Silverstone Zeus ST65ZF Author: jonnyguru Date Posted:26/07/2005 04:28.22 SLRating: Bottom Line: The Silverstone Zeus ST65ZF is HARDCORE. It's more power supply than most people need, but if it's in the budget and you want no holds barred, this is a power supply for you. Article Navigation Introduction Testing Under Load Crossloading Connectors Conclusions Pages: 1 2 3 4 5 6 Discuss This Article

Crossloading

The subject of the ST65ZF's crossload requirements have come into question and I was asked to run some extremely crossloaded tests.  The 5V "requires" a minimum load of 10A if the combined 12V output is 30A to 38A and a minimum load of 15A is required if your combined 12V load is 38A or greater.

Now certainly 10A or 15A is quite a bit of a load for a 5V rail, but so is 30A or more on the 12V rails!  You have to look at the crossload requirement in perspective.  The greatest load on your 12V rail will likely be your CPU, or CPU's, and perhaps a pair of PCI express video cards.  But even with these devices running at full force, you're not going to meet 30A.  Assuming you had enough drives to help exceed the 30A threshold, you would also have a 5V load that goes with that.  And the 5V load of your drives is static where your 12V load is not.  So personally I do not think the crossload requirement is an issue if you're really going to use this power supply to it's full potential.  And if you're not going to use the power supply to it's fully potential, then it's a completely non-issue because you're not going to get the 12V rail up to 30A!

A "quick and dirty" experiment was done to determine the effects of crossloading this power supply out of spec.  Essentially, the 12V load was set really high, while the 5V load was really low.  The results (voltage readings are only on the 12V1 and 12V3 because these are the two rails I used):

The key to this table is not to look at each row of voltages, because all of the voltages are well within spec.  The thing to look at is how much each voltage fluctuates with a mere 1A change in load on the 5V rail.  That's pretty drastic.  But again, 5V loads tend to be VERY static.  The sort of "drop" illustrated in this test is unrealistic. 

So let's look at the flipside.  What if the 5V rail was unrealistically low, and the 12V rail was high?  This is a more realistic scenario as it can emulate a sudden barrage of firepower during a game, or a writing a large file to a RAID 5+1 array...

Note that the results are very much the same.  All of the voltages are within spec, but the fluctuation is dramatic.  But once we get the 5V rail up over Silverstone's suggested 10A load, all of the rail stabilize and maintain 11.80~11.81V all of the way up until the point where there was 12A on the 5V rail, and then the 12V started to completely stabilize.

Point is, there is good reason for Silverstone to publish a minimum 5V load for their power supply.  Despite the hypothetical load tests, I feel that most people shouldn't have anything to worry about for the very reasons I had mentioned at the beginning of this page...  If you're not going to have at least a 10A load on the 5V rail, you're probably not going to put more than 30A on the 12V.  And if you're going to put more than 30A on the 12V rail, you're probably going to have at least 10A on the 5V.  Just keep in mind what happens if you don't have this balance.

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