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Electrical Specs Copperhead Initiators?

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ApolloMaker

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Howdy All ----

Building my own igniter supply and am planning on running rebuildable Aerotech 29mm motors. I cannot find any electrical specs for the 4" and 8" Copperhead initiators. So far, all I have found is that 12V from a supply that will deliver 3 amps will work OK. But nothing solid in the way of what Aerotech would specify as minimal or average requirements for reliable operation of the Copperheads.

Any help appreciated -- my present design will deliver 12 volts at 3 amps. Also, anyone know where Aerotech might have posted their required parameters.


Cheers --- Bob --- :D
 

Handeman

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Bob, not sure what you mean by "building my own igniter supply". If you mean a launch controller, I would suggest searching here and in the archives. Lots of great threads on controller designs and builds. You'll find most people use motorcycle/ATV/garden tractor batteries, car starters, or rechargeable battery packs. Almost all will be 12V or more and be able to source 8 or more amperes. More amps is better.

If you are making your own igniters to replace copperheads, then I would make the same suggestion. There are some threads about homemade igniters here, but you might find more on that subject over at Rocketry Planet.
 

GregGleason

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This might be "reverse" engineering of sorts, but my guess is that AeroTech's Interlock™ electrical launch delivers spec amperage to fire the CH's.

I did find this quote about the CH's from AeroTech:

Make sure that your launch controller power supply is capable of delivering 12 volts at a minimum of 3 amps to the igniter. A fully-charged car battery or 12 volt gel-cell is recommended.
You can email them questions. I have asked them questions and I received satisfactory responses.

I do have to ask the question based on your avatar: did you used to work at North American building CSMs?

Greg
 

El Phantasmo

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Are you trying to build and ignition system as close to minimum requirements as the copperheads call for?

I built an igniter using a 12V 7A "alarm" battery. I put it in a Radioshack project box. It has an arming switch, continuity light, launch button, terminal posts and handles. The continuity light activates when the launch button is pushed. This helps to reduce the chance of the continuity current setting off the ignitor. If the continuity light doesn't come on or cuts out then the circuit is open. It'll ignite a fleet of copperheads.
 
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artapplewhite

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To understand what a Copperhead needs you need to understand how it's made.

Start with two thin sheets of copper foil with a thin sheet of flexible plastic in the middle as an insulator. Next, cut this "sandwich" into very narrow strips. Crimp one end to make a few corrugations to better hold the pyrogen. Dip the corrugated end in a slurry of conductive pyrogen and let it air dry.

The resulting igniter is simple and cheap but is somewhat lacking in reliability and repeatability. It also requires a special connecting clip or a modification to standard alligator clips to keep from shorting it out when hooked up to a normal launch controller.

There are many ways Copperheads can fail:
1. The two copper layers can form a partial short along their long edges, especially if they weren't cut cleanly or were mishandled when they were made or stored.
2. One or both of the thin copper foil leads can break, usually where the igniter has been folded.
3. The "teeth" of normal alligator clips can pierce the copper foil and plastic insulator resulting in a partial short.
4. The resistance of the conductive pyrogen can vary depending on how thick and how well stirred up the slurry was when the igniter was dipped. It is this variability in resistance that makes it hard to quantify the amount of current needed to set off the igniter.

If you have a current limited power supply, a partially shorted igniter will absorb all the power and bypass the pyrogen. A high current supply can "burn" through a partial short which then allows the current to reach the pyrogen. This is one reason why holding the launch button down for a few seconds eventually gets the motor going.

Art Applewhite
 
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