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4-Molex to PCI-e?

F

Fickster287

n00b
Joined
Mar 30, 2007
Messages
24
I've seen the adapter that takes 2 4-pin molex connectors and combines them to a PCI-e plug. How do you calculate the available current to the PCI-e?

Basically I'm wondering if I use one of these with my 480W PSU thats rated +12V1 @ 15A and +12V2 @ 18A will be enough for an 8800GTS and quad core. I can't find out what manuf. it is, since it came with my old alienware and just says 'Alienware' all over it.
 
Fickster287 said:
I've seen the adapter that takes 2 4-pin molex connectors and combines them to a PCI-e plug. How do you calculate the available current to the PCI-e?

Basically I'm wondering if I use one of these with my 480W PSU thats rated +12V1 @ 15A and +12V2 @ 18A will be enough for an 8800GTS and quad core. I can't find out what manuf. it is, since it came with my old alienware and just says 'Alienware' all over it.
Click to expand...

you might be alright. The GTS versions use 115-125w @idle, and 150-175w under load, IIRC. Someone may correct me on this, for exact specs. I believe I'm in the ballpark, though. Your 480 could be a bit taxed. Most manufacturers recommend at least a 550W for single core and single GTS. Also, it is most likely that your power supply is using the 12v1 rail to power the board (4-pin CPU connector, and 20 or 24 motherboard connector), and 12v2 to power the the Molex leads. If this is the case (usually is), then take your maximum amperate rating for 12v2 rail and multiply it by the voltage, like this:

12v2 rail = 12v * 18A = 216w

Your PCI Express slot will provide 75w of that power (card required total power) to the card from the 12v1 rail, which will decrease the load from the 12v rail (power from the 2x 4-pin molex connections to the back of the card). So then, then math is like this:

Card requirements: 150w (load)
Power from PCI Express slot: 75w (card under load)
Power from 12v2 rail: 75w (power under load)

As long as you're not exceeding the 12v2 maximum power rating with the other devices, you should be alright. You might try this, to help you find your power consumption expectancy:

http://extreme.outervision.com/psucalculator.jsp
 
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