PC power supplies

[Phil in Melbourne]

Some newer PC power supplies now have up to 4 separate 12V rails. The total
power is stated at up to 60 Amps at 12V total for an average 650W or 750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply, in
that it needs a load to start properly, and needs a pretty good load on the
5V supply to regulate well.

 

[James]

"Phil in Melbourne" <reply@tonewsgroup> wrote in message
news:47d7a1a7$0$26343$afc38c87@news.optusnet.com.au...

Some newer PC power supplies now have up to 4 separate 12V rails. The
total power is stated at up to 60 Amps at 12V total for an average 650W or
750W PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply,
in that it needs a load to start properly, and needs a pretty good load on
the 5V supply to regulate well.

If they are truely 4 seperate rails it's probably not the brightest idea to
just join them all together. 60A at 12V does seem like an awful lot and I
assume you are not going to be drawing large currents like that
continuously. Is it possible to use a 12V battery and charging arrangment?
Does the 12V have to prescisely regulated?

Simple load sharing using resistors might work to an extent but it would get
a little warm

James

 

[ian field]

"Phil in Melbourne" <reply@tonewsgroup> wrote in message
news:47d7a1a7$0$26343$afc38c87@news.optusnet.com.au...

Some newer PC power supplies now have up to 4 separate 12V rails. The
total power is stated at up to 60 Amps at 12V total for an average 650W or
750W PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply,
in that it needs a load to start properly, and needs a pretty good load on
the 5V supply to regulate well.

About a year ago Elektor magazine in the UK published a project to convert a
PC PSU for low voltage halogen lighting, but it involved re-winding the
transformer and some changes to the PCB.

 

[qmod]

Phil in Melbourne wrote:

Some newer PC power supplies now have up to 4 separate 12V rails. The total
power is stated at up to 60 Amps at 12V total for an average 650W or 750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply, in
that it needs a load to start properly, and needs a pretty good load on the
5V supply to regulate well.

I suggest you read the label again, I think you will find the 12v output
limited to a much lower level current. I dont know the output current of
the 650 0r 750W, but I just looked at the figures for a 400 watt supply
12v output is limited to 17 Amps, it is the 5v and 3.3volt outputs that
have the higher current output 28 and 20 amps respectively.

Laurie

 

[David L. Jones]

On Mar 12, 8:25 pm, "Phil in Melbourne" <reply@tonewsgroup> wrote:

Some newer PC power supplies now have up to 4 separate 12V rails. The total
power is stated at up to 60 Amps at 12V total for an average 650W or 750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply, in
that it needs a load to start properly, and needs a pretty good load on the
5V supply to regulate well.

Much simpler (and not a lot more expensive) to simply buy a purpose
designed unit:
http://cgi.ebay.com.au/1000W-12V-83A-Switching-Power-Supply-CCTV-DVR-Radio_W0QQitemZ360022982326QQihZ023QQcategoryZ20589QQcmdZViewItemQQ_trksidZp1742.m153.l1262
You get more grunt than you need, better air flow, and proper big
beefy terminals.

Dave.

 

[Mr.T]

"qmod" <qmod@internode.off.net> wrote in message
news:13tgoool5rjii67@corp.supernews.com...

Phil in Melbourne wrote:
Some newer PC power supplies now have up to 4 separate 12V rails. The
total
power is stated at up to 60 Amps at 12V total for an average 650W or
750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all
of
the separate 12V channels together?


I suggest you read the label again, I think you will find the 12v output
limited to a much lower level current. I dont know the output current of
the 650 0r 750W, but I just looked at the figures for a 400 watt supply
12v output is limited to 17 Amps, it is the 5v and 3.3volt outputs that
have the higher current output 28 and 20 amps respectively.

I could be wrong, but I believe four 15A rails is actually less per rail
than one 17A rail. Whether they can really manage 15A on all 4 rails at the
same time is another matter since that would be above the rating of a 650W
supply, not including any other voltage rails!
*Maybe* with a 750W supply. However you can't simply connect them together,
as the OP wants, in any case.

MrT.

 

On 3ÔÂ12ČŐ, ĎÂÎç5Ęą25ˇÖ, "Phil in Melbourne" <reply@tonewsgroup> wrote:

Some newer PC power supplies now have up to 4 separate 12V rails. The total
power is stated at up to 60 Amps at 12V total for an average 650W or 750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply, in
that it needs a load to start properly, and needs a pretty good load on the
5V supply to regulate well.

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[w_tom]

On Mar 12, 4:25 am, "Phil in Melbourne" <reply@tonewsgroup> wrote:

Some newer PC power supplies now have up to 4 separate 12V rails. The total
power is stated at up to 60 Amps at 12V total for an average 650W or 750W
PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

First, if any one rail draws maximum power, then other rails may
have a significantly reduced maximum.

Second, the typically 700 watt supply (unless related by engineering
sources) may only output 40 amps combined even though any one 12 volt
output can do up to 15 amps.

Third, is all outputs are connected together, then only of the four
outputs take up all load until too much current is drawn. Then that
rail may enter current foldback limiting - meaning load must be
removed to reset that rail output. One way to avert this problem is
to 'pervert' that regulation. For example, put resistors in series
with each load so that too much current from one rail causes others to
put up the load. But then learn how hot those resistors (or bipolar
transistors) must become.

Fourth, only some power supplies require a load. Some people only
know using observation. They saw one supply not work without a load;
then assumed all do that. A classic example of 'observation without
underlying facts' resulting in a myth. Does that one supply need a
load? Defined by how it is designed. Supplies sold to engineers list
this in numerical specs. But PC supplies sold to consumers without
electrical knowledge tend to forget such information. For example,
the original PC supply required no load. But the PC-AT supply did
require a minimum load for selective voltages. Minimally sufficient
specs would list a minimum current for each voltage.

 

[MisterE]

"Phil in Melbourne" <reply@tonewsgroup> wrote in message
news:47d7a1a7$0$26343$afc38c87@news.optusnet.com.au...

Some newer PC power supplies now have up to 4 separate 12V rails. The
total power is stated at up to 60 Amps at 12V total for an average 650W or
750W PSU.

If I was to need a single 60Amp channel, would it be OK to connect all of
the separate 12V channels together?

Before you mention it, I understand the limitations of a PC power supply,
in that it needs a load to start properly, and needs a pretty good load on
the 5V supply to regulate well.

I think you may have it the wrong way around, are you use 60amp is 12V and
not the 5V. If you can actually draw 60amp at 12V the supply would have to
be at least 1200W once you add the 5V and 3.3V.