Better Ematches

[frosty90]

Hi

 

I have tried many configurations of home made bridged ematch. I have tried small value resistors and just black powder for the pyrogen. These worked really well, and would fire instantly. But, something changed about the resistors I was buying, the original ones would fail with a low resistance: i.e. when it started to burn, current would keep flowing and get it hot enough to ignite the pyrogen. But now, they fail open circuit almost instantly, in open air they emmit a puff of smoke and go to like 5 megohm, where as before theyd last long enough to burst into flame. (andwould easily ignite black powder instantly) So that no longer works......

 

So I have been experimenting with just thin wire for the bridge (about 35awg i suppose, I havnt mesured it), but even with a very sensitive pyrogen (chlorate + antimony sulfide), they take about 1 to 2 seconds to pop. I have either 12v or 24 volts, but they are at the end of a long piece of cable, which is about 5 ohm. it seems the resistance of the bridge just isnt high enough to get it hot enough. (I have tried nichrome) That was my reason for using 1/4 watt resistors for the bridge in the first place. But even so, with 24v, the current though them is around 4 amps, yet even with ClO3 and antimony sulfide, they take a second or so to go off. now heres what has me frustrated: I have read that commercial Ematches will go off from as little as 50ma, and they have a fairly low resistance (right?). So why are mine so slow...?

 

Jesse

[Ralph]

I have some nice fine nichrome (few members from another forum your a member of and a couple other local pyros are using it to) contact me.

 

this was a gun shot squib I made using it to simulate a bullet hitting a hard surface this particular design is safe to use indoors. this used the nichrome I have (you can hear the click of me turning the power on on a standard PC power supply the delay is the power supply starting up and not the wire heating)

 

 

 

 

 

EDIT : light in the left corner is from another room as this was tested during the day

Edited April 25, 2010 by Ralph

[Arthur]

Probably the best available alternative to a commercial bridgewire, is a commercial bridgewire! Many other things are a poor substitute. ODA ( http://www.oda-ent.com/Price%20List.html ) lists bridgewire chips by the thousand available from the States, chose the 50g chips. Thes things fire wherever a commercial ematch would, and as "resistor chips" they sail through post and customs easily, buy the ones with NO pyrogen! The easiest pyrogen is chlorate and antimony tri sulphide, mill the ingredients separately to pass 200 mesh then bind with NC.

 

For reliability you must have a supply capable of driving one AMP down whatever shooting wire that use.

 

Edited in response to post4 below

 

Mill the ingredients separately, in different jars with different media

Edited April 25, 2010 by Arthur

[baran420]

Yikes you mill that mixture!

 

I bought a string of bud lights (100 I think) that were about 80% discounted after last Christmas. These are a thin glass tube with a very fine tungsten fillment. Using 2 small 9V batteries and 30 metres of thin wire I could light one of these lights. Then simply break end off tube or cut with abrasive disc on a Dremal and carefully pour in BP. A small ball of tissue stuffed in the end completes the super cheap e-match. I quick OUT OF DEVICE check with the DMM will confirm that you haven't harmed the filament. I again stress don’t this measurement out of the device as your meter may put enough currant through to ignite it.

 

On a fun note if the completed bud-match is dipped in Nitrocelleose lacquer a few times between drying, it actually gives a sharp report upon igniting.

 

 

[Arthur]

No I have two jars (the chlorate jar is tiny!) I mill the ingredients separately.

 

Take 475milligrammes of pot chlorate passing 200mesh, add 25 milligrammes of NC (shooters will do) POWDER mix with acetone til viscous and homogenous. This is part A

 

Take 475 mg antimony trisulphide passing 200 mesh, add 25mg NC powder, Mix with acetone til viscous and homogenous. This is part B

 

Mix parts A and B, with extra acetone as needed. Get the viscosity right with practise and the ematch dips are perfect first time and when dry, fire immediately.

 

If you can't measure milligrammes well then don't start this procedure.

 

The energy of a 50g wire melting is tiny, you really NEED a sensitive mix to take fire from a single spark. Hence this mix WILL take fire from a single spark when dry so be very careful! Usually an ematch would be covered with a lacquer to protect it from sulphur in comps, also you add ematches to a firework ON SITE, as part of preparing to fire, NOT in advance.

[frosty90]

Hmm dont take offence guys but if you read my post properly you;d have seen that 1) I do use nichrome and 2) I do use the antimony sulfide composition. It seems everytime I ask a question here I just get a generic answer, simply restating to do what Ive already explained that I have done! eg in another thread I asked where does parlon actually come from, because I would like a source other than a 'pyro supplier'. Every one said "you can just buy it from a pyro supplier". Do you even read my question?

 

 

Anyway back on topic:

 

I'll explain agian more carfully: I use either around 40 gauge copper or around 35 nichrome. the match heads end up with a resistance of around 1 ohm. I have tried black powder, H3 and Sb2S3/chlorate as the pyrogen, and all three take about 1 second to fire, with 4 amps. that works out to about 16 watts dissipated in the match head. So what is the resistance of a commercially made match head, that will fire immediately from 1 amp as arthur says? That way, I can know the sort of heating power that these commercial ematches produce to get them to fire instantly, and tune my own to similar specs using what I have on hand. Has anyone got some that they could measure for me?

If these real ematches have less than 16 watts of heating power, then I know that is not my problem, and it is something else I have to look to. If they are more, then I know that is my problem and I need to fix that.

Edited April 26, 2010 by frosty90

[Arthur]

ODA sell two kinds of chip, 35g and 50g (that's the wire -American gauge) the 50g chips are closest to commercial bridgewires. and have the right resistance as chips. We have 40g nichrome available in the UK and it is too thick and takes several amps to fire -I've tried it. A 50g bridgewire needs one amp to blow quickly, a 40g wire needs 2+ amps and a 35g wire needs five or so amps to fire quickly. Can you source 50 gauge nichrome?

 

With the fatter wires (40g and fatter!!!) the mesh size of the ingredients of the pyrogen is not critical. With the small amount of energy in a 50g wire melting the pyrogen particle size is important and the smaller the ingredients the better the performance 200# is the edge of OK performance so mill and screen the separate ingredients properly through small sieves (5 grammes of comp will dip a LOT of igs!)

 

You should check that the electrical system that you have is adequate to comfortably put one amp into the igniter down the cable that you use. 100m of bell wire will have a resistance in the order of 10 - 20 ohms. This is why some people use 24v lead acid batteries, volts go up, and the current availability goes up.

[frosty90]

Ahh ok I see, 50 gauge huh? thats pretty tiny.Yes I think my wire is around 35 awg, i cant measure it because i broke my calipers..... My chems are very fine,probably finer than 200 mesh. I'll have to try and find some finer wire then. I am definitely pumping lots of juice, like I said about 4 amps. I'd have though this would blow just about anything instantly. Oh well, I'll try to find some finer wire.

 

As an aside what would be the aproximate ignition temp. of 50/50 KClO3/Sb2S3? 300 degrees C? more?

 

Thanks

[Ralph]

Ahh ok I see, 50 gauge huh? thats pretty tiny.Yes I think my wire is around 35 awg, i cant measure it because i broke my calipers..... My chems are very fine,probably finer than 200 mesh. I'll have to try and find some finer wire then. I am definitely pumping lots of juice, like I said about 4 amps. I'd have though this would blow just about anything instantly. Oh well, I'll try to find some finer wire.

 

As an aside what would be the aproximate ignition temp. of 50/50 KClO3/Sb2S3? 300 degrees C? more?

 

Thanks

 

hello no need to find already found

[Arthur]

The bridgewire chips from ODA Ents in USA cost little each and can be soldered onto copper wire easily. I found it easier to buy these ready made than solder 50g nichrome wire. These come customs declared as resistor chips.

 

Then I found a supply in the UK of 1 foot igniters with no pyrogen and these are a fair price too -they come from China by the million to the UK without pyrogen as they can then be posted for dipping by the end user.

 

Don't guess at the ingredient mesh! 100 - 200# and they are unreliable finer than 200# and they are 100% good

[Ralph]

whats these ODA peoples website couple cents would probably be easier than cutting and warping nichrome and than attempting to solder (its a real pain to solder)

[Mumbles]

http://www.oda-ent.com/Products.htm

[Swede]

I gave up messing with bridgeless or trying to make my own, and went with the 50 gauge chips.

 

Arthur, good description of the Pyrogen. Obviously care must be taken, as it is a very sensitive mixtre. Would you recommend a dip in clear NC afterwards to seal and protect? Also, is there any reason not to scale your proportions up to 2 to 3 grams total, and store the pyrogen wetted with the NC and acetone?

[Arthur]

I use about a gramme and discard any surplus (burn in a safe place!). I dip the pyrogen covered igs in a coloured NC lacquer (you should have seen the face on the girl who sold me some yellow nail varnish! But I wasn't going to tell her what it was for)

 

The problem with storing it is that if any gets into the threads on the jar then you twist to open the jar it can go up. Work very cleanly!

 

Having become compliant now I can simply buy cases of igs so the diy ones will have to go somehow, but probably not on paid work!

Edited April 26, 2010 by Arthur

[dagabu]

Hi

 

But, something changed about the resistors I was buying, the original ones would fail with a low resistance: i.e. when it started to burn, current would keep flowing and get it hot enough to ignite the pyrogen. But now, they fail open circuit almost instantly, in open air they emmit a puff of smoke and go to like 5 megohm, where as before theyd last long enough to burst into flame. (andwould easily ignite black powder instantly) So that no longer works......

 

 

Jesse

 

Jesse,

 

I think you are having the issue with the type of resister you are using. Mouser has these for 2000pcs $20.00 delivered. The thin film snap instantly and don't light while the thick film type take too much power to initiate.

 

I now have two CD systems (Thanks Nichropulse for the initiator!) that will light one of these baby's at 500' of 22ga scab wire. I will be upping from 3Ohms to 10 with the old box so it will heat slower but there is no possible way to get cheaper igniters.