ATX Benchtop Break-Out Board

Electronics
1

I ordered new Cooler Master 460W ATX PSU for use on the Mendel90 3D printer we are building in the class. The instructions call for splicing all the lines together and adding a load resistor to the 5V rail. I’m not sure if I really need a load resistor on the modern PSU’s to make them work stable. Also I would like some tricks and tips for bundling the wires or someone that would be willing to help me and the class by modding the PSU.

2

I was looking at Lance’s (@knotbob) progress on the lockers last night and he had a little PCB he bought from Sparkfun a while back for this. It’s my understanding you still have to short two lines to keep it from being in “sleep mode”, but the product I think he was using is this: SparkFun Benchtop Power Board Kit - KIT-12867 - SparkFun Electronics. The schematics on that site should make it clear, and I will take a look later.

3

I was actually going to get one of those but my question is they have 5Amp fuses, I wonder if I can get maybe a 15 or 20amp fuse because the heated build platform requires 15amps. I was also thinking I could clip the rest of the wires I don’t need as well, but I’m not sure if both 12V rails go through the main ATX 24 pin connector.

4

You might do well to bus all the 12VDC lines together on whatever board/device you use to go from ATX to your printer, then go from there with bigger AWG wire. Less voltage drop that way.

Back to the original question, my understanding is that most ATX supplies do need at least an amp or two on the 5VDC lines to maintain regulation. At 5V, you need a 2.5 ohm resistor to get 2 amps. It’ll need to be a 10 W resistor or more. Check the power resistor section at Tanners if we don’t have any in the electronics room.

2 Likes
5

Oh - last time I checked, Tanners also has short ( 12 in ) extension cables for ATX. If you get one of those and cut off one end, you have all the motherboard wires ready to hook up in a way that will let you swap supplies later if needed.

Connectors are a little extra trouble, but they can be very helpful.

6

Thanks for the suggestions.

The instructions Nophead provides recommends:
1 THS15 Aluminium clad resistor 10R
1 THS15 Aluminium clad resistor 4R7