Home made DIY e-matches in Australia. Diy guide. Carbon film resistors. (Re-usable)

[jl88]

So for a while I have been frustrated with relying on fuse for ignition and timing when I display shells/rockets etc... There are many short comings of fuse in my opinion. Ranging from a problem in timing, a shell or rocket malfunctioning or even some one running into the firing area and being unable to halt the sequence. Hence why I started looking for e-matches.

 

Now there are several available options ranging from blanks with nichrome wire chips to ready made e-match assemblies. All of which are expensive in Australia or down right un-available. So after doing a bit of research I found that carbon film resistors would be a good option.

 

For my electronic ignition devices I use 1/4 watt 8.2ohm carbon film resistors that I buy from jaycar electronics. You can easily use from 6-12ohm resistors. This is just what was available to me that stays under 2 amps. The resistor is then soldered to a twin core wire that us connected to the firing system. Polarity is not important. I fire using a 2200mah 11.1v lipo battery from my days flying model planes. (7.4v 2200 lip also work, however allow 2 sec for ignition) Ignition occurs within 1 second and is very reliable. (To this day 100%) The resistors will glow red for at least 3 seconds and then burst into flames. The glowing red is plenty to light BP, green mix, flash etc. I use bp bound with NC lacquer as the pyrogen.

 

The other interesting thing is that I have been able to re-use the resistors after their first fire. Firing 2-3 times per resistor reliably. Re-dipping in pyrogen between shoots. Not that you need to at the cost. If anyone is interested I'd be happy to post a video with a walkthrough. Just let me know.

 

Anyway just thought I'd post it and let everyone know. All the best,

 

Jack.

Edited September 2, 2014 by jl88

[taiwanluthiers]

One way to get nichrome wires is from hair dryer elements... I can't be sure if it's nichrome but it will glow red hot when electricity is passed through it. How much is another question however.

 

You can also use conductive lamblack or graphite to make the e-match element, then dip into pyrogen. Again it may require a lot more current to ignite than commercial e-match.

 

Some have used Christmas light bulbs. Tungsten filament from old incandescent light bulbs (the bigger problem is you might not find them in Australia because a lot of countries are trying to phase them out) should work in theory, but I am not sure how fragile they are.

[Arthur]

One of the "usual suspects" in the USA will ship suitable resistor chips for something like 10cents each (by the thousand) These are the real thing just no wires or pyro.

[dagabu]

Interesting, the Chinese E-matches on eBay (safe to ship and store) run about $.25 each while both Mouser and DigiKey run about $.50 each even in large quantities for resistors. Where did you find the $.10 resistors Arthur?

 

I got a box of the new E-matches (.3m) and they seem to work just like the old pyrogen type.

[jl88]

Hey dagabu. These resistors are available in the USA and are relatively cheap. http://www.oda-ent.com/Price%20List.html these were the chepest blank matches I found.

 

The 1/4 watt resistors I use are 3 cents each. Hence why I didn't try to get real e matches.

[dagabu]

Nope, those are ODA match heads, not resistors, I have at least 2000. Again, where did you find 1/4 watt resistors for $.03 each?

[Bobosan]

Here for .02/ea per 100

 

http://www.alltronics.com/cgi-bin/item/CF_8_2/search/8.2-ohms-1-4W-CF-Resistor

 

or here for .03/ea per 200

 

http://www.allelectronics.com/make-a-store/category/530200/resistors/1/4-watt-resistors/1.html

[jl88]

Yeah they seem identical to what I use.

[dagabu]

NICE!

[schroedinger]

One question which ressistor will fire faster, the one with a high ohm or with a low ohm number?

[jl88]

One question which ressistor will fire faster, the one with a high ohm or with a low ohm number?

The simple answer is that a low resistance allows more current through. This will ignite the resistor faster. However be careful, most firing boxes have a limit to how much current they can supply.

 

You can work out how much current will be theoretically used by the calculation current = voltage divided by resistance. We know the resistance and we know the voltage. Therefore to calculate current used simply divide voltage over resistance in ohms.

 

For example my 8.2 ohm resistor and 12v battery you do 12/8.2 = 1.4 amps.

If you lower the resistance to say 4 ohms it would look like 12/4 = 3 amps. It would also ignite faster.

[ivars21]

For me resistors are just too slow, takes ~1sec to start 1ohm resistor with 12V car battery. I prefer 40awg nichrome wire coated with H3 + NC, takes fire under 100ms and quite reliable.

Edited September 3, 2014 by ivars21

[schroedinger]

Ok, i won't worry too much about the amperes, as my system can fire up to 20 amps.

I also gues that a ressistor of 0.1 w would fire faster right?

Are only carbon film resistors useable or can the metall type ones also be used?

[jl88]

Yeah .1 watt will fire faster. It will also 'try' and draw 120 amps. So there are some potential problems as well. I have some metal resistors to test, but haven't bothered as the carbon work so damn well. I think the reason carbon is preferred is that it doesn't "open circuit" as readily as metal type resistors.

 

As for speed of ignition, I have found that more sensitive compositions obviously ignite earlier. My black powder in NC lacquer ignites well under 1 second. And that's just off a 3 cell lipo battery and 8.2 ohm resistor. Seemingly half that with flash style pyrogens. (Possibly h3 as well?)

 

Just a quick question ivars21, why does it need to ignite faster than a second? (This is a genuine question no disrespect meant) The reason I ask is, surely the less than one second delay would be carried across your display, making it fairly consistent? However there is probably something I am missing.

[ivars21]

I just prefer them instantaneous Not now, but once I will be making shows with music in my backyard 100ms over 1s may become useful I agree though, resistors are much less hassle to wire up etc... Also my firing system is designed for short (~100ms) pulses.

Edited September 3, 2014 by ivars21

[Arthur]

A typical igniter will fire at 500mA for 20ms. this is using about 50 gauge wire. This means they demand little from the control box. They have a typical resistance in the order of 1.5 ohms. This is probably the best choice between faster and more fragile or slower and more robust.

 

Fatter wires and 0.125w resistors all take more current which means better batteries and shorter fatter wires.

[jl88]

Jeeze that is fast. I guess the only thing is that they have to be dipped in a fairly sensitive composition for reliable ignition as the heat generated is far less.

 

As for fatter wires. The duration doesn't allow excessive heat to build up. I use the really crappy wire that comes with speakers as its freely available.

[schroedinger]

Well using ressistors is just interesting because it is so much less work, compared to using NiCr wire. NiCr fire at instant and is quite riliable, but much more work. If you are using them, get a winding tool for string from a fly fishing shop, it really helps with handling the small wires.

 

For wire i found that the cheapest wire can be made from network cable, just get the cheapest cat. 5 utp type twisted pair cable you can get, (e.g. http://www.ebay.com/itm/50FT-75FT-100FT-200FT-CAT6-RJ45-Cable-UTP-Ethernet-LAN-Network-Patch-Wire-Black-/300857144082?pt=LH_DefaultDomain_0&var=&hash=item460c7bb312).

These contain 4 double strands of really thin wire, so a 100 m cable makes 400m of e-match cable. They are sufficient for use with NC/graphite type igniters (they don't heat up), so should also be ok for the ressistors.

[cornz]

Hi, complete beginner to all this but has anyone tried tantalum capacitors wired in reverse to ignite pyrotechnics. I was making a wave bubble and had wired one back to front, with a 12v supply it went off with a right bang, big noise and big flash.

[lloyd]

Corns,

Having spent the first 25 years of my life's work earning money in the electronics (and computer electronics) field, I can say 1) they can work, 2) they're not even reasonably-reliable as to timing, and 3) it takes a lot of current to get one to actually explode with a flash.

 

Ordinarily, one wouldn't have enough current-carrying capacity in long, thin (say 24-ga. to 28-ga.) shooting wires to reliably make one actually 'arc over' enough to ignite composition. And, you'd never know (within 2-3 tenths of a second) when it was actually going to 'pop', unless you avalanche several amps at a relatively high voltage through one. So, I wouldn't want to use them for timed cues.

 

Incandescent filaments coated with pyrotechnic composition are much more reliable. (Ummm... they call those "electric matches" <grin>)

 

Lloyd

Edited May 20, 2017 by lloyd

[OldMarine]

Those tiny Christmas tree lights were my go to before I could buy Chinese E-match.

[patsroom]

Look up " Christmas Light Igniters " there is some infor on the subject of cheap and easy e-matches. I have used toilet paper and finger nail polish on the filament and it looked to me like a strike match burning (just burning). the Nail Polish was NC base. I have used black powder in the glass tube after the tip was broken off. Just use care and you can crack open the glass and remove it all or just the tip of the bulb as needed.......Pat

[OldMarine]

I would usually heat the very end with a butane torch and then dip the tip in cold water. I'd get a clean break without damaging the filament.

[Nessalco]

I'm in the midst of sorting through and discarding unnecessary stuff, and I came across a pack of ematches I made at least 10 years ago. Darkflash and H3. They popped instantly on a 1.5 volt battery, and were surprisingly aggressive - more so than I remembered them.

 

KO

[PeteyPyro]

There is a conductive paint-like nickel based compound by MG Chemicals, and available from MCM Electronics. It is used to repair broken printed circuit board foil traces. I used it when making solder-less repairs to circuit boards and remote controls years ago. A 9 gram tube was about $10 from MCM Electronics, and would go a long way to coat many hundreds of ends of 26 gauge two conductor wire. When dried, a 1.5 volt battery would heat this to the point that it would deflagrate almost instantly. A second coat with NC and priming powder ensured an adequate flame that would ignite even visco. I've been able to make over 1000 ematches in a few hours using this method. It saves me hundreds of dollars, and produces a quality product that compares favorably to commercially available ones. I get the 2 conductor copper wire cheaply enough, use a guillotine type paper cutter to chop off a dozen or so meter long leads at a time, and dip, rather than paint, a tiny dot of this nail polish like compound onto the last 1/8th inch of the wire. There is no need to formally strip the insulation off of the wires, if they are stretched a bit while cutting, since the insulation stretches a but more than the wire, and it will retract back after cutting, to reveal the bare copper wire ends.

I've had no failures so far, and these ignighters are reliable, long as the wires aren't stressed by pulling them apart.

There is a silver based conductive pen that makes very low resistance connections, but we want higher resistances here, since we WANT heat production, in this case.

Once set up, I find that dipping, drying, redipping in NC/prime dust takes little time for mass production. of ematches.