Alpha PAL 8942 PIV Heatsink

Add Your Comments

Very good PIV performance — Joe

SUMMARY: A very good choice for PIV cooling.

Alpha PAL 8942

A while ago we took a look at the Alpha PAL 8045 Socket A version. It’s not a stretch (actually, it was) for Alpha to come up with a PIV version; all the elements are there (spring loaded bolts, shroud, etc) and, aside from different sizing, it looks a marginally easier to manufacture. The base

Base

is simpler – no step for a socket cam. The base finish is very good but not exceptional – there are very fine polishing marks on it; lapping might improve performance a tad but I think not worth the effort (the marks are on the base are exaggerated by the flash angle).

The fins are typical Alpha:

Fins

Lots of them and hexagonal shaped. All told – typical Alpha quality.

Readers have been asking for a range of fan speeds when I test heatsinks, and I’m in the process of setting up testing for this. In the interim, I tested the Alpha with the following fans:

  • Delta AFB0812SH, spec: 47 cfm @ 4000rpm, 40 dBA
  • Delta FFB0812SHE, spec: 68 cfm @ 4800rpm, 48.5 dBA
  • YS Tech FD1280329B-2F, spec: 56 cfm @ 5400rpm
  • Vantec SF8025L (Stealth), spec: 27 cfm @ 2050rpm, 21 dBA

I measured noise using a Radio Shack sound meter placed 8″ from the fan’s intake and found the following:

Fan
dBA
RPM
Watts
Delta FFB0812SHE
67
4800
10.4
YS Tech FD1280329B-2F
71
5500
7.6
Delta AFB0812SH
60
4000
6.1
Vantec SF8025L
<50
2070
1.2

Manufacturers meter sound at 3 feet from the fan, so the dBAs I measured do not correspond to the manufacturers ratings. However, the relative rankings are roughly similar.

THE TEST

The Alpha PAL 8942 was first tested on the CPU Die Simulator which gives results that are unaffected by motherboard influences. I then tested it on a Lucky Star with a PIV 1500, which is modified to read CPU case temps directly, as an example of what users might see on their systems.

TEST RESULTS – CPU Simulator

Heatsink
Die Temp
Ambient Temp
Delta
C/W
Alpha PAL 8942/YS Tech 5500rpm
40.8 C
19.1 C
21.7 C
0.29
Alpha PAL 8942/Delta 4000rpm
42.5 C
19.1 C
23.4 C
0.32

TEST RESULTS – Motherboard
CPU/Motherboard

CPU Case

Ambient Temp

Delta

C/W

CPU MBM Temp

Lucky Star, PIV 1500, Delta 4800rpm

29.6 C

19.5 C

10.1

0.17

25 C

Lucky Star, PIV 1500, YS Tech 5500rpm

30.0 C

19.7 C

10.3

0.18

25 C

Lucky Star, PIV 1500, Delta 4000rpm

30.4 C

19.1 C

11.3

0.20

26 C

Lucky Star, PIV 1500, Vantec Stealth 2070rpm

35.7 C

20.7 C

15.0

0.26

30 C

Delta = CPU temp – Ambient Temp
C/W = Delta / CPU Watts

Interpreting C/W: For every watt (CPUw) that the CPU
consumes, the HSF will limit the CPU’s temperature rise to (C/W x CPUw)
plus the temperature at the HSF’s fan inlet. For example, at an ambient temp of 25 C, a C/W of 0.25 with a CPU radiating 50 watts means that CPU temp will increase 50 x 0.25 = 12.5 C over ambient temp, or 37.5 C. The lower the C/W, the better.

Die Simulator results place the Alpha PAL 8942, with the Delta 4800rpm, in the top rank of heatsinks tested (Heatsink Ranking).

Graphing the results shows the tradeoff between rpm – hence noise – and C/W – cooling performance:

C/W vs rpm

The difference between aggressive cooling/high noise and “reasonable” cooling and noise is about 4C over 100 watts. Very low noise will cost you about 9C in cooling over 100 watts. For a CPU radiating half that, the difference starts to fade very quickly (note: 38 dBA is the generally accepted noise standard for PCs).

The C/Ws shown here are at high load for at least 30 minutes – the number of times most users even come close to this loading is minimal.

The upshot is that for the AVERAGE user who is not pushing the CPU and spends most of the time for surfing and email, a quiet fan, such as the Vantec Stealth, can do the job OK. Each user must make a choice, balancing cooling needs vs noise tolerance. The graph above gives an indication of what these choices might yield.

CONCLUSIONS

Alpha’s PAL 8942 is a fine choice for PIV cooling. Depending on how aggressive your cooling requirements are, noise can range from the sublime to the ridiculous.


Email Joe