I am designing a pyrotechnic firing system. At first I was planning on using Molex connectors with 15 conductors, 10 hots and 5 grounds. The original plan was to have all of the 12vdc come from the firing box, though the cables with molex connectors, and to sub boxes called "rails" in the pyrotechnics industry, that would split the 15 conductor cable into 10 speaker type hookups. I am now looking to have each rail include a battery, and have an SCSI CN50 connector cable carry a higher voltage, lesser current ac signal to a relay, which would allow the 12vdc current from the battery to flow to the igniter. This would lessen the cost of the cables dramatically, and allow for less voltage loss over the 100ft+ distance that seems to plague dc. I have included my original plans. Any suggestions are much appreciated.

 

I've built a couple of these.

One issue I have with your idea of putting batteries in the rails is safety. If you have one battery in the central box, your arming switch disconnects the battery AND SHOULD short-circuit the power bus downstream so that stray charges don't fire your squibbs. If you put a battery in the rail, you have a source of electricity right near your explosives. If the box was banged, it could bounce the relay contacts and BOOM. Even if you had a safety in each rail that disconnected the battery, someone has to arm it and that someone would be close to the explosives as well. You would have to have a way to ensure that the relay was OK and that the contacts were open before connecting (an arc/spark can weld them shut.) You would not know you had a component failure until it was too late.

Personally, I would NEVER do it like you are suggesting.

We kicked it around for the same reasons that you indicated, too many wires, cost etc. and experimented with radio links, multiplexed schemes using microcontrollers and the like but decided that simple was safest. Burns hurt a long time.

Who are you doing this for?

 

You have a point, relays seem too unreliable. I am quite used to having a power source in the rail, and it is most beneficial as to prevent any lag. I have experience with the fireone system, which has a battery in every rail. I planned on having a 3 pin xlr connector as well. One conductor for the common for the relays, and two conductors for dc power to the units, which could be used instead of a battery, that way the arming switch would still kill all power and there would be no possible stray currents. I am building this for myself.