Electric Matches
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- Require low current to fire so that it can be used with common rocketry electronics. Most motor igniters require far more current than rocketry electronics can deliver to an igniter.
- A short burn with little flame - long enough to ignite the ejection charge but not too long to ignite the recovery system or airframe.
- Reliable
Most rocket motor igniters are high current igniters, and will not work with most rocketry electronics. Motor igniters are designed to produce a large fireball for a long period of time (1/2 - 1 second), which is not desireable inside a rocket's airframe. Igniters acceptable as ejection charge ignition are listed below. (Electrical igniters are also sometimes called electric matches.)
- Daveyfire SA2000 N28B
- Daveyfire SA2000 N28BR
- Oxral
- Atlas
- HiRMI
The list may not include all available low current igniters. Manufacturers come and go, and models change.
The list does not include photographic flashbulbs. The author does not believe that flashbulbs are acceptable as ejection charge igniters due to questions of reliability and accidental firing.
Daveyfire Inc.
Daveyfire is a company that manufactures igniters for consumer products like automobile airbags, the blasting industry and the military. They are also used by the fireworks display industry. The igniters are very reliable. (Note: Daveyfire is a specific company, not a generic term for "electronic matches" or ejection charge igniters. Some rocketry supply vendors incorrectly sell other brands of igniters as "Daveyfires.")
Daveyfire products suitable for ejection charge igniters are models SA2000 N28B, SA2000 N28BR and SA2000 N28F. The N28B is most commonly used. The N28BR model is the same as the N28B except that it has 3 times the pyrogen. The N28F burns about 20 times longer than the N28B, but the burn time is still brief. Details are listed below.
| Model | Bridgewire Resistance (Ohms) | Max No Fire Current (Amp) | Min All Fire Current (Amp) | Ave. Firing Time | Explosive Charge Per Head (grams) | Wire Color |
|---|---|---|---|---|---|---|
| SA 2000 N28B | 1.6 +- 0.3 | 0.20 | 0.37 | 2 ms at 1 Amp 1 ms at 3 Amp |
0.16 | white |
| SA 2000 N28BR | 1.6 +- 0.3 | 0.20 | 0.37 | 2 ms at 1 Amp 1 ms at 3 Amp |
0.48 | orange |
| SA 2000 N28F | 1.6 +- 0.3 | 0.40 | 1.00 | 40 ms at 2 Amp | N/A | black |
Some rocketry supply vendors sell Daveyfire igniters in small quantities. They can also be purchased in bulk only (usually a minimum order of one box of 100 igniters) from the company listed below.
Coonies Explosive, Inc.
P.O. Box 2062
Hobbs, NM 88241
Voice: 505-393-0166
Fax: 505-393-6060
Oxral
Oxral igniters have worked well for ejection charge igniters. Some rocketry supply vendors sell them. They are also sold by Skylighter, Inc., a fireworks supply company.
| Bridgewire Resistance (Ohms) | Max No Fire Current (Amp) | Min All Fire Current (Amp) | Ave. Firing Time | Explosive Charge Per Head (grams) |
|---|---|---|---|---|
| 2 | 0.20 | 0.50 | N/A | N/A |
Atlas
Atlas igniters have been sold by Skylighter, Inc., a fireworks supply company. The author has no other information about them.
HiRMI
The HiRMI, Hi-Reliability Electric Match, igniter is sold by Blacksky.
| Bridgewire Resistance (Ohms) | Max No Fire Current (Amp) | Min All Fire Current (Amp) | Ave. Firing Time | Explosive Charge Per Head (grams) |
|---|---|---|---|---|
| 2 | 0.10 | 0.40 | N/A | N/A |
Recommendations
Safety is important. Massive rockets can inflict significant personal injury, including death, and create major property damage when the recovery system fails. One failure mode is a defective ejection charge igniter. Although the failure rate of commercially manufactured igniters used to ignite ejection charges is low, a redundant igniter can be a good idea. Rocketry altimeters and timers can fire two low current igniters per charge. The author believes that it is a better idea to spend an extra $2 to $3 on extra igniters than to watch a rocket nose into the ground, a car or person.
Submitted by Dean A. Roth
