ErikSedell Posted September 24 Posted September 24 (edited) Hi all. my first post here with a topic that frustrates me at the moment. Normally I use nichrome wire soldered to my leads for ignition. Can’t order visco in Sweden, and I don’t want to use fuse for rocket motors. But the soldering takes some time and the igniters are quickly used up. So I wanted to use carbon film resistors, especially for testing new compositions/igniter designs for the ease and cheapness of just connecting a resistor and ignite. But the resistors won’t burn/flash/glow for me. I have now ordered and tried 1/4 and 1/8W carbon film resistors in 1, 2.2, 5.6 and 10 Ohms and they all just fail in open circuit mode. At most a little puff of smoke but no intense heat. I’m using a 9.6V, 3000mAh NiMH battery pack for RC hobby as power source. The nichrome just flashes away but not the resistors. Any ideas on what’s going wrong here? Are new carbon film resistors designed specifically not to burn when overloaded? If so, are there brands/manufacturers that do burn as intended? I’m especially interested in 1/8 resistors for the small footprint. is my power source the problem? If so, how come it works with nichrome? looking forward to get some input from you. //Erik Edit: please suggest another thread if there is one that suits this discussion better Edited September 24 by ErikSedell
Arthur Posted September 24 Posted September 24 There is probably NOTHING that imitates a standard firework igniter. The closer you can get to a 2mm length of 50 swg of nichrome wire the better. They must have reliable fire and not fire properties other than that they are too dangerous. Getting the compound right is essential. Remember that swg is a British Imperial measure ( clag.org.uk/swg.html ) is one example of a conversion chart.
FrankRizzo Posted September 25 Posted September 25 Erik- You are correct, most new manufacturer resistors have been designed not to fail by bursting into flames (marketed as "flame proof"). The ones that you want are old mfg 10ohm 1/8W carbon film resistors.
Richtee Posted September 25 Posted September 25 (edited) I dunno... I use 30 AWG nichrome and just a NC/BP mix with a bit of dark AL added. Never fails. You cut the wire about 5” long and “double it back” to the “bridge” you leave maybe .25” long..depending on application. A little longer for wrapping visco. Wrap the visco with the bridge part, and coat with mix. Or, dip the other style. I have a vid here somewhere on the visco version. Hmmm... here... EVisco.mp4 Edited September 25 by Richtee
ErikSedell Posted September 25 Author Posted September 25 Thank you Frank. Is mfg the manufacturer? Any idea if they can be found and ordered?
FrankRizzo Posted September 25 Posted September 25 1 hour ago, ErikSedell said: Thank you Frank. Is mfg the manufacturer? Any idea if they can be found and ordered? No, I was just referring to "old manufacture". I don't have any brand names to recommend, unfortunately.
ErikSedell Posted September 26 Author Posted September 26 Thank you Frank. I will start searching for old stock
ErikSedell Posted September 26 Author Posted September 26 19 hours ago, Richtee said: I dunno... I use 30 AWG nichrome and just a NC/BP mix with a bit of dark AL added. Never fails. You cut the wire about 5” long and “double it back” to the “bridge” you leave maybe .25” long..depending on application. A little longer for wrapping visco. Wrap the visco with the bridge part, and coat with mix. Or, dip the other style. I have a vid here somewhere on the visco version. Hmmm... here... EVisco.mp4 Thank you, will reconsider my nichrome ignitors, making them simpler and faster to make
Richtee Posted September 26 Posted September 26 9 hours ago, ErikSedell said: Thank you, will reconsider my nichrome ignitors, making them simpler and faster to make I'd suggest that. Besides, low ohmage, low wattage resistors were/are not a thing in high demand anyway. You’d be more likely to find a 10 ohm 10 watt resistor. The key is to “double up” the lead wire, making the “bridge” heat twice as fast as the leads.
ErikSedell Posted September 27 Author Posted September 27 12 hours ago, Richtee said: I'd suggest that. Besides, low ohmage, low wattage resistors were/are not a thing in high demand anyway. You’d be more likely to find a 10 ohm 10 watt resistor. The key is to “double up” the lead wire, making the “bridge” heat twice as fast as the leads. Yes, i noted the doubling. That’s a very convenient way.
brad224 Posted September 30 Posted September 30 WIREOPTIM has many sizes of excellent nichrome wire at really good prices. i’ve used everything from 40 awg (too thin for these old eyes and fumbling fingers) to 28 awg, (much thicker and easier to handle.) i gave up on soldering long ago, now i bend a quarter inch of the lead wires, wrap nichrome on one side 3 or 4 times and crimp it, leave up to an inch “overhang” and then fold, wrap and crimp the other side of the lead. requires really sophisticated tools (ie: a $4 pair of harbor freight needle nose pliers), less than perfect eyes, and has worked for me without fail. 1
Richtee Posted September 30 Posted September 30 (edited) 3 hours ago, brad224 said: WIREOPTIM has many sizes of excellent nichrome wire at really good prices. i’ve used everything from 40 awg (too thin for these old eyes and fumbling fingers) to 28 awg, (much thicker and easier to handle.) i gave up on soldering long ago, now i bend a quarter inch of the lead wires, wrap nichrome on one side 3 or 4 times and crimp it, leave up to an inch “overhang” and then fold, wrap and crimp the other side of the lead. requires really sophisticated tools (ie: a $4 pair of harbor freight needle nose pliers), less than perfect eyes, and has worked for me without fail. It's amusing how complicated folks wanna make things. Just wait ‘till their fingers hurt and they can’t see crap any more On Edit: At least I can STILL smell crap to avoid it Edited September 30 by Richtee
Arthur Posted September 30 Posted September 30 (edited) There are at least three videos on YT of Chinese factory manufacture of igniters/e-matches which show a low cost (high skill) method of making the igniter chips, soldering the nichrome bridge wire and adding the comp and the wires. It should be possible to glean the entire process except the ignition comp from the videos. The board is SRPB double sided printed circuit board probably about 1mm thick, SRPB is cheaper and NOT flame retardant (FR1) so finds little use in western printed circuits, BUT in this case if it's cheaper it's better because igs are single use! GRP is used for modern pcb's because it's stronger and is made to be fire retardant (FR4). The glass fibres may harm cutting tools. wires.co.uk have helped me find fine gauges of wire, you must see whether they will ship small orders to your country. YOU will have to research suitable primer compounds, and how to source the ingredients. The lacquer has (IMO) a nitrocellulose base which is either bought, or stolen from your wife/sister/gf as out of fashion nail varnish. Edited September 30 by Arthur Added
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