# Awful PSU - Is this really as bad as I think? SEMPRE!



## Fapguy (Oct 2, 2008)

The PSU in question is a Sempre bd-701ctp12-e - 700 watt "green" PSU.

I really dont believe that it is in fact a 700W psu. The specs I was able to find on their (ugly as hell) website was this:

```
12cm Fan, 1xFDD, 2xHDD, 4xSATA, 2x PCIe, 20+4 main power, 8 pin power connector, power cord
• Case: malt black
• Fan: orange
• Input Specifications:
• Voltage: 220~240 VAC 
• Frequency: 47 Hz to 63 Hz 
• Output Specifications:
• Output Max. 700W
• Red: +5V 25A
• Yellow: +12V1 29A
• Yellow/Black: +12V2 29A
• Blue: -12V 0,8A
• Orange: +3,3V 25A
• Purple: +5VSB 3,0A
• Gray: P.G
• Black: Ground
• Green: PS On
```
So, can anyone explain this to me? The system it has been powering for a half year or so is a 1045T and a 7850 +2HDD's and a few 12cm fans.
*It squeals at idle!*

Is it worth keeping or is it dangerous to have in the system?


----------



## DBCooper (Jun 11, 2010)

Hi there Fapguy,

I don't think "Sempre" power supplies are good brands at all. If you want a great, reputable power supply brand, go with either SEASONIC, XFX, and ANTEC-HCG power supplies. You can't go wrong with either of the three brands.


----------



## Fapguy (Oct 2, 2008)

DBCooper said:


> Hi there Fapguy,
> 
> I don't think "Sempre" power supplies are good brands at all. If you want a great, reputable power supply brand, go with either SEASONIC, XFX, and ANTEC-HCG power supplies. You can't go wrong with either of the three brands.


I knew that already, and those are usually the same brands I buy, except Antec for some reason costs alot more than the others here. I have an OCZ 750W fully modular one myself, got really good reviews. Use a XFX ProSeries 850W in another system  Just judging from their website, this is probably the worst brand for PSU's you can find, I'm guessing... But it's not my PC and the actual owner doesn't "fear" that anything bad will happen using crappy PSU's. No matter what stories I show her, she just says "if it works, it works"

Can you perhaps explain in easy words why a PSU like this is a bad idea, just so she can hear it from another person?

Unkown parts, subpar quality, unstable voltages, I couldn't find any information anywhere except for the obviously wrong specs on their own website. Not to mention, no reviews anywhere... and I couldn't test it myself (don't have equipment on hand).


----------



## Fjandr (Sep 26, 2012)

Well, without pulling it apart I can't tell you if any of the problems common on low-quality PSUs apply. If it doesn't have adequate protection built in (and really cheap PSUs frequently don't), it could potentially be a fire hazard.

Here's how a review of a really bad PSU goes: Death of a Gutless Wonder III: The Labors of Hercules Review


----------



## Fapguy (Oct 2, 2008)

Fjandr said:


> Well, without pulling it apart I can't tell you if any of the problems common on low-quality PSUs apply. If it doesn't have adequate protection built in (and really cheap PSUs frequently don't), it could potentially be a fire hazard.
> 
> Here's how a review of a really bad PSU goes: Death of a Gutless Wonder III: The Labors of Hercules Review


Thank you! This PSU was I think she said no more than 20-30 usd (and thats in DKK converted to USD, really TOO cheap)


----------



## Panther063 (Jul 13, 2009)

The power rating of 700W is usually the peak power usage, not a stable maximum power rating that can be sustained safely. Avoid cheap power supplies as they often only show the peak power.


----------



## Fapguy (Oct 2, 2008)

Panther063 said:


> The power rating of 700W is usually the peak power usage, not a stable maximum power rating that can be sustained safely. Avoid cheap power supplies as they often only show the peak power.


Yet another thing I didn't think of.

Thank you!

also, the PSU is rated at 29 Ampere on the 12volt line, what does this mean? How can a "700" watt PSU only deliver 29 amps on the 12v?


----------



## Bill_Bright (Dec 17, 2004)

There is nothing wrong those "published" specs. What gets my attention is what is NOT listed - the _efficiency_ rating of the supply. And when a maker does not mention the efficiency, it is a good sign it has a lousy, bell-curve efficiency rating - that is, it achieves peak efficiency at just one load level, then drops off significantly on either side from there. 

But the load a computer puts on a PSU is constantly varying - from a few watts when idle to several 100 watts when fully tasked. A quality (*80 PLUS* Certified) PSU maintains a "flat" efficiency curve of at least 82% across the full range of expected loads. I prefer Corsair, Seasonic, and Antec PSUs, but understand achieving a high, flat efficiency requires quality design, quality parts, and quality construction - regardless the brand name stamped on the case, or the components inside.



> the PSU is rated at 29 Ampere on the 12volt line, what does this mean? How can a "700" watt PSU only deliver 29 amps on the 12v?


The formula for DC power is I (amperes) x E (volts) = P (power).

There are two 12V rails on that system. 

29A x 12V = 348W
348W x 2 = 696W (close enough to call it 700W).


----------



## Fapguy (Oct 2, 2008)

Bill_Bright said:


> There are two 12V rails on that system.


Ahhhh, that's what I couldn't figure out.... So it has two rails, that makes sense.


----------



## gcavan (Aug 13, 2009)

> • Output *Max.* 700W


To me, a maximum output rating on a supply, is a red flag. That would be the absolute maximum the manufacturer rates it at. However, it would really surprise me if it is actually capable of supplying that much power without self destructing. Regardless, any power supply which sings to me goes to the recycler.


----------



## Fjandr (Sep 26, 2012)

Well, all power supplies have to list a maximum power draw. That's required by pretty much every governmental appliance certification entity in existence (UL, CE, etc.). It doesn't necessarily have to be in wattage, but that can be easily calculated from the voltage input and max. amperage draw (Ohm's Law, as mentioned by Bill above).


----------



## Bill_Bright (Dec 17, 2004)

> To me, a maximum output rating on a supply, is a red flag.


I think that is common, even among the more respected brands. The fact they state the current on the 12V rails raises a "green" flag, in my book. 

It is when a PSU maker does NOT report the current ratings that should raise the red flags. 

I note the Seasonic X Series, reports "total" (which to me is the same as "maximum") wattage. 

Corsair says "total power" too.

As does TP-650G - antec.com.

And a Yellow (cautionary) flag would be if they include the +5V and 3.3V current ratings in the "total" or "maximum" wattage ratings - which is kinda what Antec did. :sad: But Antec shows how it got its total power (though not sure how 120 + 550 = 650, at least that is conservative and not exaggerated). If that information is not provided, it would turn the yellow to red.



> Well, all power supplies have to list a maximum power draw


Just to ensure no (or at least less) confusion, power "draw" (from the wall) is different than power output. And note the draw deals with AC, not DC so the Ohm's Law formulas don't exactly apply as you need to factor in Power Factor, capacitance, reactance and more. The draw from the wall does need to be posted on the device but it does not tell you the resulting power outputs. There are many factors that affect that, not least of which is efficiency, which varies with the load (though to a lessor extent with 80 PLUS certified PSUs). For example, a very efficient PSU rated at 85% efficiency still outputs just 85 watts for every 100 watts it draws from the wall. That extra 15 watts is lost in the form of heat.


----------



## Fjandr (Sep 26, 2012)

> But Antec shows how it got its total power (though not sure how 120 + 550 = 650, at least that is conservative and not exaggerated).


It's listed that way because the 12V combined load can go up to 550W so long as the non-12V loads do not exceed 100W, or the combined non-12V load can hit 120W so long as the 12V load does not exceed 530W. Most decent manufacturers break down their maximum ratings that way, because a good PSU can handle loads adaptively (to a certain degree, anyway).

For example, it's conceivable a manufacturer could build a supply in such a way that the 5V/3.3V subsystem could output 500W, and the 12V subsystem could handle 500W as well, but the maximum output could, in totality, only hit 750W.

Yes, I understand the total draw is quite a bit more complex when dealing with AC (yay, calculus), but it will always tell you important things about the maximum DC output. Namely, the DC output maximum will always be less than the maximum AC draw. That's why a stated maximum output isn't actually a red flag unless, of course, it's far lower than the AC draw would otherwise suggest. That last part was all I was really attempting to point out.


----------



## greenbrucelee (Apr 24, 2007)

that psu isn't even on the psu database as far as I can see.

But from what I can see is it isn't even 70% efficient so thats a big no no in my book.

When looking for a good psu a good sign is that it using high grade Japanese capacitors in some they are aluminum and in some they are gold. Ones with gold capacitors generally have a high efficiency rating and usually have a longer shelf life.

Some Seasonic psu's have an 80% efficieny rating but when tested it is actually about 92. Apparently they are working on a design which will be 95+ efficient, although I will believe it when I see it.


----------



## Bill_Bright (Dec 17, 2004)

> It's listed that way because the 12V combined load can go up to 550W so long as the non-12V loads do not exceed 100W, or the combined non-12V load can hit 120W so long as the 12V load does not exceed 530W. Most decent manufacturers break down their maximum ratings that way, because a good PSU can handle loads adaptively (to a certain degree, anyway).


Except standard ATX Form Factor motherboards and ATX devices used in the vast majority of computers don't use -12V (or -5 either). They use +12, +5 and +3.3V. 

I realize many computer PSUs are often used in other applications, like custom POS workstations where -12V may be needed, but I don't feel when a computer PSU is being marketed as an "ATX compliant" computer power supply, it should include wattage values the user will never see. There should at least be an asterisk in the specs to explain the differences.

To be sure, Antec is one of my preferred PSU brands. But I feel Antec's marketing weenies are "spinning" the specs a bit.  But at least, as I said above, it is in a conservative and not exaggerated manner - or they fat fingered 120 instead of 100 on their calculator!


----------



## greenbrucelee (Apr 24, 2007)

some manufacturers do make conservative figures i.e rounding it up a bit when putting down the specs but some just lie pure and simple.

Most of us will know the PSU make that paid review sites to say their psu's were good when infact they had a habit of exploding when pushed to near their so called max output and their so called sli units couldn't handle sli.

I wont mention the brand so the forum doesn't get in any trouble but this brand is still going and their 900w gs units only come out at 785w.


----------



## Bill_Bright (Dec 17, 2004)

> but some just lie pure and simple.


All the more reason to do your homework and research professional review sites - sites where real electronics technicians using real power analyzers and measuring equipment, with proper and varied loads, actually test and verify and compare products. 

I wish they were like Consumer Reports who buy their products off-the-shelf and don't test samples supplied by the maker. Samples that may have been specially selected by the maker to shine. 



> Most of us will know the PSU make that paid review sites to say their psu's were good when infact they had a habit of exploding when pushed to near their so called max output and their so called sli units couldn't handle sli. I wont mention the brand so the forum doesn't get in any trouble but this brand is still going and their 900w gs units only come out at 785w.


No doubt, some review sites are not professional review sites. In fact, their reviews are often almost verbatim from the product's brochure.  But not all are that way so it is important to read more than one. 

Also, don't judge a review site by their forum. One site known for quality PSU reviews has a forum full of "helpers" :nonono: who really don't have a clue when it comes to properly sizing a PSU - but they feel since they are associated with the site, they are the authority. Not so. 

This is also where 80 Plus Certification comes in handy. PSUs have to earn that certification. They can't just buy it, or print it on a label.

But still, to your 785 vs 900 scenario, this is where adding a nice 10 - 30% buffer when sizing your PSU can help ensure you will have enough power today, and in two years when you decide to add a couple drives, more RAM and a hungrier graphics card.


----------



## greenbrucelee (Apr 24, 2007)

I have always gone by adding 30% to what you really need but I have always overclocked were adding extra voltage is needed but a 30% buffer also to me makes sure I have enough power.

Now if you see my system under my name you will see I am running a seasonic 650G series psu now I don't really need it but I am overclocked to 4.5GHz running a 1.32vcore which is very little and my gpu is recommended to be powered by a 500w psu but as said I always add 30% to that.


----------



## Fjandr (Sep 26, 2012)

Bill_Bright said:


> Except standard ATX Form Factor motherboards and ATX devices used in the vast majority of computers don't use -12V (or -5 either). They use +12, *+5 and +3.3V*.


I guess I should have been more clear: the "-" in "non-12V" is a dash, not a minus sign. The bolded numbers are what I was referring to by "non-12V" outputs.

After looking at a half dozen PSUs from as many manufacturers, all have maximum rail output ratings that, when added up, exceed the overall maximum output.


----------



## Bill_Bright (Dec 17, 2004)

Fjandr said:


> I guess I should have been more clear


:facepalm: No, I think I should have downed another cup of coffee before I replied. I re-read what you said now and see that you were quite clear! My apologies - especially if I made it more confusing.



> my gpu is recommended to be powered by a 500w psu but as said I always add 30% to that.


I look at the GPU maker's recommendation only as a very rough guide because they base that on some arbitrary "average" computer they think most users have. They have no clue if using an entry-level dual core CPU or monster 6-core. They don't factor in multiple monitors (with extended desktop), extra RAM sticks, extra drives, fans, expansion cards, alternative cooling, etc. 

That's why I use and recommend the *eXtreme PSU Calculator Lite* (and no other PSU calculator). This calc lets you add or remove different drives, fans, cards, and more so you can see how much your system needs. 

It provides a minimum, and a recommended that pads the results with a buffer. But you can easily increase that buffer to allow for future upgrades (and component aging) by setting both TDP and system load to 100% and setting Capacitor Aging to at least 10%.

FTR, for regular helpers, I don't hesitate recommending the pro version of that calculator. One nice feature it has it UPS recommendations too.


----------



## Fjandr (Sep 26, 2012)

No worries. I do that myself on more occasions than I'd like to admit. :smile:

As for that calculator, it's definitely a nice find. Honestly, it should probably be pinned to the top of the PSU and/or build sub-forums.


----------



## Fapguy (Oct 2, 2008)

Wow, I'm gone for a few days and comments are flooding in.

Thanks for everything so far, she finally understands why you can't just buy good hardware and skimp on the power supply. 

"so it's pretty much the heart of it all" <-- her words. also what i've been trying to tell her, but never would've listened, hehe...


Anyways, any ideas why it would start squealing at IDLE, and not at load? That's really the only question left


Thank you!


----------



## greenbrucelee (Apr 24, 2007)

yes because its made from crap material and has no quality to it and is basically crap.


----------



## Bill_Bright (Dec 17, 2004)

> yes because its made from crap material and has no quality to it and is basically crap.


Or it is just worn. When idle, the fan likely does not spin very fast so the fan hub is almost just floating on the bearings and banging around in the mechanical "slop". When the fan spins faster when the system is generating more heat and starts really pushing air out, all that Sir Newton and "equal and opposite reaction" stuff comes into play and pushes the fan back against the air flow and the bearings, taking out the "slop" in the drivetrain, if you will, and no more noise. At least until the bearings wear more - which they eventually will, if they don't just seize first. 

That's if it is even the fan causing the noise. 

Transformer windings can "sing" under certain loads too, as can some capacitors.


----------



## greenbrucelee (Apr 24, 2007)

I had a psu where the capacitors whistled when under load. A couple of years a go I had two corsair psu's which were noisy the fan bearings were shot from new and also there were big power fluctuations in idle and load. Corsair deemed them faulty from the factory and should have passed their quality control but there is always a percentage that will get past this.

With lower quality ones there may not be a quality control process


----------



## Fapguy (Oct 2, 2008)

Bill_Bright said:


> That's if it is even the fan causing the noise.
> 
> Transformer windings can "sing" under certain loads too, as can some capacitors.


I can verify it is not the fan, I stopped it with a pen when it was making the noise. And we aren't just talking "low" "singing" it was literally screaming, sort of like when one of those old 4870's or 4890's or 5870's were pushing out 3000+fps, I think I had tinitus for an hour or something after trying to pinpoint where the squealing came from


----------



## Bill_Bright (Dec 17, 2004)

> I stopped it with a pen when it was making the noise.


Certainly a conclusive test though I recommend just making it slow down for second instead of stopping as that will change the pitch of the sound - if coming from the fan - making it easy to determine if the fan is the source while still providing cool air.


----------



## Fapguy (Oct 2, 2008)

Bill_Bright said:


> Certainly a conclusive test though I recommend just making it slow down for second instead of stopping as that will change the pitch of the sound - if coming from the fan - making it easy to determine if the fan is the source while still providing cool air.


Ah yes yes, hehe, I didn't just jam it in there, I slowly stopped it with a finger and put the pen in, so I guess I did also do that :grin:


----------

