j.c.f.'s Athlon Overclock Phase
II
Another thing that changed was the source of current to
run the TECs with, I wanted a bit more than 7V across the TECs and even given 300W power
supplies it's still asking a lot to expect it to drive two TECs and an 800MHz Athlon as
well:
Of course you can't just use an ATX supply as is, you
have to strap the supply up so it will turn on at all and you also have to load up the 5V
rail a bit otherwise it won't stay on.
| ATX 20 pin power connector |
|
Pin# |
Pin# |
|
| 3.3V |
11 |
1* |
3.3V |
| -12V |
12 |
2 |
3.3V |
| COM |
13*(Gnd) |
3 |
COM |
| PS-ON |
14* |
4 |
+5V |
| COM |
15 |
5 |
COM |
| COM |
16 |
6 |
+5V |
| COM |
17 |
7 |
COM |
| -5V |
18 |
8 |
PW-OK |
| +5V |
19 |
9 |
5VSB |
| +5V |
20 |
10 |
+12V |
I use an old power supply connector off
a dead ATX mother board (heat guns are marvelous devices) with pins 13 and 14 connected to
get it to turn on a 10 ohm resistor across pins 5 and 6 for the load. It's all wrapped up
in black electrical tape so the photo doesn't show too much:
I can hear the cognoscenti going "only 10
ohms?" As others have noted, you need at least a 2 amp load on the 5V rail
before you get 12V out of the 12V rail, with my 0.5A load I only get about 9.3V, and
therein lies the beauty of the whole arrangement. You'll remember that I
noted earlier on that my aim is to keep the cold plate just above ambient room temperature
as I'm not about to fully insulate the thing to prevent condensation from forming -- which
isn't to say that I don't have a can of expanding latex insulation laying around the place
incase I get carried away one day, it's just not today. Nor is that to say that the cold
plate doesn't have insulation stuck to it, it does so the TECs aren't pumping ambient air
heat around for no good purpose, it's the CPU that hasn't got insulation, to do that
involves major structural changes to my rig.
Traditionally you either need a variable supply and or
a variable fan speed control to be able to choose your cold plate temperature, the
variable supply being pretty durn expensive. Here, by adding or removing resistors across
the 5V rail you can have your variable supply for the cost of a regular PC power supply.
For instance, if I stick another 8.2 ohm load in there the voltage jumps up to 10.2V, fans
speed up, TECs start working harder and the cold plate temperature starts going down.
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