Ematch failure?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

billdz

Well-Known Member
Joined
Feb 10, 2017
Messages
1,375
Reaction score
120
Last week I launched a dual deploy rocket. The flight was good but the main chute deployed at apogee, apparently the NC was not on tight enough. So a long walk to get the rocket but otherwise all seemed fine.

Later inspection revealed, however, that the ematch and ejection charge for the main chute never fired, so perhaps I was fortunate that the main chute deployed on its own. On the pad, the altimeter beeped as it should (PerfectFlite MAWD, 3 beeps), so the ematch was properly connected. Apparently something happened in the air, because now the ematch looks unused but it reads open on a meter. The battery tests OK. So apparently either 1) the altimeter worked as it should but the ematch was defective, 2) the altimeter was defective and failed to hit the ematch with sufficient current for ignition, or 3) somehow the premature ejection of the main chute caused the ematch to open.

Any thoughts? I've heard of ejection failures (guess that's why redundant altimeters are a good idea) but this is the first time it has happened to me.
 
When you connect your matches or other wires to the altimeter, do you then tug on them a tad? To see if they truly are connected?
Your apogee event was (i'll use the word violent for lack of a better word) violent enough to deploy the main. It could have done 'something' (add a dozen different possibilities here) to your electronics.
Did you try firing the 'faulty' ematch with just a battery?

Tony
 
When you connect your matches or other wires to the altimeter, do you then tug on them a tad? To see if they truly are connected?

Did you try firing the 'faulty' ematch with just a battery?

I have at agree with this method. Nearly all of my failures to fire were due to a lousy connection or broken wire.
 
The only ematch failure I’ve ever had was a match that passed the altimeter continuity test, flew in a rocket with redundant altimeters, but failed to light. Connecting it to a battery afterwards didn’t fire it either, even though it seemed to have low impedance.
 
Good advice all around here. Try it with a battery (WEAR GLOVES AND EYE PROTECTION). If it pops, it came loose in the air or broke off. If it doesn't pop, bad match.
 
Thanks for the replies. The ematch read open on a meter so I didn't think about trying a battery. But to be certain I just tried a battery and it did not fire. Connections were solid, I did give them a tug. So it seems somehow the match opened during the flight. There was continuity on the pad. Kind of scary, hope bad matches are rare. Guess the only way to guard against a bad match is to fly with redundant altimeters.
 
Was this a name-brand e-match, or a generic Chinese one? I'm on my second box of J-Tek's and I haven't had a failure. Maybe I'm just lucky.
 
I have had (a very small number of) failures with the Chinese matches, but always during prep, detected with an Ohmmeter.

It's really impossible to say with any certainty why you would get continuity on the pad with an open match. Many permutations exist, and you might as well draw straws to pick one.

But yes, a back-up altimeter (if you can fit it in the AV bay) increases the odds of success, as do doubling the matches on a single altimeter.
 
The reason it shows continuity on the pad is likely because it is not open. I have had a few matches over the years not fire. I test every match upon installation and they are not open. They also pass the check on the pad. After the flight, I checked each match that did not fire. In each case, they were open. The match is faulty and it happens. See post 3# of this thread:

https://www.rocketryforum.com/threads/how-do-you-test-ematches-for-ejection-charges.125587/
 
The only ematch failure I’ve ever had was a match that passed the altimeter continuity test, flew in a rocket with redundant altimeters, but failed to light. Connecting it to a battery afterwards didn’t fire it either, even though it seemed to have low impedance.

I wonder if it has an internal short?
 
Does your (OP) altimeter record battery voltage during the flight? Looking at that may be informative.


Tony
 
The ematch was from CJ, I've used many of his with no prior issues. The altimeter does not record battery voltage but my voltmeter says the battery has plenty of juice.

I've looked at some threads on using 2 ematches per channel, seems there is debate on whether to wire them in series or parallel. Redundant altimeters would be an even better solution, but the consensus seems to be that the use of 2 ematches with one altimeter substantially lowers the failure rate.
 
Ok, I will give you the likely scenario about why your ematch failed to fire. I discovered this when I spent 5 years making my own blanks when the supply of matches was going to seemingly dry up if we lost the ATF lawsuit. I made my blanks from scratch as the commercial ones had a high failure rate for me.

I'll tell you why. They solder the wires on double sided PC board and some of the blanks, the solder runs out to the tip and crosses the supposed clear
nichrome wire gap. Well if the solder wicks along the wire guess what? The solder absorbs some of the heat energy and not enough heat flux is generated to pop the pyrogen before a segment of the wire breaks and the current can no longer flow. You see, there is only that .045" gap that the wire crosses is where all the heat has to be generated to start the pyrogen before the nichrome opens. Heating solder is not what you want your bridgewire to be doing.

Now when I made certain I "didn't" run solder all the way out to the end and left some bare nichrome on either side of the blank guess what? 100% success as long as I measured 1 to 2 ohms on a meter after the pyrogen cured.

I gave up making my own as they are a lot of work and the pyrogen has to be treated with respect. Yes I bought the component chemicals and mixed minute amounts myself. I don't trust any of the supposed "ready mix" ematch pyrogens out there. (Motor "starters" the commercial stuff is fine though.)

Some folks use two matches per channel and I believe Jim Hendrickson has commented on that in the past. The question is parallel or serial wiring?
With parallel the resistance is low and some electronics might not register continuity. Serial wiring of two matches one would want to be sure of a good strong connection and the electronics can deliver enough current into 2 to 4 ohms.

Soooooo............. That's how you can have continuity on a "seemingly" good ematch and still have a failure. The key here is the pyrogen doesn't fire and the match is open with no continuity after you recover the remains.

Now of course, if you take an offending ematch and apply a battery and it "pops" somehow current wasn't delivered properly to the nichrome bridge. I trouble-shooted a problem I didn't really have onsite and missed wiring one of the ematch legs properly and had an apogee failure. Remains laid out for a week and were returned to me a year and a half later. If stupidhead had left the rocket alone, it might have flown nominally!!

I buried the end of the charge in the ground a short distance, applied a 9V battery and heard the muffled discharge although I did see that I missed the terminal and that bare copper wire out in the open when I examined the terminal block. I suspect that's what happened after the loss and my deduction was correct. That was before I had cataract surgery.

I have some admonishments posted somewhere around here on TRF not to attempt to make ematches from scratch due to the higher inherent risk
with the components. Several who I consider much smarter than me agreed. Kurt
 
Kurt, great explanation, makes a lot of sense, thanks.
The question is parallel or serial wiring?
With parallel the resistance is low and some electronics might not register continuity. Serial wiring of two matches one would want to be sure of a good strong connection and the electronics can deliver enough current into 2 to 4 ohms.
So what's the verdict, series or parallel? Sounds like parallel is better as long as the altimeter registers continuity. Although somewhere I read an opinion that series is always better. Do most altimeters deliver enough current into 2 to 4 ohms?
 
So for the dummies like me who have a multi meter but don't know how to us it, now do you test for the 1 - 2 ohms?
 
So for the dummies like me who have a multi meter but don't know how to us it, now do you test for the 1 - 2 ohms?
See the meter to ohms (Ω), then touch the two probes together -- meter should read zero. Then touch one probe to one wire on the ematch, and the other probe to the other wire -- meter should read 1 or 2 ohms.
 
I think the situation was a simple match failure. It was open and unburned after the flight.

The only question is if it had about 1 ohm of resistance before the flight? Did you measure the match before? If you did and it was good, and bad after the flight, the most likely and reasonable explanation is the altimeter did what it was supposed to do and the bridge wire on the match melted and opened, but the pyrogen did not burn, in other words, a match failure.

I've had two of these failures. Unfortunately they were ematches from two different manufacturers on the same DD flight. Fortunately the rocket was on the edge of stability and fell flat from apogee and was recovered undamaged. Both matches were tested before the flight and were about 1 ohm. After the flight, both matches were open.
 
new...and researching. Is this what I'd look for for making ematches?
https://www.pyrocreations.com/uncoated-e-matches-3-ft.html

Yes...but...you may not like what I say below.

I've made motor starters for nearly 25 years. I will not make ematches.

If my motor starter doesn't work, I wait til the range is open, run out and put in a new one. If a homemade ematch fails the result could be disastrous. And I've spoken with a guy who had a failure and rocket destroyed with his homemade ematches.

IF you choose to make ematches, I would suggest something resembling the NASA model. Make a large batch, at least 50 and more is better, and test half of them at random. If every single one works, the rest have a fair chance of being okay. If even one fails...use that batch with boost to make motor starters.

Commercial matches can be had for around a buck each. (I test more than half of them by using them to start motors and consumer fireworks.) How much $ did you put in your rocket, motor, and altimeter?

I'm too experienced with destroying my rockets to give them yet another path to destruction. :(

Best -- Terry
 
Yes...but...you may not like what I say below.

I've made motor starters for nearly 25 years. I will not make ematches.

If my motor starter doesn't work, I wait til the range is open, run out and put in a new one. If a homemade ematch fails the result could be disastrous. And I've spoken with a guy who had a failure and rocket destroyed with his homemade ematches.

IF you choose to make ematches, I would suggest something resembling the NASA model. Make a large batch, at least 50 and more is better, and test half of them at random. If every single one works, the rest have a fair chance of being okay. If even one fails...use that batch with boost to make motor starters.

Commercial matches can be had for around a buck each. (I test more than half of them by using them to start motors and consumer fireworks.) How much $ did you put in your rocket, motor, and altimeter?

I'm too experienced with destroying my rockets to give them yet another path to destruction. :(

Best -- Terry
where do you get commercial matches?
 
Don’t make ematches. I have some posts around here outlining the negative. Took me 5 winters to get consistency and if you think some of the commercially available matches have problems, the blanks are even worse. The chems are sensitive and one should only make a teeny-tiny bit. Ask around with locals where they get the ready made matches.
Oh, I had to resort to making my own blank chips and I have a PC board shear on hand to do it. A real PITA as every chip has to be checked under magnification to be sure some of the copper hasn’t been cut cleanly and shorts the other side. A jig has to be built to solder the lead wires to the chips. The bridgewires have to be “perfectly” soldered. If some solder flows out to the end, that can lead to failure.
This is not something one can learn in an afternoon and with the commercial options out there, just isn’t worth the time.
Oh, one other thing. The longer I had my home made ematches sit in a cool dry place, it appeared that the reliability improved. Just a half cocked observation. I gave up on making them years ago and didn’t habvve the “guts” to fly them in a single altimeter configuration. Oh get an ohm meter that can measure low resistances and not just a simple continuity LED. Was weird in some of my matches would read “high” like 8 ohms but still a AA battery set them off. Kurt Savegnago
 
531 dual deployment flights since 1995 using Oxrals, Daveyfires, and J-Teks. One match per charge. Determined cause of some of the failures, 3 definitely bad ematches, 2 definitely altimeter failures. Rest undetermined either not enough left do examine or destroyed by other causes such as a cato. Total failure rate 2-3%
 
where do you get commercial matches?
I've gotten mine from eBay suppliers from China. I don't recall who the actual vendor was, I just picked one that was low priced. Three separate orders of 100, possibly from different vendors, and all have worked flawlessly.

If there's any concern, it's cheap enough to test a bunch of them. Like I said, I've used mine for both consumer fireworks and boosted with a strip of fast propellant as motor starters. I don't recall a single failure.
 
Back
Top