How Connect Electronic DC Load to ATX Negative Voltage ?

• How Connect Electronic DC Load to ATX Negative Voltage ?
  Posted by danz on 29 May, 2021 13:36
• Hi Everyone,
  
  I Have Electronic DC Load and i want to use it for simple Power Supply Load Testing. For 3.3v , 5v , 12v , and 5VSB i don't have any problem connecting to my DC LOAD. But for -12V (Negative 12V) i don't have idea how i can connect to my DC LOAD.
  
  Maybe someone can give direction how i can connect my DC LOAD or maybe i need some other device. I try to search some information in other PC Review web like Tomshardware , Anandtech , etc they can test all PSU Voltage 12V , 5V , 3.3V , 5VSB and -12V using several DC LOAD Tester without any problem but i can not find any information how they connect DC LOAD wire to their ATX Power Supply -12V.
  
  Thanks all.
• #1 Reply
  Posted by Vincenzo on 29 May, 2021 14:26
• the first method you mentioned (-12 to active load -ive and ATX GND to active load +ive) is the right way (notice the reversed black and red wires in the other testers photo). The reason for that is that it is an "Active load" which is basically a MOSFET(s) which are not bilateral like resistors.
  
  Notice in their photo, too, that the current of the ATX -12V is about 150 mA which is the least of the other voltages. The -12V ATX output has a very limited current capability, so when you connected constant current, how much that current was. You probably put too much current.
• #2 Reply
  Posted by danz on 29 May, 2021 14:35
• @vincenzo Thanks for your reply.
  
  Yes i also notice they reversed cable color in other web DC LOAD.
  
  And yes -12V in ATX Power Supply usually only max 0.3A.
  
  I try to set load only 0.05A / 0.1A to -12V and enabled my Constant Current Load my PSU still Power Off suddenly.
  
  I will try checking with other ATX PSU again.
• #3 Reply
  Posted by gamalot on 29 May, 2021 15:41
• Have you tested whether the negative input terminal of your electronic load is connected to the mains ground, if so, you will not be able to test the negative voltage out of your ATX power supply unless you use an isolation transformer.
• #4 Reply
  Posted by Vincenzo on 29 May, 2021 15:51
• Quote from: gamalot on 29 May, 2021 15:41

  Have you tested whether the negative input terminal of your electronic load is connected to the mains ground, if so, you will not be able to test the negative voltage out of your ATX power supply unless you use an isolation transformer.
  

  
  That was exactly what i was thinking about, check negative to ground in both load and power supply
• #5 Reply
  Posted by danz on 30 May, 2021 00:46
• @gamalot @vincenzo Thanks all for help and reply.
  
  I have found the problem come from my Breakout board -12V connector. Now All working normally.
  
  Problem Solved