The POW GAL 27 is a capacitive discharge firing device with an integral galvanometer. A firing circuit may be tested at any time by pressing the BLACK galvanometer button. A reading of approximately one-half full scale indicates a satisfactory circuit. The large RED safety button, when pressed, prepares the unit for firing and releases the dumping resistor. It does NOT, however, apply the firing voltage to the firing wire. When the RED button is released, the firing circuit is disconnected and the dumping resistor is placed across the firing capacitors thereby discharging them.
The YELLOW charging/firing switch has a neutral or off position. Pulling the switch backwards will charge the 10,000 microfarad (uFd) capacitors to 36 volts. Normal time for full
charge is 15 seconds. Pushing the YELLOW switch forward connects the charged capacitors to the spring loaded output terminals. Remember, the galvanometer button can be pressed even when the firing capacitors are fully charged.
TO OPERATE:
The POW GAL 27 firing circuit is powered by four 9 volt Alkaline batteries. The galvanometer circuit is powered by a single one and one-half volt Alkaline "AA" battery. Under normal use both battery supplies will last over one year. The firing batteries (four 9 volt Alkaline) should be replaced when it takes longer than 30 seconds for the meter to reach full scale. To replace batteries, place unit face down on a soft surface. Remove four screws and lift off dark gray bottom cover. Carefully lift out the assembly of four 9 volt batteries and unsnap the two contacts. Unwrap and save the tape. The instructions included with the unit show how to reapply the tape. Build a new assembly with fresh batteries and retape. Snap on the connectors and place the batteries back in the case. Replace the cover making sure the wires are not pinched in between. Replace four bottom screws (don't overtighten).
 POW GAL 27 How many caps will the Pow Gal 27 fire? There is no straightforward answer because it is a direct function of the resistance of the firing wire/line and cap. The best rule of thumb is to use what is referred to as the 2 volt/1 ohm rule. This 1 means if the cap resistance is 1 ohm and the firing voltage is 2 volts an all-fire ondition is met. Assume a firing voltage of 26 volts. If 2 volts is needed across the cap, then the maximum voltage that can be lost across the firing wire is 24 volts. 24 divided by 2 is 12, therefore, the maximum firing line resistance should' be 12 ohms. If another cap is placed in SERIES (the proper way to fire multiple caps) the required firing voltage is 4 volts and the maximum loss across the firing line would be 22 volts. 22 divided by 2 is 11 or a maximum line resistance of 11 ohms.
Battery Assembly
Place 2 9-volt A lkaline batteries side by side as shown. Wrap 2 layers of 3/4" electrical tape around the batteries as shown. Note the + and - terminals. Stretch the tape slightly while wrapping. Make 2 sets of batteries.
Approximate
9/08 |
The normal resistance of standard household power cord is approximately 8 ohms per 1,000 feet. If 1,000 feet of this type of wire were used, the maximum number of caps that could be fired is 5. Field telephone wire normally has a resistance of 50 ohms per 1,000 feet. If this type of wire is used it would take over 100 volts to meet an all-fire condition. The Pow Gal 27 will not meet this requirement. In summary, determine the resistance of your firing line with a quality ohmmeter and mark the resistance on the reel.