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24-pin ATX Power on mobo using 20-pin plug from PSU

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a b V Motherboard
October 15, 2010 9:55:30 PM

Sister-in-law gave me her old HP Pavilion a6314f desktop PC. It has an Asus M2N68-LA (Narra2) motherboard in it. AMD Athlon x2 64 5000+ CPU.

I'm going to use this PC as a second unit for my wife in our office, and as a stepping stone into a new Intel Core i7, or newer LGA1155, next year. I don't want to throw alot of money into this system, but plan on upgrade "things" in it, for use with a new build (i.e. future proof).

Already got an OCZ Agility 2 60GB SSD for OS/Programs, and pulled an Seagate 7200.11 500GB SATA II HDD out of a RAID 0 array in my rig for backups. Will use the original Seagate 7200.10 360GB SATA II HDD for data/media.

Up'd the RAM to 4GB, no problem, only $19.99 a 1GB DDR2-667 (PC-5300) stick, needed 2. I know this is a loss for future build, that's why I didn't up it to 4 or 8GB DDR2-800 (PC-6400) RAM.

Next, I would like to upgrade the video from the onboard NVidia 6150-SE GeForce 430 chipset (??) to a Radeon 5770. The new card will be future proof. BTW: the onboard graphics are rated 3rd from the bottom, and the new card 5rd from the top, in THG Graphics Card ratings/articles.

But, before I can install a PCI-E x16 graphics card, I need to upgrade from the 250W :lol:  PSU in the case. Probably going to get a Corsair 650HX Modular PSU, to be future proof. (And for only a few bucks more, a new Antec 300 case, too.)

The question I have is this: the motherboard has a 24 pin ATX power connection on it, but currently the PSU only has a 20pin connector going to it. Will I fry the mobo if I plug in a "standard" 24 pin ATX power into it? The "extra" 4 pins on the mobo are just exposed, next to the 20 pin that plugs into it.

I know it's a P.o.S., but I don't have all the cash for a full new system right now. So I'm piecing one together.

BVW: I hate pre-built systems! Dell, Gateway, or HP! No customization, or overclocking. And their motherboards are non-standard unit, usually specific to the case the are in. Non-standard mobo connectors (USB, Case, Front Panel, etc.). Well, at least this HP unit looks like the mobo could go into a "after-market" case, and have all the case connectors work with the mobo. :sarcastic: 
a b Ĉ ASUS
a c 108 V Motherboard
October 15, 2010 10:21:45 PM

In theory, a 20-pin mobo PSU connector will work on a mobo with a 24-pin socket, but it's risky because the 20-pin connector may not provide enough power. What's the difference? Long ago, while PC's were still in their youth, the mobos were designed and built with only a 20-pin socket, this is due to the lower power/quality CPUs from the same era. As more powerful CPUs were invented, stability became an issue. Thus, the 24-pin socket was designed and incorporated.

I assume you're referring to the 250 W PSU, as a 650 W w/ only 20-pin is odd. Secondly, I'd be cautious with building too much on to that 250 W PSU (if that is what you're using), with all those extra devices, you could be putting too much load on the low quality PSU.
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a b V Motherboard
October 15, 2010 10:47:00 PM

To clearify:

If I upgrade to a 650W PSU, will the 24-pin ATX power connector fry my mobo, as it only uses a 20-pin power connection from the 250W PSU now, even though it is a 24-pin connector on the mobo?

Yes, I need to up the 250W PSU [if] I get a Radeon 5770, which requires a PCI-E connector, which the 250W doesn't even have. I doesn't even have SATA connectors, it has a Molex 4-pin to SATA 15-pin power adapter(s). I added a Molex to 2-SATA spitter, but I think I still have a open molex connector from the PSU.

As is, I'm really already max'ing the 250W to over 289W, with the CPU, mobo, onboard gfx, DVD R/W+, 2-7200rpm SATA HDD. The SSD doesn't use much power. This is according to newegg's calculations here. Now, if I add a 90mm case fan ($4), it gets scary!
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a b Ĉ ASUS
a c 108 V Motherboard
October 15, 2010 11:12:14 PM

foscooter said:
To clearify:

If I upgrade to a 650W PSU, will the 24-pin ATX power connector fry my mobo, as it only uses a 20-pin power connection from the 250W PSU now, even though it is a 24-pin connector on the mobo?


Uhh... are you sure you're clarifying? Your statement suggests that you question if a 24-pin plug (connector) will fry your mobo. But your statement also suggests that your mobo uses a 20-pin socket ?(connection), coming from a 250 W PSU that has a 24-pin plug (connector).

If you're asking what I think you are, then the scenario goes like this:

The mobo is from an HP, which uses a 250 W PSU. This 250 W PSU has a 20-pin plug that connects to the mobo, which has a 20-pin socket. If you upgrade to the 650 W PSU that uses a 24-Pin plug, will it fry your mobo, which again, has only a 20-pin socket?

If that is indeed what you're asking, then you'll be fine. The PSU 24-pin is backwards compatible to a 20-pin; the extra 4 pins can be disconnected from the 24-pin plug, leaving you with a 20-pin plug. As far as voltage and frying goes, the PSU will not push more current than the mobo needs. The PSU acts as a reservoir of power, in that you take what you need.
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a c 207 Ĉ ASUS
a c 716 V Motherboard
October 15, 2010 11:35:32 PM

No, you could have a 1000w PSU and it wouldn't fry your MOBO.
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a b V Motherboard
October 18, 2010 6:58:31 PM

Quote:
The PSU 24-pin is backwards compatible to a 20-pin


Thank You.

Maybe I shoulda taken pictures.

To re-clarify:

Current set up: 250W PSU with only a 20-pin ATX power connector; Asus M2n68-LA mobo has a 24-pin connector. 20-pin plugs into 24-pin, and works.

Upgrade: 650W PSU with 24-pin ATX connector; same mobo. Will the new PSU help or hinder the current mobo?
Need it for SATA (current) and PCI-E connections (future). Current set up is already stressing the PSU.

Sorry, just looked again: the 650W PSU has a 20+4 Motherboard connector. So it should work either way?
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a b V Motherboard
October 18, 2010 7:01:06 PM

Best answer selected by foscooter.
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