How do I Build a 6/12 volt launch controller?

[rubenmromero]

Walked through RadioShack and have an idea. Need professional help/advice thuogh.

[GDJ]

Easy. You need a high amperage automotive relay, a momentary push button, key switch, LED lamp (single diode 12v), some 6 gauge wire with battery alligator clips, 50 feet of 16 gauge 2 conductor wire, and a project box big enough to fit it all in.

Ready?

[eggplant]

You most certainly do not need a relay! You need a battery, a switch, a button, and some wire. Just get all of that and then I will help you put it all together. Welcome to the forum!

[bobkrech]

Easy. You need a high amperage automotive relay, a momentary push button, key switch, LED lamp (single diode 12v), some 6 gauge wire with battery alligator clips, 50 feet of 16 gauge 2 conductor wire, and a project box big enough to fit it all in.

Ready?

WHAT? Do you have a clue how big 6 gauge wire is? It is totally unnecessary.

You don't need a relay, but if you use one this is all you need http://www.allelectronics.com/make-a...E-RELAY/1.html and this is the wiring http://www.allelectronics.com/make-a...E-RELAY/1.html The relay will pass 100 amps in a launcher applicaion, and multiconductor 14 gauge wire is plenty for that current as well. The relay draws about 0.1 amp so 100' of 18 gauge zip cord is plenty here. A standard superbright LED in series with a 500-1000 ohm resistor is all you need to limit the current through the LED to 10 to 20 ma.

If you don't use a relay 16 gauge zip cord is fine for runs to 50'.

You do not need a key switch. You need a removable interlock.

Search the forum and the archive for all kinds of launcher plans.

Bob

[GDJ]

WHAT? Do you have a clue how big 6 gauge wire is? It is totally unnecessary.

You don't need a relay, but if you use one this is all you need http://www.allelectronics.com/make-a...E-RELAY/1.html and this is the wiring http://www.allelectronics.com/make-a...E-RELAY/1.html The relay will pass 100 amps in a launcher applicaion, and multiconductor 14 gauge wire is plenty for that current as well. The relay draws about 0.1 amp so 100' of 18 gauge zip cord is plenty here. A standard superbright LED in series with a 500-1000 ohm resistor is all you need to limit the current through the LED to 10 to 20 ma.

If you don't use a relay 16 gauge zip cord is fine for runs to 50'.

You do not need a key switch. You need a removable interlock.

Search the forum and the archive for all kinds of launcher plans.

Bob

Okay, eggplant and bobkrech, yeah I do know how big 6 gauge wire is. The copper conductor just under 5.5 mm in diameter. I've been a Heavy Truck Technician for the last 17 years. Read my Member's Information. I'm not an idiot, and I do design things that may be considered overbuilt, but they are 100% reliable.

Here is my rationale for my proposal, if you're interested:

1) Relay - Can pass as much current as possible to the igniter(s). Don't have to rely on a light duty automotive switch to transfer a hefty amount of current, even if it's under one second.
2) Pushbutton momentary switch - Pretty obvious. Push down, makes contact. Release the button, current stops.
3) 12V LED: Self limiting for current, thanks to the current limiting resistor. 20mA is about right, so you have very little current going to, say, a Quest ignitor.
4) Alligator clips with 6 ga (oh hell, lets shrink it to 8 ga) wire - Alligator clips hook on the posts of a battery, and making good proper contact. Heavy wiring is more for being robust.
5) 50 or so feet of 16 ga 2 conductor cable - Gives you all the room you would need from little 1/4 A rockets to HPR.
6) Key switch - Turns the whole unit off. Acts like a safety key.


Not really aiming this at eggplant, but bobkrech, you sounded off like I was a complete idiot without asking for any reasons as to why I suggested the parts I did. You attacked me. I don't appreciate that.

[jus_rockets]

What type of battery are you guys using with your 12v launch systems?

[GDJ]

What type of battery are you guys using with your 12v launch systems?

I prefer Lead Acid car batteries. Don't have to charge them that often, lots of current capacity, pretty flexible for ambient temperatures (ie plenty of current when it's -20C).

I don't like the weight I have to lug around, but at least it only has to move to the car, launch site, back in car, then home. I can eat my wheaties for that.

[hornet driver]

one 1972 chevy p/u, 100 ft speaker wire, one set vice grips,one pair rubber gloves, one roll duct tape---wait a minute--I think the guy trying to launch cats gave me this------on a serious note---I've thought about a small mower/motorcycle battery in the future---thoughts?

[GDJ]

one 1972 chevy p/u, 100 ft speaker wire, one set vice grips,one pair rubber gloves, one roll duct tape---wait a minute--I think the guy trying to launch cats gave me this------on a serious note---I've thought about a small mower/motorcycle battery in the future---thoughts?

Yeah, that should work alright. Certainly lighter than mine!

[fyrwrxz]

Oh snap! No wonder the guy at Pep Boys looked at me funny when i asked for a 6/12 volt battery....

(this is actually quite coincidental as I'm sitting here building a club launcher for TARC support later today)

[chadrog]

What type of battery are you guys using with your 12v launch systems?

A much more portable option is a motorcycle / lawn tractor battery. They can be had for twenty to thirty bucks and light anything as well as a larger battery. My battery stays permanently installed in my 12v launch controller, hinged lid allows access for charging.

[rubenmromero]

Ok.Thanks for all the info from all.Very much appreciated.Only thing I am not clear about is how to wire in the lamp/led for continuity.

[rockets4kids]

Just get one of these:

http://www.walmart.com/ip/Schumacher...ndingMethod=rr

They are exceptionally convenient.

As others have said, a relay is not necessary for Estes igniters, but if you are planning to use HPR igniters you will definitely want a relay. If you are clustering with Estes igniters, a relay can also be very helpful.

You don't need a fancy relay, a generic 20 amp relay from the auto parts store is just fine, you should be able to pick one of these up for under two bucks.

BTW: Here is a good circuit and description:

http://www.jimwools.com/rocketslaunchctl.php

[bobkrech]

GDJ

Igniters are simply resistive heaters coated with pyrogen and they follow
Ohm's law, V=RI.

Most igniters have resistances between 1 and 2 ohms. They will draw between 1 amps per volt to 0.5 amps per volt. As they heat up, the resistance increases and the current draw drops.

Current not voltage is important for a heater, as the purpose of a heater is to deliver power. Power is I^2 R. If you double the curerent the power increase by a factor of 4, triple it and the power goes up by a factor of 9 etc.

The most parameter for an igniter is the all-fire and no-fire currents. Your continuity circuit should not supply more than 10-20% of the maximum no-fire current, and the firing circuit should be able to deliver atleast 2 or 3 times the minimum all-fire current rating so the igniter actuates prompty. At 3 times the all-fire current, most igniters take only 1 or 2 milleseconds to activate.

The resistance of 14 gauge wire is 2.5 milleohms/foot. 100 ft of 14 gauge zipcord has a resisance of 200 x 0.0025 = 0.5 ohms, and will supply 2 amps per volt or 24 amps with a low impedence 12 volt battery into a dead short. In a direct fire circuit without a relay the circuit resistance in series with a 1 ohm igniter is 1.5 ohms. The current capability for the circuit is 1/R = I/V = 1/1.5 = 0.67 amps per volt. If the igniter all-fire current is 2 amps, then provided that the battery voltage is greater than 3 volts, the igniter activates. A 12 volt low impedence battery would be dumping 8 amps into the circuit so activation would be prompt, even without a relay.

A relay launcher with 14 gauge wire and clips would have a resistance of 0.05 ohms. It will supply 20 amps per volt due to the shorter wire length and with a 12 volt low impedence battery, that's 240 amps into a dead short which is plenty.

If you read the data sheet for the automotive relay I referenced you will see that it takes more than 150 amps to weld the contacts. That won't happen if an ignitor is in series with the relay.

If you were trying to turn over a big truck diesel in -40C weather, you would need 6 gauge wire because you're pulling big current for seconds and the wires will heat up and raise the resistance. In a launcher application, you only need 14 gauge wire, because the currentl is only high for a few milliseconds before the ignite itself gets hot and cuts down the current.

Here is a good source of general information on launchers and igniters from Estes.

Bob

[GDJ]

Bob, I'm not disagreeing with anything you typed here, nor are any of the facts you typed up new to me at all. It's all part of my job.

I could nitpick about the size of wire that you gave for your example on trucks, but I won't go there either. What's the point?

I already read the information (thank you) ad nauseum before.

What I design and build here is built for longevity and ,as low as possible, chances of failure due to poor current/voltage/parts. Obviously I cannot control the quality of igniters, but by building what I have (and I've assisted hobby acquaintances with very similar builds of launch controllers) that even iffy igniters light. By using the parts I listed anything from a Quest igniter to the biggest Copperhead (or whatever is larger) will fire, everytime, and safely.

I stand by my previous statements, and I stand by my design. I respect your right to disagree and build what you feel is right.

In short....There is more than one way to do things.

Good day.

[rockets4kids]

In short....There is more than one way to do things.

Indeed, there is kill, overkill, and super-duper overkill. On the ground, going with 6 GA wire isn't going to hurt anything. Trying to loft something with that degree of over-building is a different story entirely...

[GDJ]

Indeed, there is kill, overkill, and super-duper overkill. On the ground, going with 6 GA wire isn't going to hurt anything. Trying to loft something with that degree of over-building is a different story entirely...

....and if you come up with a design that suits your need, then that's fine by me. If it works for you, go for it.


I've said enough on this subject.