TM 5-811-7
(d) Find the voltage drop through the stub anodes given that the rectifier output is 80 volts, the
anode current (I) is 1.02 amperes, and the resistance (R) is 9.54 ohms:
E = IR
E = 1.02 A x 9.54 ohms
E = 9.73 V.
(e) Find the total voltage drop in the stub anode circuit.
ET = 0.033 + 9.73
ET = 9.76 V.
(f) Since the stub anode voltage is below the 45 volts calculated for the main tank anode circuit, the
necessary current adjustment can be made through a variable resistor in the stub anode circuit.
(17) Choose a stub anode circuit variable resistor.
(a) The resistor should be able to carry the maximum anode circuit current and have enough
resistance to reduce the anode current by one-half when full rectifier voltage is applied to the anode circuit.
(b) Stub anode circuit data are: rectifier output = 80 volts, anode current = 1.02 amperes, and anode
resistance = 9.54 ohms.
(c) The variable resistor rating is found by
R = E/I,
where E = 80 volts and I = 1.02/2 or 0.51 ampere. Thus,
R=80/0.51
R = 156.9 ohms
Resistor's ohmic value = 156.9-9.54
= 147.4 ohms.
To find the resistor's wattage rating --
P = I2R
(eq D-11)
P = (1.02)2 x 147.4
P = 153.4 W.
The commercially available resistor that nearest meets the above requirements is a 175-watt, 200-ohm,
1-ampere size.
(18) Find the riser anodes' resistance. To get the maximum desired current in the riser (3.62 amperes),
the resistance limit is calculated as follows:
R = E/1,
where E = 43.45 volts and I = 3.62 amperes. Thus,
R = 43.5 V/3.62 A
R = 12.0 ohms
(19) Design the riser anode.
(a) Type FW (1-c-inch by 9-inch) string-type anodes cannot be used in the riser because the
maximum anode current discharge of 0.025 ampere per anode would be exceeded. The number of type FW
anodes required would be 145, placed continuously throughout the riser. This number is too high. The best
choice of anode for a flexible riser string is type G-2 (2-inch by 9-inch) high-silicon cast-iron anode.
D-21
Previous Page
