8 replies to this topic

[Frozentech]

I finally decided to give the world of electrics a small test. I bought a bag of 50 pre-tinned nichrome 'chips' from Skylighter to use as the heat element. Easy to solder on some twinlead wire as the nichrome was already tinned. I used the formula from Skylighter for the primer, a 50/50 mix of KClO3 and Sb2S3, mixed to a slurry in 5% NC. Coated that with meal BP in 5% NC slurry, and a final dip of 5% NC laquer.

Then I ran down to the local electronics store ( Radio Shack ) and picked up a plastic box, pair of spring loaded speaker wire terminals, a couple LED lamps, SPST switch and a momentary pushbutton. I wired 4 9VDC batteries in series/parallel, for 18 V with twice the current capacity/longer life.

Works great ! I was doubtful if I could run enough wire to be back in a safe zone, 150 or more away for rocket and shell launches, so I tested the system through a 500 foot spool of the twinlead wire shooting wire, and got instant ignition with a nice *pop* and flare of fire. Tomorrow night I will be letting my daughter fire her first 3" shell while I video She's totally jazzed by the idea that *she* gets to fire it.

What are you guys' favorite pyrogens for e-matches ?

[fishy1]

i like cheap and easy BP.

[Karl]

Im building a firing box as we speak!

It's supposed to be a Rocketry controler but it work's off the same principal. It works using two seperate units ;

The handheld unit, runs off a 9v battery and has a Keyswitch and 3 Ultra Bright LED's for easy to see on/off, armed and fire signs at night.

The second unit is the relay box. It has two, 16A car relays, houses 2 7.2v Ni-Cad batterys and lets you change between 7.2v and 14.4v. An additonal feature is a continuity test and Piezo siren when everything's armed.

Should fire anything I put infront of it.

[Frozentech]

Im building a firing box as we speak!

It's supposed to be a Rocketry controler but it work's off the same principal. It works using two seperate units ;

The handheld unit, runs off a 9v battery and has a Keyswitch and 3 Ultra Bright LED's for easy to see on/off, armed and fire signs at night.

The second unit is the relay box. It has two, 16A car relays, houses 2 7.2v Ni-Cad batterys and lets you change between 7.2v and 14.4v. An additonal feature is a continuity test and Piezo siren when everything's armed.

Should fire anything I put infront of it.

What did you pick as the current limit for the continuity testing ? I tried 23 mA and the ignitors did NOT go off, and plain Nichrome didn't get hot enough to burn me at that current level... I unfortunately goofed and blew the fuse in my ammeter testing the ignition current All I know for sure is that I have enough, using 18 VDC.
For the moment until I can get better data on the fire / no-fire current of these ematches, I've modified my box to remove the continuity testing, and so far I've tested 4, and fired 1 device, and all 5 worked instantly.

[littlejohny]

I am planning on making a firing box, The power will hopefully be from 1 9v battery wich will charge a 35v 2200uf capacitor apart from the fact I only have a vague idea of how capacitors work . I need a very basic circuit diagram with its correct name beside the component wich I can't seem to find. I have lots of capacitors ranging from 10v 2.5 uf right up to 250v 10uf etc.

[Arthur Brown]

UK commercial igniters are 20mA No Fire and 500ma Certain fire. So keep continuity checks well below 20 ma and calculate the availability of at least 500ma down the firing wire and across the series wired igniters. The mid range from 20m - 500ma is dangerous because you do not know what will happen and you may have to "clear" an unfired item.

[Karl]

What did you pick as the current limit for the continuity testing ? I tried 23 mA and the ignitors did NOT go off, and plain Nichrome didn't get hot enough to burn me at that current level... I unfortunately goofed and blew the fuse in my ammeter testing the ignition current All I know for sure is that I have enough, using 18 VDC.
For the moment until I can get better data on the fire / no-fire current of these ematches, I've modified my box to remove the continuity testing, and so far I've tested 4, and fired 1 device, and all 5 worked instantly.

Frozentech,

I used 0.15mA for the current limit on my controler.

Cheers,
Karl

[Frozentech]

Frozentech,

I used 0.15mA for the current limit on my controler.

Cheers,
Karl

Karl,

Does .15mA give enough power during continuity check to directly drive your (I presume) LED indicator ?

[Karl]

No, .15mA wont drive anything.

If you understand electronics, heres a jpg of my SCH file.