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I don't understand "dual power input"

P

Philippine Mango

Diamond Member
On video cards now, they draw so much power that they use two power connectors, I don't get this, HTF does this make any sense? Why can't they draw the same amount of power from one molex connector instead of distributing it into two? Either way, if you've got a rail with 3 molex connectors and you hook up 2 to the video card, one to the HDD, it's the same thing as hooking up 1 molex connector to the video card and 1 to the HDD, right??? This doesn't really make much sense to me.. Also, another way to bypass this limitation is to get a molex splitter for another plug....
 
Can't say I've seen any cards use more than one Molex style connector for their power.

Certainly, before the introduction of the Molex PCI-E connector, there were a number of cards which would use more power than could be supplied by the popular AMP (disk drive) connectors.

The AMP connectors are rated only for 8 A - so if a card needed close to 90 W or more then it would overheat the connectors. In fact, the AMP connectors aren't particularly reliable, and if non-genuine connectors are used (like on cheap PSUs), then the safe maximum can drop to 5A or less.

The PCI-E connector carries 2 seperate 12V wires, spreading the load over 2 sets of pins - this allows double the current/power flow.

A similar thing could be achieved by using 2 sets of AMP connectors, the load would be spread over the 2 connectors, so reducing the heat. However, you're left with the possibility of someone not connecting one of the connectors, and burning out the other.

The Molex connectors have a number of advantages - they're reliably keyed, so they can't be connected incorrectly, and they lock in (whereas the AMP connectors just push in).
 
Yes the PCIe connectors, they have a split out for two molex power connectors and to me it just seems a bit pointless if you're using the same wire, what are the wires rated for anyways?
 
Old timers would remember the 6800ultra had 2 molex connectors.
I don't remember the power consumption of the card but it wouldn't be close to newer cards like the x1900xt/xtx which are very beastly, and I remembered many people used modex splitters on the 6800u without any problems.
 
You're meant to use separate power cables. Using two instead of one means that in effect the two cables are in parallel, which means the resistance they present is halved. This means less power is lost as heat in the wires, and less voltage is dropped across them. So it's more efficient, and ensures that the voltage seen by the video card is closer to what it's meant to be.
 
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