PC PSU repurposing

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
I am going to repurpose a PC PSU & I have a question about minimum  
loading.  Many/most PSU's require minimum loads on their outputs for the  
outputs to be powered,  The PSU that I have powers its outputs without  
loads.  Is it a bad idea to run it that way?  Thanks, Bob

Re: PC PSU repurposing
On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt

Quoted text here. Click to load it

Check the voltages. They can have weird cross-regulation.


--  

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
We've slightly trimmed the long signature. Click to see the full one.
Re: PC PSU repurposing
On 21-1-2019 17:36, Bob Engelhardt wrote:
Quoted text here. Click to load it
when I use one I put  100 ohms on each output voltage.

That seems to work.

Else connect an old harddisk to provide a bit of load.

Re: PC PSU repurposing
Today, PSU can operate without load ; they are regulated.even with no  
load (flyback).
At minimum, they loose power in the leakage elements and the flyback  
circuitry.


Quoted text here. Click to load it



Quoted text here. Click to load it

Quoted text here. Click to load it


Re: PC PSU repurposing
On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt

Quoted text here. Click to load it

I've been using one as a bench supply for some years with no ill
effects and no minimum load.  The one I have seems to only regulate
the +5 line and the 12v lines are "unregulated" (set only by the turns
ratio on the step-down transformer)

The +5 regulates the primary side of the transformer via a high
frequency square wave and this provides line regulation to the 12 V
but no load regulation.

Re: PC PSU repurposing
Load the +5 one amp. That means a 5 o hm resistor, and it will be dissipating 5 watts of course.  

You could try to get by with less load but that may vary from PS to PS.  

Re: PC PSU repurposing
On Mon, 21 Jan 2019, Bob Engelhardt wrote:

Quoted text here. Click to load it
I have some surplus general purpose switching supplies that came with load  
resistors on the output.  Kind of odd, but one way of making sure it  
works.  I guess the rest was cheap enough that adding power resistors, and  
wasting power, was still efficient.

Of course, PC power supplies have an intended use, an expectation of a  
certain amount of load, so it makes sense that they wouldn't bother with  
loading resistors.

   Michael


Re: PC PSU repurposing
Thanks for the replies.

I'm using the PSU's 12v as a source for this buck-boost converter:
https://tinyurl.com/ycbytxdv
and I was worried about instabilities. I guess that I should have said that.

Google hits on the question said that the 12v output needed a 1A minimum  
load and I didn't like the idea of a 12W resistor.

I'm going to put a 1/2A load on the 5v, cause it can't hurt and deal  
with a 12v load if I have to.

Thanks again,
Bob

Site Timeline