12V 8 pin CPU plug, do i need to use it? GA-MA790FX-DS5 + PHENOM II

[bugzy1977]

My computer was working fine with the 4 pin motherboard connector, with the 5200+, but now seems to not post with the phenom II 940.

Do I need to connect an 8 pin motherboard connector, instead of just the 4 pin one?

reason I ask is, i need to know before I buy an adaptor molex to 8 pin motherboard connector.

any help would be greatly appreciated.

 

[Shadow703793]

Yes, probably.

Also you MAY need to update BIOS.

Looking at the CPU Support chart:
http://www.gigabyte.com.tw/Support/Motherboard/CPUSupport_Model.aspx?ProductID=2694#anchor_os

Looks like you need to update BIOS.

Note: DO NOT UPDATE BIOS FROM Windows(@BIOS). Use QFlash.

 

[dragonsprayer]

higher the voltage and wattage the more the full 8 lines are needed

if the mobo gives you 75w at 1.3v the rest comes from the atx connector

at 1.5v 50 watt = 33 amps

that is why there is 8 pins

use cpuz to check the wattage of the cpu, i suggest 8 pin for i7 since they run 150w

 

[dragonsprayer]

again, phenon ii and i7 all interchange able as far as design and wattage and speed for the most part (3.6-3.8 vs 4.2-4.3 for i7)

at stock speeds and low voltage 4 pin may be fine if your running 100-120w

but if your running i7 wattage of 150w the 8 pins reduce the load, heating etc

 

[RetiredChief]

dragonsprayer
You are correct on "recommended" 8 pin connection for wattage =>130 Watts.
But suggest you skip the "voltage" as the voltage at the connector is +12V +/- 0.5 V.
The voltage that you elude to is on the output side of the VR.

Reason on using 8 pin vs 4 Pin is to reduce the IR drop across the connector pins. Excessive current on a single pin could cause it to overheat and melt the plastic.


+1 on Shadow's post.

 

[dragonsprayer]

you may misunderstand me

but agree retiredchief

 

[jsc]

higher the voltage and wattage the more the full 8 lines are needed

if the mobo gives you 75w at 1.3v the rest comes from the atx connector

at 1.5v 50 watt = 33 amps

Sort of correct. If the CPU is pulling 75 watts @ 1.5 volts, that's 50 amps. But at the 12 volt connector, a bit over 6 amps. The PWM regulator on the motherboard is pretty efficient - over 90%.

Using a 4 to 8 pin adapter will help the motherboard, but will not do anything for the I^2*R losses in the 4 pin EPS cable.

 

[RetiredChief]

jsc
That is exactly the reason for 8 vs 4 pins. Individual current thru traces on MB and thru the socket connection is halved by using 8 pins. It's not just about the I^2*R losses. It's about heat, that loss is in the form of heat at the pins. If it was not for this then the 4 Pins would be fine and no need for 8

Added
Example 120 W 12V = 10 Amps.
In 4 wire connector that would be 5 Amps per Pin (before you say = 2.5 A remember they are in series so two pairs) @ only 1/100 ohm contact resistance that would still be 1/4 W dissipated at the pin if that resistance is 0.05 ohms then the power dissipation jumps to 1.25 W ( does not sound like much - but try touching a 1 Watt resistor dissipating 1 W.

In an 8 pin connection the current drops to 2.5 Amps per pin.
@ 0.01 ohms = .0625 W (Vs 0.25 W)
@ 0.05 ohms = .3125 W (vs 1.25 W)