Using a ATX12V PSU to power a ATX12VO motherboard. Is it possible?

[Earl Dadanur]

The question is simple enough. If I had a system with an ATX12VO motherboard could I use a normal ATX power supply. Gamer's Nexus has an article that says that it may be possible to make an adapter. But I can't seem to find any known working examples. I personally am looking for a solution to this because of a prebuild I'm looking to upgrade. With my only limiting factor at this point being the power supply. Anyone got any ideas?.

[akio123008]

I'm not sure what method ATX12VO uses to power on the supply, but if it's similar to what the old standard does (the paperclip test) there's nothing that would stop you from doing it.

 

you'd only have to wire up the right connectors to the power supply, which would probably involve cutting wires and some soldering. Essentially you're making an adapter indeed.

[Earl Dadanur]

Well my concern is the 12 volt standby that ATX12VO uses vs. ATX12V's 5 volt standby.

[Windows7ge]

Normal ATX PSU's use a 5V standby pin to trip the PSU on/off. If the new standard does the same thing but with 12V then it should be doable with the right adapter but the adapter might have to actively step the voltage down as the PSU standby pin might not like 12V when it's expecting 5V.

[Earl Dadanur]

Alright then. Now where to find one or how to make it is all I need to figure out then. 

[akio123008]

1 minute ago, Earl Dadanur said:

Alright then. Now where to find one or how to make it is all I need to figure out then. 

You probably don't. It's active low; the motherboard pulls the voltage down to send a power on signal. That just means it pulls down 5 instead of the expected 12V, but it still pulls it down, so it still triggers the PSU.

[Earl Dadanur]

So could I test this by just plugging it in without major risk to the motherboard?

[Windows7ge]

2 minutes ago, akio123008 said:

You probably don't. It's active low; the motherboard pulls the voltage down to send a power on signal. That just means it pulls down 5 instead of the expected 12V, but it still pulls it down, so it still triggers the PSU.

Then maybe I have it backwards. The motherboard expects 12V but it'd only be given 5 on the standby pin.

 

That'd be even more problematic wouldn't it? Since things like USB ports and LEDs would still need the 12V standby power...

[akio123008]

1 hour ago, Earl Dadanur said:

So could I test this by just plugging it in without major risk to the motherboard?

Assuming you wire it right I don't see why not. It's just applying a lower voltage to the power on pin on the motherboard, but given that it's lower than what it's designed for it's pretty safe. As for the power wires, 12V is 12V, the board doesn't care what supplies it, so in that sense you should be fine too.

 

But again, make sure to wire it right, one mistake there could be is extremely likely fatal

[akio123008]

1 hour ago, Windows7ge said:

Then maybe I have it backwards. The motherboard expects 12V but it'd only be given 5 on the standby pin.

 

That'd be even more problematic wouldn't it? Since things like USB ports and LEDs would still need the 12V standby power...

It probably would. That means your USB ports and stuff won't work when the thing is off. Perhaps it could work though, because the DC-DC converter on the motherboard might accept 5V as an input as well, that depends on the converter.

 

When it's powered on though, it'll work fine.

 

[Earl Dadanur]

I personally dont like charging things off my desktop anyway. 

[Earl Dadanur]

Still wish I could find an example of someone doing this. 

[Windows7ge]

3 minutes ago, akio123008 said:

It probably would. That means your USB ports and stuff won't work when the thing is off. Perhaps it does work though, because the DC-DC converter on the motherboard might accept 5V as an input as well, that depends on the converter.

 

When it's powered on though, it'll work fine.

 

That is a possibility but if the output of the onboard DC-DC converter is 5V the loss during conversion might drop it down to a point where it has issues.

 

I wonder if this could be done using 12V if we threw a 12V relay into the mix...  If we could somehow tie the signal enable pin on the relay to the 12V standby pin then we could have that run the PSU 5V enable pin.

[akio123008]

1 hour ago, Windows7ge said:

I wonder if this could be done using 12V if we threw a 12V relay into the mix...  If we could somehow tie the signal enable pin on the relay to the 12V standby pin then we could have that run the PSU 5V enable pin.

You could have working USB ports if either the converter supports 5V in (I'm sure some can but it depends on which one is on the board) or if you somehow route the 5V applied to the standby pin directly to the ports. If you really don't care about having working USB ports when powered off, then I guess it doesn't matter.

[akio123008]

35 minutes ago, Earl Dadanur said:

Still wish I could find an example of someone doing this. 

I'd do it but I don't have one of those boards.

[Earl Dadanur]

Just and idea but what if I just used a different 12 volt wire? Wouldn't that just mean that their would be no standby power? Wouldn't that just mean the USB ports wouldn't provide power when the computer is off?

[akio123008]

1 minute ago, Earl Dadanur said:

Just and idea but what if I just used a different 12 volt wire? 

What exactly do you mean by that?

[Earl Dadanur]

 

1 minute ago, akio123008 said:

What exactly do you mean by that?

Instead of having the adapter link the 5 volt standby run into the 12 volt standby pin just have a different 12 volt line run into the standby.

[OrionFOTL]

55 minutes ago, Windows7ge said:

Normal ATX PSU's use a 5V standby pin to trip the PSU on/off.

Not at all. ATX PSUs use the PS_ON pin (a 0V - 2V signal) to turn themselves on/off.

[akio123008]

1 hour ago, Earl Dadanur said:

 

Instead of having the adapter link the 5 volt standby run into the 12 volt standby pin just have a different 12 volt line run into the standby.

On a power supply, all the pins are at GND (0V) when the thing is off, except for the power on pin, which is at 5V (on a normal PSU). The motherboard can trigger the PSU by shorting this 5V to GND. On 12VO it's the same, only now the power on pin is at 12V. (edit: apparently not) The principle doesn't change though; the motherboard still just shorts it to GND to trigger the PSU.

 

If you have a 12VO motherboard, and a regular ATX supply, you can connect the 5V power on pin from the supply to the power on pin of the motherboard. It's expecting 12V there, but that's not an issue; it'll just pull down the voltage to 0V regardless, and therefore the PSU will turn on.

 

 

 

[Windows7ge]

10 minutes ago, akio123008 said:

You could have working USB ports if either the converter supports 5V in (I'm sure some can but it depends on which one is on the board) or if you somehow route the 5V applied to the power on pin directly to the ports. If you really don't care about having working USB ports when powered off, then I guess it doesn't matter.

I'm now realizing my idea wouldn't work because the 12V would be disabled in standby mode. We only have 5V to work with (although there are 5V relays too).

 

At this point the only idea I have would be to step the 5V up to 12V but I've seen on most PSUs the Standby Power is current limited to ~1A. I'm not sure how well that'd go over...

[akio123008]

8 minutes ago, akio123008 said:

the motherboard still just shorts it to GND to trigger the PSU

important note: shorting a voltage to ground can only ever be done on the power on pin, because this one is specifically designed to not deliver any current and be driven to 0V easily (pullup).

 

Other (power) wires coming out of the PSU may never be shorted to GND, because, well that's shorting out the PSU which is at best some fuse blowing up and worst case a fire hazard.

[Windows7ge]

10 minutes ago, OrionFOTL said:

Not at all. ATX PSUs use the PS_ON pin (a 0V - 2V signal) to turn themselves on/off.

...and you read this where?...It's true the voltage gets pulled down when you (for example) short PS_ON to GND but when open circuit (Standby) the voltage is +5V.

[akio123008]

2 minutes ago, Windows7ge said:

...and you read this where?...It's true the voltage gets pulled down when you (for example) short PS_ON to GND but when open circuit (Standby) the voltage is +5V.

perhaps the lower threshold for the PSU to turn on is 2V?

[OrionFOTL]

12 minutes ago, Windows7ge said:

...and you read this where?

... The literal ATX specification. LOL. Point 3.3.3. https://www.intel.co.jp/content/dam/www/public/us/en/documents/design-guides/resellers-power-supply-design-guide-changes.pdf

0-0.8V low, 2V high, and none or at most -5.25V open circuit.

 

The signal has no relation to the +5VSB rail. In fact, on ATX12VO power supplies, it's behavior and specifications don't change at all: it's the same 0-0.8V for low state, 2V for high and at most -5.25V open circuit. https://www.intel.com/content/dam/www/public/us/en/documents/guides/single-rail-power-supply-platform-atx12vo-design-guide.pdf