Homemade Low Current Electric Match

Prerequisites:

• Reader understand middle school physics (Ohms Law)
• Know what's a lead wire is and how to use it
• Know what are static charges

Disclaimer: This is not a holding hand instruction, but a document for my own purpose and liking. Do this at your own risk. Keep your fingers attached at all time.

  There are probably a million blogs and tutorials on the net on how to make these - especially in rocketry forums. Many of them require nichrome wire, and the most annoying part - high power voltage to ignite them (like a car battery or at least 9V cell). Does it suck when you want to make something go boom but you don't have enough voltage in your pocket?

18650, Alkaline and Lithium batteries can do the trick, yes. But sometime you are limited by the micro controller current capability (a toy car, an Arduino board...) and you don't have a relay or MOSFET to drive the current. That sucks!

I'd like to share HOW I did it. With minimal resource, and 3 Volts.

The bridge wires are made from fine steel wool. The smaller it is, the less current required to ignite, but also harder to work with, because it would be so fragile. A sneeze and they will snap! I personally would not go any lower than #00000 - that 5 zeroes. Tiny bridge wires are also a hazardous, because the ignition current required is so low, static charge could potentially set it off.  Imagine handling your satchel charge in cold dry weather, you never know if  the block of HE right in front of you could go off at any second! I prefer a thicker bridge for more dangerous, high power works.

For this write up I'll be using #0000 because static won't set it off, but the require current is low enough that a pair of AA will do just fine.

The wool I bough online is the cheapest that I can find - you should know by now I'm living the life of a near hobo :)

And cheapest mean shitty quality control. I picked out 4 different sizes of strands. With the most left being the smallest, the most right is largest. But I'm not complaining, it's like buy 1 get 3 more free, a win for me.

I did some test and the thinnest wire works very well with AA batteries. So let's use it

For a 4mm long bridge, my multimeter reads 1.4 Ohms (the probes themself are 0.4 Ohms)

The heavier and shorter the bridge, the less resistant it has

I use Category 5 Ethernet cable because that's what I have plenty. Use whatever lead wire that you have/like.

CAUTION: CAT5 ethernet cable are easily oxidized and will increase its resistant overtime. Some even breaks in half and become trash. Consider a proper lead wire if you plan to store your e-match for a long period.

This is the thickest bridge wire, almost triple the cross section. Measured at 0.6 Ohm.

The thinnest wire successfully ignited with about 2.8V (1.4V each cell). These are the shittest kind of battery - Zn and manganse dioxide type cells, output about 980 mA and even less. If this works, any expensive alkaline or lithium cell like Eveready or Duracell will work.

The wire should not only get hot, it also need to BURN. The burning process gives off a lot of heat, ensuring good detonation. 

 

AA cells struggle with a thicker wire, as shown below.

As you can see in the 2nd example, the wire barely heated enough. It probably will ignite whatever Primer compound that you have, but will done so unreliably. I won't trust my life with that thing tho.

But 18650 and other hi-power source kicked that up in an instance. So there can be some flexibility depend on what kind of battery you have.

Literally an electric match. Tested with a radio controlled detonator.

Note that this device can output 8V @ 7 Amperes. Way more than what the e-match need. But having a low current match is useful if your batteries are running low.
It's important that you do experiment on your own and see what fits YOUR need. Then develop further from there

 

Another CAUTION: Black Powder are corrosive. Exposing bridge wire and metal contacts will cause them to erode over time. There were multiple times my ignitor wire dissolved into the BP causing a miss fire. When dissecting it, the whole bridge wire and two exposed metal lead wire were disappear!

 

In the early 2000s I learned to use 1.5v light bulbs but it's difficult to get my hands on those as LED has overtaken its place now a days.

External reading:
In this article, under the section "Igniter Calculator" there's an in depth explaination for bridge wire calculation. However the author were using Imperial Unit. That can fuck your brain up :)