Reuse Your Old Stuff, or ‘Nothing Goes To Waste’

Make that old AT Power Supply a useful addition to your ATX case. – Antonios S. Andreatos

Sure, you’ve got a modern PC now and that old AT case hides somewhere in the garage. But you need extra power in your new ATX case, and you don’t want to buy a new one. So what can you do? It’s time to exploit your old stuff! Tools you’ll need include: soldering iron, drill, screwdrivers, wire cutter, file.

If there is not enough space in your case, then you must:

• Go for a new case (e.g. full tower) with a bigger Power Supply (PS), or
• Replace the existing PS with a bigger one. Keep the old PS on your workbench for experiments (±12V, ±5V, +3.3V is not bad). See Tables 1 & 2 for connector polarity.

But if there is enough room in your case, you can add an extra PS. If you still have that old AT case, you can extract the PS. Here’s a few tips on how to reuse it.

Take the old (AT or ATX) PS, which we’ll call auxiliary PS (AU PS from now on), & locate a good spot for it in your case. Take measures, drill four 2mm holes and many 3mm-wide holes for the fan (if there aren’t such holes already). Then screw the PS & connect the ground to the ground of the case PS.

Connect the old PS to the case PS externally, through a male-to-female power cord. AT PS’s also have a black power cord ending up in the case power switch (usually a pushbutton).

You can still use it as an ON/OFF switch or, you can put a rocker switch shown below:

Make a proper hole for on an unused FDD or CD-ROM drive bay cover (using the drill & file) & fix it there. Polarity is shown below:

If the AU PS is ATX, it doesn’t have such a cord nor any switch. But there is an easy way to switch it on without connecting a good motherboard (M/B) to it.

ATX PS’s have a wire (no.14) on the M/B power connector called POWER ON, colored green (see Table 2). If you connect this to the next wire (no. 13 or 15, GND, colored black), the PS will start. So, take another simple switch, affix it on the empty bay cover & connect it to the POWER ON & GND.

Now you have a lot of extra power plus many “molex” connectors to feed extra fans. Since the two PS’s are not synchronized, connect the critical drives & CPU cooler to the case PS & all auxiliary stuff (fans) to the AU PS. Start the AU PS first.

If the PS is out of order, you can still take advantage of it: Open it and you will find:

1) A 3″ wide fan, which – most probably – still works. You can use this fan for extra cooling in your PC, as described below. You’ll also need a male molex connector. Connect only two poles, GND & +12V (yellow).

2) Lots of cables with female 4-pole molex connectors for powering HDDs, CD-ROM drives etc. Take a male molex connector, solder there the cables & make an extension power cord for many drives & fans (see photo 4). In this photo, the male molex connector is the black one (taken from an HDD), but usually you can get white ones such as the one connected to the fan pictured above.

3) Electronics engineers & hobbyists will also find in the old PS many usable parts such as voltage regulators, rectifiers, big & small caps, heat sinks, switches, small screws w/ nuts, etc.

You can put extra fans at the front & back side of the case & below the hard discs for better cooling.

Many cases have a fan at the lower front blowing air into the case. In order to blow the hot air out of the case, we can add an extra fan at the back side. If there is room, you can also put an extra fan over the CD-ROM drives, since the hot air tends to go up.

Another place for putting a fan is below the HDDs. For detailed How-Tos and additional ideas, look in the Overclockers.com index under HARD DRIVES and CASE COOLING.

If you have two empty drive bays, you can use a big 3″ fan (perhaps from another PS). If there is only one empty bay, you must use 1-2 small fans such as the ones used to cool 486’s or Pentiums.

1) If you need extreme cooling, you can increase fan rpms by feeding them from the -5V PS output instead of GND. In this way, you’ll apply 17V to the fans instead of 12. Test the fans before though, using your workbench PS. (I have seen this somewhere but I can’t remember where; perhaps at www.overclockers.com.)

2) How to figure out fan air flow direction : Take a PS fan & look for two little arrows stamped in the side. The horizontal arrow shows the fan rotation direction, while the vertical shows the air flow direction. By changing fan orientation though, you can achieve the opposite direction. (Don’t change the polarity, it won’t work!)

3) You may wish to feed a fan from the appropriate mobo pins, in order to monitor its rpm’s through the BIOS or other special programs. In this case, the polarity is as follows:

4) Check the fan power by looking at the label for amperes. Voltage is almost always 12V, current though varies; 0.08 A is low, 0.1 A is medium. Above 0.1 A is OK for critical applications such as CPU cooling. Rpm’s are also important. You can monitor them using programs such as Hardware Monitor, Motherboard Monitor & MBProbe.

ACKNOWLEDGEMENTS The author wishes to thank Andriana Pantelopoulou, Gerasimos Mykoniatis & Jim Demos for their help.

Antonios S. Andreatos – Greece