questions about relays

Hello all,

I am a model rocket enthusiast. Recently, I have toyed with the idea of cluster motor models. The hardest part of this is igniting all motors simultaneously. I have researched this and the common consensus seems to be that I must build myself a relay add on ignition system, which utilizes a DPDT 10 amp 12 volt DC 130ms coil relay, and also a larger, probably sealed lead acid battery with at least 30 amps. Now, I have a book which says: "The firing system (my existing four AA ignition system) should be wired to the coil. The normally closed contacts should be shorted together. The normally open contacts should go to the launch battery. And the center pole contacts should go to the rocket and clip whips."

Ok, my question is, what does all that mean? What is meant by "the normally closed contacts should be shorted together?" Ok thanks for any help. Oh, and also, if any of you feel like helping me build this system, you can visit this website where I get a lot of information from. It even has a wiring diagram (which is about has clear as mud to me). I also use a book called "Handbook of Model Rocketry, seventh edition." The website (it's a pdf file) is: http://www.narhams.org/tech/006-Clustering.pdf . Thanks again for any help.  

Yes, a jumper is an electrical connection between two points.

-Michael 

RockinF150, I wasn't aware this was a car audio forum. I don't see why it matters though. Now, I have another question. This project calls for a 4 pin socket. Will that take the place of a jumper? What is a socket anyway? Yeah yeah I know this is a "questions about relays" thread....but I figure you can answer this one, cause you, or at least Mja1962, have been so good so far.

A socket is somthing to plug the relay into.  It is used so that the relay may be changed without the need for unsoldering it.  The relay plugs into the socket.  Four pins correspond to the four contacts on the relay.  Not using a socket is okay, but using one makes replacing the relay much more convenient.  The socket provides an alternative to hard-wiring the relay.  A jumper can be a short piece of wire joining  the contacts you wish to connect.  Also, by placing the jumper across the socket's pins, you don't have to worry about installing another jumper if you replace the relay.

Here are some pictures of relays and sockets:  

http://www.tessco.com/products/displaySkus.do?groupId=619&subgroupId=63

-Michael

Ok Michael, you've been really helpful. Another question though: when you said "the socket provides an alternative to hard-wiring the relay," does that mean a socket can change the amps or voltage? And if I installed the jumper on the socket, and I wanted to change the socket and all, that means that the socket will still have the jumper, right? Oh, and as far as "placing the jumper" on the normally closed contacts of the relay/socket, how must I do this. Does it involve soldering? I hope not.

Thanks!

The socket does not change amps or voltage.  It simply provides a means to conveniently change or replace the relay.  An analogy to the concept of a socket would be a desk lamp, where the lamp is the socket and the bulb is the relay.  You don't have to use any tools to change the bulb.  If the bulb was soldered in, you couldn't change it very easily. 

Once the socket is installed, you should never have to change it.  As for soldering, it has nothing to do with whether or not you use a socket - you should solder your connections.  The decision is whether to solder to a socket or directly to a relay.  The difference is that if you use a socket, you will only have to solder once, even if the relay ever needs to be replaced. 

-Michael