PSU maxed out?

[Travis King]

When I turn on my cold cathode tube lights inside my case, the computer acts
like it wants to shut off. The case fan lights and cold cathode light keeps
getting slightly dimmer. Also, the fans slow down some. When I flip the
switch for the cold cathode lights back off, they spin a little faster and
the case fan LEDs get slightly brighter again. Is it that my PSU is getting
maxed out? It's a 400W power supply.

3 case fans all with blue LEDs
Asus A7V333 motherboard
AMD Athlon XP 2400+ 2.2GHz CPU
Kingston HyperX PC-3000 512MB RAM
Chaintech NVIDIA GeForce3 Ti200 128MB DDR TV out video card
Creative Soundblaster Live! 5.1 sound card
Linksys 10/100 network card
Memorex 52x32x52 CD RW drive
Lite On 16x DVD drive
Panasonic 3 1/2" floppy drive
Western Digital 80GB 7200RPM 2MB cache HD
Western Digital 120GB 7200RPM 8MB cache HD
Mad Dog dual cold cathode lights
Proview 19" monitor (CRT)
Logitech Z-560 speakers
Logitech Elite mutlimedia keyboard (PS/2)
Logitech blue optical wheel mouse (PS/2)
3 external blue tube lights that pulsate to sounds (USB)
Visioneer 5800 USB scanner
Microphone (microphone input)
Canon i560 printer (USB)
Belkin Surge Master surge protector (model f5c240)

 

[Paul]

When I turn on my cold cathode tube lights inside my case, the computer acts
like it wants to shut off. The case fan lights and cold cathode light keeps
getting slightly dimmer. Also, the fans slow down some. When I flip the
switch for the cold cathode lights back off, they spin a little faster and
the case fan LEDs get slightly brighter again. Is it that my PSU is getting
maxed out? It's a 400W power supply.

3 case fans all with blue LEDs
Asus A7V333 motherboard
AMD Athlon XP 2400+ 2.2GHz CPU
Kingston HyperX PC-3000 512MB RAM
Chaintech NVIDIA GeForce3 Ti200 128MB DDR TV out video card
Creative Soundblaster Live! 5.1 sound card
Linksys 10/100 network card
Memorex 52x32x52 CD RW drive
Lite On 16x DVD drive
Panasonic 3 1/2" floppy drive
Western Digital 80GB 7200RPM 2MB cache HD
Western Digital 120GB 7200RPM 8MB cache HD
Mad Dog dual cold cathode lights
Proview 19" monitor (CRT)
Logitech Z-560 speakers
Logitech Elite mutlimedia keyboard (PS/2)
Logitech blue optical wheel mouse (PS/2)
3 external blue tube lights that pulsate to sounds (USB)
Visioneer 5800 USB scanner
Microphone (microphone input)
Canon i560 printer (USB)
Belkin Surge Master surge protector (model f5c240)

Go to the BIOS Hardware Monitor, and watch the voltages when
you switch on the extra load. The power supply is generally
specified for +/- 5% regulation, and if you see about 10%
variation, then you might need another PSU.

You have to remember, that PC power supplies are "sloppy"
when it comes to regulation. There is one primary side circuit
pumping a transformer, giving multiple secondary outputs. It cannot
regulate too tightly, with the standard power supply architecture.
You may want to find a supply that claims to have separately
regulated outputs, as that should improve the load behavior.
The Antec Truepower makes this claim, but I've never read a review
which actually opened up the supply and demonstrated the components
in it that make this possible. One thing the Truepower does have,
is remote sense wiring for the three major supplies - you can see
two wires going to some pins on the ATX20pin power connector. That
means the power supply is able to observe the voltage as it enters
the motherboard.

In some cases, it is better to have two power supplies, if you have
toys in the computer. For example, if you have a 20 amp Peltier
cooler, that should be run from a separate power supply, as if one
of those is plugged into the same supply as the rest of the
motherboard, the PSU will shut down.

HTH,
Paul


HTH,
Paul

 

[Travis King]

The voltages for most of the things went down a little with the cold cathode
lights on.

 

[Travis King]

All voltages are within the +-5% threshold though... Once in a great while,
the VCORE will drop down a little more -5%, but then it immediately goes
above the set VCORE to around +2%.

 

[Travis King]

By the way, I'm using Asus Probe and I'm watch them while the computer's in
idle. Except for the VCORE, the other voltages are around -2%.

 

[Paul]

The voltages for most of the things went down a little with the cold cathode
lights on.

This article has an example of a cold cathode tube. The tube draws
3W, which would be 12V @ 0.25A, and is next to no current. There
is an inverter circuit, which converts the 12V to somewhere between
200V and 1000V (I've seen 620V mentioned elsewhere). With that range
of voltages, it means the inverter runs open loop, and the voltage
will climb, the less load is placed on it. I would never run the
inverter without a load connected to it.

http://www.dvhardware.net/modules.php?name=Reviews&rop=showcontent&id=8&page=1

Even if the inverter is 50% efficient, and it actually draws 0.5A,
that is about the same power as a disk drive draws for the motor.

Can you post the readings on the three supply rails, with the CCFL
off and with it on ?

It shouldn't be affecting things that much.

A cheap and dirty inverter can also inject noise backwards into
your computer power supply. That can fool the regulation circuitry.
I know, because I built a HV supply when I was younger, and it
generated so much back EMF, it killed the power supply I had it
connected to

HTH,
Paul

 

[Travis King]

Asus Probe
Athlon XP 2400+
CPU usage: 0%

-OFF-
CPU temp: 55 C/131 F
MB temp: 38 C/100 f
CPU fan: 4383RPM
Chassis fan: 2235RPM
+12V: 11.936
+5V: 4.892
+3.3V: 3.248
VCORE (1.675): 1.648

-ON-
CPU temp: 56 C/132 F
MB temp: 39 C/102 F
CPU fan: 4354RPM
Chassis fan: 2205RPM
+12V: 11.872
+5V: 4.892
+3.3V: 3.248
VCORE: 1.568 (but has gone up to 1.712)

 

[DaveW]

If you are using an "Inexpensive" 400 watt power supply, yes you have
overloaded it because it cannot really output 400 watts into a real world
load. I would recommend for your system that you get a 480 or 550 Watt
Antec Tru Power power supply unit before you burn out some of your computer
components with that undersized power supply you are using.

 

[Paul]

Asus Probe
Athlon XP 2400+
CPU usage: 0%

-OFF-
CPU temp: 55 C/131 F
MB temp: 38 C/100 f
CPU fan: 4383RPM
Chassis fan: 2235RPM
+12V: 11.936
+5V: 4.892
+3.3V: 3.248
VCORE (1.675): 1.648

-ON-
CPU temp: 56 C/132 F
MB temp: 39 C/102 F
CPU fan: 4354RPM
Chassis fan: 2205RPM
+12V: 11.872
+5V: 4.892
+3.3V: 3.248
VCORE: 1.568 (but has gone up to 1.712)

<<snip>>

A change of 0.064V is well within reason, given that the
measurement circuit has limited resolution anyway. At 11.87V,
that is only 1% on the low side, and no reason to panic yet.

The human ear is very sensitive to pitch changes, and your
CPU and chassis fans amplify the effect of that small voltage
change. It is annoying when you hear that, and I replaced at
least one power supply here, just based on noticing that as
the months pass, the fans were changing more and more with
load.

I would say there is nothing to worry about.

HTH,
Paul

 

[Geno]

On Mon, 12 Jul 2004 05:12:41 -0400, (e-mail address removed) (Paul) wrote:
With P4 Motherboards and CPU'S the important Power Supply Leg is the
+12V leg. To insure good Motherboard stability including CPU cooling
you need a Power Supply that has a Minimum Amperage of 16 amps output
on the +12V leg. If you have that +12V 16A output you will have NO
PROBLEMS whatsoever. You can run up to 6 fans and not affect your
stability at all. GUARANTEED!!! I'm running an inexpensive PSU. It's a
350W PSU but the +12V leg output is 18A and I haven't had a single
issue with my system yet. I have a 3.06 Ghz Hyper-Thread on an ASUS
P4S8X-X and my CPU under full load holds at 47 degrees C and at idle
it holds at 38 degrees C. Use the +12V 16A or more rule of thumb and
system stability and CPU cooling issues will disappear.

HAVE A GREAT DAY