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Scope: The scope of this project is to repeatably light several fireworks simultaneously (Mandalorian Whistling Birds Vambrace build). This requires that the only action required to light more firework rockets would be to load them into the device. I have looked into the ways people have done this in the past but all the options I've seen are consumable or one time use. I've built a proof of concept design and now I'd like to improve it. My initial prototype uses the nichrome ribbon I removed from a car cigarette lighter coil. I chose to start with this since it was a cheap source that uses 12V. The fuses of the fireworks rest on the coil and as I apply 12V to the coil it heats up and they ignite.

The issue I am facing is that the coil takes awhile to heat up (no calculations in first design for efficiency) so I would like to design one that heats up faster and has more surface area coverage. I would still like to use my 12V LiPo battery. I can do the equations to figure out voltage, length of wire, amps, and produced heat but what I'm having trouble with is figuring out how to suspend the coil, ensure it maintains its shape, and doesn't short to the metal chamber it's nested in. I plan to use 28-30 gage nichrome wire which is not very rigid. I'm also dealing with a small space of less than a 2" diameter tube. Any ideas?

Thank you in advance for any suggestions you may have.

Edit: Thanks everyone who answered and provided suggestions! From your responses I have learned that mica, alumina ceramic, or other ceramic compositions will work well as an insulating material. Also, the use of thin stainless steel sheet may work well as the heated element for ignition.

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    \$\begingroup\$ In the past mica sheet was used for this kind of application. \$\endgroup\$ Apr 23 '20 at 0:38
  • \$\begingroup\$ Second the idea of mica. You can order it online or take apart an old toaster. \$\endgroup\$ Apr 23 '20 at 2:09
  • \$\begingroup\$ Macor machinable ceramic, from Corning, is a composite of 50% mica and 50% glass. It is easily drilled and cut with a hack saw, and it good to around a thousand degrees. It looks like a pure white homogeneous ceramic. The mica content is what makes it machinable: micro cracks always terminate in ultra tiny mica particles. Anyway, I have used it and it will hold up well. Mica itself is fine, though. \$\endgroup\$
    – Ed V
    Apr 23 '20 at 2:41
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Between the two options of a self-supporting heated element, and a supported heating element, the self-supporting one will have lower mass, so will heat faster.

Self-supporting means short and fat, so unfortunately low resistance. However, there are lots of designs, and maybe modules, to get low voltage high current from 12 V sources, think low voltage 100 amp supplies to CPUs and GPUs.

I'd go with sourcing some thin stainless steel sheet, which has an astonishingly high resistivity, and cutting some into an inverted 'V' shape. Clamp the two arms between two bolts, the pointy bit would then point up and be able to penetrate into the bottom of the rocket, achieving good contact with the fuel. The bolts would need to pass through ceramic or glass, but maybe you could use GRP and face it with mica or something to survive the short, albeit intense, launch heat. I've been using some fake roofing 'slate' recently as a flame baffle in a propane kiln, and that seems to hold up well.

This would be a design for an intermediate life element, robust enough to serve several launches, but cheap and sufficiently easily replaced to not have to be built to survive 100s of them.

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  • \$\begingroup\$ Thanks for your response! This gives me a new perspective that I think will be very useful. \$\endgroup\$
    – dutenh
    Apr 23 '20 at 13:40
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I would think ceramic (alumina, typically) would work well. It has the benefit of providing thermal insulation, so the wire will lose less heat (heating time will be shorter.)

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Mica sheet might be suitable for this application. In the past it was used for high-temperature fixtures and for electrical insulation. As @SpehroPefhany mentioned it can be sourced from an old toaster or ordered online. These days I believe ceramic is more typical for these applications.

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