4.2 BATTERIES 
Three nickel-cadmium batteries are provided: two 10-ampere-hour batteries (one spare) 
for minimum-weight tests and one 40-ampere-hour battery for use when two motor-generator sets 
are required in the model. The batteries are of sintered-plate construction which permits the 
high-current rates required. Each battery has 34 cells and an open-circuit terminal voltage 
of 44.2 volts when fully charged. The internal voltage drop reduces the terminal voltage to 
36 to 38 volts under load. Each battery is large enough so that no more than 50 percent of its 
capacity is consumed during a test run. However, as the batteries age, their capacity dimin- 
ishes and replacement is necessary when one-half capacity is reached. 
4.3 MOTOR-GENERATOR SETS 
The motor-generator sets were specially designed to incorporate 3 kilowatts into as 
compact and as light a piece of equipment as possible within the limits of good design stand- 
ards. The set is composed of a 36-volt, 150-ampere, 7600-rpm, d-c shunt motor driving an 
intermittently rated 3-kilowatt, 0-300-volt, separately excited d-c generator. The motor is 
capable of withstanding the 49 volts which is applied by the battery charger during charging 
operations. The generator output is continuously variable from zero to 300 volts and is con- 
trolled by the error regulator which supplies the generator field. The generator, which can 
deliver a current of 10 amperes, feeds through a reversing relay to a series motor for propulsion. 
The 3-kilowatt rating is based on the following duty cycle: 
kw for 2 minutes; noload, 10 minutes 
kw for 2 minutes; noload, 10 minutes 
kw for 2 minutes; noload, 10 minutes 
kw for 2 minutes; noload, 10 minutes 
kw for 2 minutes; noload, 10 minutes 
co ae ee 
& 0 Com 
Other duty cycles may be used provided the motor-generators are not allowed to overheat. 
A resistance temperature detector (RTD) unit is imbedded in the motor field and con- 
nected to a bridge circuit. A small meter shows the field temperature in degrees Centigrade 
divided by 100. 
If the meter approaches full scale, the motor-generator set should be allowed to cool 
off before proceeding with model tests. The maximum cooling rate will be obtained by. allow- 
ing the motor-generator to run without load. 
4.4 ERROR REGULATOR 
The error regulator is a feedback device which regulates motor-generator output by 
control of field current. As shown in the block diagram (Figure 9), the control signal and a 
portion of the generator output are compared in the magnetic modulator which has two isolated 
inputs. A regulated d-c internal reference is resistively mixed with the generator output. The 
signals applied to the modulator are mixed in the magnetic circuit and produce an output at 
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