MJG/Electricmatch starters

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When I first started getting interested in clustering, I tried to follow Boris Katan's recommendations on www.bpasa.com. His results through the years are above reproach and he makes a strong case for a mixture of series and parallel (https://bpasa.com/Rocketflite.htm), though he was using Rocketflite igniters instead of the MJG's we are discussing here. I did end up cloning his Cluster Box which has worked very well for me. So no, I wouldn't say that cluster igniters should *always* be wired in parallel, but in this case they definitely should.
 
From reading his page, he's using short series (2-3 max) wired in parallel to reduce the overall peak current required when using large clusters - usually more than 6 motors at once. He's also using heavy duty 12 V power supplies.

If you're not using 6+ motors, stick with parallel....
 
I've been using MJG BP starters for a couple years now, strictly for clusters, mostly 5 and 7 motors. They've been very reliable. The regular size are a tight fit in B6/C6 nozzles, so the mini size are better for those. Regular size fit fine in C11/D12 nozzles. I always wire them in parallel, and use a 12v relay system.
 
I wasn’t actually able to fit the BP igniter *inside* the nozzles of my C motors, I had to tape them against the nozzle. Do you have a photo of how exactly you set yours up?
 
The minis (blue/white wires) I’ve used fit all the way in. The regular sometimes only go part way in, but enough to tamp a small bit of wadding alongside the wire. There were a few that didn’t fit at all, so I just saved those for D12 clusters. No photos, sorry. I’m out of regulars at the moment, just have the minis.
 
Joshua F Thomas said:
Indeed, that's why I asked. The rocket igniters should be wired in parallel; they're not the same as the igniters used for fireworks.
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I’ll be honest. I resent that you would lecture Terry McCreary, a person who has served rocketry in many ways and who knows more than a thing or two. The “igniters used for fireworks” are exactly the same ematches that CTI packaged with their motors for the past nearly 20 years and which many of us use for clusters and staging along with Pyrodex pellets or some other augmentation.

Joshua F Thomas said:
On a more practical note, if your series igniter fails for a firework the firework just doesn't go off; fail is safe. If one of your rocket igniters does not ignite, the rocket can launch with under-powered motors, and that *is* a safety problem! Parallel igniters on a rocket aren't just good wiring practice, they're a safety feature.
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Not really. An electric match In series that fails open may prevent all the motors from igniting. Just like fireworks that’s a safe failure.
In parallel the odds are extremely high that when one igniter fails others will still ignite. That’s the dangerous failure.
 
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Joshua F Thomas said:
I bench tested one of the black-powder igniters today for minimum current. My constant-current power supply is set for 12 V and I increase the current until ignition occurs. 18g wire of about 12" is used between the igniters and power supply.

Resistance testing on my remaining BP igniters gave these resistance values in ohms: 10, 11, 18, 20, 24, 36, 38, 48, 53

This is a pretty wide range of resistance, so people using these for clusters should consider testing their igniters ahead of time and using those that have the nearest set of resistances.

I used the worst case igniter, the 53 ohm one in my remaining group. The igniter did not trigger until 1.250A of attempted current.

I'll do some tests on my composite igniters next.
Click to expand...
This is not truly a test of minimum current. By the time each igniter lights you have already been preheating it, for some possibly random period of time. A better test would be to take 10 or more and from a cold start hit them all with a specific current for a specific period of time. Then increase the current and grab a different 10 cold igniters. Note when one of the ten lights. That’s higher than the “no-fire” current. Repeat with Eventually you’ll get to a current that lights all of them reliably. That’s the “all fire” current.
For resistive/conductive pyrogens all that gets a side order of random.
 
Steve Shannon said:
I’ll be honest. I resent that you would lecture Terry McCreary, a person who has served rocketry in many ways and who knows more than a thing or two. The “igniters used for fireworks” are exactly the same ematches that CTI packaged with their motors for the past nearly 20 years and which many of us use for clusters and staging along with Pyrodex pellets or some other augmentation.
Click to expand...

I'm not intending to lecture and I apologize if it comes off that way. I said the the igniters used for fireworks were different because MJG has different ones for fireworks than for rocket. I am an educator and my "voice" might sound like a lecture, which text communication on the internet seems to amplify. I'm also a life-long student, and if I need to learn something, then I'll be happy to learn from those more experienced.

Steve Shannon said:
Not really. An electric match In series that fails open may prevent all the motors from igniting. Just like fireworks that’s a safe failure.
In parallel the odds are extremely high that when one igniter fails others will still ignite. That’s the dangerous failure.
Click to expand...

I'm not sure I agree here. For example, let's say you have three igniters in series and they all have minor differences between them. Because of these differences, the second of the three igniters fires before the other two. The electrical connection to the others igniters is cut, preventing them from firing. At best you get the first two to fire. Your rocket launches on two of three motors, which isn't great. Or it could fire on just one, which would be even worse. Actually, since the electrical connection is completely cut from all igniters in series at that point, it seems highly likely that *only* the one would fire.

Is there something I'm missing here where less than all the motors igniting is a good thing?
 
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Steve Shannon said:
This is not truly a test of minimum current. By the time each igniter lights you have already been preheating it, for some possibly random period of time. A better test would be to take 10 or more and from a cold start hit them all with a specific current for a specific period of time. Then increase the current and grab a different 10 cold igniters. Note when one of the ten lights. That’s higher than the “no-fire” current. Repeat with Eventually you’ll get to a current that lights all of them reliably. That’s the “all fire” current.
For resistive/conductive pyrogens all that gets a side order of random.
Click to expand...

Indeed! My later tests in this thread showed that the pyrogen seemed to be allowing more current to pass after it had been given a low current for a while. The purely restive checks here were not useful in the end. I had been following the methodology used by J. R. Brohm in his Igniter Continuity Tests paper, and that methodology doesn't seem to apply for these types of igniters.
 
Joshua F Thomas said:
I'm not intending to lecture and I apologize if it comes off that way. I said the the igniters used for fireworks were different because MJG has different ones for fireworks than for rocket. I am an educator and my "voice" might sound like a lecture, which text communication on the internet seems to amplify. I'm also a life-long student, and if I need to learn something, then I'll be happy to learn from those more experienced.



I'm not sure I agree here. For example, let's say you have three igniters in series and they all have minor differences between them. Because of these differences, the second of the three igniters fires before the other two. The electrical connection to the others igniters is cut, preventing them from firing. At best you get the first two to fire. Your rocket launches on two of three motors, which isn't great. Or it could fire on just one, which would be even worse. Actually, since the electrical connection is completely cut from all igniters in series at that point, it seems highly likely that *only* the one would fire.

Is there something I'm missing here where less than all the motors igniting is a good thing?
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I think what you’re wrong about is the belief that as soon as an electric match works it goes to open. These are designed to be used in series and as Terry pointed out all of them will have done their job before one of them opens.
 
Whether an ematch goes open circuit and when depends very much on how much current is applied. Apply just enough and the bridgewire will likely survive for some time. Apply significantly more than that and the wire will fail quickly.

As for testing all-fire and no-fire currents, this is a variety of sensitivity testing which is an area with a lot of research. My tests using a D-optimal method are out of date now but the procedure for testing any other igniter is the same.

All of the Estes bridgewires survived.
 
Steve Shannon said:
I think what you’re wrong about is the belief that as soon as an electric match works it goes to open. These are designed to be used in series and as Terry pointed out all of them will have done their job before one of them opens.
Click to expand...

They are designed to have manufacturing tolerances such that a string in series is all guaranteed to ignite before going to open? Is that correct? How many igniters in series are typically allowed?

There seem to be a bunch of different types of igniters (not even counting the Estes igniters). What counts as an "electric match" versus something else? I was under the believe that electric matches were regulated by the (US) federal gov't, is that not the case? For example, the black powder igniters from MJG that I was testing, I did not think counted as "electric matches".

Thanks in advance.
 
UhClem said:
Whether an ematch goes open circuit and when depends very much on how much current is applied. Apply just enough and the bridgewire will likely survive for some time. Apply significantly more than that and the wire will fail quickly.

As for testing all-fire and no-fire currents, this is a variety of sensitivity testing which is an area with a lot of research. My tests using a D-optimal method are out of date now but the procedure for testing any other igniter is the same.

All of the Estes bridgewires survived.
Click to expand...

Ooh. Thanks. I have to develop good statistical analysis methods for my labs, and this will be good for review.
 
Joshua F Thomas said:
They are designed to have manufacturing tolerances such that a string in series is all guaranteed to ignite before going to open? Is that correct? How many igniters in series are typically allowed?
Click to expand...

A single match generally requires just 1.5 v, so a 12 v car battery will handle eight in series. I don't know if the pyro guys do more than that but I'd guess that some do. Guaranteed to ignite? Well, no starter can be absolutely guaranteed to ignite. But if I were planning to ignite six or seven rocket motors simultaneously, or to airstart more than one motor, I'd have no qualms about boosting ematches with a strip of fast-burning propellant, and connect them in series.

One nice thing about series ignition is that the current requirement is low, so the wire gauge can be small. Pyro operators usually use 22 ga wire, I think.

Best -- Terry
 
electricmatch said:
there is a mini version, at .11" instead of .15", and I'd like your feedback on if they fit, as i can make notes on there for future customers.
Click to expand...

I believe I have the Minis. Other than their not fitting into the Q-Jet nozzle, I don't have any feedback on them as of yet.
 
prfesser said:
A single match generally requires just 1.5 v, so a 12 v car battery will handle eight in series. I don't know if the pyro guys do more than that but I'd guess that some do.
Click to expand...
It has been a while since I helped at a fireworks show but I know that some older systems were capacitive discharge. They used a DC to DC converter to boost a 9V battery up to some higher voltage. (It can be too high!) Mostly so that they could push decent current through hundreds of feet of wire. That sort of system would work best with a series connection.

Tastes vary between pyrotechnicians and depending on the firing system so it was always best to ask their preference before connecting ematches in series or parallel.

That doesn't happen as much as it used to. With modern computer controlled systems it is usually one shell per cue and let the programmer sort them out.
 
electricmatch said:
Also, do not try to use any in series except for the firewire initiator.
Click to expand...
Never ever ever, did I say ever...wire igniters in series. As soon as the first one goes the circuit is cut, and the others will not go. You night get lucky but not reliable. I AM the cluster king...

Rockets and fireworks are different, if a fireworks shell does not go off, no big deal, but if a motor in your rocket fails to light then it is a potential problem, EXAMPLE: your central motor in your cluster duck fails to light but the other six do...guaranteed high speed ground (Or someone's head) impact...
 
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.
 
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Fred,

Would series be reasonable for a standard nichrome starter, augmented with pyrogen with BP motor clusters?
I’ve never done more than three motors and with the lighter rockets, if two just lit, the rocket would “get by”.
I used parallel wiring with good 12 volt battery. Most of the time, it worked. If series would be a better option with plain nichrome I’d give it a shot. Heck, the ones I got are small clustered modrocs. Kurt
 
Series works if you have two things:
1 - sufficient voltage to push the all-fire current.
2 - A dip that forms a conductive plasma ball.

But - Nichrome is pretty high resistance. Use Ohm's law [V=IR] to figure out if you have enough voltage.
For instance - if your matches are 2-Ohm and you need 1-AMP all-fire, you can fire a max of six from a 12V battery. If your igniters are 6-Ohms, you only can use two assuming the same 1A all-fire current. In that case, moving to a 24V ignition system would allow you to light four at once.

Know you igniters.
 
Joshua F Thomas said:
I believe I have the Minis. Other than their not fitting into the Q-Jet nozzle, I don't have any feedback on them as of yet.
Click to expand...
you did order minis. that's got to be a small throat then. From what i saw online, the Q-jets are composites, so if the minis don't fit, we currently do not have any options that would work.
 
all multiple fireworks are wired series and they all go using ematches
 
FredA said:
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.
Click to expand...

I feel like the caveats on the series setups are:

1) High current source
2) Low variation between activation time among any set of igniters

#2 is the more critical one here. If the igniters you are working with are manufactured to tolerances that allow them all to fire with-in 0.01s of each other, then I suspect you’re going to be ok - everything will ignite before physical and electrical forces have a chance to break the igniter chain or otherwise prevent them from successfully firing.

If you cannot guarantee that consistency, then parallel setup should allow current to continue to flow and fire all the igniters. Effects of the engines blast and lift-off come into effect if the delay is too long, but I suspect they’re not anywhere nearly that variable.

I will continue to wire my igniters in parallel because a) I don’t know the tolerances of the igniters and b) the manufacturer recommends it.

It would be very interesting to either get manufacturers data on this; or for someone with a high-speed camera to run data collection with both series and parallel firings.
 
So ignition is more random. Plus, the first match that fires SHORTS the array and draws all the current, slowing the other matches.
Click to expand...

I have a small critique here. While the match firing and going to zero resistance will increase the current draw, the resistance of the wiring is non-negligible and puts a cap on total current draw. The second is that the current-time curve matters; if you deliver enough current to cause thermal heating sufficient to start ignition, you should be able to reduce subsequent current without changing ignition.

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].
 
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
 

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