PC PSU repurposing

[Bob Engelhardt]

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]

On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt
<BobEngelhardt@comcast.net> 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

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]

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.

 

[Look165]

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 Êcrit le 21/01/2019 à 20:06 :

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]

On Mon, 21 Jan 2019 11:36:57 -0500, Bob Engelhardt
<BobEngelhardt@comcast.net> 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

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.

 

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]

On Mon, 21 Jan 2019, 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

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]

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

 

[none]

In article <q24sf901sib@news4.newsguy.com>,
Bob Engelhardt <BobEngelhardt@comcast.net> 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

I solved this by having a 50 mA power on LED running from the 5 V line.
You don't want a PSA without indication anyway.

Groetjes Albert
--
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

 

[Look165]

Normally, a good PSU is capable of running correctly without load.

albert a Êcrit le 15/05/2019 à 15:05 :

In article <q24sf901sib@news4.newsguy.com>,
Bob Engelhardt <BobEngelhardt@comcast.net> 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
I solved this by having a 50 mA power on LED running from the 5 V line.
You don't want a PSA without indication anyway.

Groetjes Albert

 

[default]

On 15 May 2019 13:05:20 GMT, albert@cherry.(none) (albert) wrote:

In article <q24sf901sib@news4.newsguy.com>,
Bob Engelhardt <BobEngelhardt@comcast.net> 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

I solved this by having a 50 mA power on LED running from the 5 V line.
You don't want a PSA without indication anyway.

Groetjes Albert

I suspect this idea that PC supplies need a minimum load began because
some did in the early days, but these days? No.

I looked at a schematic of one and the 5 volt supply was the only
regulated supply. The others derived line regulation because the 5V
set the standard, but the others had no load regulation at all - the
voltage was strictly a matter of the turns ratio of those transformer
windings.

There's always the chance that you may run into one of the old power
supplies, but this idea that they all need some minimum load is simply
not true.