Clayton said:
What are the extra 4 pins on the 24 pin PSU? my current PSU has 20 pins and
is 305W, I am having problems with the computer starting up and sometimes
reboots automatically while loading the Dell logo screen then gives me the
screen saying "start windows normally" when I select this it starts fine.
I have a 24 pin 350W psu and had to buy an ATX adaptor 24 pint to 20 pin and
installed that and still does it, would the extra 4 pins that is not being
used need to be used? or are they there for PCI-E video cards? btw my
motherboard is AGP using power from one of the 4 pin molex plugs
Thanks
Here are three specs. Each one labels the main power connector and the wires.
The first one is historical, and shows how pin 18 used to have -5V on it.
-5V is no longer used. The third one is for the 24 pin connector.
http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf
http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
The ATX main connector, works by having some wires in parallel. The connector
has more than one 3.3V wire. The connector has more than one 5V wire. Each
wire can safely carry 6 amps. Four wires in parallel can carry 24 amps.
The 24 pin connector adds more (redundant) wires. It increases the number
of 12V wires, from one to two. This is important on an SLI or Crossfire
motherboard with two PCI Express slots. Video cards like some version of
the 6600 family, draw 12V @ 4A from the video slot. Two cards would draw
8 amps. The one 12V wire on a 20 pin connector, could not safely
carry that current. Thus, for safety, a 24 pin connector is recommended
when using SLI/Crossfire configurations. For a single video card, the most
common answer will be, that a 20 pin connector is good enough.
The above has nothing to do with the power rating of the PSU. The PSU
still has to have enough maximum output amps for the connected load(s).
The above rules are more concerned with burning a connector pin because
you allowed too much current to flow through it.
The fact that your motherboard is AGP, doesn't change the concerns about
burned connectors. But with AGP, the practice is probably to load
the lower voltage rails, and those have a goodly collection of wires in
parallel.
If I had to guess, one possibility is the 350W is still not enough power.
You can take a multimeter and probe the main power connector. The metal
in each hole can be touched, while the computer is running. I connect
the (-) lead of my meter to a screw on an I/O connector on the back
(with an alligator clip). Then, I only have to handle the (+) probe
ti check each pin on the main connector. The expected voltage from the
above docs, would look something like this. This is extracted from the
third document above. Note that the multimeter, or the hardware monitor
page in the BIOS that measures the voltages, have a limit to their
precision, so some of the nonideal result is measurement error. My
multimeter is about 1.5 to 2% accuracy on the various scales.
Table 2. DC Output Voltage Regulation
Output Range Min. Nom. Max. Unit
+12V1DC (1) ±5% +11.40 +12.00 +12.60 Volts
+12V2DC (3) ±5% +11.40 +12.00 +12.60 Volts
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC (2) ±5% +3.14 +3.30 +3.47 Volts
-12VDC ±10% -10.80 -12.00 -13.20 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts
(1) At +12 VDC peak loading, regulation at the +12 VDC output can go to ± 10%.
(2) Voltage tolerance is required at main connector and S-ATA connector (if used).
(3) Minimum voltage during peak is greater than 11.0 VDC
HTH,
Paul
