48 replies to this topic

[Andrew]

When you want to buy ematches, the general rule is: "The more you buy, the cheaper the price.

Ofcourse you can spend al you money on the expensive Bickford ones, but try the ones from Cosmos for example.

And for the legal part, over here in Europe ematches are classified under UN 1.4S. This is the lowest cathegory in pyrotechnic products, free in transport or stock, and not to hard to purchase. Never the less Europe has some countries which do not allow citizens to purchase them without the required certifications. 1.4S post oders or prarcels is a complete different story...

Not all of them are 1.4S.

Anyway the S category has been almost abandoned! I think it was in 2005 when all 1.4S devices were stripped of their classification and reinserted into the classification system as 1.4G with the reasoning that hardly any had actually been tested. Now to regain or gain S status the devices need to be independently tested at the cost of several £k. As you can imagine not many have taken the opportunity to do it.

The only e-matches that you can now guarantee as being 1.4S are those without any explosives in, which means they do not even need to be classed as 1.4S anyway.

[Mumbles]

You know, I'm not sure about what kind of resistance they have. I never really tested it. A 9V battery is generally what I use to set them off. Works right away. For longer distances on the leads, I may go with something like a 12V car battery just to be sure though.

[digger]

You know, I'm not sure about what kind of resistance they have. I never really tested it. A 9V battery is generally what I use to set them off. Works right away. For longer distances on the leads, I may go with something like a 12V car battery just to be sure though.

I will give the bridgeless ones a go in the next day or two. I will let you know how they go.

G

[Arthur Brown]

As he doesn't visit often, I will offer you notes from someone's lectures on pyro safety.

Firing current Igniters are current devices, they fire when the current through exceeds the firing current. They do NOT fire when the current is below the no-fire current limit. There is a gap where the performance is unspecified - they might or might not fire. don't go there a failed ignition is dangerous.

I = V/R that is, Current = Voltage divided by Resistance

Where I is our electrical current flow, V is our voltage and R is the resistance of our wire.

This equation is called Ohm’s Law

So let’s look at a simple example. We already know that a commercial pyrotechnic igniter has a resistance of 1.6 Ω. What happens when we connect this across a 9 V battery?

Well, using ohm’s law we can put the numbers into the equation and see what we get…

I = V/R = 9/1.6 = 5.625 A

So a current of 5.625 Amps will flow through the igniter. With our knowledge that 0.5A is enough to fire an igniter we can see that we have more than enough current to fire the device.

As mentioned above, wire has resistance. The twin cable we use to wire up pyrotechnic devices (bell wire) has a resistance of about 10Ω per 100m for each wire.

What happens when we put an igniter on the end of a 100m length of cable?

Well, the resistance is now 10 + 1.6 + 10 = 21.6Ω.

Using ohm’s law we can put the numbers into the equation and see what we get…

I = V/R = 9/21.6 = 0.417 A

So a current of 0.417 Amps will flow through the igniter. Which is just below the 0.5A guaranteed fire figure. So it may or may not fire.

If you determine the properties of the igniter you can use these equations to determine whether a particular combination will fire safely.

[digger]

If you want to be completely accurate then you need to include the internal resistance of the 9v battery. If you are talking about a pp3 or similar then these can only deliver an amp or so at short circuit. So the internal resistance is high (or about 9 ohms from ohms law).

This is where lead acid batteries win as they have very low internal resistances and therefore can drive high currents.

Does bell wire really have a resistance of 0.1Ω per meter? That seems rather high. I have a few boxes of cat5e in the garage, I will measure the resistance of one of those to get an idea of resistance, as bell wire should be a lower resistance (larger cross sectional area).

G

[Arthur Brown]

Bell wire does have a significant resistance, those figures came from a professional theatre consultant who is usually right! But check for yourself.

This is why the NATO command wire on a 1000m reel is a mighty affair. Their firing pulse is about 30joules from a capacitor charged to 500 ish volts. MOST of that is lost in the cable.

Failure to allow for cable losses is why the unthinking have misfires. The igniter may well pop off a PP3 at home, but with a device 50 metres away the circuit may not be strong enough.

[digger]

Bell wire does have a significant resistance, those figures came from a professional theatre consultant who is usually right! But check for yourself.

This is why the NATO command wire on a 1000m reel is a mighty affair. Their firing pulse is about 30joules from a capacitor charged to 500 ish volts. MOST of that is lost in the cable.

Failure to allow for cable losses is why the unthinking have misfires. The igniter may well pop off a PP3 at home, but with a device 50 metres away the circuit may not be strong enough.

I agree that all factors need to be taken into consideration. I have just measured the resistance of 400m of cat 5e which has a diameter of 0.5mm and it measured 20Ω on the nose (Fluke traceable calibrated multimeter) so about 0.05Ω per meter.

What diameter is the core of the bell wire normally used? This will allow me to calculate its resistances (ratio of cross sectional areas, resisters in parallel etc).

G

[cooperman435]

Ok. Time to ask for your favourite (tested!) ematch pyrogens....

I've got my ematch almost perfect now, but for inconsistencies with the pyrogens. I'm sure when I put up the demonstration on my page, loads of you will laugh at just how easy I've made my system, getting round the problem of broken bridge wires etc. Very fast, cheap and very easy.

I've tested quite a few compositions. Bp seems to be the best, but I think this is because all the others have used NC laquer as a binder, which is brilliant as it's fast to dry and waterproof, but tends to pop on ignition as it's so hard and can extinguish the head because of the force.

Give me a hand and I'll tell you all!!!

[StephF]

Give me a hand and I'll tell you all!!!

Gives a big hand to Coops

*and the crowd roars !*

[cooperman435]

Lol I see someone has recovered from their hangover then Steph hehe

I do think though that a lot of you will be quite impressed though with the system Ive worked out. I estimate the cost of 200 ematches to be about £4 so really cheap and theres no soldering or copper clad board in sight.

If anyone has any sub 40swg nichrome wire I would love a bit to test....... Im hoping to get some 44swg or finer soon but want to experiment with some first as its not cheap.

[portfire]

Lol I see someone has recovered from their hangover then Steph hehe

I do think though that a lot of you will be quite impressed though with the system Ive worked out. I estimate the cost of 200 ematches to be about £4 so really cheap and theres no soldering or copper clad board in sight.

If anyone has any sub 40swg nichrome wire I would love a bit to test....... Im hoping to get some 44swg or finer soon but want to experiment with some first as its not cheap.

Phill>If your still using the same system to make them as when we met,please post details.I'm sure MANY would like to know.

I'll back phill in saying,that i was quite impressed as to the way he made them,(i probably didn't show that,as you were the first other pyro id met,and was abit nervous lol.. ) sooo simple.

Although i haven't started making e-matches yet,i will be using phills process.....So post the details

dean

[dr thrust]

please tell us phill ! the suspense is killing me! my ematches are sh*te! sometimes they work, sometimes not

[cooperman435]

OOOOO


the power I feel at my finger tips.........



Il do some photos this weekend and put a tutorial up on the page for you all then......

[Draco_Americanus]

I my self have a whole spool of nichrome wire waiting for a use, I had thought about useing low resistance SMD resistors and just solder wires to them and dip into a pyrogen. What other types of pyrogen can be used? I had noticed that Skylighter sells kits with thier own mix for the pyrogen.

[cooperman435]

I also tried the reistor method but found that they were really un reliable and needed still quite high power to be pushed into them before they did much. Due to the way they are made the actual nichrome film is encased in ceramic material so they rarely get hot before popping and killing themselves. Maybe 1 in 50 ignited whereas Id guess at more like 1 in 200 fails with the new method.