PSU shuts off when load connected to ATX wires

Thread Starter

339

Joined Jun 1, 2021
13
This circuit shuts off almost immediately.
1622563056560.png
This circuit runs perfectly, even with no load on the Molex.
1622563121607.png

Is my PSU dead? If not, how do I fix it?

After the first circuit shut off, I could reset it by turning the POWER switch off and on.
 

Thread Starter

339

Joined Jun 1, 2021
13
Welcome to AAC.

"Any load"? What have you tried? How much current does the load draw?
I tried a 200mA case fan, a 450mA case fan, a 1.5A case fan, a 300mA CPU fan, a 300mA GPU fan, and a 150mA chipset fan for both circuits.
 

MisterBill2

Joined Jan 23, 2018
8,736
All of those supplies need a load of several amps on the FIVE VOLT supply to operate. Without that load they shut down. It is cheaper to make them that way, and why would a computer supply need to run unloaded? Never.
So not enough load on the 5 volt line is the problem. Use 2 or three ohms.
 

Thread Starter

339

Joined Jun 1, 2021
13
All of those supplies need a load of several amps on the FIVE VOLT supply to operate. Without that load they shut down. It is cheaper to make them that way, and why would a computer supply need to run unloaded? Never.
So not enough load on the 5 volt line is the problem. Use 2 or three ohms.
If nothing is attached to the ATX pins, it still runs. It can power circuits via Molex.
 

sagor

Joined Mar 10, 2019
439
If it can "power circuits via Molex", then run your load from the Molex...
I don't think you are giving the full story here. What "load" are we talking about. Also, did you try the 5V load on the +5V rail to see if this fixes your problem. Without doing that, we are all just spinning our wheels and not going anywhere. While the Molex may be able to supply a small bit of power, the PSU monitors the current loads based on regulation of the +5V rail. The +12V is based on the +5V regulator feedback. Under a heavier load on +12V, the PSU may sense that the +5V has no load and since it cannot monitor the 5V load, shuts down... Also, some PSU have multiple +12V rails, and you sometimes cannot parallel those together. Each +12V rail supplies different connectors, like one for the AUX for CPU power and the other for the Molex connectors. Again, no details from you...
So, listen to what people here say, put a reasonable load on the +5V rail first, and only then experiment with the +12V "load", which is still a mystery to the rest of us. How do we even know if this "load" is not too big for the PSU.
 

Thread Starter

339

Joined Jun 1, 2021
13
If it can "power circuits via Molex", then run your load from the Molex...
I don't think you are giving the full story here. What "load" are we talking about. Also, did you try the 5V load on the +5V rail to see if this fixes your problem. Without doing that, we are all just spinning our wheels and not going anywhere. While the Molex may be able to supply a small bit of power, the PSU monitors the current loads based on regulation of the +5V rail. The +12V is based on the +5V regulator feedback. Under a heavier load on +12V, the PSU may sense that the +5V has no load and since it cannot monitor the 5V load, shuts down... Also, some PSU have multiple +12V rails, and you sometimes cannot parallel those together. Each +12V rail supplies different connectors, like one for the AUX for CPU power and the other for the Molex connectors. Again, no details from you...
So, listen to what people here say, put a reasonable load on the +5V rail first, and only then experiment with the +12V "load", which is still a mystery to the rest of us. How do we even know if this "load" is not too big for the PSU.
I tried connecting a 400mA fan to the 5v rail, no luck.
 
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