Boys and girls, todays class will teach a very handy thing:
The bridgeless electric igniter.
For this we need:
Cable.
I used the typical pc data cable, but other multi-conductor cable will work too I guess.
Graphite.
But not just any graphite, you need the finely powdered stuff used in art shops and in lubrication.
If you can feel the grains, then it's not fine enough.
Keep looking, it's not that hard to find.
Dissolve a ping-pong ball (NC) in 100 ml acetone. Mix this with the graphite powder untill you get a slurry.
Black powder or any other good burning pyrotechnic mix.
Black powder may not be the best option, because it contains sulfur and is therefore
incompatible with a lot of other pyrotechnic mixtures.
This choice really depends on what the igniter is going to be used for.
If you want to be on the safe side, use astochiometric KNO3 + charchoal mix.
To your pyrotechnic mixture of choice, add 5% binder (I used dextrin) and enough water to make a slurry.
Once you've gathered all these materials and prepared the slurries:
Remove the cable's insulation for a 1-2 mm length.
Dip it in the graphite slurry, making sure all the naked conductor is covered.
Let it dry, the acetone will evaporate fairly fast.
The resistance will decrease while drying, because increasingly more graphite particles will connect.
Once the resistance has stabilised (should be somewhere between 5 and 25 Ohms) it is dry.
Once dried, dip the graphite coated igniter in your pyrotechnic slurry.
When this last coating is applied, you can let it dry, or dip it again in a dry pyrotechnic mixture.
For example some flash composition to make a hotter flame to ignite less sensitive mixtures.
Whatever you choose, don't forget to keep an eye on the compatibility of the compositions used.
As a final touch you can dip the entire igniter in a concentrated ping-pong ball-acetone solution to make it water-proof
Lastly all the ingredients and stages in order:
These igniter can ignite from a 6 volt powersource in less then a second, depending on the resistance value.
The higher the resistance, the lower the current will be and the longer it will take for it to glow.
Resistance (Ohm) = Tension (Volt) / Current (Ampere)
So if you can't get them fast enough, get a power source with a higher voltage.
Below is a picture of a detonator using a bridgeless igniter:
It is composed of a 2cm long and 2mm diameter plastic drinking straw, an igniter
without pyrotechnic coating and 0,08 grams double salts [+/- 0.01 grams], marked in red.
As end plugs little balls of tissue are pressed alongside wires and at the end of the charge.
Credit for this idea is given to frogfot, from whose site I got the idea:
Frogfot improvised fuses
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