anyway, I guess the contactor will go in the garbage.

Nichrome is the best bet.

 

[The Visionary]

Do what I do when I don't get a response that I like with no experience attached to it. (NO OFFENSE INTENDED TO ANYONE) Try it and see. Make some up and dry fire them. Video it and compare it to a nichrome igniter. Make up 10 and see if any fail to light. Apply science to it. At worst it just won't work and when someone asks everyone would have your experience to go on.

 

[ADiehl]

I Use the strands from the inside of 28ga aluminum wire to make igniters, and have used similar copper strands in the past. All used a decent lacquer pyrogen and I've never had a problem igniting 2 of em on a fully charged 12v Dewalt drill battery. However, It does take a lot of current which is a GOOD thing for reliable pyrogen initiation. If memory serves me correctly, Power=V^2/R so the lower the resistance the greater the power dissipated (heat). Of course, the reason we don't have copper heating elements on our electric stoves is because supplying all that energy is a little problematic...

Final conclusion: use whatever you can get away with for the capabilities of your launch system. If you use a 9v battery, use nichrome. If you have a 10 farad capacitor bank at your disposal, go for the biggest wire you can fit in a motor . Your copper wire should work just fine in the average launch system.

Andrew D.

 

[Micromeister]

Thanks for refreshing my memory fellers. I had thought of most of this stuff but wanted to test the waters.

Bob, I had also heard tensile strength was an issue, thanks for clarifying this.

Well shux, since I have a bunch of nichrome anyway, I guess the contactor will go in the garbage.

Dick:
if it's very thin diameter and long enough lengths, you might want to earmark if for use wiring up all those low volt LED illuminated Night vehicles.