PC PC GAMES

I mentioned on the podcast yesterday that I’d do a quick write on single rail power supplies, multiple rail power supplies and ratings to look out for.

I’ll use the situation that I personally experienced as a reference.

Some time ago, I bought a 750w Silverstone unit.  The Strider ST75F, I believe was the model number.  Got rave review, served me well for a year or two, until……   Upgrade time came around.  I had caught a sweet deal on a pair for Radeon HD4850′s at launch and was planning to run them in Crossfire.   At the time, I was using a P35 Asus board.  Well with the P35 chipset, crossfire support on the PCI-E lanes was off balance.  I was running one card at PCI-E x16 and the other at PCI-E x4.  After some testing, I found that I was not getting the performance that I should have expected because the second card was starved for bandwidth.  I needed to get a new motherboard.

So I did.  Settled on the Gigabyte X48-DS4 (first mistake).  Ordered it on newegg.  Got the board in a few days later.  Tore the rig apart, put it all back together.  Did a fresh windows install, got crossfire working as advertised. YES!  Now it’s time to overclock!

This is where things went downhill.  At the time, I was using a Q6600 as my CPU.  Since I was running it at 3.2Ghz on my poor old P35 board, I figured I could at least get that same speed out of this new highend X48 board.  Right?

Wrong….  I was never able to get the rig to run stable with both Radeons and the overclocked Q6600 at the same time.  I tried everything.  After a week or two of dealing with an unstable system, and I was becoming pretty desperate.  On a whim (and grasping at straws), I called Karsten and asked if I could borrow his PSU (a 750w PC Power and Cooling) for a few hours.  After a little explaining and agreeing to put his rig back together, he agreed.  Needless to say, I was at his door with my rig within 10 minutes.

So I swapped the PSUs out, fired up my rig and all was good.  Rebooted to try the overclock on the CPU again.  Low and behold, it was stable!  I even got a little greedy and bumped the speed up to 3.4Ghz.  Ran some tests, played some games for a bit.  OMG, this thing was stable!   So, what was the cause of my instabilities?   Both units were 750w.  There shouldn’t be much difference…  Boy was I wrong.

This is the sticker on the side of the Silverstone I had.  See in the center under output where it says +12V1, +12v2, +12v3 and +12v4.  That means this particular unit has 4 12v rails.  Not a big deal, right?  That’s what I thought too.  Well, if you look again, you can see that each rail can handle a max load of 18Amps.  That is were my problem was coming in.  After doing some research, I found that one of those rails were dedicated to powering just the CPU.  With my modest overclock, apparently 18Amps of current simply wasn’t enough!  WTF?!  I just bought this unit about a year ago!   A PSU has always lasted me at least 3 computer builds!

Now, compare that to the sticker of the unit I borrowed.  See that 1 +12v rail with a whopping 60Amps?  Sure, its less than the combined amperage of the Silverstone, but what good is that if you can’t get the power where it needs to be?   Even with this unit being 12A down from the other, it STILL ran the rig stable.  My guess is that the CPU needed 20-24Amps in order to maintain stability.  While it may not have needed that power at idle, it was definitely needed under load.  When it couldn’t get the power it needed, the PSU freaked out and tripped, causing the machine to reboot.

So, word to the wise.  When shopping for a PSU that you are expecting to last you a few builds, you can’t go wrong with a big ass single 12v rail.

Be Easy,

The Wanginator