Question Is there a minimal power output for PSU?

rbogomolec

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Nov 16, 2017
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What I mean is: I have a 850W PSU. I bought it cuz everyone was saying I need the juice for my RX 6800 XT. Turns out that after undervolting it, it needs only like 120-130W at most, when playing Shadow of Tomb Raider on 4k, 60fps lock, all settings high. That's how I like to play my games, so I'm not gonna crank the settings to ultra or raise the fps cap or anything like that. My CPU is also underclocked and doesn't go above 50-60W. When I'm not gaming the consumption is significantly weaker.

So, is there a downside to this? Or is the PSU just happy that it has to do 5-25% of work instead of 60-85% of work? Also, if it is bad, what can happen? Like, can a PSU stop working of fry other components because of underload? In my head it just means an easier life for the PSU and more wiggle room for me if I want to crank up the power usage or add new more demanding components to my PC. But I thought I'd rather ask you guys here.

As for my PSU, it's a Seagate B12-BC-850. I know it's mid range and not top range, but it has 80+ bronze, all the OPP, OVP, etc protections and a 5 year warranty. I'm willing to take the risk and believe in it even though it didn't cost 200+ € like all the other top range "safe" PSUs ;)
 

rbogomolec

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Nov 16, 2017
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no issue, just that your bronze unit at 200watt load will draw 240watts from wall
Ooooh, that's how it works? I see... I really don't understand much about this PSU story, I always thought that knowing about CPU and GPU is enough. All this PC building thing really ain't easy 😅 Cool, tnx for the explanation!
 
Ooooh, that's how it works? I see... I really don't understand much about this PSU story, I always thought that knowing about CPU and GPU is enough. All this PC building thing really ain't easy 😅 Cool, tnx for the explanation!
its just power supply, think of it as charger of your phone, even if you get stronger charger, your phone wont get charged faster, power draw would be same
 
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sonofjesse

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No problem. Most power supplies have an curve if you have a 1800 watt power supply (say gold) and only need 100 watts its not super efficient. You would be better off with a 350 watt Gold power supply (not counting upgrades etc) as far as the $$$ it would cost you, but this is still a very small amount.

No worries party on.
 
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Misgar

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@kerberos_20

I'm not sure I agree that a phone won't charge any faster with a "stronger" charger. My smartphone has a USB-C socket and I use a variety of 5V USB sources to charge the phone.

If I use the USB2 port on an old laptop, the current supplied to the phone is limited to a nominal 500mA by the USB standard and the phone charges slowly.

If I use the standard USB3 port on a laptop, the current is limited to a nominal 900mA. My phone charges faster than from USB2.

I have a number of power bricks with USB-A sockets but they have different maximum current outputs. For my 1A power brick, the phone charges at roughly the same rate as from a USB3 laptop port.

If I want to charge my phone quickly, I use the 2.5A power brick. The phone draws 1850mA (1.85A) and charges in half the time compared with USB3 from my laptop.

I have not measured the voltage supplied to my smartphone when it draws 1850mA but it's probably still the default 5V, because I'm not using a USB-C PD cable.
 

Math Geek

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@kerberos_20

I'm not sure I agree that a phone won't charge any faster with a "stronger" charger. My smartphone has a USB-C socket and I use a variety of 5V USB sources to charge the phone.

If I use the USB2 port on an old laptop, the current supplied to the phone is limited to a nominal 500mA by the USB standard and the phone charges slowly.

If I use the standard USB3 port on a laptop, the current is limited to a nominal 900mA. My phone charges faster than from USB2.

I have a number of power bricks with USB-A sockets but they have different maximum current outputs. For my 1A power brick, the phone charges at roughly the same rate as from a USB3 laptop port.

If I want to charge my phone quickly, I use the 2.5A power brick. The phone draws 1850mA (1.85A) and charges in half the time compared with USB3 from my laptop.

I have not measured the voltage supplied to my smartphone when it draws 1850mA but it's probably still the default 5V, because I'm not using a USB-C PD cable.

wasn't explicitly said but i believe what he was trying to say is something along the lines of "the phone won't pull any more power if the charger is all of a sudden capable of giving more than the phone can use." obviously this implies that the charger can already give as much power as the phone asks for. if that is the case, then an even stronger charger would not be of any benefit, nor would it hurt anything.

your case is that, you are using various chargers that are capable of providing less than the phone asks for or more depending on the charger/port. so of course you're going to see a difference in how it charges the phone.

not exactly what the OP or any of the responses is referring to.
 

Karadjgne

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Phones, mice, keyboards, external drives, or anything else plugged into a PC are Power on Demand items, meaning they'll pull as much power as is demanded upto their own limits of demand, according to the availability of power supply.

But that goes all the way back to the motherboard, which is also a Power on Demand item, it'll demand a specific amount of power at any given time, according to the sum of all that's in use on it, and thats what the psu will supply.

Some ppl run into issues when the demand for power exceeds what the psu can supply, others can run into issues when the supply is too much for the demand. For instance, you'd not use a 1600w psu with a 200w demand pc, the efficiency and capacity of that 1600w supply isn't really made to supply something so low, it's like using a sledgehammer to shape a diamond ring.

Typically, you want a psu that's higher rated than the maximum the pc could possibly pull, but at the same time puts normal use demand in the 50-70% bracket. That puts the psu at maximum efficiency, maximum thermal and noise efficiency, but still leaves room for power spikes from equipment such as the gpu, which keeps the psu inside its protection capacity.

850w psu, that normally handles @ 400w and can deal with a card that can spike upto a 700w+ total draw, perfect.
 
May 24, 2023
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Let's take an example. You have a phone that charges at 27W, and is ONLY compatible with 27W chargers. You decide to put a 63W charger. It will charge, but not faster. And you got a charger that is not very efficient. Of course, it charges your phone, but it's not very efficient power wise.
Same goes for a PC. Your setup only needs 300W? You'll be fine with a 450W PSU, or even a 400. Getting a 850W PSU is literally useless, because it's not very efficient. Of course, it will work, but it won't be efficient at all.
 

Karadjgne

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PC generally uses around 300w. That's constant draw. That's under the current workload. Change games for something far more intense, pulling more power to cpu and gpu, and could easily see 400w+ constant draw. Figure any gpu can run short duration power spikes of double it's rated use. So if Op is pulling 400w, that's 100w on cpu, 100w on the motherboard and 200w on the gpu. That'll be the trigger point. About 600w range. A good quality 550w could handle that no worries, but not all psus are built the same, there's plenty of garbage 650-850w psus around that can't handle more than 50ish %. Meaning a 600w spike can easily shut them down, blow them up, start fires.

Psu choice is important. Not just for its claims, but for what it can do vs those claims and what it will do. A Corsair RMx 850w on a pc that can barely hit 400w on a bad day is overkill, a Circle 850w on that same pc is seriously pushing your luck.