Computing stuff tied to the physical world

Desktop power supply

In Hardware on Jun 25, 2011 at 00:01

Apart from a variable lab suppy (mine does 0..15V @ 0..3A), I’ve often wanted a simpler supply with just a few fixed voltages and say 500 mA. For experimentation, a weak supply which collapses under too much load is in fact better, because it can help avoid damage (which is almost always thermal and due to large currents).

Today, I decided to put something together, using parts which have been lying around here for some time.

It starts with an encapsulated switching AC/DC converter. I used a Traco 04115, i.e. 15V @ 4W. That addresses the AC mains side of things and limits the power involved in the circuit. Then I added 4 adjustable switching power supplies, which I got off eBay last year:

Dsc 2594

They are all running in parallel, using 15V as input. You’re looking at the bottom side of the box, BTW – the bottom plate of this particular box has nice little rubber feet.

The hardest part was deciding how to bring the power out of the box. I didn’t want large jacks – this thing is a dekstop power supply! But leaving wires with various valotages coming out and dangling all over the desk is also not such a good idea.

The solution I chose, was to bring out everything together via a 40 cm piece of 6-core cable:

Dsc 2595

The cable is squeezed behind one of the enclosure’s inner posts for strain relief (the AC mains cable has a knot in it for the same reason).

At the other end sits this thing – ready to take lots of jumper wires:

Dsc 2596

I still need to figure out how to attach labels to it. This is the pinout (with the cable pointing up):

Screen Shot 2011 06 23 at 18.34.21

No idea how yet, but it would be best if this were placed as label on top of the experimenter’s board in the middle, hiding the solder joints and clearly indicating which pin is what.

As it turns out, this power supply is considerably more powerful than I expected. The 15 V AC/DC converter will in fact go up to twice its rated power, i.e. over 500 mA, before the short-circuit protection sets in.

Due to the nature of switching regulators, the other voltages provide even more current: I was able to pull well over 1A continuously from the 3.3V supply. Although at those levels, the voltage did drop to 3.1 V.

Efficiency was not a primary goal, since this desktop supply is relatively low-power anyway, but the entire setup draws 0.7 W unloaded, and about 10 W when pulling 15V @ 500 mA out of it. I don’t expect to be loading this power supply down much, let alone getting into heat problems, even though the box is completely closed.

Oh, and in case you hadn’t noticed – another baby step in dealing with AC mains…

  1. That’s rather neat, I should build me one of those. I’ve got a nice laptop PSU which doesn’t have a laptop anymore, I think it’s either 16 or 19v, so that’s a good smooth starting point.

    Do you have a link for those variable regulator boards? Although maybe I’d want something with tighter current control, laptop PSU can do some serious spot welding!

  2. Second the link to those switching regulators. Or close-up photos of them ;-)

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