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airpet

High draw from wall (without pressing the power button on the case) - is this normal?

12 minutes ago, airpet said:
I have a corsair RM750x (purchased in 2016) plugged into a Gigabyte Z490 Vision G with i7-10700K.

A lot of times, as soon as I turn on the switch on the power supply but not on the case, the UPS alerts me to a power surge. When I measure it using a tool, I see anywhere from 80-200W being drawn without the computer being turned on, albeit only for a second or two at most.

I had this similar behaviour with an X99 board but I attributed that to a failing board rather than the power supply.

Is this normal? I don't believe so but I still need a second opinion. I never saw this behaviour before but I neither had a UPS nor a power measurement tool then, so I don't know if this has been happening for a long time.

Time to RMA this power supply?
 

What you are seeing is what's called 'inrush current'. Basically, it's the energy needed to fill the capacitors, inductors, transformers, and other components up to full prior to them actually doing something. Almost any electronic device (all but the most basic devices, like toasters) will have an inrush current of some form or another. That's why some (high draw, normally) electronics spark when you plug them in; the spark is a sign of high inrush current. You don't see that spark with your PC because you have a physical switch, so the plug is already in when you allow the inrush current do, well, rush in.

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Posted · Original PosterOP
I have a corsair RM750x (purchased in 2016) plugged into a Gigabyte Z490 Vision G with i7-10700K.

A lot of times, as soon as I turn on the switch on the power supply but not on the case, the UPS alerts me to a power surge. When I measure it using a tool, I see anywhere from 80-200W being drawn without the computer being turned on, albeit only for a second or two at most.

I had this similar behaviour with an X99 board but I attributed that to a failing board rather than the power supply.

Is this normal? I don't believe so but I still need a second opinion. I never saw this behaviour before but I neither had a UPS nor a power measurement tool then, so I don't know if this has been happening for a long time.

Time to RMA this power supply?
 
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The capacitors in the PSU have to fill up when the switch is turned on.

 

Why are you turning the power supply switch off in the first place?


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Posted · Original PosterOP
3 minutes ago, Enderman said:

Why are you turning the power supply switch off in the first place?

New build. I'm testing different components and fan configurations to see what works well, since the case is old.

 

3 minutes ago, Enderman said:

The capacitors in the PSU have to fill up when the switch is turned on.

So even a 200W draw is fine?

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Just now, airpet said:

New build. I'm testing different components and fan configurations to see what works well, since the case is old.

 

So even a 200W draw is fine?

Yeah it's normal.


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1 minute ago, airpet said:

So even a 200W draw is fine?

it's only a short burst to charge the capacitors


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Posted · Best Answer
12 minutes ago, airpet said:
I have a corsair RM750x (purchased in 2016) plugged into a Gigabyte Z490 Vision G with i7-10700K.

A lot of times, as soon as I turn on the switch on the power supply but not on the case, the UPS alerts me to a power surge. When I measure it using a tool, I see anywhere from 80-200W being drawn without the computer being turned on, albeit only for a second or two at most.

I had this similar behaviour with an X99 board but I attributed that to a failing board rather than the power supply.

Is this normal? I don't believe so but I still need a second opinion. I never saw this behaviour before but I neither had a UPS nor a power measurement tool then, so I don't know if this has been happening for a long time.

Time to RMA this power supply?
 

What you are seeing is what's called 'inrush current'. Basically, it's the energy needed to fill the capacitors, inductors, transformers, and other components up to full prior to them actually doing something. Almost any electronic device (all but the most basic devices, like toasters) will have an inrush current of some form or another. That's why some (high draw, normally) electronics spark when you plug them in; the spark is a sign of high inrush current. You don't see that spark with your PC because you have a physical switch, so the plug is already in when you allow the inrush current do, well, rush in.

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6 minutes ago, airpet said:

So even a 200W draw is fine?

16 minutes ago, airpet said:

albeit only for a second or two at most.

 

I would say that the PSU is fine since when you initially plug it into the wall (even if the system isn't running), it needs some current for a short amount of time for charging internal capacitors. Since you mentioned it's only for a second or two seconds, this sounds normal, although if it's consistently taking high wattage for a long time with the system not running and just plugged into the wall then I would consider RMA options if still available.


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The capacitors are supposed to be big enough to hold enough charge to keep computer running without input power for around 15-20ms ... so think how much energy to give 500+ watts to your components for around 10-15 ms

 

Most power supplies actually have a simple circuit to slow down the charging up of the capacitors, which are like black holes when empty, sucking as much energy as they're given... without the limiters in place, in the process of charging up, the fuse in your electrical panel could trip, because for a few ms the power supply will take a high current ... most power supplies will try to limit the current draw to around 40A (so 110v/230v x 40A ... a lot of watts for a few ms)

 

// and this by the way is one of the reasons why it's not a good idea to constantly turn off and on the power supply from that power switch - each time you do it, there's sparks inside the switch damaging the contacts, and those switches are often only rated for 20-30A and for a second or so every time you're pushing 40+ amps through that switch.

 

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Posted · Original PosterOP

Okay. Thanks everyone.

 

I learnt something new today. For a brief moment, I was afraid I had a potato power supply which damaged an expensive motherboard. And did not want the same thing to happen to the new one.

 

But all of you have clarified it well. 🙏

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5 minutes ago, mariushm said:

// and this by the way is one of the reasons why it's not a good idea to constantly turn off and on the power supply from that power switch - each time you do it, there's sparks inside the switch damaging the contacts, and those switches are often only rated for 20-30A and for a second or so every time you're pushing 40+ amps through that switch.

They're rated for a continuous load of 20-30A. A 40A peak, other than instantly tripping the average house's circuit breakers, wouldn't damage them in the slightest. Arcing might cause some damage, but unless you're switching your PSU on and off 10 times a day I wouldn't worry about that in the typical lifespan of a PSU.


¯\_(ツ)_/¯

 

 

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