Switchable 6/12 volt power to igniters ?

[Dale Saukerson]

I'm about to be a BAR again. Except for three weeks ago, have not flown in ten years or more. With a relay launcher I helped repair for someone, I noticed that 12 volts would make some igniters almost explode rather than controlled burn (true for Solar's, Copperheads, and Q2G2).

Have any of you tried using 6 volts instead of 12 (on a relay system) for igniting single motors ?
I'm wondering if doing so has proven to result in more reliable motor ignition, either BP or AP propellant.

 

[Peter Olivola]

Voltage isn't the likely cause of what you observed. The most common cause of ignitor "explosion" is a sealed nozzle. Yes, you have to keep the igniter firmly against the propellant grain, but you don't want the chamber sealed. It has to vent to give the grain time to ignite before the igniter is pulled away by the pressure of its own combustion.

I'm about to be a BAR again. Except for three weeks ago, have not flown in ten years or more. With a relay launcher I helped repair for someone, I noticed that 12 volts would make some igniters almost explode rather than controlled burn (true for Solar's, Copperheads, and Q2G2).

Have any of you tried using 6 volts instead of 12 (on a relay system) for igniting single motors ?
I'm wondering if doing so has proven to result in more reliable motor ignition, either BP or AP propellant.

 

[Dale Saukerson]

This was ground testing of the system and igniters, not installed in motors.
They tend to instantly burst, rather then a steady pyrogen burn.
Explode was a bad term. Sorry.

I do hope to never seal off the chamber.
For that kind of fun I'll dig out some FSI E-60s that have seen a few basement temp cycles :y:

 

[Peter Olivola]

Like a common match? That isn't what you want. You want the igniter to heat the maximum surface area as quickly as possible. Particularly with composite motors where the distribution of fuel/oxidizer isn't uniform. Also, by ignition from the heat element (wire) igniter material is dispersed into the grain material as it burns which aids propellant ignition. A little "push" from the already burning igniter material embeds the not yet fully burned igniter material into the grain.

This was ground testing of the system and igniters, not installed in motors.
They tend to instantly burst, rather then a steady pyrogen burn.
Explode was a bad term. Sorry.

I do hope to never seal off the chamber.
For that kind of fun I'll dig out some FSI E-60s that have seen a few basement temp cycles :y:

 

[MarkII]

You mentioned that Copperheads were one of the igniter types that "exploded" ("popped" is a word that I have seen used more often in reference to some igniter phenomena) when they were given 12 volts of DC. As far as I know, Copperhead igniters do require the use of a 12 volt ignition system, though. Such a system may be overkill for the other brands if you are using only single igniters, but it is highly advisable for clusters. (You may already know this.) I have used my AeroTech Interlock Controller with a 12 volt power supply for all of my personal (non-club) launching for the past few years. The majority of it has been with Estes Solar igniters in single-motor set-ups, while a significant smaller quantity have been with MicroMaxx igniters, and there were even a couple of Quest Tiger Tails in there, too. I have had good, prompt ignitions during all of that time, with zero incidents of bridge wires vaporizing before they could touch off the motors.

 

[Micromeister]

With Clustered BP motors we want the igniters to bring the BP up to burn temp as quickly as possible. We WANT to push as many AMPS of current not necessarly Volts into the igniters as practical for a given relay. It usually easier to find Higher Amp capacity batteries in 12Volt units, so 12 volts systems are "Normally perferred" for cluster application.
Personally; I use a 40amp DPDT relay breaking both sides of the 12volt battery system with max. of 24" long 16gauge stranded copper clip leads on the load side, and very heavy wire leads #6 Stranded copper on the battery side to ensure as high an amp load as I can from my relay.

Because all igniters, leads and other factors can slightly delay ignition of individual motors, super fast heating is very desirable as we want all motors lit before or very shortly after first motion of the model. The Lighter the model the Quicker first motion will occur. If you leads are to short or connections too weak this first motion can yank the clips for the igniters before they have had the slit second needed to do their job.