 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Off topic archive. : 230 VAC PC PSUs - Should they be imported
| Author | Message | ||||
| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Friends, Just been told by sPuDd on this forum that electrolytic caps dry out on PC PSUs and then the ripple on the mobo caps dries them out and then the PC stops! Great! Just having tried to fix a friend's PC unsuccessfully as the mobo has most likely gone west, I wonder how much of this problem is caused by the rating of PSUs to be only 230V??? In Oz we have 240 V plus/minus 7%, which means the voltage to the 230 V PSU goes easily to 250V or more. This +/- figure is the official state electricity co. figure and does not even talk of the actual high-voltage spikes in our power supply. Do I have a point here or in other words: Am I right or are you wrong? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5036 |
Yes the mains voltage in Oz is 240 ( give or take 20 ), but the PC PSU's are still operating in their safe range. Only a couple of the caps in the PC are exposed to this mains voltage, the rest are at 12v, 5v, 3.3v etc. When the mains is rectified and fed into a cap(s), the DC voltage is about 335v ( Peak AC volts = AC x 1.4 approx ). The caps in question are usually rated at 350v or 400v, so they are operating within their ratings. However, big spikes on the mains can push the voltage over the caps limit, and BANG! Electroytic caps "drying out" is another problem. Cheaper caps dry out sooner, and caps exposed to heat even quicker. Its a common problem in switch mode powersupplies. A TV technicians bread and butter job is replacing the caps in a VCR or TV power supply, fixes many faults. I've replaced the caps on pc motherboards to get a few more years life out of them. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks, Glenn. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
sPuDd Senior Member  Joined: 10/07/2007 Location: AustraliaPosts: 251 |
G'day Dom, Welcome to the world of SMPSU's. The pain has begun :-) SMPSU's regulate their output almost regardless of the input voltage. Hence why most SMPSU's can go from 90-240VAC. This is (was) my favorite 550W ATX PSU that I rebuilt several times (6 years old): 
This is (was) my favorite Ti4600 Gforce video card (6 years old): 
If you feel up to it, and its a hobby, have a go changing the caps in an ATX PSU or maybe a motherboard where the caps are on the way out. You can sometimes tell by the X in the top of the cap bulging up that its about to go pop. Try to use the same or better voltage and capacity, and use good quality low ESR caps. sPuDd.. It should work ...in theory |
||||
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi sPuDd, I envy where you live. The PC power supplies I have seen that are over a year old have started to rust, or are full of fluff and dust. These look mint. Good to see stuff can still look good after 6 years. Gordon. become more energy aware |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
It's common knowledge that capacitors are nowadays the most unreliable components in electronic equipment. The rated lifetime of many electrolytic capacitors is only about 8000 hours. That's less than a year of continuous use... Exposure to heat will decrease their lifetime even more. They usually fail by increased ESR (equivalent series resistance). Their capacity still stays about the same (usually within tolerance), so they test fine when checking their capacity with a DMM. However, due to the increased ESR they're no longer able to perform their function. Back when I still routinely repaired electronics I grabbed the ESR meter to check out caps even before I reached for the DMM. It was the single most useful piece of test equipment for repairing electronics I have ever owned, along with the DMM. When the ESR tested more than about 5-10 ohms (depends on the voltage rating and capacity) I replaced the capacitor. Amazingly, some measured up to ~150 ohm while still performing their function (depends on how they're used in the circuit). Sometimes they'll bulge, but I've replaced plenty of failed, high-ESR caps that had not (yet) bulged. And the best thing of an ESR meter: you can test in-circuit, without having to desolder the caps. The latest incarnation of my ESR meter was loosely based on a design published in Elektor/Elektuur, september 2002, a simple one with digital readout. You'll find plenty of other designs too if you google the web. Some simple analog ones up to PIC-controlled devices. Here's a picture of mine, built on perf board: 
If you're into repairing electronics, the next thing you should get after a soldering iron and DMM is an ESR meter, even before considering getting an oscilloscope. (though a scope can easily be used too, with some added electronics, to test capacitors for ESR). Dick Smith also has a kit (K7204/K7214) of an ESR meter for sale: http://www.flippers.com/esrktmtr.html If you hadn't noticed yet... I love my meter. A tremendous time and labour saving device. And an eye-opener as to how unreliable electrolytic capacitors really are. Peter. |
||||
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dom, You may notice that in most pc power supplies they have only 200volt electro's on the input, rather than the 400v ones Gizmo refers to. This is because the two (notice it has 2 identical 200v ones) capacitors are in series across the rectified 240vac (so about 340vdc.... 170v across each 200v unit). This configuration is neat to drive a half bridge topology. This system seems to be the mainstay of pc psu'S. I havent seen this style of thing much elsewhere. In other power supplies (tv's, monitors etc) they use a single switch topology, and the caps will be 400vdc as they see the full rectified 240vac (340vdc). Usually only 1 cap is sufficient. ............oztules Village idiot...or... just another hack out of his depth |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
[quote=Oztules]This system seems to be the mainstay of pc psu'S. I havent seen this style of thing much elsewhere.[/quote] I understand this is done for easy switchover from 110Vac to 230Vac (or 240Vac  ). All it takes is one single-pole switch to change voltage, in effect turning the rectifier into a voltage doubler for 110V. Spudd's photo show the switch in between the two power receptacles, with 2 blue wires attached to it. If there's no external switch on the PSU, there's usually a wire-jumper on the board that does the exact same thing.
I figure this method isn't used much in other equipment (e.g. TVs) as these devices are unsuitable for use in different places anyway because of differences in local broadcast standards (PAL vs. NTSC). To get back to Dom's original point: the 4% higher voltage (240/230=1.04) doesn't reduce lifetime expectancy of elcos. Unlike e.g. in the case of incandescent bulbs, where lifetime goes down by a factor of about 1.04^10 = ~1.53. So an incandescent lamp that's rated for 1000 hr at 230V would (be expected to) survive for about 650 hours at 240V. But elcos aren't incandescent lamps. Peter. |
||||
| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Not as frightening as the last picture at least 
Village idiot...or... just another hack out of his depth |
||||
| sPuDd Senior Member Joined: 10/07/2007 Location: AustraliaPosts: 251 |
He's a kinda funny looking bear. I think he needs a beer stat nurse!! Is he a channel barge bear Dinges? sPuDd.. It should work ...in theory |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
[quote=Oztules]Not as frightening as the last picture at least[/quote] Yeah, I got too many complaints about that one. Well, actually only one complaint, from Ron, telling me that when reading my replies, the good-looking guy in my avatar was distracting him. The things one does to keep him happy... Spudd, I may change my mind and use an image of Dr. Bunsen as avatar instead... 
Peter. (with apologies to Dom for the thread diversion) |
||||
| sPuDd Senior Member Joined: 10/07/2007 Location: AustraliaPosts: 251 |
Mi Mi Mi Mi Mi Mi Mi !!!! It should work ...in theory |
||||
| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
[quote]I figure this method isn't used much in other equipment (e.g. TVs) as these devices are unsuitable for use in different places anyway because of differences in local broadcast standards (PAL vs. NTSC). [/quote] If they run single switches, they will probably have 100-250vac stamped on them. As a general rule they will be under 200 wattsor so. This covers most domestic stuff (tv's, monitors etc. Over a few hundred watts they tend to go to half bridge, and over 500w to H bridge topologies....yes I know I have seen 500W single switch stuff, and half bridge up to 1kw, but normally, single switch for less than 200w. Dual switch for more.... and full H bridge for real power. So I'm not sure just the ease of voltage selection was the cause, as the single switch stuff is flexible enough to do both (turn your monitor around and look at the power requirements... probably 100-250vac 50/60hz... covers most stuff without series caps and voltage doublers. Having said that, the earlier small psu's ,200w, had single switches and had the voltage doubler series caps as well..... so I think it was a power thing that dictated the cheapest topology with the bonus of simple dual voltage. .......strangepork..bzzzt I mean Julius...bzzzt I mean oztules Village idiot...or... just another hack out of his depth |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Why I brought this topic up: 1. Many PCs delivered to TAFE (WA) had 220 VAC (European voltage?) PSUs delivered to them and they failed, so TAFE in their next specification decided to insist on 240VAC PSUs in their next purchasing contracts. As the person writing the contract documents knew his stuff one wonders why there was an insistence on 240 if it does not make any difference to the life of the unit? 2. There is a rumour going around TAFE that the successful company simply change the stickers on the PSUs from 220V to 240V! 3. The odd TAFE student knew how to upset me by simply shifting the switch from 230V to 110V leading to a blown fuse and one less PC in the class room. Guess who fixed it? 4. I prefer Dinges as the magician rather than as a bear as he on this forum or Fieldlines manages to demonstrate levitation with a fluorescent background from the nuclear reactor nearby. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
 Print this page |
