Heated bed and power supply issue

Hey all, here's the story... please help, I'm stuck, thanks!

I am using a Cooler Master 500 watt PSU, 12V1 rated at 16amps, and 12V2 rated at 16amps.

If the USB is connected, and the PSU is on, and then I try to turn on the heated bed with pronterface, the PSU shuts off.

If the USB is connected and I turn the heated bed on with pronterface, THEN turn on the PSU... the heated bed turns on fine. If I then shut off the heated bed, the PSU shuts off.

Is my PSU too weak to handle it? Why does it work if I turn on the power supply AFTER activating the heated bed? Why does the PSU shut off when I STOP the heated bed in that case?

I thought it was the 5V load issue, so I hooked up a DVD rom drive, sata power connection... no change.

I'd appreciate any help, thanks!

Maybe you need a load on the 12V before the PSU will work. Try connecting a case fan to one of the molex connectors and see if that works.

here take a look at this, you probably need to load some of the lines, and there are some other things you might need to do as well [uzzors2k.4hv.org]

Thanks for the help. I had a case fan hooked up, but same issue. I'll take a look at that link... I'm thinking about just powering the bed from a spare xbox power brick I have laying around, and leaving the rest to the psu. Our maybe use the power brick only?

The power brick is 12v 16.5 amps. .. That should work for everything, and be more stable than the atx psu right?

16.5 amps should be enough for most cases. Personally, I'm just using a broken Antec Smartpower PSU (bad 5vsb) and have no problems at all running my j-head+PCB heatbed. I don't even have to load the unused rails. If I had an x-box power supply, I'd probably use that since it would be smaller and look better (and I've heard they're cheap). I doubt the x-box PSU is any more "stable" than a computer PSU though. My PSU is a "modular" kind where you can connect accessory cables as needed, so I just run my reprap off the auxiliary 12v power connecter that's needed by some motherboards. I'm using RAMPS, so I connect 2 yellow + 2 black wires to the "11A" circuit, and 1 yellow+1 black to the "5A" circuit.

if worst comes to worst and it just dont work... haha... just get a 12v switching psu on amazon for 30 bucks shipped [www.amazon.com] i have this same model, works great. its like a good woman it just puts out without a fuss, or maybe a hooker not sure, anyways youve got options.

Thanks all! I'd just like to report that the xbox power brick works GREAT. It also looks very tidy and neat.

I'm using an Xbox power supply also. I have the 203watt version. I use it for everything and it works great. I have some info on my websites as well if anyone needs some help modifying their Xbox psu. I love it I can tuck my power supply and my electronics all under my print bed including a cooling system. I like the portability of the Xbox psu. The Xbox psu has great power protection and cooling system. Built really well.

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