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PSU basics - how did psu change from version 1 to version 2?

Y

you2

Diamond Member
A couple of threads below i asked if I would need to upgrade my psu or simply get a 20 to 24 adapter.

In the process I've been trying to find out exactly what changed in the atx psu spec that resulted in a new version.

Can someone please provide a brief list of the changes or a pointer to a faq/document that describes the changes (I tried a google search but couldn't come up with the magical terms).



I guess I'm trying to understand when it is safe to simply 'convert' the psu via adding an adapter or when a new psu is actually required (other than current requirements).
Thanks!
 
Originally posted by: you2
If I understand this correctly there is no difference other than the connectors? Is this correct ?
(this is the link that seemed to have the best comparison)
http://en.wikipedia.org/wiki/ATX
Click to expand...
This may not be part of the AXT specifications but modern systems can draw up to 85% of their power from the 12v rails so modern PSU are configured accordingly.
 
The -5V line has disappeared entirely from the spec - 12V is the next to go. A 20A limit on each +12V rail is recommended for safety reasons (but single-rail PSUs are still preferred - just don't grab the 12V lines while you're taking a bath :roll: ). If more than one 12V rail is present, they will be separately curent-limited. I think the +5V standby rail was upped to a minimum of 2A (quite a few PSUs are supplying 3A on that rail now). And a few other negligible things.

To be ATX 2, you don't have to supply more than 50% of the available power on the +12V rails, but if you buy a PSU for a modern mobo (since they power the CPUs and the PCI Express slots, etc. off the +12 rail now), you should choose one like that.

.bh.
 
Now I'm back to being confused. If the -5v is gone how can I use an atx on an atx2 mb ? Somehow I think this should be simple but I'm not grasping something very basic here.
 
The -5V line hasn't been used since ISA slots were common on mobos (and it wasn't even used much then) - nothing uses it any more. About the only thing that still uses the -12V are some multiport serial cards.

.bh.
 
Aha. I think I understand the flaw of my earlier statement. Even though they might be on a pin nothing on the motherboard uses the current from the pin. So as long as my psu has enough amperage on the rail there has been no real change from atx 1.3 to atx 2.3. Bleh wonder why the changed the plugs. Sound kind of artificial
 
Originally posted by: you2
Aha. I think I understand the flaw of my earlier statement. Even though they might be on a pin nothing on the motherboard uses the current from the pin. So as long as my psu has enough amperage on the rail there has been no real change from atx 1.3 to atx 2.3. Bleh wonder why the changed the plugs. Sound kind of artificial
Click to expand...

They added more 12v pins for safety reasons. Having too much power run through only so many pins/wires is inherently dangerous.
 
the 24-pin ATX connector allows more current to be supplied safely as the total is spread over one more wire for each of the major rails: +5, +12, and +3.3. Many of the 24-pin connectors are split so you don't have to use the extra 4 pins if you still have a 20-pin ATX mobo. Or if you have the room like I do, you can just leave the extra four pins hang past the end of the 20-pin socket. The 2x4 CPU connectors are often split too so you can use just the 4-pin (2x2) part if that's what your mobo needs - but even that connector can be allowed to lap over if there is room. You can't plug them in wrong without forcing.

.bh.
 
Originally posted by: Zepper
- just don't grab the 12V lines while you're taking a bath :roll: ).
Click to expand...

Human body resistance varies from person to person. It can also vary depending on wet skin or other conditions (wearing a ring on at the point of contact .......).

But, I don't think 12V DC can shock you under any circumstances.

I always thought that the safety issue Intel wanted to address was the possibility of a spark in case of an accidental short. Such a spark could cause a fire to start if a flammable material was nearby.

I realize this is not the main concern of the poster. But, I would like to know if I am mistaken. So, please correct me if I am wrong.
 
Over 20 Amps of 12VDC can KILL YOU (and some zippy's can put 60 Amps on the single +12 rail) - just depends on how short a path you give it to your heart!

.bh.
 
Originally posted by: Zepper
Over 20 Amps of 12VDC can KILL YOU (and some zippy's can put 60 Amps on the single +12 rail) - just depends on how short a path you give it to your heart!

.bh.
Click to expand...

Actually, less than 1 Amp DC is enough to kill you if it goes through your heart.
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

But, you need a lot more than just 12V DC to pass 1A through your heart. The reason is that the current is determined by the resistance in the path of the voltage. Human body resistance is much higher than 1 kilo Ohms. Even if it was 1 kilo Ohms, the current would by 12V / 1000 = 12mA.
 
IAC, the whole point to it is that the split rail thing was an idiot-proofing measure, never technically sound from the get-go and even its initiator, Intel, has pretty much given up on it. Unfortunately for marketing purposes the PSU makers will keep doing them because the average PC owner/buyer is technologically illiterate.

.bh.
 
Originally posted by: Zepper
IAC, the whole point to it is that the split rail thing was an idiot-proofing measure, never technically sound from the get-go and even its initiator, Intel, has pretty much given up on it. Unfortunately for marketing purposes the PSU makers will keep doing them because the average PC owner/buyer is technologically illiterate.

.bh.
Click to expand...

And, that is a shame. I wish (quiet) PSU makers like Seasonic offered single-rail supplies.
 
Originally posted by: Zepper
Over 20 Amps of 12VDC can KILL YOU...
Click to expand...
I work around electricians (and electricity) every day, and they've told me several times, "Don't let anybody fool you! Volts kill." I know they're not here to defend themselves, but I take their word for it... so should you!

Having said that, I've been shocked several times by leaky 480 volt circuits and 120 -- bad grounds and such. Never got shocked on 277 -- don't know why not, but...

Personally, I can start feeling it at around 40 volts -- kinda tingly, like little needles rubbing against you. 60-80 volts will give you a pretty good jolt -- you definitely know something is up. 100 volts and over hurts like a SOB!!!

Anyway, electricity isn't anything to take for granted, regardless of the volts or amps. These guys are fanatical about lockout/tagout, and I've seen them get bit a few times...
 
Originally posted by: VinDSL
Originally posted by: Zepper
Over 20 Amps of 12VDC can KILL YOU...
Click to expand...
I work around electricians (and electricity) every day, and they've told me several times, "Don't let anybody fool you! Volts kill." I know they're not here to defend themselves, but I take their word for it... so should you!
Click to expand...
It's the current that kills, but there won't be any current unless the voltage is high enough. A voltage of 100kV won't do jack all if the current is 10^-8 A.
 
Originally posted by: Howard
Originally posted by: VinDSL
Originally posted by: Zepper
Over 20 Amps of 12VDC can KILL YOU...
Click to expand...
I work around electricians (and electricity) every day, and they've told me several times, "Don't let anybody fool you! Volts kill." I know they're not here to defend themselves, but I take their word for it... so should you!
Click to expand...
It's the current that kills, but there won't be any current unless the voltage is high enough. A voltage of 100kV won't do jack all if the current is 10^-8 A.
Click to expand...

:thumbsup:
 
I don't the current in my 4 year old trupower 430 to kill - i just want to make sure it is ample to power a new mb....
 
Originally posted by: Navid
Originally posted by: Zepper
IAC, the whole point to it is that the split rail thing was an idiot-proofing measure, never technically sound from the get-go and even its initiator, Intel, has pretty much given up on it. Unfortunately for marketing purposes the PSU makers will keep doing them because the average PC owner/buyer is technologically illiterate.

.bh.
Click to expand...

And, that is a shame. I wish (quiet) PSU makers like Seasonic offered single-rail supplies.
Click to expand...
The Seasonics are single rail designs, they just split the out and put limits on the max amps that can be drawn.

The original S12 is split two ways which in theory might not be enough for high-end SLi or Crossfire builds, but the new M12 and Energy Plus S12 are split four ways so you can basically treat it as a single rail PSU.
 
Originally posted by: Operandi
Originally posted by: Navid
Originally posted by: Zepper
IAC, the whole point to it is that the split rail thing was an idiot-proofing measure, never technically sound from the get-go and even its initiator, Intel, has pretty much given up on it. Unfortunately for marketing purposes the PSU makers will keep doing them because the average PC owner/buyer is technologically illiterate.

.bh.
Click to expand...

And, that is a shame. I wish (quiet) PSU makers like Seasonic offered single-rail supplies.
Click to expand...
The Seasonics are single rail designs, they just split the out and put limits on the max amps that can be drawn.

The original S12 is split two ways which in theory might not be enough for high-end SLi or Crossfire builds, but the new M12 and Energy Plus S12 are split four ways so you can basically treat it as a single rail PSU.
Click to expand...

Call it dual rail or whatever. What I have highlighted is what I do not want!
 
The ATX pins are rated by Molex for 9A each. I'm sure that the larger 4 pin Molex connections have a higher rating. http://www.molex.com/ for those that want to look around.

I bet we will see no issue with 4 rail PSUs limited to 18~20A per rail, with a combined 12V output of 60A.

You guys can figure it out for me because I won't be upgrading untill Vista SP1 is out. 😀
 
Originally posted by: Navid
Originally posted by: Operandi
Originally posted by: Navid
Originally posted by: Zepper
IAC, the whole point to it is that the split rail thing was an idiot-proofing measure, never technically sound from the get-go and even its initiator, Intel, has pretty much given up on it. Unfortunately for marketing purposes the PSU makers will keep doing them because the average PC owner/buyer is technologically illiterate.

.bh.
Click to expand...

And, that is a shame. I wish (quiet) PSU makers like Seasonic offered single-rail supplies.
Click to expand...
The Seasonics are single rail designs, they just split the out and put limits on the max amps that can be drawn.

The original S12 is split two ways which in theory might not be enough for high-end SLi or Crossfire builds, but the new M12 and Energy Plus S12 are split four ways so you can basically treat it as a single rail PSU.
Click to expand...

Call it dual rail or whatever. What I have highlighted is what I do not want!
Click to expand...

The Energy Plus S12 and M12 have 4 18A 12v outputs (rails) coming from 1 12v source. With 4 output stages you don't have to worry about what limits are on what rails; single / multiple rails isn't a limitation in such a configuration.
 
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