Forum Thread

How inefficient can PSUs be?

bonkman 28,540 1,901 December 12, 2015 at 05:05 PM
Years ago, I built my htpc and used the 250W PSU that came with the case (miniATX PSU form). Not surprisingly, it died about 1.5 years later, fortunately not harming any components. They accepted it under RMA and sent me a 500W350W dual fan replacement. It's done the job and has surprisingly lasted 3+ years. However, I think one of the fans is getting noisy and I'd like to replace it since I replaced my system with a new haswell build. I've been thinking about getting a picopsu but I'm not sure which power adapter I should get.

According to my Kill-A-Watt, my system usually pulls 45-55W when I am using it. The other day, I tried to max it out with an unrealistic situation where I was recording 3 channels, "watching" a DVD, while also streaming HD video from a website. During that situation, I was pulling 75-82W at the wall.

I was thinking of getting a picoPSU 80 with a 60W ac adapter. Do you think that will be sufficient? I figure that even in the 75W load situation, my PSU is only 70% efficient at best, meaning 53W load. This would require the PicoPSU to be about 88% efficient (if I ever wanted to run that stupid situation), which is right on the boundaries of its abilities from what I read. However, is that 70% estimate even remotely accurate? I've tried to do research on how inefficient PSUs can be but have turned up nothing. This is the PSU. [evertek.com] Do you think my PSU's under 70% efficient? Over? Do you agree the 60W adapter would be enough?

Thanks for any insight!

20 Comments

1 2

Sign up for a Slickdeals account to remove this ad.

#2
Quote from bonkman View Post :
Years ago, I built my htpc and used the 250W PSU that came with the case (miniATX PSU form). Not surprisingly, it died about 1.5 years later, fortunately not harming any components. They accepted it under RMA and sent me a 500W dual fan replacement. It's done the job and has surprisingly lasted 3+ years. However, I think one of the fans is getting noisy and I'd like to replace it since I replaced my system with a new haswell build. I've been thinking about getting a picopsu but I'm not sure which power adapter I should get.

According to my Kill-A-Watt, my system usually pulls 45-55W when I am using it. The other day, I tried to max it out with an unrealistic situation where I was recording 3 channels, "watching" a DVD, while also streaming HD video from a website. During that situation, I was pulling 75-82W at the wall.

I was thinking of getting a picoPSU 80 with a 60W ac adapter. Do you think that will be sufficient? I figure that even in the 75W load situation, my PSU is only 70% efficient at best, meaning 53W load. This would require the PicoPSU to be about 88% efficient (if I ever wanted to run that stupid situation), which is right on the boundaries of its abilities from what I read. However, is that 70% estimate even remotely accurate? I've tried to do research on how inefficient PSUs can be but have turned up nothing. My PSU is some Chinese no-name. I literally mean no-name -- there's no branding on the box other than a Chinese girl giving a peace sign. laugh out loud I know PSUs are not efficient when under 10% load, though I doubt my PSU can come anywhere near the 500W it claims. Do you think my PSU's under 70% efficient? Over? Do you agree the 60W adapter would be enough?

Thanks for any insight!
80-plus PSU are only guaranteed to be >80% efficient between 20 and 80% load. Everything outside of that bound is fair game. Anyway, on to specifics:

Your best bet is to take a look at some professional reviews. The first one I could find claims that at 80W, the Pico PSU 80 is drawing 95W from the wall: http://www.silentpcreview.com/art...page3.html. In its sweet spot, it's about 84% efficient, which means not enough for you.

In general, unless you need to, running electronics at capacity is not a great idea. Are there particular reasons not to get a more capable AC adapter?
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#3
Quote from quotidian View Post :
80-plus PSU are only guaranteed to be >80% efficient between 20 and 80% load. Everything outside of that bound is fair game. Anyway, on to specifics:

Your best bet is to take a look at some professional reviews. The first one I could find claims that at 80W, the Pico PSU 80 is drawing 95W from the wall: http://www.silentpcreview.com/art...page3.html. In its sweet spot, it's about 84% efficient, which means not enough for you.

In general, unless you need to, running electronics at capacity is not a great idea. Are there particular reasons not to get a more capable AC adapter?
Thanks. But that's not the question I'm asking. 84% efficient is fine for me. My regular load is basically always <60W at the wall with my crappy PSU which I'm confident isn't 84% efficient.

I'm asking how inefficient my PSU might be. That will allow me to judge what adapter I need. As I said, my KillaWatt tells me that when I'm using my HTPC as I usually would, I pull around 55W. If I have a 70% efficient PSU, That means my load is around 40W, requiring only 67% efficiency for the Pico which is easily within its abilities. If my PSU is worse than that, it's even more easily attainable.

So my question is really is a 70% efficiency estimate reasonable for a terrible PSU? If that estimate is too low and I could actually expect 80% efficiency, maybe I do need a more powerful adapter as this would mean my regular load is creeping towards 50W which doesn't leave much overhead in case there's a strange power surge. OTOH, if 70% efficiency is too high an estimate, I'm definitely OK.

And the particular reason is cheapness. The combo Pico80 + 60W adapter is $35 while buying Pico80 +80W adapter would be about $50 and a 102W adapter would add another five or six bucks.
Reply Helpful Comment? 0 0
Last edited by bonkman December 12, 2015 at 07:14 PM
I heart slickdeals:

$12: 10 (good!) DVDs
$138: Zen X-Fi 32 gb
$4: ToyStory 1&2 BR/DVD + 2x TS3 movie tix
$45: 8 bags M&Ms+ 4Orville 6packs + 2 Redbox +3 blurays+ 2 DVDs+ 4 movie tix+ 1 Bisquick
$262: 50" LED TV
$281.99: mower+ 3 barstool+ 2 tailgate grill+ 6fertilizer+sawzall+4pillows+edger+swimsuit+2WiiU AfterglowPro +2sandals + sprinkler + 50' hose -- SYWR
One happy wife!
Running video game deal list: $155 bought me
3DS: DKCR, ALBW, PkmnY, MarioGolf, Starfox, FE:A
WiiU: NinLand, BatmanAC, AC4, W101, NG:RE, MK8, Pikmin 3, NSLU, 3DWorld, ZombiU
#4
Quote from bonkman View Post :
Thanks. But that's not the question I'm asking. 84% efficient is fine for me. My regular load is basically always <60W at the wall with my crappy PSU which I'm confident isn't 84% efficient.

I'm asking how inefficient my PSU might be. That will allow me to judge what adapter I need. As I said, my KillaWatt tells me that when I'm using my HTPC as I usually would, I pull around 55W. If I have a 70% efficient PSU, That means my load is around 40W, requiring only 67% efficiency for the Pico which is easily within its abilities. If my PSU is worse than that, it's even more easily attainable.

So my question is really is a 70% efficiency estimate reasonable for a terrible PSU? If that estimate is too low and I could actually expect 80% efficiency, maybe I do need a more powerful adapter as this would mean my regular load is creeping towards 50W which doesn't leave much overhead in case there's a strange power surge. OTOH, if 70% efficiency is too high an estimate, I'm definitely OK.
A TERRIBLE PSU generally (not specifically a computer PSU) could have as low as 40-50% efficiency across load ranges that are likely to occur.

PSU efficiency depends on the load. A power supply (non-computer) I designed back in college was 80-95% efficient for loads 50-105% of design capacity. But for smaller loads the efficiency was much lower. At a load of 5% it was less than 20% efficient but only drawing a small amount of power in total. It's hard to design a PSU that gets good efficiency across a wide range of loads.

I'm doubtful a smaller / more efficient PSU will save you more than 5-10 watts.

I'm not saying the Pico PSU wouldn't work, but the ac adapter and the pico PSU each have an efficiency and the total efficiency is the product of the two.
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#5
Quote from jkee View Post :
A TERRIBLE PSU generally (not specifically a computer PSU) could have as low as 40-50% efficiency across load ranges that are likely to occur.

PSU efficiency depends on the load. A power supply (non-computer) I designed back in college was 80-95% efficient for loads 50-105% of design capacity. But for smaller loads the efficiency was much lower. At a load of 5% it was less than 20% efficient but only drawing a small amount of power in total. It's hard to design a PSU that gets good efficiency across a wide range of loads.

I'm doubtful a smaller / more efficient PSU will save you more than 5-10 watts.

I'm not saying the Pico PSU wouldn't work, but the ac adapter and the pico PSU each have an efficiency and the total efficiency is the product of the two.
Thanks for the response. The beauty of the PicoPSU is that it acts upon a low range of loads. The combined efficiency is around 80-88% depending on what adapter you're using and what load percentage.

Saving me 5W would be about a 10% efficiency boost over what I have and 10W would be closer to 20%. Based upon what you said about bad PSU efficiency, that might be reasonable -- and would make me quite happy as that would mean that I'm only using around 35W and pulling just over 40W from the wall.
Reply Helpful Comment? 0 0
Last edited by bonkman December 13, 2015 at 04:32 AM
Joined Jun 2008
I Trade Your Bing Credit$
733 Posts
82 Reputation
#6
i got a pico with a shitty brick, only as good as my Corsair 430W Bronze,

just got the recent front page deal, 400W Platinum $25@newegg
10% better. even at low load 50W
Reply Helpful Comment? 0 0
#7
I don't see your computer specs posted. those would be helpful. let alone posting exactly which PSU you're currently using.

the answer to your question is likely somewhere around 50% efficient at best for a no-name supply at less than 10% load. even really good power supplies aren't particularly efficient at low load levels.
Reply Helpful Comment? 0 0
Last edited by elfenix December 13, 2015 at 07:11 AM
#8
Quote from bonkman View Post :
Thanks. But that's not the question I'm asking. 84% efficient is fine for me. My regular load is basically always <60W at the wall with my crappy PSU which I'm confident isn't 84% efficient.

I'm asking how inefficient my PSU might be. That will allow me to judge what adapter I need. As I said, my KillaWatt tells me that when I'm using my HTPC as I usually would, I pull around 55W. If I have a 70% efficient PSU, That means my load is around 40W, requiring only 67% efficiency for the Pico which is easily within its abilities. If my PSU is worse than that, it's even more easily attainable.

So my question is really is a 70% efficiency estimate reasonable for a terrible PSU? If that estimate is too low and I could actually expect 80% efficiency, maybe I do need a more powerful adapter as this would mean my regular load is creeping towards 50W which doesn't leave much overhead in case there's a strange power surge. OTOH, if 70% efficiency is too high an estimate, I'm definitely OK.

And the particular reason is cheapness. The combo Pico80 + 60W adapter is $35 while buying Pico80 +80W adapter would be about $50 and a 102W adapter would add another five or six bucks.

Ah, gotcha. Like others, 70% seems like a reasonable upper estimate to me for an old crappy PSU, but I'm just guessing.
Reply Helpful Comment? 0 0

Sign up for a Slickdeals account to remove this ad.

Joined Jun 2008
I Trade Your Bing Credit$
733 Posts
82 Reputation
#9
Quote from elfenix View Post :
the answer to your question is likely somewhere around 50% efficient at best for a no-name supply at less than 10% load. even really good power supplies aren't particularly efficient at low load levels.
a no brand 500W, usually no brand is over rated, so it's possible using over 10%, i looked at cheap psu benchmark before, they're about $7 each, lowest is 63% at 10% ( they're over rated, so that's not at their true 10% load)
Reply Helpful Comment? 0 0
Last edited by Left4Deal December 13, 2015 at 09:29 AM
#10
Quote from Left4Deal View Post :
i got a pico with a shitty brick, only as good as my Corsair 430W Bronze,

just got the recent front page deal, 400W Platinum $25@newegg
10% better. even at low load 50W
That's what I suspected. A better normal power supply can outperform the pico (though the wall adapter is significant). The trick would be to avoid over sizing the PSU too much, the best case would be something like a 200W 80+ silver or better from a good mfg.
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#11
Quote from Left4Deal View Post :
i got a pico with a shitty brick, only as good as my Corsair 430W Bronze,

just got the recent front page deal, 400W Platinum $25@newegg
10% better. even at low load 50W
Unfortunately, my case only takes SFX/uATX PSUs. It makes finding a deal difficult.
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#12
Quote from elfenix View Post :
I don't see your computer specs posted. those would be helpful. let alone posting exactly which PSU you're currently using.

the answer to your question is likely somewhere around 50% efficient at best for a no-name supply at less than 10% load. even really good power supplies aren't particularly efficient at low load levels.
Not sure why specs make a difference because I posted the power data, but it's an intel G3220 CPU w/ onboard graphics, 2x4GB Adata RAM, and GIGABYTE GA-H81M-HD3 mobo. Also has a bluray drive and a 1.5TB seagate HDD.

I dug up the box and found I misremembered -- it's a 350W PSU. I also managed to track it down online. This is it. [evertek.com]
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#13
Quote from quotidian View Post :
Ah, gotcha. Like others, 70% seems like a reasonable upper estimate to me for an old crappy PSU, but I'm just guessing.
Quote from Left4Deal View Post :
a no brand 500W, usually no brand is over rated, so it's possible using over 10%, i looked at cheap psu benchmark before, they're about $7 each, lowest is 63% at 10% ( they're over rated, so that's not at their true 10% load)
Quote from jkee View Post :
That's what I suspected. A better normal power supply can outperform the pico (though the wall adapter is significant). The trick would be to avoid over sizing the PSU too much, the best case would be something like a 200W 80+ silver or better from a good mfg.
I updated my OP. I actually found the box and it's a Just PC 350W PSU [evertek.com]. I can't find any other specs on it, though.

The difficulty I'm running into is the limited choices of SFX/uATX PSUs. Newegg only shows 4 PSUs that match the criteria and are <400W. Of those, only this seasonic [newegg.com] has a fan in a position that makes sense for my case and a bunch of reviews say that noise is a concern. They also say it may not fit because of not actually fitting SFX standards.

I suppose I could try to find a low profile case that takes a full ATX PSU but that's probably not a cost-efficient solution. Another solution would be just to replace the fans. Is that possible to do? I'm decently comfortable toying around with circuit boards.
Reply Helpful Comment? 0 0
Last edited by bonkman December 13, 2015 at 05:01 PM
#14
For a quiet / fanless htpc or other small form factor pc, something like the pico psu makes a lot of sense. It just may not be the most efficient, stable, and robust option. But it could be one of the more efficient options, it's hard to know.

The PSU you have currently said mATX on the page you linked to earlier which I interpret as mini not micro...
Reply Helpful Comment? 0 0
Joined Nov 2006
disgruntled caveman
28,540 Posts
1,901 Reputation
Original Poster
#15
Quote from jkee View Post :
For a quiet / fanless htpc or other small form factor pc, something like the pico psu makes a lot of sense. It just may not be the most efficient, stable, and robust option. But it could be one of the more efficient options, it's hard to know.

The PSU you have currently said mATX on the page you linked to earlier which I interpret as mini not micro...
I don't think mini atx is a thing. mini itx, sure.

strangely, I found the PSU on the newegg site (made in 2006 according to reviews) and it says atx though the reviews say sfx.
Reply Helpful Comment? 0 0
Page 1 of 2
1 2
Join the Conversation
Add a Comment
 
Copyright 1999 - 2016. Slickdeals, LLC. All Rights Reserved. Copyright / Infringement Policy  •  Privacy Policy  •  Terms of Service  •  Acceptable Use Policy (Rules)  •  Interest-Based Ads
Link Copied to Clipboard