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7 AC Power Draw and
Thermal Dissipation
This section provides detailed information about the
amount of power and current drawn from the AC
mains by Com-Tech amplifiers and the amount of heat
produced under various conditions. The calculations
presented here are intended to provide a realistic and
reliable depiction of the amplifiers. The following as-
sumptions or approximations were made:
• The amplifier's available channels are loaded, and full
power is being delivered.
• Amplifier efficiency at standard 1 kHz power is esti-
mated to be 65%.
• In 8/4 ohm mode, typical quiescent power draw is 20
watts for the Com-Tech 200 , 30 watts for the Com-Tech
400 , 55 watts for the Com-Tech 800 and 70 watts for
the Com-Tech 1600 .
• In 70 volt mode, typical quiescent power draw is
30 watts for the Com-Tech 200 , 35 watts for the
Com-Tech 400 , and 90 watts for the Com-Tech 800
and 1600 .
• When running at full speed, typical power draw for the
internal fan is 11 watts for the Com-Tech 200 , 400 and
800 , and 17 watts for the Com-Tech 1600 (the fan is
an option for the Com-Tech 200 ).
• Quiescent thermal dissipation is related .
• The estimated duty cycles take into account the typi-
cal crest factor for each type of source material.
• Duty cycle of pink noise is 50%.
• Duty cycle of highly compressed rock 'n' roll midrange
is 40%.
• Duty cycle of rock 'n' roll is 30%.
• Duty cycle of background music is 20%.
8 Ohm Dual / 16 Ohm Bridge-Mono / 4 Ohm Parallel-Mono
AC Mains
Current Draw (Amps)
Power
Duty
Draw
Cycle
100-120 V 220-240 V
(Watts)
50%
200
2.4
40%
165
2.0
30%
135
1.6
20%
100
1.2
10%
65
0.8
Fig. 7.1 Com-Tech 200 Power Draw, Current Draw and Thermal Dissipation at Various Duty Cycles
Page 42
4 Ohm Dual / 8 Ohm Bridge-Mono / 2 Ohm Parallel-Mono
AC Mains
Thermal Dissipation
Power
Draw
btu/hr
kcal/hr
(Watts)
1.1
305
80
265
0.9
265
70
215
0.7
225
60
170
0.5
185
50
125
0.3
145
40
80
Com-Tech 200/400/800/1600 Power Amplifiers
• Duty cycle of continuous speech is 10%.
• Duty cycle of infrequent paging is 1%.
Here are the equations used to calculate the data pre-
sented in Figures 7.1 through 7.4:
AC Mains Power
=
Draw (watts)
The value used for quiescent power draw includes
both the amplifier's quiescent power draw for the se-
lected output mode and the power drawn by the fan if
one is installed (these values are listed in the previous
column). The following equation converts power draw
in watts to current draw in amperes:
Current Draw
(amperes)
The power factor of 0.83 is needed to compensate for
the difference in phase between the AC mains voltage
and current. The following equation is used to calcu-
late thermal dissipation:
(
Total output power with all
Thermal
channels driven (watts)
Dissipation
=
(btu/hr)
Amplifier Efficiency (.65)
The constant 0.35 is inefficiency (1.00 – 0.65) and the
factor 3.415 converts watts to btu/hr. Thermal dissipa-
tion in btu is divided by the constant 3.968 to get kcal.
If you plan to measure output power under real-world
conditions, the following equation may also be helpful:
(
Total measured output power
Thermal
from all channels (watts)
Dissipation
=
(btu/hr)
Amplifier Efficiency (.65)
Com-Tech 200
L O A D
Current Draw (Amps)
Thermal Dissipation
100-120 V 220-240 V
btu/hr
kcal/hr
3.1
1.4
380
95
2.6
1.2
325
85
2.0
0.9
270
70
1.5
0.7
215
55
0.9
0.4
160
40
Total output power with all
x Duty
channels driven (watts)
Cycle
+ Quiescent Power
Amplifier Efficiency (.65)
AC Mains Power
Draw (watts)
=
AC Mains
Power
x
Voltage
Factor (.83)
Duty
.35
x
x
Quiescent Power
Cycle
+
Draw (watts)
.35
x
Quiescent Power
+
Draw (watts)
70 V
AC Mains
Current Draw (Amps)
Thermal Dissipation
Power
Draw
100-120 V 220-240 V
btu/hr
(Watts)
210
2.5
1.1
340
175
2.1
1.0
300
145
1.7
0.8
260
110
1.3
0.6
220
75
0.9
0.4
180
Draw (watts)
)
x 3.415
)
x 3.415
kcal/hr
85
75
65
55
45
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