Low +12V problem. Solved.

[attuoz]

I have a 750watt PSU that has an output spec of 12V x 62A = 744watt. 

 

urtq7i8.png (695×119) (imgur.com)

 

Now my PSU is old and under 450watt load, i get 10.6V readings from 12V rail. Confirmed with multimeter, measured from GPU PCIe cable.

 

oL7NcUn.png (484×186) (imgur.com)

 

Question is; 10.6V x 62A = 657watts. Can i continue using this PSU as long as my max load is under 650 watts?

[Dujith]

That voltage is well beyond the tolerance (+12V 5% allowed). So i'd suggest you replace the PSU

Even if it was the -12V rail (10%) you are still beyond the tolerance

[attuoz]

1 minute ago, Dujith said:

That voltage is well beyond the tolerance (+12V 5% allowed). So i'd suggest you replace the PSU

Even if it was the -12V rail (10%) you are still beyond the tolerance

I think that 5% tolerance only makes it so you don't get a 500w psu when you pay for a 750w. It's like a psu standart.

It doesn't mean a PSU with higher than 5% tolerance should be trashed.

Correct me if i am wrong. With some source if possible.

[jj9987]

1 minute ago, attuoz said:

I think that 5% tolerance only makes it so you don't get a 500w psu when you pay for a 750w. It's like a psu standart.

It doesn't mean a PSU with higher than 5% tolerance should be trashed.

No. If the PSU is supposed to output 12V, it has to be within 5% tolerance. Too high voltage and components will start to break/burn. Too low voltage and components might not start/run or they might pull too much current, overloading the PSU and lowering the voltage even further.

 

That's just physics.

 

If it's an old PSU and it can't keep up the voltage demand, you will soon run into troubles, such as your PC not booting.

[Dujith]

No, for any voltage rail there is a fixed tolerance so the equipment you hook up to it (Motherboard, Drives, ect) does not fry or break.

For very simple reasons: lower voltage means it will draw more current to get the same amount of power it needs.

 

I'm not talking about the power, i'm talking about what is allowed for the voltage tolerance. 2 very different things.

 

And for a source thats the ATX standard as applied by all manufactures. For example EVGA: EVGA FAQ

[mariushm]

No, the voltage MUST be withing 10%, prefferably within 5%.  It should be within 11.7v ... 12.3v

 

Mechanical hard drives have motors which are designed to run at 12v, if the voltage goes outside some reasonable range, the rotation speed will be different and the hard drive will have a hard time finding the data on platters, if it would work at all.

 

The VRMs (dc-dc converters) which power the processor and the video card also expect to have a voltage close to 12v, they're "optimized", the components in the circuit are carefully picked so they work well with a voltage close to 12v - if it's too far from 12v, those circuits can overheat, or "hiccup", or cause other issues which can damage those components over time.

 

A switching power supply constantly monitors the output voltage and adjusts the switching frequency to send fewer or more pulses through that transformer, to keep the voltage very close to 12v.  Some power supplies will be designed to output a bit more like 12.2-12.3v on purpose to account for voltage losses on the wires between the power supply and components.

 

So something's wrong with that power supply, either in the feedback mechanism or with its voltage referece.

 

Be careful though to actually measure at the 12v connector, not the -12v wire in the 24 pin connector.   The easiest would be to insert the meter probes in a molex (hdd) connector, the black and yellow wires in the plug.

 

The -12v can be -10v or even -8v, it's a very tiny power supply (usually under 1A) and it's only used by the motherboard for the serial ports, and even then the serial port circuitry on a motherboard only consumes a few mA of current. 

So without anything connected to -12v, nothing actively consuming power, the power supply is not "working hard" to keep the voltage very close to -12v.

 

 

[Kilrah]

4 minutes ago, mariushm said:

Be careful though to actually measure at the 12v connector, not the -12v wire in the 24 pin connector.   The easiest would be to insert the meter probes in a molex (hdd) connector, the black and yellow wires in the plug.

He measured on the PCIe cable so there's no -12V there.

[attuoz]

1 hour ago, mariushm said:

No, the voltage MUST be withing 10%, prefferably within 5%.  It should be within 11.7v ... 12.3v

 

Mechanical hard drives have motors which are designed to run at 12v, if the voltage goes outside some reasonable range, the rotation speed will be different and the hard drive will have a hard time finding the data on platters, if it would work at all.

 

The VRMs (dc-dc converters) which power the processor and the video card also expect to have a voltage close to 12v, they're "optimized", the components in the circuit are carefully picked so they work well with a voltage close to 12v - if it's too far from 12v, those circuits can overheat, or "hiccup", or cause other issues which can damage those components over time.

 

A switching power supply constantly monitors the output voltage and adjusts the switching frequency to send fewer or more pulses through that transformer, to keep the voltage very close to 12v.  Some power supplies will be designed to output a bit more like 12.2-12.3v on purpose to account for voltage losses on the wires between the power supply and components.

 

So something's wrong with that power supply, either in the feedback mechanism or with its voltage referece.

 

Be careful though to actually measure at the 12v connector, not the -12v wire in the 24 pin connector.   The easiest would be to insert the meter probes in a molex (hdd) connector, the black and yellow wires in the plug.

 

The -12v can be -10v or even -8v, it's a very tiny power supply (usually under 1A) and it's only used by the motherboard for the serial ports, and even then the serial port circuitry on a motherboard only consumes a few mA of current. 

So without anything connected to -12v, nothing actively consuming power, the power supply is not "working hard" to keep the voltage very close to -12v.

 

 

Alright. Hard Drive part convinced me. Because one of my drive is bugging lately. I will replace the PSU.

[Juular]

Thermaltake Smart DPS G is 5 years old, it isn't that old, are you sure you're looking at the right PSU ? There are a lot of Thermaltake Smarts. Because if these readings are confirmed with a multi-meter there are definitely something wrong and you shouldn't use it.

[attuoz]

1 hour ago, Juular said:

Thermaltake Smart DPS G is 5 years old, it isn't that old, are you sure you're looking at the right PSU ? There are a lot of Thermaltake Smarts. Because if these readings are confirmed with a multi-meter there are definitely something wrong and you shouldn't use it.

Smart DPS G 750W Gold (thermaltake.com)

 

Purchase date 2017 september.

[Spotty]

1 minute ago, attuoz said:

Smart DPS G 750W Gold (thermaltake.com)

 

Purchase date 2017 september

That's not that old, and is still within the warranty period. Contact Thermaltake support and explain the issue and see if you can get a replacement unit.

Even if you end up buying a different model PSU if you can get a replacement sent from Thermaltake you could sell it, give it to a friend, or keep it as a spare.

[attuoz]

4 minutes ago, Spotty said:

That's not that old, and is still within the warranty period. Contact Thermaltake support and explain the issue and see if you can get a replacement unit.

Even if you end up buying a different model PSU if you can get a replacement sent from Thermaltake you could sell it, give it to a friend, or keep it as a spare.

Already replaced with Asus Rog Strix 850W.

 

I ll try to get Thermaltake replaced but its probably going to take a month.

[attuoz]

New and Old PSU comparison here: 

Sadly it didn't increase my 3dmark score.