1 Topic by rcullan

  • rcullan
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Topic: ATX Power Supply Low Voltage

Hey all,
I bought a relatively cheap ATX power supply to replace the hacked laptop charger that came with my solidoodle 2, it is rated for 40+ amps on its single 12V rail so I bought this figuring it would be perfect. The 10A laptop charger gets REALLY warm when the printer is running.

But I have an issue, I am only getting about 11.8V coming out of the power supply and as a result my print bed is struggling to get to 90C, it takes almost an hour and will not get over 91C.

Any suggestions as to how I can improve the 12V voltage output? Has anyone seen a similar issue? I have seen a few people who have recommended adding a ~10W power resistor to the 5V rail. But I'm not an expert and fail to understand how modifying the 5V line can improve the volatge output on the 12V line. Currently I dont have anything hooked up to any of the 5V or 3.3V lines.

Thanks!

2 Reply by ronsii (edited by ronsii 2013-11-23 23:02:10)

  • ronsii
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  • Registered: 2012-10-28
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Re: ATX Power Supply Low Voltage

Some ATX power supplies will not give the rated output to the 12v side if there is not a certain amount of draw on the 5v side... so if you are not drawing anything on the 5 volt buss then you may not get full rated amps on the 12 volt buss.


The 10watt resistor is just to put a draw on the 5v side... so you if you want to draw 10 watts of power you need a 2.5 ohm resistor at 5 volts.

3 Reply by rcullan

  • rcullan
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Re: ATX Power Supply Low Voltage

ronsii,
Thanks so much. I actually found a two 5ohm 5W power resistors that I had lying around. I wired them up in parallel so now I have 2.5 ohm drawing off the 5V line. I got a boost from this in the 12V line of about 0.6V, so now at 12.4V my print bed is getting up to 94C. Still not where I want it but its alot closer now.

Thanks for your input!