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20-pin atx connector in a 24-pin slot?

Last response: in Components
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I posted this thread in the general homebuilt, but the traffic in that section is almost nonexistent. Sorry about the identical thread, but I NEED input on this.

So:

I'm putting together a box with the ECS A780GM-A motherboard. This build is for a friend of mine who's old socket 939 board died.


The question: We're cannibalizing as much from the old box as possible, and I am hoping to reuse the power supply. It has a Hipro 300w atx PSU rated at 16A on the 12v (according to the sticker on the PSU), which has a 20-pin atx power connector (as well as the separate additional 4-pin connector, which goes elsewhere on the motherboard). The ECS motherboard has a 24-pin connector though, will plugging the 20-pin connector from the PSU work? What am I risking here? If we're not risking damaging the board and just risking not powering up then I plan on trying with this PSU as we want to get this box up and running without any more expenditure. (If it is absolutely necessary then my friend is willing to buy a new PSU, but we're trying to avoid this if possible.


System specs:
ECS A780GM-a motherboard
AMD64 X2 4000+ AM2 65w processor
2GB Transcend DDR2 800 dual channel kit
Seagate 7200.8 200GB HDD
Unknown brand DVD-RW drive
Hipro 300w ATX PSU (16A on the 12v)


Looking for quick input, as I want to have this box up and running this afternoon. Thanks in advance!


EDIT: To be sure, I did research before making this post. I have found some posts on another board saying it will work, but the info is from 2004. I just want to make sure this is possible on this brand new motherboard.

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I'm just remembering when I tried to upgrade on a budget and had an Ultra X connect PSU, same kinda situation. Mine was a 400 watt and had 16A on the 12v+ rail. Even on an old socket 939 3500+ when I upgraded and tried to keep my PSU, the PSU didn't take it too well.

I have to agree with dokk2 on this. It really does depend on the motherboard, but even still, you'd be running the power supply rather hard. It would just make more since to get something like a 420w, so that way the PSU can relax a bit, and should be more reliable as well.
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It should work, as all of the pins are simply paralleled up on the motherboards I have seen, however they went over to a 24 pin connector for a reason, which is that with certain processors and configurations the amount of current through each pin exceeds its design limitation and could cause the connector to get too hot damaging both the motherboard and power supply connector. (Something that is not uncommon if you gat a bad connection.)

Its not as simple as "jack up the amps" as much as you can through the 12V rails. Many people think that the rating on a power supply = more amps on the 12v rails. This simply is not true. Every company tests their power supplies differently and unfortunatly there is just no standard.

Anyway, to answer your question I give you the experience I had. I too was doing something similar a year back and found out that even with a low power draw and a low amperage draw, the computer was still not stable. I found out after doing a lot of 'reasearch' on the internet that the reason was because those extra four pins on the 24 pin power supply are for the increased power requirement of the PCI-express circuits. If you simply leave them disconnected then the PCI-express circuits do not get enough amperage and you will get gross instabilities. You should at least try getting a 20-24 pin adaptor and try using only the most efficient processor and RAM you can get. You might be able to get away with that power supply that way. I was able to do that in the end and it worked well. I had a 500W Ultra X connect power supply which put out 18A on the 12V rail but my components weren't as efficient as what you can get now.

pjm is pretty much right, with a note that depending on the specific MB design, just plugging the 20-pin connector may not work (see kona's answer).
After looking at the specific features of your MB, I'm quite sure that 16A total on +12V is NOT going to be enough for the MB, no matter if you use a 20-pin or 24-pin connector. Since you're moving up to a modern MB with modern +12V power needs, get a decent PS for it. Here's a cheap but decent-quality entry-level PS: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thanks a lot, guys. These are the replies I was looking for. I explained to my friend that he would probably need to get a new PSU, so he's prepared to do so. Hopefully we'll have the new one in early next week and can get this build off the ground. Thanks again everyone, I just needed affirmation of my fears about the old PSU.

EDIT: This is the PSU I am going to recommend that my friend purchase
FSP Group ATX350-PA ATX 12V (v 2.2) 350W Power Supply
Power supply Authority
Motherboard Authority

I use my P5W(e6600 + X1900XT Antec 380) with 20 pins and it worked fine. the same went for a AM2 biostar board. 250(15 amps on 12) watt psu FTW. Never a problem yet...

Now with the further replies I'm temped to try with the existing PSU to see if it will run as is and watch for stability problems. My main concern is risking damaging components...

This is frustrating, I'm going to sleep on it and consider building tomorrow.
Motherboard Expert

24-pin connectors are used now because PCI-Express x16 slots can provide more power to graphics cards than AGP slots. This could be important for upper-midrange graphics cards that don't use a PCI-Express supplementary power cable for primary graphics power, but lighter PCI-Exprss loads don't need it.

Crashman said:
24-pin connectors are used now because PCI-Express x16 slots can provide more power to graphics cards than AGP slots. This could be important for upper-midrange graphics cards that don't use a PCI-Express supplementary power cable for primary graphics power, but lighter PCI-Exprss loads don't need it.


That info helps, this setup will be using the 780G's integrated video. I've talked to my friend and he is ok with building as is. We'll watch for stability problems and he knows that he ultimately will need a better PSU.

Thanks for all the replies.
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