Mendel Prusa + RAMPS 1.2 - first build - mini ATX gives only 8.54v

Hi all,

I'm a noob.

I've built my RepRap, however I'm currently having a problem.

My micro ATX (http://qs.kapouta.com/7) was providing 8.54v when connecting yellow/black instead of the expected 12v.

I was able to get it to get 11.84v by playing with the pins (see attachment). With this I can get either all axis or extruder + hotend/thermistor working separately.

However once I turn the hotend on, the axis motors stop working well missing steps and become noisy.

I tried to increase the power on the Polulu however that didn't do it. I read somewhere that I could (should?) join several yellows / black wires to provide more amps, however since I'm using the "Reserved N/C" I cannot do that.


My questions:

Any ideas on what I'm doing wrong? Or is the 8.5v a sign that the microATX is broken and I just need to get a new one?

Thanks in advance,
Feiteira

Most likely the reason you only got 8.4V is because you need to have a dummy load on the 5V rail to get the correct voltage on the 12V rail.

The reason you got more voltage on the NC pin is that it is -5V on some PSUs, but only low current.

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[www.hydraraptor.blogspot.com]

PC PSU's are a crap shoot, some require significant (often over 1A) on the 5V line to get anywhere near 12 V on the 12V line,