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POWER & CONTROL UNIT
This is the part of Active-Cool's system that really separates it from other
peltier coolers. It combines two functions into one PCI-based module: It's
a PSU to provide power to the TEC, and it contains a controller chip which
regulates the power supplied to both the TEC and the heatsink fan. It can
also control a case fan, through its onboard Molex connector. It uses a separate
AC power connection as a power source for the Peltier unit, to avoid adding
additional load to the PC's PSU.
Unlike a typical TEC, which runs at full power all the time, the AC4G monitors
and controls the temperature of the cold plate. The danger with a conventional
TEC is that while the CPU is at idle or under low load the temperature of
the cold plate can drop to the point where condensation occurs on it, a potentially
dangerous and damaging situation. The AC4G controls the voltage being fed
to the Peltier unit, ensuring that the cold plate temp never drops below 28°C,
removing the risk of condensation.
The second major function of the control unit is to adjust the speed of the
heatsink fan. The unit starts the CPU fan at 6 volts, stepping it up to 8
or 12 volts if the coldplate plate temperature rises above a critical value.
The functions of the unit are well described by Active-Cool:
The Power and Control Unit is a PC card containing an AC/DC switching
mode power supply and a microprocessor controller. The power supply, which
receives AC input directly from the electric network (through a plug in
the bracket of the card), provides the power to the thermoelectric unit.
The power supply is controlled by the microprocessor.
The microprocessor controller receives input from the ambient temperature
sensor and the CPU temperature sensor. The microprocessor samples the temperature
more than 40 times per second, and adjusts the cooling power of the thermoelectric
unit and the speed of the CPU and case fans accordingly.
To reduce computer noise, the microprocessor normally runs the CPU and
case fans at 6 volts (½ power, drastic reduction in noise). When the temperature
of the ambient air rises, the microprocessor operates the PC case fans at
higher power until temperature is reduced. If the CPU temperature rises,
the microprocessor initiates a carefully orchestrated reaction. First, power
is increased to the (virtually noiseless) thermoelectric unit. If this is
insufficient, then additional power can be supplied both to the thermoelectric
unit and to the CPU fan. When the thermal load is reduced, the fans can
return to quiet operation. During short bursts of processor load, the fans
are often not needed.
Active-Cool advertises that the AC4G can be installed in any PC "in
90 seconds or less". While I made no attempt to make a race out of it,
they are probably not far off. The heatsink mounts easily, you slide the power
unit into a vacant PCI slot, connect the wiring harness, plug in the AC cord
to the back, and you're done.
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