• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

12V too high...advice needed urgently

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

starfarer

Registered
Joined
Jan 3, 2001
Hi I was running xp1700xp Tbred b @2ghz and was running the prime95 for 27hrs before i left for work. When i came back i found comp dead. Changed to my old generic 300W PSU and it's running ok till now(running prime95@ same spec). The readings from SisoftSandra , MBM and USDM all matches to an accuracy of 0.001% and Here's from MBM(after running Prime for 2hrs):
+5.00 = 4.95
+12.00 = 12.95
-5.00 = -5.50
-12.00 = -12.93
+3.3 = 2.78
cpu = 32C(full load)
Case = 23C

Is there any reason for concern? It'll probably take 1 week to get back my 2thmax(EPOX)HE370 PSU and don't wanna take any risk to my remaining components(Just built rig 4 days before)
Epox8rda+, XP1700@2Ghz(10x200) 256MB Samsung Original DDR400 @CL2.5, 6,3,3(crap memory and waiting for TwinMOs). Thank YOu.
 
Please notice how low your 5 Volt supply is. often in cheap supplies and even sometimes in more expensive ones the voltage sample for the regulation is taken off the 5 volt line. This means logically that when more current is drawn from the 5 Volt line the duty cycle from the drive circuit increases proportionately.
In most computer power supplies the 3.3 Volt line is regulated by a buck regulator off the 5 Volt line. You have an extremely heavy load for some reason on the 5 Volt line. The 12V and -12V are both proportionately high therefore it is a logical assumption that both voltages are taken off the same transformer. Or there are two transformers driven in parallel by the main switching transistors.

I repair power supplys for industrial equipment and we have one that in the case of a break in the 5 Volt line somewhere before the sampling point (which by the way in this case is on the processor board) the 8.5 volt supply will go to 18 ++ Volts. The first time you see this behaviour you will be stumped. You have no 5 Volt supply but the 8.5 volt supply reads 18 volts! I remember hunting for this problem the better part of the day once. Then finding a broken inductor on the 5 Volt line. The feedback circuit saw no short and no voltage at the sample point so it assumed logically that the duty cycle was not high enough so opened it full throttle. Since the transformer is a common single one in this case, the 8.5 volt supply went full throttle out of regulation. Incidentally if the load is increased on the 8.5 Volt line the 5 volts will rise to a point though not as much (because it is the regulated line) due to a principle called reflected impedance. This is the same principle that caused your 12 Volts to rise.

The conclusion now that you have the theory, is this 1 Volt or so doesn't make that much difference in the 12 Volt line. Most devices that use it, regulate it at the usage point. The others don't care that much. Disk drives, for example use it only for motors and they control the speed by duty cycle to the motor or phase control so 11-13 volts is tolerable. Don't worry about it the low 5 Volt line is of more concern since it indicates there may be considerable wattage being drawn on the 5 Volt line.
 
All that having been said, I think you'll be okay as long as your system is stable. Although that 3.3 is awfully low. If you're overclocking, I would probably back it off a bit.
 
I didn't pay much attention to the 3.3 but that's correct. in fact that is probably where your current is going. So I would agree back off on the processor frequency until you get a better supply.
 
Ok i upped the voltage for memory from bios and it's now around 2.90 for +3.3V line. All other voltage remained same. Will now i be safe?
 
Don't always rely on what your computer voltage read out tells you. It's a known fact they're often off. Stick a multimeter on your +5 and +12 and see what it is. I would believe a multimeter before the computer.
 
i am running a new 300 watt power supply for my mobo, one fan, and one cdrom. i also have a old 90 watt supply running two hard drives, a cd-rw, the floppy (who ever uses one anyway), and a total of 6 12 volt fans. most ventilate the case. there is one drawing fresh air in over the hard drives and under the cd roms straight at the prossessor fan. they are both case size fans and pull some air, i have constructed a duct between the one cooling the heatsink and front and back sides of the slot one card my pIII 800e coppermine is on. that fan is fed air from the one between the drives fresh from the front side of the case. this way i don't stress either power supply real hard and my processor runs at idle at an unbelievable 71F and rarely gets over 105F for more than a second. the only problem i have is cold starts, it takes 2-4 boots to get her running. there are other fans pointed directly at the mobo, so i guess i am cooling those all important capacitors too much. you power supply guru's see any harm in this? for the smaller psu i have a switch mounted on the front and a LED that lets me know the fans are on and the switch allows me to shut down the second PSU when i power the rest of the computer down.
this way my computer isn't collecting dust all the time. i have run this setup for some time now with no problems. as long as i first turn on the secondary PSU first i dont have to worry about burning out a chip. i don't see why folks don't do this more often, espescially if they run a pelteir. they can isolate the neutral grounds on two PSUs and run the +12v and the +5v in series to get +17v or run the two 12+ together to double the amperage. this can be a handy trick for those who want to power those power hungry cooling systems on the cheap.

whatcha think? any improvements necessary or is this setup fine the way it is? i got the idea to run them in parrallel from another website. i have run subwoofers in series, and even series parrallel to lower the ohms down into to 4 ohm territory, sometimes down to 1 ohm to get the amp to push more amps thru my subs. they must be rated to be stable at 4 ohms, or in some instances lower. most folks don't run 1 ohm across a bridged amp, but it works and works well. it's what we call a "cheater" amp. if it can be done with a system pumping 94 amps thru some subwoofers, surely it will work with a couple of cheap PSU's. (if done correctly). that sound system i had at 94 amps was pumping a true 800 watts of bass into two 15 inch kevlar coned speakers (or drivers for those of us in the buisiness).

well i guess i just wrote a book, so i will let you go, give me some feedback. wisdom.
 
"often in cheap supplies and even sometimes in more expensive ones the voltage sample for the regulation is taken off the 5 volt line."
In the dell supplies, a flyback regulator provides the 12v, then buck regulators step down the 12v to 5v and 3.3v.
BTW, dell supplies use an IGBT in a TO-3 case as the main switchmode transistor(that is [H]ard).
 
Well I searched the net about this voltage of +5,+12 and +3.3V and couldn't find a thing about +3.3V. Everybody seems to have problem in +5v line. In the meantime i checked through others readings and guess waht? My +3.0V line is way too LOW :mad: man this is LOW with what other are getting(always higher). Maybe my board Epox8rda+ culprit?Couldbe the reason that my 2thmax(here in Asia Epox name)HE370W power supply went dead. Never had chance to see waht was the reading with that PS but gone for warranty service(4 days old). Anybody with nice info/link for all this voltage explanation(expecially with +3V line)?
 
quote:by starfarer

" Ok i upped the voltage for memory from bios and it's now around 2.90 for +3.3V line. All other voltage remained same. Will now i be safe?"

I have found mbm5 somtimes says the agp voltage or the the voltage of the ram instead of the 3.3v rail. Sometimes stuff like that get misconfigured and can be confusing. Maybe you can do a test and lower the ram voltage to 2.5v and see if the 3.3v goes down as well and then raise it up a bit and see if it goes back up? That may help you figure out that the 3.3v rail mbm5 reading is reading the wrong rail, hope this helps out.
 
I just did that and I know the +3.0V line corresponds with the memory Voltage in Bios. If i lower say to 2.66V for memory on MBM for +3v line it display 2.64 .
 
Back