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

[lloyd]

Good deal! I'm an EE in a past life, so I'm familiar with that material. I never thought to try it for that purpose, though.

 

What's the resistance of it, once dried on 'separated' Cu wires like that?

 

Lloyd

Edited June 3, 2017 by lloyd

[Arthur]

The whole point of electric igniters is that they take fire instantly from a small current, at a long distance from a firing box. For this purpose they have a resistance in the order of 1 ohm.

[lloyd]

Arthur,

I quite-well understand how they are supposed to work. Gee, I can even recite Ohm's Law!

(Just kiddin' around, so don't get yourself offended! I was an electronics professional by 1966! )

 

I wasn't asking what resistance 'normal' e-matches have, I was asking Petey specifically about his 'nickel bridge' matches.

 

Petey, while you're at it, have you characterized the guaranteed no-fire and guaranteed all-fire currents?

 

LLoyd

[PeteyPyro]

Hey lloyd, I'll get out my old constant voltage/constant current lab variable power supply out and test some for go/no go voltage thresholds. I only use them with my cheap Chinese remote/launch boxes. They must be below the resistive threshold for continuity confirmation, since the LED for the circuits continuity does light dimly, as it should. I'll post results later today, as I'm getting ready for the 4th

[Arthur]

When people in the UK were trying to make ematches there was a rush to formulae including carbon black, this was just conductive enough but the resultant igs were not instant.

[PeteyPyro]

I pulled a handful of 10 igniters and tested them, starting low. They smolder at 0.4 vdc, and all flamed reliably above 1.5 vdc.

They drew between 0.8amps to 1.7 amps at 0.4 vdc, which varied probably due to differences in the thickness of the bridged area. They read between 0.3 and 0.6 ohms, probably also due to differences of the bridged cross-sectional area.

I 'watered down' the conductive compound with acetone to produce the thin bridge between the conductors. It took me a little time to get the consistency just right, and once achieved, I had to add more acetone every periodically to maintain viscosity.

I noted that the ones that I only tested at low smoldering (0.4 vdc) voltages wouldn't fire unless I upped the applied voltage to 6 volts or more. I measured the smoldered one's resistance, and they were much higher than they started with. I guess that when I let out the carefully measured amount of smoke incorporated in their manufacture, resistances changed 😨.

Long story short, once the wires are prepped, and the dips lined up, this has proven to be a cheap way to make a year's worth of igniters in one sitting.

[Richtee]

So..altho I have not experimented with this stuff.. why not just shove some smaller ( 20-ish AWG) into a small ball of 00 steel wool and dip in NC? Seems pretty straight forward.

 

Twist the wire to about .25 inch to the end, strip and into the wool. 12V will fire every time.

 

Hmm.. OK I tried this out. Kinda surprised..less than reliable. Gonna try 24V for grins tho. Hmmm... interesting.

Edited June 5, 2017 by Richtee

[lloyd]

Interesting, Petey! Now that you ran the voltage, consider: matches are characterized by all-fire and no-fire currents... <grin>

 

Lloyd

Edited June 4, 2017 by lloyd

[PeteyPyro]

So true, Lloyd. I didn't read your previous comment closely enough, being new to electrical firing system characteristics (and by forum definition, an amateur pyro at that). I now realize that you're looking for all fire/no fire currents, not merely the applied electromotive force or voltages for all fire/no fire. I wish that I had X-ray vision, so that I could look back through the NC/prime coating over these electroconductive bridges, but I can't. So finding the e-match with the thinnest bridge, and therefore presumably the highest resistance to current, will take my ancient VTVM (vacuum tube volt meter). It has resistance measuring capabilities as well, without igniting them by placing too much voltage on the igniter leads, or too much current through them. Tomorrow I'll revisit my igniter drawer and find a few that have a fairly high resistance to destructively test. I'm not going to unshunt and measure all of them, just look for several with smaller 'heads' to them (and hopefully thinner bridges). I'll test several with the highest resistance, as they will heat up more, amp for amp, than ones with lower resistances. It's as easy as pie (P=IE). I'll post threshold limit results for all fire current and no fire current. I'll also continue with my bp rocket preps for the big day! July 4th can't come soon enough for me.

[OldMarine]

I scanned an article in AFN VII today that mentioned the use of PCB repair paint as a bridging substance. The author mentioned needing to add extra fine Ti to get the resistance and flame where he wanted it to be but also stated there were several different formulae for that product. I'll re-read it tomorrow and pay more attention to details. Very interesting subject!

[MrB]

How does a "real" pyro controller verify continuity? Lov voltage, and what ever current needed for them to read back, and a limit on how much can get feed to the circuit?

[lloyd]

MrB,

The voltage at the supply end is not critical. It's the current through the match that matters. To that end, whatever the firing system's 'rail' voltage, a resistor in series with the match limits the current flow. Generally, that current is set to about 10% of the guaranteed no-fire current for commercial matches.

 

Lloyd

[FBpyro]

Iv'e used carbon film resistors before, 1/8th watt 10 ohm and they do work but take a while to heat up. For two years in a row now I just make my own from scab wire, strip the end and wrap a strand pulled from #3 steel wool around a few times. Dip it in a NC and BP slurry comp and let dry and it works just as good as the commercial ones.

[lloyd]

Remember that power (in Watts) = I^2 * R. So, within reason, smaller value resistors will heat up faster.

 

Say your 10-ohm resistor conducted 1.2A on a 12V system. That's 14 watts, so they ought to heat up in a couple-hundred milliseconds. (just tested one, and they burn up with sparks in about 0.5s)

 

But now consider using a 4.7-ohm, 1/8W. That's 2.55A, or 30.6 watts. Those ought to go quicker. Just testing one, it seems to go about the instant power is applied.

 

2.2-ohm dissipates 65 watts!

 

Of course, at some point, you overwhelm the ability of your firing lines to carry the current needed. When I tried a 1.5-ohm, my cheap 28-gauge clip leads wouldn't carry the current. THEY got hot, instead of the resistor's doing it! <grin>

 

Lloyd

[PeteyPyro]

For what it's worth, I found this electric match comp posted on Cannonfuse's website under article 7 on special compositions. I haven't tried it yet, but it looks interesting. Petey.

 

Electric Match

Source: PML, post by Mike Carter <pyro@primenet.com

Comments: This composition does not require the use of a bridge wire. The composition itself acts as a resistor. Comments from the poster: "The matches fire just fine on 200 feet of #16 guage wire and a standard 12V battery two at a time. Sometimes there's a delay...I haven't tested these on the high power electric firing systems so I don't know how they fare."

Preparation: 1) Bind in water. Make CMC & Water into a mostly soupy mess. Add components into a container and mix well. 2) Dip freshly stripped wire with both conductors about 1mm or slightly less between them, evenly parallel. The longer the exposed metal on the wire, the less Ohmage the match will have. Allow to dry in vertical hanging position. Redip as necessary. I find that two dips is just fine. 3) Once the comp is dry, you will need to coat it with NC (Nitrocellulose) laquer. I find that two dips in the NC laquer is enough to keep the very brittle comp from cracking or splitting while manuevering the wire into your shell or mine or rocket motor. I normally will color the double-dippers with some Iron Oxide stirred into the NC Laquer so I have a visual that they're unsuitable for firing whistle motors. (Double Dipped tend to go BANG, and destroy the motor).

Potassium chlorate, Ball milled into a fine powder.....16

Conductive lampblack..............................3

Magnalium (50/50), 200 mesh.......................3

Atomized aluminum, 120 mesh.......................2

Zirconium, 200 mesh (optional)....................2

CMC Binder (carboxymethylcellulose)...............5