I can only assume that all the fuse wires get hot enough to ignite the comp before one goes open circuit.
Exactly. Igniters are current fired devices and for series use it helps if they are pretty much identical. The stage effects are very good in this respect. A series loop guarantees the same current to every igniter.
Taking a worked example, imagine firing a front of 5 mines with standard e-matches (2 ohms each) on a 100m (15 ohms) of bell wire from a 24v gell cell (0.2 ohms). The series loop would give you 0.95 amps current through every match and reliable ignition. In parallel, splitting 1.5 amps between 5 igniters on the end of the 100m wire would be unpredictable at best.
For rockets with rather less uniform high current igniters, a gell cell firing the matches in parallel on short wires via a remotely activated relay seems to be the way to go.
Interestingly, series wiring is also used for runway lamps on airfields. Each fixture is wired via a transformer to preserve continuity but the same principle applies - with a constant current loop you can guarantee that each lamp is equally bright over several miles of wiring.
Edited by BrightStar, 16 April 2008 - 11:40 AM.
