Page 45
Com-Tech Power Amplifiers
Reference Manual
7 AC Power Draw and
Thermal Dissipation
“““““
Soft-Start”
inrush current limiting, protects the house
circuit breaker when several amps are turned on simul-
taneously.
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 pro-
duced under various conditions. The calculations pre-
sented 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 estimated
to be 65%.
• In 8/4 ohm mode, typical quiescent power draw is 20
watts for the Com-Tech 210, 30 watts for the Com-Tech
410, 55 watts for the Com-Tech 810 and 70 watts for the
Com-Tech 1610.
• In 70 volt mode, typical quiescent power draw is
30 watts for the Com-Tech 210, 35 watts for the
Com-Tech 410, and 90 watts for the Com-Tech 810 and
1610.
• When running at full speed, typical power draw for the
internal fan is 11 watts for the Com-Tech 210, 410 and
810, and 17 watts for the Com-Tech 1610 (the fan is an
option for the Com-Tech 210).
• Quiescent thermal dissipation is related .
• The estimated duty cycles take into account the typical
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%.
• 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)
=
Total output power with all
channels driven (watts)
x Duty
Cycle
Amplifier Efficiency (.65)
+ Quiescent Power
Draw (watts)
The value used for quiescent power draw includes both
the amplifier’s quiescent power draw for the selected
output mode and the power drawn by the fan if one is
installed (these values are listed in the previous col-
umn). The following equation converts power draw in
watts to current draw in amperes:
Current Draw
(amperes)
=
AC Mains Power
Draw (watts)
x
AC Mains
Voltage
Power
Factor (.83)
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 calculate
thermal dissipation:
Total output power with all
channels driven (watts)
Thermal
Dissipation
(btu/hr)
=
+
Quiescent Power
Draw (watts)
x
.35
Duty
Cycle
x
Amplifier Efficiency (.65)
(
)
x 3.415
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 con-
ditions, the following equation may also be helpful:
Total measured output power
from all channels (watts)
Thermal
Dissipation
(btu/hr)
=
+
Quiescent Power
Draw (watts)
.35
x
Amplifier Efficiency (.65)
(
)
x 3.415
8 Ohm Dual / 16 Ohm Bridge-Mono / 4 Ohm Parallel-Mono
L O A D
50%
40%
30%
20%
10%
200
165
135
100
65
305
265
225
185
145
265
215
170
125
80
95
85
70
55
40
210
175
145
110
75
340
300
260
220
180
2.4
2.0
1.6
1.2
0.8
3.1
2.6
2.0
1.5
0.9
2.5
2.1
1.7
1.3
0.9
Duty
Cycle
AC Mains
Power
Draw
(Watts)
btu/hr
Current Draw (Amps)
1.1
0.9
0.7
0.5
0.3
1.4
1.2
0.9
0.7
0.4
1.1
1.0
0.8
0.6
0.4
4 Ohm Dual / 8 Ohm Bridge-Mono / 2 Ohm Parallel-Mono
70 V
Com-Tech 210
80
70
60
50
40
kcal/hr
380
325
270
215
160
85
75
65
55
45
100-120 V 220-240 V
Thermal Dissipation
btu/hr
Current Draw (Amps)
kcal/hr
100-120 V 220-240 V
Thermal Dissipation
btu/hr
Current Draw (Amps)
kcal/hr
100-120 V 220-240 V
Thermal Dissipation
AC Mains
Power
Draw
(Watts)
AC Mains
Power
Draw
(Watts)
Fig. 7.1 Com-Tech 210 Power Draw, Current Draw and Thermal Dissipation at Various Duty Cycles
