Where am i going wrong

[libby lou lou]

Hi,Have got into building my own rocket motor and need to make e-matches as i need to set the igniter deep inside the motor, i have tried two 9v batteries in parallel, 30ft of speaker wire, one strand i would say is copper, the other maybe chromed/nickel plated wire ?

At the business end, 60 awg nichrome wire, sat on a match head, dipped in cellulose, then dipped in magnesium powder. When i try to ignite a match, at the most i bet the tiniest whisp of smoke but no ignition, when i put the e match to the battery with only 3 inch of wire, it lights immediately, is the copper wire i'm using too high a resistance? Apart from using a car battery, what else do i do ?, thanks......

 

[DetlefSchmitz]

I used to use torch bulbs with the glass removed...
Yes I think you need to make the resistance of the fusing wire a lot more than the feed wire so that the whole battery voltage ends up across the fuse. So thinner wire for the fuse.

To be fair, now I think about it, I also used a relay (plus a torch battery), local to the fuse, made out of a Woolworths door bell, rewired to just close and not cycle. But that is not really needed if you get the resistances right.

 

[libby lou lou]

Thanks, that the type of answer i am looking for....

 

[endecotp]

is the copper wire i'm using too high a resistance?

Probably. If you have a multimeter you can measure it.
Try with your two 9V batteries in series.
A car battery won't help, but more 9V batteries might.

 

[Robin0577]

Maybe this would be considered as spoiling the fun, but you could use ready made igniters.....

http://www.lemaitreltd.com/p/Igniters/FeXOqTlaanI

Ideally fired from a capacitor discharge firing system to help get around the cable resistance problem...

Edit to add: These units also have a current limited test facility, allowing you to check your cable and connections without the risk of firing the charge.

http://www.lemaitreltd.com/p/6-Way-and-2-Way-Controllers/khe2btGMrgk

These items are readily available from theatrical suppliers such as AC Entertainment http://www.ac-et.com/ , 10 Out Of 10 Productions http://www.10outof10.co.uk/acatalog/Le_Maitre.html , Stage Electrics http://www.stage-electrics.co.uk/shop/sales/effects-and-effect-machines/pyrotechnics , Or White Light http://shopwl.com/ .

No license is needed to buy these items, they are available to anyone over 18.

 

[Doggit]

It's more likely to be the chrome nickel wire that's the problem.

 

[libby lou lou]

Probably. If you have a multimeter you can measure it.
Try with your two 9V batteries in series.
A car battery won't help, but more 9V batteries might.

the long wires each read 3.1, the short 3 inch x2 pieces + 1 inch n/c wire all in one piece reads 2.7....too close?

 

[endecotp]

So I think you're saying that the total resistance when using the long wires is 3.1 + 2.7 + 3.1.
If 9V is sufficient when it's just 2.7, then trippling the voltage to 27V (or a bit more) should overcome the extra resistance.