Review: ActiveCool AC4G Thermoelectric cooler

Cooling
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TESTING

The proof is in the test results. The AC4G was tested in two different configurations; one with the stock 70mm fan, and again with the SPCR reference standard 80mm L1A.

The testbed is as follows:

  • XP2100+ T-bred (1733Mhz) 62.1 watts max
  • Gigabyte GA-7VM400M motherboard with onboard VGA
  • 512 megs of PC2100 RAM
  • Whatever HDD and PSU happened to be lying around. For all subjective noise comparisons the HDD was allowed to power down before the analysis.

Notes on Testing Conditions

- Ambient temp was within 0.5° of 22° for the testing period.
- Temps were recorded from the internal diode with Motherboard Monitor 5.
- CPUBurn was used to achieve load temps, idle temps were read while at the Window's desktop.
- A standard multimeter was used to measure the voltage being fed to the CPU fan, the case fan Molex, and to the Peltier unit itself.
- A Kill-A-Watt meter was connected to the Power unit to report on its AC draw.

Stock Fan (Full voltage)
CPU Temp
°C/W
Power Unit AC Draw
CPU Fan voltage
Case Fan voltage
Peltier voltage
Idle
33°C
-
9 watts
6.0 v
6.3 v
6.5 v
Load
38°C
0.26
39 watts
6.0 v
6.3 v
14 v
Stock Fan (@ 5v max*)
Idle
35°C
-
26 watts
6.0v (2.5v@fan)
6.3 v
12.2 v
Load
47°C
0.40
64 watts
12.0v (5.0v@fan)
12.2 v
19.2 v

*For the reduced voltage testing, a Zalman fanmate was placed between the CPU fan and the power unit and adjusted to the level that would provide a maximum of 5 volts to the fan. The number in parentheses reflects the voltage measured after the Fanmate. The CPU fan must be connected to the power unit, if it isn't the unit goes into failure mode and refuses to allow the machine to boot.

The results at full speed are impressive. The 0.26°C/W is top tier for conventional CPU coolers, and the fact that the CPU fan is still at 6 volts shows that the AC4G isn't even breathing hard yet. The problem is the noise: It is simply out of the question for SPCR. Even at idle the noise is way beyond what any of us would consider quiet.

The noise has two sources; besides the obvious CPU fan there is also a tiny fan inside the power/control unit. At 6 volts, the CPU fan is significantly louder than a Panaflo L1A at 12v. Its noise is raucous and whiny, with a noticeable clicking component. But it's really the fan inside the power unit that produces the most annoyance; full of high pitch whine, rattles, and wind turbulence. It was so bad that I felt compelled to disassemble the power unit just to see what was making such a racket.

With the cover off we can see the guts of the Power & Control unit. Essentially it's a neatly packaged PSU. The offending fan is quickly identified: A a 35mm centrifugal blower which exhausts out through the PCI slot. Its purpose is to keep the PSU components cool by drawing air in under the plastic cover and across the aluminum heatsinks attached to the MOSFETs. For the remainder of the testing the fan was disabled (by jamming a plastic cable tie into its blades) and the plastic cover was left off the power unit to allow the internals to cool themselves via convection. No instability or overheating problems were seen, even under the most strenuous of testing.

NOTE: Leaving the cover off during operation is NOT a recommended mod, especially for those with errant fingers. The heatsinks attached to the MOSFETs are most definitely live, very much full of electricity that can ZAP you.

At 2.5 volts, the CPU fan spins smoothly, and actually has less clicking that it did without the Fanmate. Perhaps the Fanmate's circuitry softens the signal wave from the PWM? At load, the CPU fan is running at a Fanmate restricted 5V, and has nearly the same noise characteristics as it does at 6V stock. Still significantly louder than an Panaflo L1A is at 12 volts. The 0.40°C/W at load is quite good, but the noise level is still unacceptable.

Of particular note is the AC load that the unit is drawing from the outlet. At 64 watts it is nearly as much as the rest of the entire system draws. (80-85 watts) It is important to remember that in a normal case environment that a large portion of that extra 64 watts of heat would be being dumped inside the case, and would result in higher interior ambient temps. Adding 64 watts is like adding a second CPU, or a very high-end graphics card.

With a Panaflo 80L1A Swap

For this series of tests the SPCR reference Panaflo L1A fan was mounted in place of the stock 70mm. The same method of using the Fanmate to reduce its voltage was employed. Allowing the power unit to have full control over the L1A produced the best results, achieving a balance between noise and cooling.

Unfortunately the power unit's use of PWM to control the fan speed soured the mix by introducing a very noticeable clicking to the Panaflo. But reducing the noise to even this level is a dangerous tradeoff. The temperature of the heatsink itself reached over 100°, well beyond the 80-85° generally cited as the max safe operating temperature for a peltier element. Continuous use at that load would almost definitely shorten its life.

L1A reference Fan (Full voltage)
CPU Temp
°C/W
Power Unit AC Draw
CPU Fan voltage
Case Fan voltage
Peltier voltage
Idle
34°C
-
20 watts
6.0 v
6.3 v
10.1 v
Load
43°C
0.34
64 watts
8.7 v
9.0 v
19.2 v
L1A reference Fan (@ 5v max*)
Idle
50°C
-
64 watts
12.0v (5.0v@fan)
12.2 v
19.2 v
Load
68°C
0.74
64 watts
12.0v (5.0v@fan)
12.2 v
19.2 v

CONCLUSIONS

The Active-Cool AC4G is interesting product, and a clear leap forward in the conventional thinking about peltier cooling... but its noise performance is not yet up to SPCR standards. The AC4G is hampered primarily by its heatsink and fan. A higher performing HSF combination would surely reduce both temps and noise. A quieter way to cool the Power & Control unit is also necessary before PC Silencers can fully adapt this product.

An improved Active-Cool package could become successful as Intel's super-hot >100W Prescott-core P4 processors come on-stream. For Prescott-based PCs, especially in small packages, it may be one of the few practical cooling options.

Personally, I think an interesting experiment would be to attach the huge HeatLane Zen heatsink in place of the AC4G's stock heatsink and fan. The fact that the aluminum fin and heatpipe structure can be seperated from the copper base means the peltier element can be easily inserted into place. The increase in temperature differential would improve both convection cooling capacity and the conductivity of its heatpipes. (Editor's Note: Sounds like an itch Russ has to scratch. We'll have to find him a Zen HS.)

Pro:
  • Easy installation
  • Interesting adaptation of peltier technology
Con:
  • Expensive. You can achieve similar (or better) performance from a conventional HSF, at 1/3rd the price
  • Noisy stock fans.

Much thanks to Active-Cool for the review sample.

* * * * *

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