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Voltage question

A

ajac

Member
Here are my currrent voltage use by mbprobe:

5 = 4.87
3.3v = 3.18 used
+12v= 11.84 used
-5v= -3.70 used
-12v= 8.29 used


Looks like I am cutting it close. Maybe a better power supply will help out.
Hmmm any suggestions?



Anthony
 
This really belongs in general hardware, but anyways...
The -12 and -5 really worry me. I'd look for a new power supply if your computer is having problems.
 
what kind of power supply is it? how long have you been seeing those voltages? is your system stable? hardware monitoring software can be incorrect with reading voltages sometimes, so verify the correct readings with a mulimeter.
 
Originally posted by: ajac
Sorry thought it was to technical of a question but what watage should I get? right now at 380 hmmm
Click to expand...

size isnt important. quality is.

well, dont get a 150 obviously, but you dont need more than 300 unless you have a whole lot of internal components or you are eccentric.

antec, enermax, and sparkle have always worked out well for me. reliable, quiet, and the rails are right on target usually.
 
Well my brand is Antec its the sl400 but output is only 380 on 5v 12v and 3v I think was thinking about getting thier TRUE430 I saw at bestbuy.
 
Originally posted by: ajac
Here are my currrent voltage use by mbprobe:

5 = 4.87
3.3v = 3.18 used
+12v= 11.84 used
-5v= -3.70 used
-12v= 8.29 used


Looks like I am cutting it close. Maybe a better power supply will help out.
Hmmm any suggestions?



Anthony
Click to expand...

??? what do you mean "used"
I'm thinking that maybe you have a misunderstanding of something
(Or else, I have a horrible misunderstanding!)


on the -12V rail, the voltage should be -12V, +/- a little variation.
What should change, based on the number of and type of devices is the current drawn, not the voltage.

Someone please correct me if I'm wrong.
 
When more current is drawn, the voltage will drop if not properly regulated. Don't try this at home, but it can be easily demonstrated in that if you stick a paperclip across a power outlet lights on the circuit will dim due to the excessive current draw.
 
Originally posted by: DrPizza
Originally posted by: ajac
Here are my currrent voltage use by mbprobe:

5 = 4.87
3.3v = 3.18 used
+12v= 11.84 used
-5v= -3.70 used
-12v= 8.29 used


Looks like I am cutting it close. Maybe a better power supply will help out.
Hmmm any suggestions?



Anthony
Click to expand...

??? what do you mean "used"
I'm thinking that maybe you have a misunderstanding of something
(Or else, I have a horrible misunderstanding!)


on the -12V rail, the voltage should be -12V, +/- a little variation.
What should change, based on the number of and type of devices is the current drawn, not the voltage.

Someone please correct me if I'm wrong.
Click to expand...

im pretty sure you are correct
 
Originally posted by: bobsmith1492
When more current is drawn, the voltage will drop if not properly regulated. Don't try this at home, but it can be easily demonstrated in that if you stick a paperclip across a power outlet lights on the circuit will dim due to the excessive current draw.
Click to expand...

isnt that just due to lack of necessary current?
 
Yeah; I'm just saying that as the current draw changes, the voltage may change as a result since the PS can't supply sufficient power (P=IV).
 
Originally posted by: bobsmith1492
Yeah; I'm just saying that as the current draw changes, the voltage may change as a result since the PS can't supply sufficient power (P=IV).
Click to expand...

good point 🙂
 
Originally posted by: MrDudeMan
Originally posted by: bobsmith1492
Yeah; I'm just saying that as the current draw changes, the voltage may change as a result since the PS can't supply sufficient power (P=IV).
Click to expand...

good point 🙂
Click to expand...

It's to the point just beyond what I understand quite well...
after you pass the nice "clean" formulas and go into the real world applications for electricity...

But, for the most part, doesn't the power supply go from 110V AC to the lower DC volts by means of a transformer? (plus diodes, capacitors, etc. to give a nice smooth DC voltage)

Now, since P=IV, and we know Power isn't sufficient... in a transformer, which of the two: I or V is maintained? I would have thought it was V, not I... thus, the voltage stays the same and the current decreases.

edit: or is a computer power supply more sophisticated with more complicated wiring than a simple transformer? I've actually never taken one apart... I probably should.
 
Originally posted by: DrPizza
But, for the most part, doesn't the power supply go from 110V AC to the lower DC volts by means of a transformer? (plus diodes, capacitors, etc. to give a nice smooth DC voltage)

Now, since P=IV, and we know Power isn't sufficient... in a transformer, which of the two: I or V is maintained? I would have thought it was V, not I... thus, the voltage stays the same and the current decreases.

edit: or is a computer power supply more sophisticated with more complicated wiring than a simple transformer? I've actually never taken one apart... I probably should.
Click to expand...

Modern power supplies do NOT work like this. The kind that you are talking about is a "linear" supply, while modern electronics use a "switching" technique.

Now, on to theory... Let's assume that computers DID use a linear supply, so that I can answer the 2nd part of your question...

If a transformer is overloaded, then I believe that one of two things could happen (but my specialty is digital, not power supplies):

1) The core gets saturated. As the load increases, the primary sucks more current, in which case the magnetic field gets more intense in the core. At some poing, the core becomes saturated (can't hold any more magnetism, in a sense). If you assume a resistive load, the voltage AND the current would both drop. According to Ohm's law, R=V/I. And if the resistace is not changing, then I and V will both track each other.

2) The windings overheat and burn out. Then, I=0, V=0, P=0.

PS: Switching supplies can still have voltages on the capacitors. Unless you like getting 170V or more dumped into your fingers, be VERY careful. And 120V lines are 120V RMS. The peak voltage is almost 170.
 
It's the voltage that will drop. If you short something out, it will draw as much current as can be provided; then the voltage will drop until P=IV once again (unless something burns out like harrkev said).
 
Those look like values under load. Lots of power supplies probably behave like that... but you'll have to spend big $$ to get more accurate voltages.
 
Well I figured it out. It was the motherboard. I put back in my old 2600 xp cpu and motherboard and now everything is running fine. Guess the money I was saving up to buy a psp I will use to get a socket 939 instead now.Since my amd 64 system was a socket 754 the CPU is fine though just the motherboard is gone. Well the AGP port anyway.
 
The rule on a power supply is +or- 5% and ignore the negative voltage. which means your fine on the PS
 
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