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About +12v and 3.3v changing

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November 19, 2010 4:47:19 AM

I want know, when pc power supply +12V changing like 11.9, 12.0....12.4 and +3.3v changing 3.2... 3.4. What happen to the system? Is it normal? Are 12.4v and 3.4 normal? What happened when those values are changing? thanks

More about : 12v changing

a b ) Power supply
November 19, 2010 5:55:23 AM

Basically what dipankar2007ind said.

This is normal, and safe as long as it stays within ATX specifications: +/- 10%.

so
3.3v can go from 2.97v - 3.63v
12v can go from 10.8v - 13.2v

Although it does get increasingly dangerous if it gets closer to the boundaries, and considered severe if it goes past. As long as you are well within these boundaries though, you're fine.
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November 19, 2010 10:22:19 AM

You are correct. But I want to know, what effect it to mother board, vga, ram or cpu?
Those pc parts use internal voltage regulation or over clocked or get over temperature or nothing happened. thanks
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a b ) Power supply
November 19, 2010 10:49:56 AM

Basically the CPU's voltage is regulated by the onboard VRM's, so it doesn't realy affect the CPU, it's all safe. Same counts for the mobo.

However, if it is ouside of ATX specifications, or the power is very inconsistent then it can create numerous stability issues and possibly cause long term damage to your components, possibly kill them in an instant. The fluctuations you describe of 0.4 volts change on 12v rail is perfectly safe though, nothing to worry about., start worrying when it gets above 13 volts, or below 11 volts
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a c 271 ) Power supply
November 19, 2010 1:13:47 PM

ATX only allows 5% on the 3.3V, 5V, and 12V lines, it allows 10% on the -12V rail which is rarely used, so the limits on the voltage ranges are 3.135-3.465V, 4.75-5.25V, 11.4-12.6V. Ideally you want it to be close to its nominal values so the voltage regulation circuitry for each component doesnt have to work as hard, but they can usually handle just fine right up to the edge of ATX spec.

The reason the voltage changes is that when you draw more power you have more current going through the wires so you have a larger voltage drop, the power supply will usually slightly increase the voltage on its end to compensate for this but its rarely perfect. From the numbers you posted your 3.3V rail is about 3% regulation which is decent and your 12V rail is a bit over 3%, not too bad, certainly nothing to worry about it wont hurt anything, assuming those values are true. If you are measuring them with software they likely arent accurate. BIOS measurements are usually pretty good but a digital multimeter is the only way to be really accurate.
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a b ) Power supply
November 19, 2010 3:57:37 PM

hunter315 said:
ATX only allows 5% on the 3.3V, 5V, and 12V lines, it allows 10% on the -12V rail which is rarely used, so the limits on the voltage ranges are 3.135-3.465V, 4.75-5.25V, 11.4-12.6V. Ideally you want it to be close to its nominal values so the voltage regulation circuitry for each component doesnt have to work as hard, but they can usually handle just fine right up to the edge of ATX spec.

The reason the voltage changes is that when you draw more power you have more current going through the wires so you have a larger voltage drop, the power supply will usually slightly increase the voltage on its end to compensate for this but its rarely perfect. From the numbers you posted your 3.3V rail is about 3% regulation which is decent and your 12V rail is a bit over 3%, not too bad, certainly nothing to worry about it wont hurt anything, assuming those values are true. If you are measuring them with software they likely arent accurate. BIOS measurements are usually pretty good but a digital multimeter is the only way to be really accurate.

Learned something new!

All my answers we're right!! :whistle:  /sarcasm

Thanks man!
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November 19, 2010 10:41:24 PM

PCI-Express video cards require more 12V power (like gxt460....gtx580 and ati hd5770......) when +12v changing, effect it to vga card? Do they use voltage regulation? Or vga card gets over temperature or over clocked or nothing happened ? thanks!
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a c 271 ) Power supply
November 20, 2010 8:07:12 PM

No component on the card runs on 12V, thats super high for most transistors, they have on board voltage regulators that drop it down to the voltage they want, usually only a couple of volts. If the 12V drops the regulators have to work a bit hotter and they get a bit hotter but their output voltage stays the same, if the voltage goes up they work a bit less but the output stays the same.
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