Design of a Percussion and Electric Primer Gun Firing 

Power Supply

by Peter T. Bartkowski

ARL-TR-6987 July 2014

Approved for public release; distribution is unlimited. 
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Army Research Laboratory

Aberdeen Proving Ground, MD 21005-5069

ARL-TR-6987 July 2014

Design of a Percussion and Electric Primer Gun Firing 

Power Supply

Peter T. Bartkowski

Weapons and Materials Research Directorate, ARL

Approved for public release; distribution is unlimited. 
ii

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1. REPORT DATE (DD-MM-YYYY)

July 2014

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Final

3. DATES COVERED (From - To)

December 2013

4. TITLE AND SUBTITLE

Design of a Percussion and Electric Primer Gun Firing Power Supply

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Peter T. Bartkowski

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Research Laboratory

ATTN: RDRL-WMP-E

Aberdeen Proving Ground, MD 21005-5069

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 REPORT NUMBER

ARL-TR-6987

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12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

The U.S. Army Research Laboratory has designed and built a new power supply to fire laboratory guns in support of armor 

research. The new power supply is specifically designed to drive a solenoid into a percussion primer or ignite the M52A3B1

electric primer. To reduce power requirements, it uses charged capacitor banks to drive the solenoid or ignite the primer. This 

report details the design and construction of the power supplies.

15. SUBJECT TERMS

power supply, gun, percussion, electric primer, capacitor

16. SECURITY CLASSIFICATION OF: 

17. LIMITATION

OF ABSTRACT

UU

18. NUMBER

OF PAGES

30

19a. NAME OF RESPONSIBLE PERSON

Peter T. Bartkowski

a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified

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410-278-0210

Standard Form 298 (Rev. 8/98)

Prescribed by ANSI Std. Z39.18
iii

Contents

List of Figures iv

1. Introduction 1

2. The Existing System 1

3. New System Design 1

4. Circuit Design 2

5. Unit Construction 3

6. Field Testing 4

7. Conclusions 6

Appendix A. Circuit Schematic 7

Appendix B. Circuit Board Layout 9

Appendix C. Component List 11

Appendix D. Instrument Panels 15

Appendix E. Instrument Case Interior 19

Appendix F. Photo of Completed Unit 21

Distribution List 23
iv

List of Figures

Figure 1. Electric primer signals......................................................................................................4

Figure 2. Percussion primer signals.................................................................................................5

Figure 3. Signals for measuring time delays....................................................................................5
1

1. Introduction

The U.S. Army Research Laboratory has multiple laboratory gun firing ranges that use both 

percussion and electric primers for initiation. Currently, a combination of a linear power supply 

and a switch button panel is used to fire the guns. After replacement power supplies failed to 

adequately perform, an analysis was conducted to determine the power supply requirements. It 

was found that the design of a dedicated firing unit was the most appropriate way to replace the 

old hardware, as commercial laboratory gun firing products do not exist.

2. The Existing System

The existing firing system consisted of a Hewlett Packard no. 895A linear power supply

(0–320 volts of direct current [VDC], 0–1.5 amperes [A]) connected to the firing line via a 

mechanical switch or solid-state relay to fire the gun. The voltage was varied on the power 

supply depending on whether a percussion or electric primer was used. 

New replacement switching power supplies failed to adequately activate the solenoid used to 

initiate the percussion primer. The new power supplies could not provide enough surge current 

for the initial pull of the solenoid, which can be over 50 A. The old linear power supply has large 

filter capacitors on its output, which does provide the surge current to fire the solenoid. Modern 

switching power supplies have a much lower capacitance output and are electronically current 

limiting. Buying a new switching power supply with the necessary current capability would 

require a unit over 3500 W and necessitate upgrading the electrical power to support the device.

It was decided that a custom-designed dedicated capacitor-based power supply was a better 

approach. 

3. New System Design

The new power supply is designed to fire both the M52A3B1 electric primer and percussion 

primers. The percussion primer is initiated using a Trombetta solenoid model Q610-A1V24. The 

M52A3B1electric primer is designed to function with a 2-μF capacitor charged to 160 VDC. 

Due to the long length of some of the firing lines in use and the large surge currents, a 60-μF 

capacitor charged to 190 VDC was chosen. The Trombetta solenoid has a specified operating 

voltage of 24 VDC. Solenoids can typically be over driven to a certain extent if they are used in a 
2

pulsed mode of operation that has no continuous draw. Tests were conducted to evaluate the 

impact power of the solenoid using the existing original power supply and compare the results to 

various combinations of capacitance and voltage to be used in the new power supply. The tests 

indicated that a 34-mF capacitor bank charged to 65 VDC resulted in better impact performance 

than the original power supplies set to 160 VDC. Lowering the voltage results in a reduced 

probability of solenoid failure.

As new instrumentation techniques such as high-speed video and laser interferometry have been 

introduced into our gun testing, event timing has become critical. To improve the initiation 

timing, input and output trigger signals became desirable and were included in the new design. A 

debounce circuit was incorporated to clean up the manual push-button signal to fire the gun and

reduce jitter.

The entire firing system including the power supplies is now enclosed within a single 3-U rack

mount enclosure. A keyswitch is present to control the system power and a toggle switch selects 

between electric and percussion primers. Two push-button switches are available for firing the 

gun. One is the main fire switch, which incorporates a debouncing circuit, while the other is a 

back-up firing switch to be used if the main fire switch fails. It directly connects the charged 

capacitor to the firing line, bypassing all of the debouncing circuit should it fail to perform. The

trigger input can be used to allow an external device to fire the gun. A single trigger output can 

be used to trigger other devices or monitor timing. Light-emitting diode (LED) indicators on the 

front panel indicate power on (Power) and fully charged capacitor bank (Ready). The firing line 

connects to the unit using a military-style circular bayonet connector. 

4. Circuit Design

The circuit schematic (appendix A) has two sections. The top encompasses the capacitor banks 

and voltage charged (Ready) indicator while the bottom section includes the input, output, and 

debounce circuitry. 

There are two capacitor banks, each with its own power supply. The electric primer bank 

consists of capacitors C1 and C2 and is charged by the 200-VDC power supply V1. Resistor R1 

limits charging current to 40 mA. Even though charging occurs in a few seconds, this resistor is 

mounted to a thermal heat sink to allow for the possible fault condition in which a capacitor or 

firing line may become shorted. The percussion primer bank consists of capacitors C3–C7 and is 

charged by a 70-VDC power supply V3. Resistors R10–R12 limit the charging current to 

233 mA and are also mounted to thermal heat sinks to handle a possible fault condition. An 

LM393 dual voltage comparator chip (X1) monitors the charge voltage of each bank through a 

voltage divider network and compares it to a reference voltage of 4.7 V from the zener diode D1. 

The comparator chip will sink current from the LED D2 to indicate when the capacitor bank is 
3

greater than approximately 95% charged. Switch 1 (A and B) is a double-pole double-throw 

switch that adjusts the system for firing either the electric or percussion primer. Pole A of 

Switch 1 connects the LED D2 to the output of the comparator that corresponds to either the 

electric or percussion capacitor bank. Pole B of Switch 1 connects the solid-state fire relay to 

either the electric or percussion capacitor bank. 

The trigger circuitry is powered by a 10-VDC power supply V2. The LED D13 indicates that 

power is on. The unit can be fired by depressing the Fire button or providing a positive pulse to 

the Trig In BNC connector. Any signal higher than 1.0 V will trigger the unit. Overvoltage of the 

input is prevented by a combination of spark gap X10 and transient voltage diode D10. The 

spark gap clamps input voltage to 75 V. Resistor R22 limits the surge current while diode D10 

further clamps the voltage to 15 V. A 555 timer chip (X12) provides debouncing of the switch 

while sending a monostable 250-ms pulse to the solid-state relay to fire the primer. Transistor Q1 

pulls the trig line of the 555 timer low when the fire button is depressed, or a positive pulse is 

received at the Trig In connector. The timer then puts out a 10-V pulse to solid-state relay 

(SSR) 1 to connect the capacitor bank to the firing line, thus initiating the primer. Resistor R30 is 

in parallel with the firing line connector to dump the energy from the capacitor bank should the 

firing line not be connected while firing. Diode D12 is a flyback diode to eliminate voltage 

reversals from the solenoid during operation. The Trig Out signal is provided by transistors Q2 

and Q3. This output is protected from overvoltage by transient voltage diode D11 and spark gap 

X11 with resistor R29 limiting surge current. The output signal is a 6.8-V positive pulse.

A back-up momentary fire switch is also provided on the front panel. This is intended to be used 

only if the main firing switch fails to initiate the primer. It bypasses all the trigger conditioning 

and directly connects the capacitor bank to the firing line. In this mode of operation, no Trig Out 

signal will be present.

The circuit performance was modeled using MicroCap 10.0 software prior to circuit board 

construction. Prototype circuit boards were fabricated by a printed circuit board manufacturer

(appendix B). A full list of all components used can be found in appendix C.

5. Unit Construction

The enclosure is dismantled to cut the panel face, rear, top, and bottom panels with a laser or 

waterjet (appendix D). The face panel is cut to accept all the buttons, switches, indicators, and 

connectors. The rear panel is cut to accept a power cord receptacle. The top and bottom panels 

are cut to provide cooling vents and mounting holes for the power supplies and the circuit board.

The circuit board is populated with components and soldered in place by hand. It is then bench 

tested and adjustments made to the two potentiometers X2 and X3 to ensure the ready indicator 

lights up when the two capacitor banks are approximately 95% charged.
4

After installing the photoresist printed face and rear plates, all the indicators, switches, and 

connectors are then mounted to the front and rear panels. The two power supplies and circuit 

board are mounted to the bottom panel. Final wiring is done by connecting all the front and rear 

panel components and power supplies to the circuit board with hook-up wire. Then the enclosure 

is reassembled to complete the unit.

6. Field Testing

The unit was bench tested to ensure performance. A digital oscilloscope was used to record 

signals during firing. Three channels were simultaneously recorded: (1) Input Trigger, (2) Output 

Trigger, and (3) the voltage on the firing line. Figure 1 shows the signals recorded for the electric 

primer test. Figure 2 shows the signals recorded during the percussion primer test. 

Figure 1. Electric primer signals.
5

Figure 2. Percussion primer signals.

To measure circuit time delays, the test was repeated with a faster oscilloscope time base. As 

seen in figure 3, the time delay between input and output triggers is less than 10 μs. The delay 

between trigger input and firing line voltage is 600 μs due to the turn on time delay of the 

solid-state relay. Note the noise present on the input trigger line. The fire button was used to 

trigger the unit, and bouncing of the switch is obvious. The trigger out line and the voltage on the 

firing line is clean, however, due to the debouncing circuit.

Figure 3. Signals for measuring time delays.
6

7. Conclusions

The new firing unit is a reliable upgrade to the previous firing system. It was specifically 

engineered to fire both percussion and electric primers. The debounce circuit produces more 

accurate timing and firing with modern instrumentation techniques. The addition of trigger input 

and trigger output gives the unit more flexibility in interfacing with other instruments during 

testing. Lowering the voltage and increasing the capacitance driving the solenoid will increase 

the reliability and life of the solenoid. All the delays in the electronics are very repeatable and 

less than 1 ms—short compared with the 10s of milliseconds required to fire the guns. 
7

Appendix A. Circuit Schematic

 

This appendix appears in its original form, without editorial change.
8
9

Appendix B. Circuit Board Layout

 

This appendix appears in its original form, without editorial change.
10
11

Appendix C. Component List

 

This appendix appears in its original form, without editorial change.
12

Nomenclature Manufacturer Part #

(All resistors 1/4 watt unless otherwise specified)

R 1 5k 8W TO220 Ohmite TCH35P5K10JE

R 2 100k 1W

R 3 2k

R 4 1k

R 5 500

R 6 5k

R 7 5k

R 8 5k 3W

R 9 360

R 10 100 6W TO220 Ohmite TBH25P100RJE

R 11 100 6W TO220 Ohmite TBH25P100RJE

R 12 100 6W TO220 Ohmite TBH25P100RJE

R 13 1k

Heat Sink Ohmite #FA-T220-25E

Heat Sink Ohmite #FA-T220-25E

Heat Sink Ohmite #FA-T220-25E

Heat Sink Ohmite #FA-T220-25E

R 20 1k

R 21 50 1W

R 22 470 0.5W

R 23 1k

R 24 100k

R 25 10k

R 26 1k

R 27 1k

R 28 50 3W

R 29 5 1W

R 30 50 2W

R 31 500

R 32 10k

Fuse Holder 5mm, PCB mount

Fuse 1.25A, 5mm

C 1 30uf 250VDC film Genteq 41L2300

C 2 30uf 250VDC film Genteq 41L2300

C 3 6800 uf 80-100VDC SLPX682M100H9P3

C 4 6800 uf 80-100VDC SLPX682M100H9P3

C 5 6800 uf 80-100VDC SLPX682M100H9P3

C 6 6800 uf 80-100VDC SLPX682M100H9P3

C 7 6800 uf 80-100VDC SLPX682M100H9P3

C 8 100 nf 50V

C 10 4.7uf 50V

C 11 100 nf 50V
13

C 12 100 nf 50V

C 13 47 uf 50V

Or Jumper (cap will cause 

solenoid to unlatch automatically

D 1 1N5230B (4.7V zener)

D 2 LED Yellow Lumex SSI-LXR3816SYD-1

D 10 1.5KE15A

D 11 1.5KE6.8A

D 12 IN5408

D 13 LED Green Lumex SSI-LXR3816SGD-1

Q 1 2N2222A

Q 2 2N2222A

Q 3 2N2222A

X 1 LM393N

X 2 pot 100 (1 turn) Bourns #3386P-1-101LF

X 3 pot 1k (1 turn) Bourns #3386P-1-102LF

X 10 Surge Arrestor CG75L

X 11 Surge Arrestor CG75L

X 12 LM555CN

SW 0 Toggle SPST ALCOSWITCH SWK121F314

SW 1 Toggle DPDT Honeywell 2NT1-3

SW 2 Pushbutton mom Eaton #8943K28

SW 3 Pushbutton mom Eaton #8943K28

V 1 Power Supply Acopian B200GT10

V 2 Power Supply Acopian 10WL300

V 3 Power Supply Acopian B70GT30

SSR 1 Solid State Relay Teledyne #S60DC40

Case Parts

Circuit board

Case OKW #M5930035-AL

Push button guard Grayhill #10C1015-1

BNC Bulkead Recepticle Amphenol #112424

BNC Bulkead Recepticle Amphenol #112424

AC inlet recpticle Shurter #6100.3200

Power cord Volex # 17602 10 B1

Firing Line Recepticle Canon #CA3102E16S-4SB

Firing Line Plug Canon #CA3106E16S-4PB

Recepticle Cap Canon #ICA121003-4
14

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15

Appendix D. Instrument Panels



 

This appendix appears in its original form, without editorial change.
16

Front Panel Graphics
17

Cutouts for Front and Rear Panels
18

Cutouts for Top and Bottom Panels (identical)
19

Appendix E. Instrument Case Interior

 

This appendix appears in its original form, without editorial change.
20
21

Appendix F. Completed Unit

 

This appendix appears in its original form, without editorial change.
22
23

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