What happens if you hook a 20-pin PS to a 24-pin mobo?

[MUKid]

So a friend of mine put together a computer, and his power supply only had a 20-pin mainboard connection and a 4-pin supplemental connector. His motherboard had a 24-pin main power socket. We hooked up the 20-pin to the main socket, and the 4-pin connector to a different socket (not the empty 4 pins on the main socket, heh) and everything seems to work fine. He's been using it for a month now with no troubles, but I just started getting worried that I helped him do something bad... So will it explode in a few months or what?

 

[secretanchitman]

yep, you can use 24 pin with the 20 pin mobo. it'll be kind of crooked at the end, and im sure you plugged it in right, because he's been using it no problem...but someone else back me up, because im not 100% sure though...

i do know that you can use a 20pin with a 24pin mobo...im 100% sure on that.

 

[Matthias99]

Usually the motherboard is wired so that you can plug in just a 20-pin connector, and leave the extra 4 pins blank (they're just extra +12V feeds and grounds).

If the PSU isn't a piece of junk, and you're not running some super-mega-high-end system, you should be fine.

 

[batmanuel]

Check the manual on the mobo. My Intel 915PBL motherboard can use a 20-pin PSU even though it has a 24-pin connector, but when you do that you don't get as much power supplied to the PCIe x16 slot as you do with a 24-pin PSU. To make up for this, my board has an extra molex connection right by the x16 slot that provides the slot with extra power if you are running a graphics card that needs lots of power. Without the connector plugged in, the slot can only put out about as much power as an AGP slot.

If your friend doesn't have the extra molex connector on his board, then he could run into issues down the road if he is using a card like a 6600GT (which you know needs the extra power from the PCIe slot because the AGP version has a power connector that is missing from the PCIe versions of the card). With a lower end graphic card you should be fine. I've been running an X300 in my board with no issues.

 

[MUKid]

To make up for this, my board has an extra molex connection

Is that extra molex just the 4-pin auxiliary connector, or does it use one of the standard connectors from the PSU?

 

[batmanuel]

It is a standard flat 4-pin molex from the PSU, just like you use to plug up a PATA hard drive or an optical drive. If your friend has one on his mobo, it'll likely be right by the x16 slot(s). Some of the newer boards have phased this extra connector out. I think mine only had it because it was one of the first PCIe boards on the market and Intel wanted to make sure that the PCIe graphics card had enough juice if the builder couldn't find a 24-pin PSU (which were pretty rare in December 2004). Since 24-pin PSUs are plentiful nowadays, most board makers have dropped this extra molex connector on the mobo.

 

[MUKid]

Huh, very interesting. I looked over the motherboard manual, but I don't see any information on what would happen if a 20-pin connector is plugged in. Is there a diagnostic or something that can be run to see if a PCIe card is functioning correctly? He has a 7800GT - I think it might be high-powered enough to need the extra power.

 

[1Dark1Sharigan1]

Originally posted by: MUKid
He has a 7800GT - I think it might be high-powered enough to need the extra power.

That's what the auxiliary power connector is for . . .

I used to use a 20-pin PSU with my 24-pin PCI-E MSI motherboard and never had any problems . . .

 

[MUKid]

I'm sorry - are you talking about the square 4-pin connector, or are you talking about a flat connector like batmanuel was mentioning? Because as I said, he does have the square connector hooked up, but only 20 pins on the main connector.

I'm thinking that it'll probably be fine, but since I helped him put it together and he's relatively hardware-illiterate, I feel obligated to follow up if he's losing performance and we aren't aware.

TIA...

 

[batmanuel]

Originally posted by: 1Dark1Sharigan1

Originally posted by: MUKid
He has a 7800GT - I think it might be high-powered enough to need the extra power.

That's what the auxiliary power connector is for . . .

Keep in mind that the PCIe slot is adding in the equivalent to one extra aux. connector on the card. My manual states that if the video card exceeds a certain wattage, the molex needs to be plugged in for that particular board.

Personally, if I had that much money invested the video card, mobo and processor, I'd get a new 24-pin PSU just to be sure that you're not going to screw up something (either immediately or down the line). It's not a lot of money to spend for the peace of mind that you're not going to screw up your system by cheaping out on the PSU.

I might be overly cautious, but there are many tales of woe that have been told by people who tried to cut corners with the PSU and lost equipment because their gamble didn't pay off. If you were using a lower end card, I'd say go for it. With a 7800GT, I'd tend to be more careful with the choice of power supply.

 

[elecrzy]

should work fine. i have the original trupower 430 (20pin psu) powering the 820, x850xt, and 3 hard drives.

 

[sandeep108]

Should work fine. I added a 20>24 pin adapter just to ensure things don't explode. But the few weeks I used just the 20 pin (I have a 6600GT) things worked quite ok. There is a huge thread on this somewhere.