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NateB

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The take-away would be to design a system that delivers a large amount of “instant” current, on the order of 10 x [# igniters] x [all-fire current spec].
This is what capacitive discharge systems do. I used one when we had 24 ematches in series on one cue for a 300' line of salutes we wanted to lift at the same time.
 

Joshua F Thomas

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I have a BA in physics, minor in chemistry and math, Masters in computer science

your point?

I was just pointing out that the majority of ematches are consumed by the fireworks industry, and this is what they use for guidance

they can use hundreds or thousands at each show, we can use a handful at each launch
No offense was taken or given; but a single link to "electricity 101" came across as "you don't know how electricity works". A comment along the lines of "common fireworks practice can be found here: " might have better communicated your intent.

re: fireworks, I think it's still relevant (and was mentioned before) that the use-case and failure modes are not the same between fireworks and rockets. Failure to ignite all motors can be safety hazard; failure to ignite a firework just prevents the firework from launching. While we can take their experience and try to apply it to our case, what is best for them may not be best for us.
 

FredA

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Yes, Kinda, sorta.

It's all about area under the current waveform's pulse warming the pyrogen to it's ignition temp using some resistive element.
Hit the element too hard and it will die, sometimes explosively, before transferring sufficient energy - so you really don't want TONS of current.

Variations in resistance, the pyrogen's activation temp and it's physical intimacy with the heating element all add to unit-to-unit variability.
This is why I would use commercial units compared to hand-made unless your quality control is very tight.
My beloved stash of Daveyfire BR's is my choice for these applications....unfortunate they are no longer in production.

In parallel systems the plasma lowers the resistance in the legs going to plasma-balls which has the net effect of taking more current - Ohms law -- how much and the when is arguable and depends highly on the whip-clips - but it's not positive, that's for certain.
 

Joshua F Thomas

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Interestingly (from a physics POV), plasma actually isn't Ohmic, and doesn't follow the V= IR rules; the amount of current it passes is a complex function of mean-free-path of elections and the temperature of the plasma. Doesn't really affect our rocket launches.
 

jbr

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my stash is down to 50%
I bought 400 oxral several years ago 20 cents each but they are not made anymore
I just got 200 of the chinese ones and need to try them out
 

Banzai88

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my stash is down to 50%
I bought 400 oxral several years ago 20 cents each but they are not made anymore
I just got 200 of the chinese ones and need to try them out
I've had TERRIBLE luck with the Chinese orange wire ematches when used as deployment charges. 4 batches, used almost 200 myself. 2% failure rate upon initial continuity screening, and a 5% failure rate in flight. 8% failure overall. Falls right in line with what other folks have told me about their experiences with them, so I ONLY use them for ground testing where a failure isn't such a big deal.

YES, the orange ones that failed in flight were good on the bench and good on flight electronics power up......never fired. All but one never fired even upon post crash testing..... Flight electronics have been RRC2+, RRC3, EggTimer products, and a StratoLogger CF, all with properly sized lipo batteries.

Since the recovery phase is the most critical, I switched back to MJG and haven't had a recovery mishap since.

YMMV
 

jderimig

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Ematches are not light bulbs, as FredA mentioned they are heating devices with a time element.

Nichrome wire opens when the wire melts. This occurs at ~2500F
The ematch fires when the pyrogen ignition temperature is exceeded. This is around ~400F or lower.

The temperature of the bridge wire rises linearly with time which is proportional to I2R. With reasonable current (not too high) all the bridge wires will reach and exceed the ignition temperature of the pyrogen WELL before the time when the bridge wire melts. If a particular ematch doesn't light in a series string it wouldn't light in a parallel string either.

That is how ematches are DESIGNED to be operated in series (ignition temp<<open temp). A series string of ematches is the best connection method to assure an all or nothing ignition string.

Demolition igniters are wired in series for this reason. It is very bad if you leave unexploded charges in the rubble.

Series wiring for ignition is the best practice if you:
1. Choose high quality ematches with consistent pyrogen coatings.
2. Have low difference is resistance (sort if necessary) match to match to insure the heating rates are the same for each device in the string.

A parallel igniter wiring setup cannot easily continuity check each branch in the circuit. Only one leg needs to have continuity to pass a traditional continuity test.

A series string needs all of the matches to have continuity to pass a continuity check.

You are more likely to leave an unexploded charge in the rubble or fail to light a motor in a cluster with parallel wiring of your ematches.
 
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dpower

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Igniters work on current. IR Heating.
Once lit, the resulting plasma ball conducts.
This is a feature for series and a detriment to parallel wiring.

Series delivers the same current to every igniter in the set. They all fire at the same time varied only by the slight difference in resistance of the heads themselves and any differences in the firing point of the dip.

Parallel delivers unique current to each igniter based on it's resistance and the resistance of it's clip leads.
While they all see the same voltage at the same instant, ignition timing is is randomized by the different resistance in each leg.
So ignition is more random. Plus, the first match that fires SHORTS the array and draws all the current, slowing the other matches.

If you want them to all light at the same time, series is your BEST option.
Just make sure you have enough VOLTAGE to push the ALL-FIRE CURRENT through all the series matches.

Super paranoid???? Do what i do for airstarts - have a separate firing channel for each motor -- no wiring dependencies.
If the igniters have different, but constant resistance, they'll dissipate a different amount of power in both series and parallel wiring. In series, higher resistance igniters will dissipate more power at a given current, (I^2*R), so will heat up faster. In parallel, lower resistance igniters will dissipate more power at a given voltage (V^2/R), so will heat up faster. Clip lead resistance is not a differentiating factor when wires are twisted and/or soldered together. With a given supply voltage, in parallel, individual igniters will have more current flowing than when in series.
 

FredA

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More current is NOT the goal.
Equal current is. Actually equal heating is the goal and you need to assume activation temps track too.

Agree that individual resistors have individual heating properties - more reason to buy commercial to get consistency.

Soldered whips are going to help - almost NEVER see that, people don't know how to solder.

Yes, if you work hard enough, you can find away around the generalizations.
 

Kelly

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I've had TERRIBLE luck with the Chinese orange wire ematches when used as deployment charges.
[...] All but one never fired even upon post crash testing
But, post-crash, you had continuity?

I've had good luck with these actually. Though, when I'm being especially paranoid, I'll wire two in series for each deployment charge. If your testing is showing continuity before and after failure, maybe that strategy has been a good one.
 

rharshberger

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But, post-crash, you had continuity?

I've had good luck with these actually. Though, when I'm being especially paranoid, I'll wire two in series for each deployment charge. If your testing is showing continuity before and after failure, maybe that strategy has been a good one.
Good luck for me as well, couple of hundred used no failures.
 

prfesser

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Good luck for me as well, couple of hundred used no failures.
Same here too. It's clear then, that some of the China-made matches are quite reliable, while others are hit-or-miss.

For those who have gotten reliable ematches (and for those who haven't), perhaps you'd provide the vendor's name/eBay store. I haven't ordered in a long time; will try to find where I got mine.

Best -- Terry
 

timbucktoo

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I have used hundreds of Chinese matches from ebay with zero failure. I usually bought from BILUSOCN but if they were unavailable, I'd get from whoever else had the quantity I needed.
 

Banzai88

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But, post-crash, you had continuity?
All had post-crash continuity. Of the crashed ematches, only 1 fired upon post-crash hook up to a 9v battery. Never got any of the others to fire no matter what I did, even with continuity. Pre- and Post- checks performed with a calibrated Keithly DMM2001.

All the electronics have since flown at least twice more (except one RRC3 that died completely upon impact) and have triggered MJG Firewires without issue.

Of my batches of orange wires, all but one were Biluscon. Of note, every batch of matches that I have, regardless of when, where, or how I bought it has different color heads. Some are dark almost to black, ranging to red and nearly pink. My test failures occur across the lot, not centered in any one 'type' that I can tell.

ETA: I'm glad, and more than a little jealous, that others have had better luck than I have with these things! I've consigned my orange wires to ground testing only.
 
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Kelly

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I get mine from Bilusocn, too, but I don't know what that means. Are they a manufacturer? Some guy with a big garage who orders them from whatever manufacturer has the lowest bid today? :dontknow:
 

Ez2cDave

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Thanks, I didn't see that on their website . . . A little "clunky" to navigate, having to find them by "shipping from USA", rather than by what the product is.

Dave F.
 

Joshua F Thomas

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Are these things regulated? I get confused over what counts as ATF regulated or not
 

Rocketjunkie

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Are these things regulated? I get confused over what counts as ATF regulated or not
Yes they are. The only unregulated ematches are the MJG Firewires. They worked with ATFE to reformulate just so they could be unregulated.
BTW, the link showing 1000 pieces for $18.30 on Ebay is actually for 25 pieces.
 

Bamraam

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I've had TERRIBLE luck with the Chinese orange wire ematches when used as deployment charges. 4 batches, used almost 200 myself. 2% failure rate upon initial continuity screening, and a 5% failure rate in flight. 8% failure overall. Falls right in line with what other folks have told me about their experiences with them, so I ONLY use them for ground testing where a failure isn't such a big deal.

YES, the orange ones that failed in flight were good on the bench and good on flight electronics power up......never fired. All but one never fired even upon post crash testing..... Flight electronics have been RRC2+, RRC3, EggTimer products, and a StratoLogger CF, all with properly sized lipo batteries.

Since the recovery phase is the most critical, I switched back to MJG and haven't had a recovery mishap since.

YMMV
I believe ematches are susceptible to environmental conditions, I know someone who had issues with their ematches not working, though in the past they worked flawlessly. Turned out he had stored them in his somewhat humid basement, and we figured that caused the issues.
 

Banzai88

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I believe ematches are susceptible to environmental conditions, I know someone who had issues with their ematches not working, though in the past they worked flawlessly. Turned out he had stored them in his somewhat humid basement, and we figured that caused the issues.
You're probably correct. That why mine have always been stored indoors in sealed plastic bags with desiccant packs.
 
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Kelly

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I keep all my flammable stuff - igniters, propellant, etc. - in a sealed box with desiccant.
 
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