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PC PSU repurposing

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elektroda.net NewsGroups Forum Index - Electronic for beginners - PC PSU repurposing

Bob Engelhardt
Guest

Mon Jan 21, 2019 5:45 pm   



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

John Larkin
Guest

Mon Jan 21, 2019 6:45 pm   



On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt
<BobEngelhardt_at_comcast.net> wrote:

Quote:
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


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


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Sjouke Burry
Guest

Mon Jan 21, 2019 8:45 pm   



On 21-1-2019 17:36, Bob Engelhardt wrote:
Quote:
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

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.

Look165
Guest

Mon Jan 21, 2019 10:45 pm   



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.

Sjouke Burry a écrit le 21/01/2019 à 20:06 :
Quote:
On 21-1-2019 17:36, Bob Engelhardt wrote:
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

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.


default
Guest

Tue Jan 22, 2019 1:45 am   



On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt
<BobEngelhardt_at_comcast.net> wrote:

Quote:
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


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.


Guest

Tue Jan 22, 2019 1:45 am   



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.

Michael Black
Guest

Tue Jan 22, 2019 10:45 pm   



On Mon, 21 Jan 2019, Bob Engelhardt wrote:

Quote:
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

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

Bob Engelhardt
Guest

Wed Jan 23, 2019 12:45 am   



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

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