Power Tolerance

  • Thread starter Thread starter Piggy
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Piggy

Hi

Anyone know what tolerances should be expected from a PC's power supply? ie
12v +/- ? 5v +/-? etc

I have a problem with external USB hard drive devices loosing connection,
After some time checking drivers, power settings BIOS etc etc the only 2
things I can see is 1 the main board is defective or a problem with the
power supply??

Any ideas?

:o)
 
Piggy said:
Hi

Anyone know what tolerances should be expected from a PC's power supply?
ie 12v +/- ? 5v +/-? etc

I have a problem with external USB hard drive devices loosing connection,
After some time checking drivers, power settings BIOS etc etc the only 2
things I can see is 1 the main board is defective or a problem with the
power supply??

Any ideas?

:o)
Click to expand...

5%. Or, 12V should be 11.4 to 12.6. 5V should be 4.75 to 5.25. -Dave
 
Piggy said:
Anyone know what tolerances should be expected from a PC's power supply? ie
12v +/- ? 5v +/-? etc
5%

I have a problem with external USB hard drive devices loosing
connection, After some time checking drivers, power settings BIOS etc
etc the only 2 things I can see is 1 the main board is defective or a
problem with the power supply??
Click to expand...
Any ideas?
Click to expand...

Do the USB devices have their own power or do they get it from the USB port ?

If they get it from the USB port, some ports can be inadequate, cant
provide the full legal power. In that case a powered hub can fix that.

If they have their own power, it can be a flakey
USB port, try a different one if you can.
 
Hi

Yes the USB devices in question are external hard drives with a power
supply, on the main board there are 2 USB 1 & 2 USB 2 ports and they all
show the same fault with the drives connecting and disconnecting constantly!
 
I notice that the 5v line is always around 4.80v to 4.84 and 12v line is
12.4v whilst the computer is 'ticking over'
the power supply was a quality branded item, but is about 2 years old now.

Another consideration that could be unrelated (or not) is that 2 old hard
internal drives have failed in the last 2 months, the first only had bad
sectors where the second totally failed, I have fitted a new drive now that
has worked with no faults or problems for about a week. all the computer
equipment is connected via surge protected sockets.

:o)
 
Piggy said:
Yes the USB devices in question are external hard drives with a power
supply, on the main board there are 2 USB 1 & 2 USB 2 ports and they
all show the same fault with the drives connecting and disconnecting
constantly!
Click to expand...

Are all the USB devices identical ? Can you try them on a different PC ?
 
Piggy said:
I notice that the 5v line is always around 4.80v to 4.84 and 12v line is
12.4v whilst the computer is 'ticking over'
Click to expand...

How did you measure those ? Unless you used a multimeter,
the numbers dont mean much, the motherboard A/D is quite
inaccurate as you will see if you compare the reading with
what a multimeter says.

If you measured it with a multimeter, the 5V a tad on the low
side even tho its still with within spec and that might combine
with USB devices that are too picky on what they required.
the power supply was a quality branded item, but is about 2 years old now.
Click to expand...

The age shouldnt matter.
Another consideration that could be unrelated (or not) is that 2 old
hard internal drives have failed in the last 2 months, the first only
had bad sectors where the second totally failed, I have fitted a new
drive now that has worked with no faults or problems for about a week. all the
computer equipment is connected via surge protected sockets.
Click to expand...

Its possible that the power supply is glitching and that isnt
visible even with a multimeter. You need a fairly fancy peak
hold multimeter to see that sort of power supply failure and
they cost more than a new power supply so its usually better
to try another power supply to see if that helps.
 
I did check the power supply with a multimeter after reading your comments
and the 5v line is 5v also the 12v is 12.37v
 
Numbers provided by others do not take into account other information
such as how multimeters often work. 3.3, 5, and 12 volts should be
above 3.22, 4.87, and 11.7, Voltages near those minimum values either
imply a defective supply or demand further analysis with an
oscilloscope.

Also these same measurements should be taken when muliple peripherals
are being accessed simultaneously by multiple (multi-tasking) programs.
IOW CD-ROM, hard drive, network, floppy drive, complex graphics, etc
should all be exectued simultaneously when those voltages are
reconfirmed.

Too often, a 'so called' quality supply is recommended by people
without basic electrical kowledge. One characteristic of a 'quality'
supply is a long list of numerical specs provided by the manufacturer.
Inferior supplies will not provide numerical specs for obvious reasons.
Without those numerical specifications, you don't know if it is a
'quality' supply. Just another characteristic to weed out over hyped
and defective power supplies.
 
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