Igniter Performance and its Dependence on Firing Current

or……Watts a Joule?

John Lyngdal

Units of Measurement

I’m sure that most of you are familiar with volts, amps, and watts.

What’s a joule and why use this unit for characterizing igniter performance?

Units of Measurement

What’s a joule and why use this unit for characterizing igniter performance?

Answer:

1 joule is equal to one watt-second.

Using joules offers a leveled evaluation of igniter performance under situations where time, voltage, and current are all variables.

Terms and Rules

Voltage Droop - Ever heard of a case where droop was a good thing? Neither have I. Voltage droop is a firing system loss indicator present .

Ohms Law –They call it a law for a reason.The internal resistance of batteries and lead resistances of the firing leads are loss mechanisms that become more important as the current flow increases and as the system voltage decreases.

Working for a Test & Measurement Instrument Company has its Advantages

12 V Lead-Acid Battery and 1.2 Ohm Load

9 V Alkaline Battery and 1.2 Ohm Load

Battery Selection Will Impact Results

No Load Loaded Calculated

Load Cell Cell Voltage Load Current Delivered Loop

(Ohms) Voltage Voltage Droop Voltage (Amps) Joules Resistance

12V Lead-Acid 1.2 12.59 11.00 1.59 10.46 8.15 85 1.35

12V Lead-Acid 0.3 12.52 8.87 3.65 7.30 23.94 175 0.37

7.2V NiMH "C" cell 1.2 8.38 7.30 1.09 6.98 5.98 42 1.22

7.2V NiMH "C" cell 0.3 8.40 5.54 2.85 4.63 14.94 69 0.37

9V Alkaline 1.2 9.57 4.26 5.32 4.07 3.34 14 1.27

9V Alkaline 0.3 9.42 1.90 7.53 1.64 4.80 8 0.40

9.6V(8 x AA) NiCd 1.2 10.80 6.84 3.96 6.54 5.25 34 1.30

9.6V(8 x AA) NiCd 0.3 10.61 3.35 7.26 3.20 9.98 32 0.36

Quest Q2G2 Igniter 0.35 A load settingFiring time 128mS, 26 mJ.

Quest Q2G2 Igniter 1.00 A load settingFiring time 8mS, 8.2 mJ.

Quest Q2G2 Igniter 3.50 A load settingFiring time 1.8mS, 22 mJ.

Quest G2Q2 Test Summary

• The initial resistance of the G2Q2 igniter is 1.77 ohms, which is significantly higher than other model rocket igniters on the market.

• At the “All Fire current” of 0.35 A the igniter fires and creates an open circuit.

• At 3x the All Fire current” the firing time was approximately 7.0 mS.

• The Q2G2 igniters required less than 50 mJ for operation.

Estes Solar Igniter 6.00 A load settingFiring time 314 mS, 4874 mJ.

Estes Solar Igniter 12.0 A load settingFiring time 55 mS, 3197 mJ.

Estes Solar Igniter 20.0 A load settingFiring time 27 mS, 3087 mJ.

Estes Solar Igniter Test Summary• The initial resistance of the Estes Solar igniter is

0.655 ohms.• At the “All Fire current” of 2.0 A the igniter fires,

but the bridge wire remains resistive.• At 3x the ”All Fire current”, the bridge wire opens

and the firing time was approximately 300 ms.• At 10x the ”All Fire current” (20 Amps) the firing

time was 27 ms.• At 20 Amps of firing current, the system was

nearing a state where it was voltage limited. • The igniters required less than ~4500 mJ for

operation.

Igniter Performance Summary

Igniter Current Firing time Standard Relative milli-Joules Standard Relative

Setting (mS) Deviation Std. Dev. (mJ) Deviation Std. Dev.

Quest - Q2G2 0.17 A 2750* 25.5

Quest - Q2G2 0.35 A 90.7 49.69 55% 34.3 24.24 71%

Quest - Q2G2 1.00 A 7.04 1.11 16% 9.91 1.91 19%

Quest - Q2G2 3.50 A 1.79 0.08 4% 18.8 1.85 10%

Estes - Solar 6.00 A 301 40.06 13% 4639 735 16%

Estes - Solar 12.0 A 54.5 7.16 13% 3122 456 15%

Estes - Solar 20.0 A 26.7 2.07 8% 3087 234 8%

What About Clusters?

Specifically what is the best configuration,

Series or Parallel?

What About Clusters?

Specifically what is the best configuration,

Series or Parallel?

Answer:

The optimum configuration depends on the energy requirements of the igniter, the resistance of the component, and the performance of the launch system.

The Implications of Ohm’s Law

Consider a 12V launch system with a power source that can provide 20 amps of current, then model a relay based launch system around it with 100 milliohms of firing lead resistance, relay contact resistance of 50 milliohms, and clip to igniter lead resistance of 75 milliohms times 2.

The Implications of Ohm’s Law

System Loop Igniter Maximum Total Total Igniter Single Igniter System %

Igniter & Configuration Voltage Resistance Ω Resistance Ω Current (A) Power (W) Power (W) Power (W) Loss (W) Loss

System Only 12 0.25 0.00 48.0

Quest Q2G2 12 0.25 1.77 5.9 71 62 62 9 12%

Estes Solar 12 0.25 0.66 13.3 159 115 115 44 28%

Quest Q2G2 3x Series 12 0.25 5.31 2.2 26 25 8 1 4%

Estes Solar 3x Series 12 0.25 1.97 5.4 65 58 19 7 11%

Quest Q2G2 3x Parallel 12 0.25 0.59 14.3 171 120 40 51 30%

Estes Solar 3x Parallel 12 0.25 0.22 25.6 308 143 48 164 53%

Estes Solar 3x Parallel 12 0.25 0.22 20.0 240 112 37 128

Quest Q2G2 4x Series 12 0.25 5.31 2.2 26 25 6 1 4%

Estes Solar 4x Series 12 0.25 1.97 5.4 65 58 14 7 11%

Quest Q2G2 4x Parallel 12 0.25 0.44 17.3 208 133 33 75 36%

Estes Solar 4x Parallel 12 0.25 0.16 29.0 348 138 34 210 60%

Estes Solar 4x Parallel 12 0.25 0.16 20.0 240 95 24 145

3 Estes Solar Igniters in Parallel with 20 Amp Load Setting

3 Estes Solar Igniters in Parallel with 20 Amp Load Setting

3 Estes Solar Igniters in Parallel with 20 Amp Load Setting Summary

Firing time (mS)

Run #1 90

82

84

Run #2 89

93

92

Average (mS) 88.3

Standard Dev. 4.4

Rel. Std. Dev. 5%

3 Quest Q2G2 Igniters in Parallel with 2.0 Amp Load Setting Summary

Firing time (mS)

Run #1 11.6

12.4

11.2

Run #2 15.0

14.8

14.4

Average (mS) 13.3

Standard Dev. 1.7

Rel. Std. Dev. 13%

What About Series Configuration?

Is it any better, worse, about the same?

or

When should I choose to use Series or Parallel configuration?

3 Estes Solar Igniters in Series configuration with a 12 amp load setting

3 Estes Solar Igniters in Series

• All igniters fired in during the tests.• First igniter to fire appeared to be random

Time to Fire

6.00 A Load Setting 162 mS

12.0 A Load Setting 158 mS

20.0 A Load Setting 101 mS

3 Quest Q2G2 Igniters in Series

• All igniters fired in during the tests, with an audible dispersion present in the 0.35A test.

• First igniter to fire appeared to be random

Time to Fire

0.35 A Load Setting 95 mS.

2.00 A Load Setting 2.8 mS.

3.50 A Load Setting 1.6 mS.

Series vs. Parallel Summary

At 10X the specified “All Fire” Igniter current the results are:

Estes Solar Igniter Firing Time 20 A Current Setting

3 Igniters in Series 101 mS.

3 Igniters in Parallel 88 mS.

Quest Q2G2 Igniter Firing Time 3.5 A Current Setting

3 Igniters in Series 1.6 mS.

3 Igniters in Parallel 5.1 mS.

Summary

Increasing the available firing current shortens the igniter firing time and decreases the firing time variation.

Firing system resistance becomes more critical as the required firing current increases, or the system voltage decreases.

There is no clear winner in the series or parallel igniter configuration comparison. The final choice is dependent on the number of motors in the cluster and the electrical properties of the igniters.

Use of sensitive igniters mitigates the electrical limitations of launch control systems.