PSU shuts down

OK, so I self resolved the other topic, but I'm not getting anywhere with this one and I'm a bit stumped. If I have the heated bed running and shut it off through the Pronterface console, its shutting down the entire PSU. 450W PSU with 2 seperate 12V 20A rails. Should be more than enough to handle both a hot end and a heated bed. 9/10 times shutting the bed to 0 will kill the whole box. It always comes back on when I turn off the switch and turn it back on. I dont have anything set up in the RAMPS or PSU to kill through firmware.

any thoughts?

Thanks!

JW

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Josh

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//Prusa / RAMPS_1.4 & ATMega_2560 / Slic3r > Pronterface > Marlin / Luck
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... maybe you need a constant minimum load on the 12V to prevent shutting down?

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Viktor
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A little more testing this morning. I dont need to send the off command to the heated bed for the PSU to shutoff. The second the thermistor says the bed is at temp and starts dialing back power, the whole PSU craps out. So if I set bed temp to 60, it will run until bed temp returns 60 and then shut off. If I set it to 110, it will run the whole way up to 110, but still shut off when it reaches temp. Its as if a breaker is tripping in the PSU, although I dont reset anything inbetween. Simply shut off power switch and flip it back on.

I dont know why I shold need a load on the 12V. Load has been 0 for a few weeks now and it runs up to temp without problem. Its only when the current falls off completely the whole thing flops.

Off to work. More research tonite.

JW

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Josh

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
//Prusa / RAMPS_1.4 & ATMega_2560 / Slic3r > Pronterface > Marlin / Luck
//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Let me guess, atx psu? I had that same problem though more intermittently, it helped to heavily load the 5V and 12V lines, and put plenty of capacitors near the mosfets for the heaters. Basically, when the load of the PSU goes from a good hundred watts to almost zero, you get power spikes on the 12v line, and the psu shuts down to prevent frying what it thinks is a delicate computer. I never really solved the problem, and it always got worse with time with cheap atx psus. I ended up buying a 30A 12V psu from ebay, but you could try the capacitors + load first.

Different ATX PSUs have different 5V-load requirements, some need no load at all. The ATX specification demands 30% of the 12V wattage on the 5V line, which is quite a lot. Here are a few experiences: [forums.reprap.org]

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