Ac Power Draw & Thermal Dissipation; Macro-Tech 600 Power Draw, Current Draw And Thermal Dissipation At Various Duty Cycles - Crown Macro-Tech MA-1200 Reference Manual

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 the Macro-Tech 600 , 1200 and 2400 amplifiers and
the amount of heat produced under various conditions.
The calculations presented here are intended to pro-
vide a realistic and reliable depiction of the amplifiers.
The following assumptions or approximations were
made:
• The amplifier's available channels are loaded and full
power is being delivered.
• The amplifier efficiency at standard 1-kHz power is
estimated to be 65%.
• Quiescent power draw is 90 watts (an almost negli-
gible amount for full-power calculations).
• Quiescent thermal dissipation equals 105 btu/hr at
90 watts.
• 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 mid-
range 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, short duration paging is 1%.
Page 36
Fig. 7.1 Macro-Tech 600 Power Draw, Current Draw and
Thermal Dissipation at Various Duty Cycles
Macro-Tech 600/1200/2400 Power Amplifiers
Here are the equations used to calculate the data pre-
sented in Figures 7.1 through 7.3:
Total output power with all
channels driven (watts)
AC Mains Power
=
Draw (watts)
Amplifier Efficiency (.65)
The quiescent power draw of 90 watts is a maximum
value and includes power drawn by the fan. The follow-
ing 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 calculate
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)
x Duty
Cycle
+ Quiescent Power
Draw (watts)
AC Mains Power
Draw (watts)
AC Mains Power
x
Voltage Factor (.83)
)
x Duty
x .35
Quiescent Power
Cycle
+
Draw (watts)
)
.35
x
Quiescent Power
x 3.415
+
Draw (watts)
Reference Manual
x 3.415