Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On Wed, 19 Feb 2020 16:46:49 -0000, Commander Kinsey wrote:

Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

Sorry for the mention of sorry the crosspost, that was for the (rather dead) electronics groups :-)

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications.* I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use.* So I run each card off its own supply.* But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V.* If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Commander Kinsey wrote

Why do (cheap? expensive ones may be better)
PC ATX power supplies need current drawn from
the 5V line to make the 12V line work correctly?

Depends on what you mean by work correctly.

By definition, when whatever it is that decides
what mark space ratio is used with a switch
mode power supply, it has to measure the
voltage somewhere and since the spec on
the 5V rail is a lot tighter than on the 12V
rails, it makes sense to measure the 5V rail.

That means that unless the 5V rail has some
load on it, the regulation isnt great and so
you can get some odd effects on the 12V rail.

Its obvious possible to have a separate switch mode
power supply for each rail but even the more expensive
PC PSUs don't do it like that because the 5V and 3.3V
rails are normally well loaded in a PC,

I have a PC with 3 graphics cards running scientific applications.
I acquired three old graphics cards that take about 300W each,
and have loads of cheap (CIT) PSUs that are rated at 650W on
the 12V line, which is what those cards use. So I run each card
off its own supply. But the 12V line at no load, or even at 300W,
is only giving out 10 to 10.5V. If I attach a small dummy load of
an amp or so to the 5V line, the 12V line suddenly becomes 12V.

You'd be better off with dedicated 12V switch mode power
supplys. Surprisingly cheap now even at the higher powers.

Why are the two lines related in any way?

See above.

Sorry for the crosspost, I'm not sure which of these groups are active.

On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago. Can you go into more detail?

On Wed, 19 Feb 2020 17:02:33 -0000, Rod Speed wrote:

Commander Kinsey wrote

Why do (cheap? expensive ones may be better)
PC ATX power supplies need current drawn from
the 5V line to make the 12V line work correctly?

Depends on what you mean by work correctly.

If I don't load the 5V at all, the 12V becomes 10.5V. Connecting a car headlamp to the 5V rail (which draws about 1.75A) seems to make it behave.

By definition, when whatever it is that decides
what mark space ratio is used with a switch
mode power supply, it has to measure the
voltage somewhere and since the spec on
the 5V rail is a lot tighter than on the 12V
rails, it makes sense to measure the 5V rail.

That means that unless the 5V rail has some
load on it, the regulation isnt great and so
you can get some odd effects on the 12V rail.

Its obvious possible to have a separate switch mode
power supply for each rail but even the more expensive
PC PSUs don't do it like that because the 5V and 3.3V
rails are normally well loaded in a PC,

I don't understand. Surely the mark space ratio has to be completely different for the 12V and 5V rails because any computer at any given moment could be drawing more from one than the other, then differently several seconds from now.

I have a PC with 3 graphics cards running scientific applications.
I acquired three old graphics cards that take about 300W each,
and have loads of cheap (CIT) PSUs that are rated at 650W on
the 12V line, which is what those cards use. So I run each card
off its own supply. But the 12V line at no load, or even at 300W,
is only giving out 10 to 10.5V. If I attach a small dummy load of
an amp or so to the 5V line, the 12V line suddenly becomes 12V.

You'd be better off with dedicated 12V switch mode power
supplys. Surprisingly cheap now even at the higher powers.

Link me to an example, because I looked at them before, and at the high powers I need (300W per card), it's massively cheaper to buy even the top of the range PC supplies from Corsair etc., I assume because they're made in larger quantities.

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications.* I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use.* So I run each card off its own supply.* But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V.* If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

Can't be arsed. Have you heard of Google?

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications.* I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use.* So I run each card off its own supply.* But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V.* If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

You already know the answer, put a load on the 5 volt line and all will
be well.

On Wed, 19 Feb 2020 17:09:20 -0000, Andy Bennet wrote:

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

Can't be arsed. Have you heard of Google?

Yip, tried it, not the sort of thing that seems to have been discussed much. I found a discussion on stackexchange, but all anyone said was "The ATX standard requires the power supply to be within 10% of the correct voltage, at ANY loads". So clearly my cheap PSUs are not adhering to the spec, and assuming I'll take 5V from them aswell, but I want to know why this happens and why anyone would design a PSU in such a weird way. The mark space ratio to feed the 12V line and to feed the 5V line have to be seperate, to allow for varying loads on each as the computer runs. So how on earth could they be linked?

On Wed, 19 Feb 2020 17:09:30 -0000, newshound wrote:

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

You already know the answer, put a load on the 5 volt line and all will
be well.

I know the workaround, I want to know WHY this makes it work.

On 19/02/2020 17:13, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:09:20 -0000, Andy Bennet wrote:

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications.* I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use.* So I run each card off its own supply.* But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V.* If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

Can't be arsed. Have you heard of Google?

Yip, tried it, not the sort of thing that seems to have been discussed
much.** I found a discussion on stackexchange, but all anyone said was
"The ATX standard requires the power supply to be within 10% of the
correct voltage, at ANY loads".* So clearly my cheap PSUs are not
adhering to the spec, and assuming I'll take 5V from them aswell, but I
want to know why this happens and why anyone would design a PSU in such
a weird way.* The mark space ratio to feed the 12V line and to feed the
5V line have to be seperate, to allow for varying loads on each as the
computer runs.* So how on earth could they be linked?

FFS are you thick as arseholes?
I explained it to you. The clue is in the el cheapo bit. Minimum parts
= minimum cost.
****

"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

On Wed, 19 Feb 2020 17:16:10 -0000, Andy Bennet wrote:

On 19/02/2020 17:13, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:09:20 -0000, Andy Bennet wrote:

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

Can't be arsed. Have you heard of Google?

Yip, tried it, not the sort of thing that seems to have been discussed
much. I found a discussion on stackexchange, but all anyone said was
"The ATX standard requires the power supply to be within 10% of the
correct voltage, at ANY loads". So clearly my cheap PSUs are not
adhering to the spec, and assuming I'll take 5V from them aswell, but I
want to know why this happens and why anyone would design a PSU in such
a weird way. The mark space ratio to feed the 12V line and to feed the
5V line have to be seperate, to allow for varying loads on each as the
computer runs. So how on earth could they be linked?

FFS are you thick as arseholes?
I explained it to you. The clue is in the el cheapo bit. Minimum parts
= minimum cost.
****

I'm well aware it must be cost saving, but I want to know WHY it's possible to do that. The 12V and 5V rails have to be seperately controlled, or they wouldn't work at all. A typical computer is taking different currents from each all the time. They can't be linked.

On Wed, 19 Feb 2020 16:46:49 -0000, "Commander Kinsey"
wrote:

Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.

Why are the two lines related in any way?


I suppose "that is just how they work" would be too simple an answer
but it has to do with switch mode power supply design and you already
know the work around. Put a big wire wound resistor on the 5v and get
on with your life. I doubt you even need an amp. 25 ohms should do it.
(200ma)

On Wed, 19 Feb 2020 17:26:31 -0000, Rod Speed wrote:



"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

That's not how I thought SMPSs worked. Surely since the current draw on 5V can vary from 1 amp to 35 amps, and the 12V from 1 amp to 56 amps, there have to be completely seperate ratios set up? Adjusting just the 5V could have the 12V going anywhere.

On Wed, 19 Feb 2020 17:31:07 -0000, wrote:

On Wed, 19 Feb 2020 16:46:49 -0000, "Commander Kinsey"
wrote:

Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

I suppose "that is just how they work" would be too simple an answer
but it has to do with switch mode power supply design and you already
know the work around. Put a big wire wound resistor on the 5v and get
on with your life. I doubt you even need an amp. 25 ohms should do it.
(200ma)

I shoved a car headlamp on them, full beam from one PSU and dipped beam from the other. Drawing about 1.75A from each.

I might try smaller bulbs to reduce fire risk :-)

"Commander Kinsey" wrote in message
newsp.0f8u8x2fwdg98l@glass...
On Wed, 19 Feb 2020 17:02:33 -0000, Rod Speed
wrote:

Commander Kinsey wrote

Why do (cheap? expensive ones may be better)
PC ATX power supplies need current drawn from
the 5V line to make the 12V line work correctly?

Depends on what you mean by work correctly.

If I don't load the 5V at all, the 12V becomes 10.5V. Connecting a car
headlamp to the 5V rail (which draws about 1.75A) seems to make it behave.

By definition, when whatever it is that decides
what mark space ratio is used with a switch
mode power supply, it has to measure the
voltage somewhere and since the spec on
the 5V rail is a lot tighter than on the 12V
rails, it makes sense to measure the 5V rail.

That means that unless the 5V rail has some
load on it, the regulation isnt great and so
you can get some odd effects on the 12V rail.

Its obvious possible to have a separate switch mode
power supply for each rail but even the more expensive
PC PSUs don't do it like that because the 5V and 3.3V
rails are normally well loaded in a PC,

I don't understand.

That's obvious.

Surely the mark space ratio has to be completely different for the 12V and
5V rails

Nope. The high frequency chopped DC goes
into the high frequency transformer and the 5V
and 12V rails are just different output windings
on that. Look at a PC PSU circuit diagram.
http://www.pavouk.org/hw/en_atxps.html

because any computer at any given moment could be drawing more from one
than the other, then differently several seconds from now.

The current on the 5V rail whose voltage is used to vary
the mark space ratio doesn't actually vary all that much.

I have a PC with 3 graphics cards running scientific applications.
I acquired three old graphics cards that take about 300W each,
and have loads of cheap (CIT) PSUs that are rated at 650W on
the 12V line, which is what those cards use. So I run each card
off its own supply. But the 12V line at no load, or even at 300W,
is only giving out 10 to 10.5V. If I attach a small dummy load of
an amp or so to the 5V line, the 12V line suddenly becomes 12V.

You'd be better off with dedicated 12V switch mode power
supplys. Surprisingly cheap now even at the higher powers.

Link me to an example,

https://www.ebay.co.uk/itm/Transform...DPmF 8NegnqEg

That's just the one at the top of the hit list.

because I looked at them before, and at the high powers I need (300W per
card), it's massively cheaper to buy even the top of the range PC supplies
from Corsair etc.,

Not true with that one.

I assume because they're made in larger quantities.

On Wed, 19 Feb 2020 16:46:49 -0000, Birdbrain Macaw (aka "Commander Kinsey",
"James Wilkinson", "Steven ******","Bruce Farquar", "Fred Johnson, etc.),
the pathological resident idiot and attention whore of all the uk ngs,
blathered again:

FLUSH the abnormal sociopathic attention whore's latest attention-baiting
sick bull**** unread again

--
about Birdbrain Macaw's (now "James Wilkinson" LOL)
trolling:
"He is a well known attention seeking troll and every reply you
make feeds him.
Starts many threads most of which die quick as on the UK groups anyone
with sense Kill filed him ages ago which is why he now cross posts to
the US groups for a new audience.
This thread was unusual in that it derived and continued without him
to a large extent and his silly questioning is an attempt to get
noticed again."
MID:

--
ItsJoanNotJoann addressing Birdbrain Macaw's (now "James Wilkinson" LOL):
"You're an annoying troll and I'm done with you and your
stupidity."
MID:

--
AndyW addressing Birdbrain:
"Troll or idiot?...
You have been presented with a viewpoint with information, reasoning,
historical cases, citations and references to back it up and wilfully
ignore all going back to your idea which has no supporting information."
MID:

--
Phil Lee adressing Birdbrain Macaw:
"You are too stupid to be wasting oxygen."
MID:

--
Phil Lee describing Birdbrain Macaw:
"I've never seen such misplaced pride in being a ****ing moronic motorist."
MID:

--
Tony944 addressing Birdbrain Macaw:
"I seen and heard many people but you are on top of list being first class
ass hole jerk. ...You fit under unconditional Idiot and should be put in
mental institution.
MID:

--
Pelican to Birdbrain Macaw:
"Ok. I'm persuaded . You are an idiot."
MID:

--
DerbyDad03 addressing Birdbrain Macaw (now "James Wilkinson" LOL):
"Frigging Idiot. Get the hell out of my thread."
MID:

--
Kerr Mudd-John about Birdbrain Macaw (now "James Wilkinson" LOL):
"It's like arguing with a demented frog."
MID:

--
Mr Pounder Esquire about Birdbrain Macaw (now "James Wilkinson" LOL):
"the **** poor delivery boy with no hot running water, 11 cats and
several parrots living in his hovel."
MID:

--
Rob Morley about Birdbrain:
"He's a perennial idiot"
MID: 20170519215057.56a1f1d4@Mars

--
JoeyDee to Birdbrain
"I apologize for thinking you were a jerk. You're just someone with an IQ
lower than your age, and I accept that as a reason for your comments."
MID: l-september.org

--
Sam Plusnet about Birdbrain (now "James Wilkinson Sword" LOL):
"He's just desperate to be noticed. Any attention will do, no matter how
negative it may be."
MID:

--
asking Birdbrain:
"What, were you dropped on your head as a child?"
MID:

--
Christie addressing endlessly driveling Birdbrain Macaw (now "James
Wilkinson" LOL):
"What are you resurrecting that old post of mine for? It's from last
month some time. You're like a dog who's just dug up an old bone they
hid in the garden until they were ready to have another go at it."
MID:

--
Mr Pounder's fitting description of Birdbrain Macaw:
"You are a well known fool, a tosser, a pillock, a stupid unemployable
sponging failure who will always live alone and will die alone. You will not
be missed."
MID:

--
Richard to pathetic ****** Hucker:
"You haven't bred?
Only useful thing you've done in your pathetic existence."
MID:

--
about Birdbrain (now "James Wilkinson" LOL):
""not the sharpest knife in the drawer"'s parents sure made a serious
mistake having him born alive -- A total waste of oxygen, food, space,
and bandwidth."
MID:

--
Mr Pounder exposing sociopathic Birdbrain:
"You will always be a lonely sociopath living in a ******** with no hot
running water with loads of stinking cats and a few parrots."
MID:

--
francis about Birdbrain (now "James Wilkinson" LOL):
"He seems to have a reputation as someone of limited intelligence"
MID:

--
Peter Moylan about Birdbrain (now "James Wilkinson" LOL):
"If people like JWS didn't exist, we would have to find some other way to
explain the concept of "invincible ignorance"."
MID:

--
Lewis about nym-shifting Birdbrain:
"Typical narcissist troll, thinks his **** is so grand he has the right to
try to force it on everyone."
MID:

On 19/02/20 17:08, Commander Kinsey wrote:

Link me to an example, because I looked at them before, and at the high
powers I need (300W per card), it's massively cheaper to buy even the
top of the range PC supplies from Corsair etc., I assume because they're
made in larger quantities.

https://tinyurl.com/w9ntn9h

and select what you need. Plenty more.

Another Dave
--
Change nospam to techie

On Wed, 19 Feb 2020 17:01:52 +0000, Andy Bennet, another brain dead,
troll-feeding, senile asshole, blathered again:


On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer.

It's senile assholes like you who keep supplying the attention-starved troll
with all the troll fodder that makes him thrive and grow, you abysmally
stupid twit!

On Wed, 19 Feb 2020 17:09:20 +0000, Andy Bennet, another brain dead,
troll-feeding, senile asshole, blathered again:


Can't be arsed. Have you heard of Google?

Have you heard the saying, "don't feed the troll", you abysmally stupid
senile twit?

On Wed, 19 Feb 2020 17:16:10 +0000, Andy Bennet, another brain dead,
troll-feeding, senile asshole, blathered again:


FFS are you thick as arseholes?
I explained it to you. The clue is in the el cheapo bit. Minimum parts
= minimum cost.
****

Oh, look! The troll-feeding senile asshole FINALLY catches on! LOL

On Wed, 19 Feb 2020 17:09:30 +0000, newshound, another brain damaged,
troll-feeding, senile idiot, blathered again:


You already know the answer, put a load on the 5 volt line and all will
be well.

You KNOW already what this sociopath is all about, senile idiot! Yet you
KEEP feeding him! tsk

On Wed, 19 Feb 2020 12:31:07 -0500, , the disgusting,
troll-feeding senile Yankietard, blathered again:


I suppose "that is just how they work"

Yep, gfretard, YOU were still missing among the troll's loyal senile fans!
LOL Guess WHY he comes here, time and again! tsk

On Thu, 20 Feb 2020 04:26:31 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the two clinically insane sociopathic trolls' endless troll****

--
Another typical retarded conversation between our two village idiots,
Birdbrain and Rodent Speed:

Birdbrain: "You beat me to it. Plain sex is boring."

Senile Rodent: "Then **** the cats. That wont be boring."

Birdbrain: "Sell me a de-clawing tool first."

Senile Rodent: "Wont help with the teeth."

Birdbrain: "They've never gone for me with their mouths."

Rodent Speed: "They will if you are stupid enough to try ****ing them."

Birdbrain: "No, they always use claws."

Rodent Speed: "They wont if you try ****ing them. Try it and see."

Message-ID:

On Thu, 20 Feb 2020 04:02:33 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH senile asshole's latest troll****

04:02??? And you've been up and trolling since 01:50 (your first post) this
night, yet AGAIN!!! LOL So it WILL be another long sleepless night of
idiotic trolling for you again, senile Rodent! LOL

--
Website (from 2007) dedicated to the 85-year-old trolling senile
cretin from Oz:
https://www.pcreview.co.uk/threads/r...d-faq.2973853/

"Commander Kinsey" wrote in message
newsp.0f8v3prrwdg98l@glass...
On Wed, 19 Feb 2020 17:16:10 -0000, Andy Bennet wrote:

On 19/02/2020 17:13, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:09:20 -0000, Andy Bennet wrote:

On 19/02/2020 17:04, Commander Kinsey wrote:
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet
wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications.
I
acquired three old graphics cards that take about 300W each, and
have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply.
But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V
line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback
controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time
ago.
Can you go into more detail?

Can't be arsed. Have you heard of Google?

Yip, tried it, not the sort of thing that seems to have been discussed
much. I found a discussion on stackexchange, but all anyone said was
"The ATX standard requires the power supply to be within 10% of the
correct voltage, at ANY loads". So clearly my cheap PSUs are not
adhering to the spec, and assuming I'll take 5V from them aswell, but I
want to know why this happens and why anyone would design a PSU in such
a weird way. The mark space ratio to feed the 12V line and to feed the
5V line have to be seperate, to allow for varying loads on each as the
computer runs. So how on earth could they be linked?

FFS are you thick as arseholes?
I explained it to you. The clue is in the el cheapo bit. Minimum parts
= minimum cost.
****

I'm well aware it must be cost saving, but I want to know WHY it's
possible to do that. The 12V and 5V rails have
to be seperately controlled, or they wouldn't work at all.

No they don't and they do in fact work fine
like that as long as the 5V rail is loaded.

A typical computer is taking different currents from each all the time.

In fact the current on the 5V rail doesn't change much over time.

They can't be linked.

They can be and are. Look at that circuit diagram.

On Wed, 19 Feb 2020 17:31:07 -0000, wrote:

On Wed, 19 Feb 2020 16:46:49 -0000, "Commander Kinsey"
wrote:

Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

I suppose "that is just how they work" would be too simple an answer
but it has to do with switch mode power supply design and you already
know the work around. Put a big wire wound resistor on the 5v and get
on with your life. I doubt you even need an amp. 25 ohms should do it.
(200ma)

It needs more. I stuck an 18 ohm resistor on it, the 12V line went from 10.46V to 10.91V.
With the bulb, I get 11.70V. I'll stick with the bulb (which is quite capable of taking that much heat since it's designed for 12V not 5V).

"Commander Kinsey" wrote in message
newsp.0f8wi6nqwdg98l@glass...
On Wed, 19 Feb 2020 17:26:31 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

That's not how I thought SMPSs worked.

Yep, that's your problem, a lack of understanding in that area.

Surely since the current draw on 5V can vary from 1 amp to 35 amps,

It doesn't in fact vary over time in a PC,

and the 12V from 1 amp to 56 amps,

It doesn't in fact vary over time that much in a PC,

there have to be completely seperate ratios set up?

There isnt, and that works fine, because the current
from the 5V rail doesn't vary all that much over time.

As you have discovered, if there is no load on
the 5V rail, the 12V rail is well out of spec.

Adjusting just the 5V could have the 12V going anywhere.

Not anywhere, just by the amount you measured.
And only down from 12V with no load on the 5V rail,

And since that never happens in a PC, it works fine.

"Rod Speed" wrote in message
...


"Commander Kinsey" wrote in message
newsp.0f8wi6nqwdg98l@glass...
On Wed, 19 Feb 2020 17:26:31 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V
line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

That's not how I thought SMPSs worked.

Yep, that's your problem, a lack of understanding in that area.

Surely since the current draw on 5V can vary from 1 amp to 35 amps,

It doesn't in fact vary over time in a PC,

and the 12V from 1 amp to 56 amps,

It doesn't in fact vary over time that much in a PC,

there have to be completely seperate ratios set up?

There isnt, and that works fine, because the current
from the 5V rail doesn't vary all that much over time.

As you have discovered, if there is no load on
the 5V rail, the 12V rail is well out of spec.

Adjusting just the 5V could have the 12V going anywhere.

Not anywhere, just by the amount you measured.
And only down from 12V with no load on the 5V rail,

And since that never happens in a PC, it works fine.

Your other problem is that you are assuming the the
mark space ratio varys with the current on the output
rails. It doesn't.

On Wed, 19 Feb 2020 17:39:22 -0000, Rod Speed wrote:



"Commander Kinsey" wrote in message
newsp.0f8u8x2fwdg98l@glass...
On Wed, 19 Feb 2020 17:02:33 -0000, Rod Speed
wrote:

Commander Kinsey wrote

Why do (cheap? expensive ones may be better)
PC ATX power supplies need current drawn from
the 5V line to make the 12V line work correctly?

Depends on what you mean by work correctly.

If I don't load the 5V at all, the 12V becomes 10.5V. Connecting a car
headlamp to the 5V rail (which draws about 1.75A) seems to make it behave.

By definition, when whatever it is that decides
what mark space ratio is used with a switch
mode power supply, it has to measure the
voltage somewhere and since the spec on
the 5V rail is a lot tighter than on the 12V
rails, it makes sense to measure the 5V rail.

That means that unless the 5V rail has some
load on it, the regulation isnt great and so
you can get some odd effects on the 12V rail.

Its obvious possible to have a separate switch mode
power supply for each rail but even the more expensive
PC PSUs don't do it like that because the 5V and 3.3V
rails are normally well loaded in a PC,

I don't understand.

That's obvious.

Surely the mark space ratio has to be completely different for the 12V and
5V rails

Nope. The high frequency chopped DC goes
into the high frequency transformer and the 5V
and 12V rails are just different output windings
on that. Look at a PC PSU circuit diagram.
http://www.pavouk.org/hw/en_atxps.html

because any computer at any given moment could be drawing more from one
than the other, then differently several seconds from now.

The current on the 5V rail whose voltage is used to vary
the mark space ratio doesn't actually vary all that much.

Incorrect, this PSU is happy with me taking 1.75A from 5V. It's rated at up to 35A on 5V. So clearly it will be ok anywhere from 1.75A to 35A on 5V. Explain how that is possible to vary what I take from 5V without affecting the 12V regulation, yet 0A on 5V upsets it.

I have a PC with 3 graphics cards running scientific applications.
I acquired three old graphics cards that take about 300W each,
and have loads of cheap (CIT) PSUs that are rated at 650W on
the 12V line, which is what those cards use. So I run each card
off its own supply. But the 12V line at no load, or even at 300W,
is only giving out 10 to 10.5V. If I attach a small dummy load of
an amp or so to the 5V line, the 12V line suddenly becomes 12V.

You'd be better off with dedicated 12V switch mode power
supplys. Surprisingly cheap now even at the higher powers.

Link me to an example,

https://www.ebay.co.uk/itm/Transform...DPmF 8NegnqEg

That's just the one at the top of the hit list.

because I looked at them before, and at the high powers I need (300W per
card), it's massively cheaper to buy even the top of the range PC supplies
from Corsair etc.,

Not true with that one.

I'll stick to Corsair PC PSUs. That one you linked to is Chinese noname rubbish, I find those tend to overheat and break if you load them over 50%. Yours is £21 for 360W. I can get a Corsair of the same power rating for £30 that I know will work. Or 550W for £35.50.

On Wed, 19 Feb 2020 17:40:07 -0000, Another Dave wrote:

On 19/02/20 17:08, Commander Kinsey wrote:

Link me to an example, because I looked at them before, and at the high
powers I need (300W per card), it's massively cheaper to buy even the
top of the range PC supplies from Corsair etc., I assume because they're
made in larger quantities.

https://tinyurl.com/w9ntn9h

and select what you need. Plenty more.

No cheaper than Corsair PC PSUs, which I know will work and last.

On Wed, 19 Feb 2020 17:59:12 -0000, Rod Speed wrote:



"Commander Kinsey" wrote in message
newsp.0f8wi6nqwdg98l@glass...
On Wed, 19 Feb 2020 17:26:31 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

That's not how I thought SMPSs worked.

Yep, that's your problem, a lack of understanding in that area.

Surely since the current draw on 5V can vary from 1 amp to 35 amps,

It doesn't in fact vary over time in a PC,

and the 12V from 1 amp to 56 amps,

It doesn't in fact vary over time that much in a PC,

there have to be completely seperate ratios set up?

There isnt, and that works fine, because the current
from the 5V rail doesn't vary all that much over time.

As you have discovered, if there is no load on
the 5V rail, the 12V rail is well out of spec.

Adjusting just the 5V could have the 12V going anywhere.

Not anywhere, just by the amount you measured.
And only down from 12V with no load on the 5V rail,

And since that never happens in a PC, it works fine.

But PCs could vary the 5V and 12V considerably. For example when you start playing a game, the 12V changes dramatically for the CPU and GPU, perhaps by a factor of 10. **** knows what still uses 5V, but it won't be anything like constant.

On Wed, 19 Feb 2020 18:08:21 -0000, Rod Speed wrote:



"Rod Speed" wrote in message
...


"Commander Kinsey" wrote in message
newsp.0f8wi6nqwdg98l@glass...
On Wed, 19 Feb 2020 17:26:31 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0f8u1ul9wdg98l@glass...
On Wed, 19 Feb 2020 17:01:52 -0000, Andy Bennet wrote:

On 19/02/2020 16:46, Commander Kinsey wrote:
Why do (cheap? expensive ones may be better) PC ATX power supplies
need
current drawn from the 5V line to make the 12V line work correctly?

I have a PC with 3 graphics cards running scientific applications. I
acquired three old graphics cards that take about 300W each, and have
loads of cheap (CIT) PSUs that are rated at 650W on the 12V line,
which
is what those cards use. So I run each card off its own supply. But
the 12V line at no load, or even at 300W, is only giving out 10 to
10.5V. If I attach a small dummy load of an amp or so to the 5V
line,
the 12V line suddenly becomes 12V.

Why are the two lines related in any way?

Sorry for the crosspost, I'm not sure which of these groups are
active.

On el cheapo SMPS the primary supply is the 5V whose feedback controls
the conversion transformer. The 12V supply is derived from the same
transformer so if the 5V is not breaking into a sweat not enough
current
is available in the transformer secondary to get the 12volts up to
regulation.

Ok, I do have a degree in electronics, but it was a very long time ago.
Can you go into more detail?

There is no more detail. There is just the one switch mode
power supply and it controls the voltage on the 5V rail.
The 12V rail is just a different tap on the switch mode
high frequency transformer,

That's not how I thought SMPSs worked.

Yep, that's your problem, a lack of understanding in that area.

Surely since the current draw on 5V can vary from 1 amp to 35 amps,

It doesn't in fact vary over time in a PC,

and the 12V from 1 amp to 56 amps,

It doesn't in fact vary over time that much in a PC,

there have to be completely seperate ratios set up?

There isnt, and that works fine, because the current
from the 5V rail doesn't vary all that much over time.

As you have discovered, if there is no load on
the 5V rail, the 12V rail is well out of spec.

Adjusting just the 5V could have the 12V going anywhere.

Not anywhere, just by the amount you measured.
And only down from 12V with no load on the 5V rail,

And since that never happens in a PC, it works fine.

Your other problem is that you are assuming the the
mark space ratio varys with the current on the output
rails. It doesn't.

What does it vary with then?

On Wed, 19 Feb 2020 17:40:07 +0000, Another Dave, i.e. another troll-feeding
senile asshole, blathered:


https://tinyurl.com/w9ntn9h

and select what you need. Plenty more.

Another Troll-feeding Idiot

On Thu, 20 Feb 2020 04:59:12 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH senile troll****

04:59 already? LMAO You must be the dumbest piece of senile **** that ever
infested Usenet, senile Rodent!

--
Marland revealing the senile sociopath's pathology:
"You have mentioned Alexa in a couple of threads recently, it is not a real
woman you know even if it is the only thing with a Female name that stays
around around while you talk it to it.
Poor sad git who has to resort to Usenet and electronic devices for any
interaction as all real people run a mile to get away from from you boring
them to death."
MID:

On Thu, 20 Feb 2020 05:08:21 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the two subnormal idiots' endless troll****

--
Another typical retarded "conversation" between the two resident idiots:

Birdbrain: "But imagine how cool it was to own slaves."

Senile Rodent: "Yeah, right. Feed them, clothe them, and fix them when
they're broken.
After all, you paid good money for them. Then you've got to keep an eye
on them all the time."

Birdbrain: "Better than having to give them wages on top of that."

Senile Rodent: "Specially when they make more slaves for you
and produce their own food and clothes."

MID:

On Thu, 20 Feb 2020 04:39:22 +1100, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the two clinically insane trolling cretins' endless troll****

--
Another typical retarded "conversation" between Birdbrain and senile Rodent:

Senile Rodent: " Did you ever dig a hole to bury your own ****?"

Birdbrain: "I do if there's no flush toilet around."

Senile Rodent: "Yeah, I prefer camping like that, off by myself with
no dunnys around and have always buried the ****."

MID:

"Commander Kinsey" wrote in message
newsp.0f8x12x7wdg98l@glass...
On Wed, 19 Feb 2020 17:39:22 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0f8u8x2fwdg98l@glass...
On Wed, 19 Feb 2020 17:02:33 -0000, Rod Speed
wrote:

Commander Kinsey wrote

Why do (cheap? expensive ones may be better)
PC ATX power supplies need current drawn from
the 5V line to make the 12V line work correctly?

Depends on what you mean by work correctly.

If I don't load the 5V at all, the 12V becomes 10.5V. Connecting a car
headlamp to the 5V rail (which draws about 1.75A) seems to make it
behave.

By definition, when whatever it is that decides
what mark space ratio is used with a switch
mode power supply, it has to measure the
voltage somewhere and since the spec on
the 5V rail is a lot tighter than on the 12V
rails, it makes sense to measure the 5V rail.

That means that unless the 5V rail has some
load on it, the regulation isnt great and so
you can get some odd effects on the 12V rail.

Its obvious possible to have a separate switch mode
power supply for each rail but even the more expensive
PC PSUs don't do it like that because the 5V and 3.3V
rails are normally well loaded in a PC,

I don't understand.

That's obvious.

Surely the mark space ratio has to be completely different for the 12V
and
5V rails

Nope. The high frequency chopped DC goes
into the high frequency transformer and the 5V
and 12V rails are just different output windings
on that. Look at a PC PSU circuit diagram.
http://www.pavouk.org/hw/en_atxps.html

because any computer at any given moment could be drawing more from one
than the other, then differently several seconds from now.

The current on the 5V rail whose voltage is used to vary
the mark space ratio doesn't actually vary all that much.

Incorrect,

Nope.

this PSU is happy with me taking 1.75A from 5V. It's rated at up to 35A
on 5V. So clearly it will be ok anywhere from 1.75A to 35A on 5V.
Explain how that is possible to vary what I take from 5V without affecting
the 12V regulation, yet 0A on 5V upsets it.

The explanation is obvious, the mark space
ratio doesn't vary with the current, stupid.

I have a PC with 3 graphics cards running scientific applications.
I acquired three old graphics cards that take about 300W each,
and have loads of cheap (CIT) PSUs that are rated at 650W on
the 12V line, which is what those cards use. So I run each card
off its own supply. But the 12V line at no load, or even at 300W,
is only giving out 10 to 10.5V. If I attach a small dummy load of
an amp or so to the 5V line, the 12V line suddenly becomes 12V.

You'd be better off with dedicated 12V switch mode power
supplys. Surprisingly cheap now even at the higher powers.

Link me to an example,

https://www.ebay.co.uk/itm/Transform...DPmF 8NegnqEg

That's just the one at the top of the hit list.

because I looked at them before, and at the high powers I need (300W per
card), it's massively cheaper to buy even the top of the range PC
supplies
from Corsair etc.,

Not true with that one.

I'll stick to Corsair PC PSUs.

More fool you.

That one you linked to is Chinese noname rubbish,

Its just the first hit on the list. Plenty of other branded ones.

I find those tend to overheat and break if you load them over 50%.

Mine doesn't,.

Yours is £21 for 360W. I can get a Corsair of the same power rating for
£30 that I know will work. Or 550W for £35.50.

And you have to fart around loading the 5V rail. Yes, you are that stupid.

"Commander Kinsey" wrote in message
newsp.0f8x3jvpwdg98l@glass...
On Wed, 19 Feb 2020 17:40:07 -0000, Another Dave
wrote:

On 19/02/20 17:08, Commander Kinsey wrote:

Link me to an example, because I looked at them before, and at the high
powers I need (300W per card), it's massively cheaper to buy even the
top of the range PC supplies from Corsair etc., I assume because they're
made in larger quantities.

https://tinyurl.com/w9ntn9h

and select what you need. Plenty more.

No cheaper than Corsair PC PSUs,

That's a lie.

which I know will work and last.

So do the others.