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  #41  
Old 04-01-2008
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Originally Posted by treshix View Post
Ah. So it may very well be UL certified for performance characteristics very different then actual capability? If I'm understanding you right, I didn't know that.

As for the OCP on the rails being set to shut off the PSU at a higher amperage then what is specified on the labels, then that implies that the amperage limits shown for the rails on the labels are not always actually the limits, which explains why my understanding of this is confused.

Thanks for the information - that helps
Yes they can be very different, take Corsair HX620 as an example, single rail unit, specified as 3 rails on the label. FSP Epsilon specified as 15A or 18A per rail, the OCP's shuts the unit off at 22A on any rail (if I recall it correct)

The labels NEVER show the actual limit, at least not on a decent PSU.

There is always a headroom, no matter what the label tells you
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  #42  
Old 04-01-2008
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Originally Posted by Killy View Post
I still don't see how it you could potentially trap power though. Even if a rail is OCP'd at, say, 10A or something, if there's no draw from that rail that 10A is still available to other rails, right?
If each rail is limited, then you can not draw more than whatever that limit is from that rail. So if you had two +12V rails rated at 20A each, and the total +12V output capability is only 480W then you've evenly divided the +12V into two. This is bad practice because if you only were able to load one +12V rail to 10A, there's still only 20A available to the second +12V rail. Essentially, you have "trapped" 10A, or 120W, of power. It's available to the first +12V rail, but there aren't any connectors on the first +12V rail utilizing that power.

Now if you were to increase the second +12V rail's OCP to 30A, you can now tap into that "trapped" 120W. Does it make sense now?

Of course, in the "real world" you wouldn't necessarily have a PSU with 20A on one rail and 30A on the other, but I think you know where that leads to next: A PSU with three or four +12V rails with each capped at 18A or 20A or whatever the manufacturer deems "safe enough". Voila.

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Originally Posted by Killy View Post
So, in sum, it seems as if OCP is meant to prevent nasty things from happening that end up melting stuff in the PSU. The 20A or something in that ballpark limit is meant to stop a bundle of wires on that virtual rail from carrying more than that and causing some sort of catastrophe. Does this make single rails more vulnerable to melting, as OCP or OPP is only applied to a whole rail, and not into smaller bundles of wires?
Yes. One of the last commincations I had with Dave Hammock before he disappeared from the web was how a major brand single +12V rail PSU wasn't shutting down when shorted. We were literally arc welding with the PSU. Hopefully Dave's absense isn't due to the fact that he got over zealous with the welding.

MOST people won't have a problem. MOST of the time short circuit protection kicks in. Then again, MOST PSU's don't fail. MOST people don't ever have to do RMA's..... Certain measures are taken to address every possible scenario. Capping off rails is one such measure.

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Originally Posted by Killy View Post
If what I'm typing is what I believe I am typing (late at night, eyes unfocused, tired), then isn't multi-rail an inelegant solution to the true way of being safe: putting a mini OCP on each wire for the max current it can draw?
Putting a separate "circuit breaker" on each wire run would certainly be the most "elegant" way to solve a problem, but by far the most expensive. There's nothing wrong with splitting up +12V rails as long as you know "this group of wires isn't going to draw more than 10A in a real world scenario, therefore we should cap this group off at 20A." Simple and (relatively) cheap.

And threshix, I have to get back to you on your post. There's still some things you need to have explained. It's a long post, it's still early and I have to get my kid dressed and off to day care still.

As for your examples of PSU's without combined +12V rail ratings; I did say "virtually all" and even you have to admit that your examples are barely "decent" units and are all quite old. Good job on finding them at all, but you have to admit that they're the exception, not the norm.
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  #43  
Old 04-01-2008
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Originally Posted by treshix View Post
As for the OCP on the rails being set to shut off the PSU at a higher amperage then what is specified on the labels, then that implies that the amperage limits shown for the rails on the labels are not always actually the limits, which explains why my understanding of this is confused.
Well, I think Stefan may have over-simplified it a bit and I was afraid that it may cause confusion.

OCP's often work on sort of a continuous and peak type rating as well (for a lack of a better analogy right now). If a rail is rated to put out 18A, it will hold up 18A w/o problem. A short may peak that out quickly and still not trigger short cicuit protection, so they often put a bit of a buffer in there of about 10%.

For example. If I had an OCP set to exactly 18A and I shot a 18A load at it in under a second, the PSU would probably turn off. We don't want that, so we crank the OCP up to 20A, leaving the label at 18A.

This is actually why you see "240VA limit" in the ATX documents (240VA = 20A @ 12V) but see most labels showing the rail capped at 18A. They don't want to tell you it's a 20A limit and then have the PSU shut off right at 20A.
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  #44  
Old 04-01-2008
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Originally Posted by jonnyGURU View Post
And treshix, I have to get back to you on your post. There's still some things you need to have explained. It's a long post, it's still early and I have to get my kid dressed and off to day care still.

As for your examples of PSU's without combined +12V rail ratings; I did say "virtually all" and even you have to admit that your examples are barely "decent" units and are all quite old. Good job on finding them at all, but you have to admit that they're the exception, not the norm.
I'm glad you're willing to explain them, in that case

And yes, they are very much the exception and not the norm. However, it's far more likely in general that I'm working with older equipment that sort of personifies the exception that makes the rule rather then the other way around.

Hopefully that will change.

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Originally Posted by jonnyGURU View Post
Well, I think Stefan may have over-simplified it a bit and I was afraid that it may cause confusion.
That's generally true when you're bouncing back and forth between EE level knowledge and layman's knowledge, the bulk of mine being the latter. However, I do want the EE knowledge too, but I have to get my basics down pat first. (No, if you havn't noticed, they're NOT down pat yet. )

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Originally Posted by jonnyGURU View Post
OCP's often work on sort of a continuous and peak type rating as well (for a lack of a better analogy right now). If a rail is rated to put out 18A, it will hold up 18A w/o problem. A short may peak that out quickly and still not trigger short cicuit protection, so they often put a bit of a buffer in there of about 10%.
That makes a certain kind of sense.

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Originally Posted by jonnyGURU View Post
For example. If I had an OCP set to exactly 18A and I shot a 18A load at it in under a second, the PSU would probably turn off. We don't want that, so we crank the OCP up to 20A, leaving the label at 18A.

This is actually why you see "240VA limit" in the ATX documents (240VA = 20A @ 12V) but see most labels showing the rail capped at 18A. They don't want to tell you it's a 20A limit and then have the PSU shut off right at 20A.
AH!

I think I'm feeling a smidge of enlightenment. I look forward to your more lengthy explanation.
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  #45  
Old 04-01-2008
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In essence, there are accumulative amperage and combined amperage of virtual 12v rails, you want the accumulative amperage to be significantly higher than the combined amperage, to avoid your presumption in the first place -that there is "trapped" power in multi 12v rails PSU.

Ofcourse, even if the multi 12v rails PSU has it right, they still have to balance their 12v loading over those rails, so the PSU will operate at its best capability -for instance, Enermax Galaxy 1 Kw unit, it's a great Skulltrail high CPU OCing powerhouse, but if you just use a single socket CPU, and instead put 3-4 enthusiast VGA cards + some -read, a LOT of- 12v consuming devices, it won't look anywhere near good in that scenario. Or the FSP Epsilon case, when they put the all power available to the PEG into just one rail, CMIIW.
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  #46  
Old 04-01-2008
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So it's not actually 'trapped' power - it's just that if you don't spec and group rails properly, you could potentially starve them of current. That would be the same thing as putting a floppy connector on a single 18A rail and the rest of the mobo connectors on another rail - you've trapped power on the floppy rail if the other m/b connectors end up drawing more than 18A on the other rail.

But yes, I do see your point. (Finally).
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Old 04-01-2008
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Originally Posted by treshix View Post
The post that prompted this post by jonnyGURU has been snipped by me. The original post was badly formatted, rambling, and severely lacking in structure. A number of people were either confused or angered by it, so I have chosen the most challenging post to use as a response post to attempt to defend the conclusions I have drawn that I attempted (Very badly, it is true) to communicate in the original post.
And in turn I soft deleted it and the responses to it.

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Originally Posted by treshix View Post
I don't have to do the math to try and create the information that /should/ have been present on the label? Actually, when I'm troubleshooting what appears to be a power starvation issue that technically shouldn't occur from the information provided on the labels, yes, actually, I probably will feel that I do need to do the math.
Right. But again, you shouldn't have to do any math that pertains to the individual +12V rails and their OCP. These numbers are irrelevant and therefore there should be no reason to add them. They are independent designators for the capacity the manufacturer has set as a limit of current for each group of connectors on a given rail. Adding them accomplishes nothing. The only important number is the total combined capability and whether the PSU has one or a dozen rails, this number is typically in watts.

Now if the PSU doesn't provide a total combined wattage figure for the +12V, that's too bad. BUT that still doesn't mean you have to do any "math" using the figures given for each +12V rail. Even if you did, you'll never really find out what the actual maximum combined +12V capability is for that PSU, so if it's really a concern.. just put down the calculator and leave the PSU alone. If the manufacturer is "afraid" to tell us what the actual +12V capability is, it's probably not a good thing and the unit should jusst be avoided altogether.

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Originally Posted by treshix View Post
My point is that a single rail with amps limited to the wattage the PSU is rated to provide, there is a lot less math to do. Same with multi-rail PSU's.
Again... not less math. Same amount of math. There is no math pertaining to the current limit of each +12V rail. They are not additive. Never were, never will be.

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Originally Posted by treshix View Post
It's also worth noting that having all your numbers match logically is not at all required in ATX 2.2 or EPS V2.91 specifications. This is a personal bias.
I've yet to see ANY power supply where the numbers are additive.... oh wait.. I take that back. I HAVE seen power supplies that have additive rails but these PSU's are SCAMS. They'll take a 400W PSU with 300W on the +12V, 200W on the 3.3V and +5V combined and another 20W on the -12V, -5V and +5VSB and instead of calling it a 400W they'll then call it a 620W. This isn't a good thing and AFAIK said PSU's should be avoided.

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Originally Posted by treshix View Post
....some of your spelling is completely wrong!
This is nothing new.
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Originally Posted by treshix View Post
The unit CLAIMS to have three rails. Reference the information at http://www.corsair.com/products/hx.aspx

This is the information I went off of to try and make my case, albeit badly.

The internal wiring was not central to the case I was attempting to make.
Right. We're just using the fact that the label of the Corsair states that it has three +12V rails as an example. For the sake of using it as an example it doesn't matter what it the PSU is in reality.

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Originally Posted by treshix View Post
http://www.newegg.com/Product/ShowIm...W+Power+Supply

Actually, max combined load on 12v: 1080W.

Or 90A.

Amperage if you add up all the rails? 90A.
Right. But that's one of those shifty units that just adds the rails up and hopes to pull the wool over the customer's eyes. I'd be willing to be that PSU is barely a 1000W.

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Originally Posted by treshix View Post
http://www.newegg.com/Product/ShowIm...W+Power+Supply

Now, this is the kind of label I would LIKE to see - we can see easily the difference between the amperage limit on each rail, the amperage limit on the two pairs of rails, and the overall amperage limit on BOTH rails.

Now, you're saying what I'm doing is completely nonsensical, but I fail to understand why.
No, that's actually a good example. The combined +12V capability is 99A, or 1188W. But if we actually add up the +12V rails, something you're NOT supposed to do, you get 112A, or 1344W. Obviously WRONG. But it's WRONG because you're not supposed to be adding those numbers up.

We need to make sure we're comparing apples to apples here. Some manufacturers are going to use split +12V rails as a way of marketing to you that the PSU actually has more power than it really does. MOST, and I've been saying this all along and not generalizing by saying "all", power supplies have honest labels that assumes you know what you're looking at. And that's combined +12V rail is the actual +12V capability and that each "rail" current measurement is only a designation of current limit on select groups of connectors. Nothing more, nothing less.

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Originally Posted by treshix View Post
This unit is capable of delivering 1188W on the 12V rails, which considering that both 5V and 3.3V rails are listed in the same 1200W is perfectly sensible.

Especially considering that the PSU, according to the sticker, has the capability of putting its full 1200 watts on the 3.3V, 5V, and 12V rails.
Actually, it has the capability of putting out 1200W on the +3.3V, +5V, +12V if there's no load on the -12V or +5VSB. Like I said before, each table cell is an OR. Not an AND. You can put 600W on the +3.3V, +12V1, +12V2 OR put 600W on the +5V, +12V3, +12V4, but you can't put 1200W on all of them AND have a load on the -12V and +5VSB.

Try reading the label from the bottom up. Maybe that will help.

Quote:
Originally Posted by treshix View Post
This SeaSonic http://www.newegg.com/Product/ShowIm...W+Power+Supply Illustrates what I have a problem with:

We have four rails with 18A limits. We have a total combined of 38A.

We can fully utilize 2.11 rails. Why do we have four? We definately did not add an extra rail here because we needed it - No, we have four rails simply for the sake of having four rails.
More rails were added BECAUSE you DO need four +12V rails. Not just for the sake of having four rails. ?????

Like in my reply to Killy's question, if the unit only had two +12V rails and the sum of the capability of these two rails were right where the actual +12V capability of the PSU was, you really would have "trapped power." By branching off more rails, they make sure that most, if not all, of the PSU's +12V capability is usable.

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Originally Posted by treshix View Post
If you try and balance between all four rails, you're actually bleeding them dry at 9.5 amps.
Wrong wrong wrong.... You're not bleeding them dry at 9.5A each because, again, they're not additive. 18A OR 18A OR 18A OR 18A. Not AND. You can have 9 amps on one, 18 on another, 2 on another....

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Originally Posted by treshix View Post
Here's another example, a ThermalTake ToughPower this time: http://www.newegg.com/Product/ShowIm...W+Power+Supply

We have 96A available on all four rails before we hit the limit. We have a total max combined power of 62A. We could toss one of those 30A rails and still have 76A before we hit the limits. We have a 60 second peak limit of 950W on an 850W PSU. Even tossing a 30A rail, we can still hit 912W on the 12V rails alone. The amperage limits are set for a total of 1152 watts according to the sticker.
Once again... this is done to avoid "trapped power". If the sum of the +12V rails were actually additive and represented the +12V capability of the PSU, then PCP&C's FUD about "trapped power" would be true. But THIS is why FUD works. It preys on ignorance. Some people don't know any better so when they get information from an authoritative body, like PCP&C, correct or not, they assume it to be fact. The fact is that FUD is just clouding people's judgement and is causing people to regurgitate incorrect information.

To recap:

+12V rails are NOT additive. DO NO MATH pertaining to the +12V rail current limits. ONLY look at the maximum combined wattage figures and this will yield no more and no less math than any other (decent) PSU whether it has one +12V rail or half-a-dozen.

If you WERE to add up the +12V rails of a PSU, it certainly SHOULD exceed the actual +12V capability of the PSU, or even the total capability of the PSU, because you WANT that overlap so there is no "trapped power".

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Originally Posted by treshix View Post
Then why is total limitation set high enough you could blow the PSU?
You're not going to "blow the PSU" any more or any less than if the PSU had only one +12V rail. You're either going to overload the +12V or your not, regardless of the number of +12V rails. All the splitting of the +12V rails is doing is making sure you don't overload THAT GROUP of connectors on THAT PARTICULAR RAIL that has the limit on it. Again: It's NOT a measure of capability. The PSU is still only capable of putting out so much power, this power source is split up and limits applied to prevent overloading that can melt insulation, connectors, etc.

Quote:
Originally Posted by treshix View Post
I've even noted multiple PSU's which have more connectors then they have any USE for - they're adding more rails BEFORE they have any "need" to - How simply can I say this, if a PSU has five rails at 18A, /many/ people are going to assume, probably incorrectly but they will still do so, that it can provide at least a decent percentage of that 18A on all rails! Not "just 64%!" which is what we see in some of the PSU's above that I have listed as having unneeded rails.
Again, it all comes down to failsafe. The PSU has more connectors than most people need. But alas, the PSU has these connectors just the same and therefore needs to be prepared to handle a load representative of using all of those connectors. In order to be able to deliver that load AND provide the safety of a 240VA limit, they need to add more rails. Alternately, they could just increase those limits to 30A or 35A, but if it doesn't cost any more to just add two or three rails, why not just add two or three rails and keep the current limit down around 18 or 20A each?

Quote:
Originally Posted by treshix View Post
Per ATX spec version 2.2, the 24pin connector is going to have two 12v pins, but they are both on the 12V1 rail, and it has to supply the power for the SLOTS on the motherboard - of which the PCI-e mobo SLOT is rated to deliver 75W as well! While it may easily be classified as "Unlikely" for the PCI-e card to draw the bulk of it's power from the motherboard and little from the PCI-e connector, assuming that it will be so is taking a risk.

The good boards use the CPU 4pin 12V connector, which does not have a required rail, however per the ATX version 2.2 spec, this is to be used for the CPU +12v signal voltage regulators.
That is incorrect. It's not "good boards" it's ATX12V boards. And it's with ATX12V that CPU's started regulating their Vcore from the +12V rail. Prior to this, the CPU would regulate Vcore from the +5V, NOT the +12V. And the 4-pin most certain DOES have to have it's own rail to conform to ATX12V.

You're confusing ATX with ATX12V.

ATX = +5V regulated CPU Vcore, no 4-pin, no split +12V rails (because it doesn't really need it! ATX boards use AGP, not PCIe, +5V powered CPU's... +12V requirement is very low.)

ATX12V = CPU Vcore regulation is powered from a +12V source. If +12V PSU capability is > 240VA the +12V needs to be split and if split the CPU must be on it's own rail.

Quote:
Originally Posted by treshix View Post
I find no provision in spec that the PCI-e power on the motherboard slot be provided from an alternate rail. It's entirely possible I'm missing something.
Well, obviously you can't only have two +12V rails and have a PCIe connector on it's own +12V rail. Intel's ATX and ATX12V specs sort of ignores PCIe and PCIe power requirements. That's why there were so many problems with PSU's with only two +12V rails or PSU's that followed EPS12V specifications for servers (which don't use high end graphics cards to start with) instead of figuring out how to map out the connectors on their own.

It's actually Nvidia, as part of their SLI certification process, that laid down the law and said "you need to put PCIe connectors on their own +12V rail." Not Intel and not PCI-SIG.

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Originally Posted by treshix View Post
Okay, now that's just plain insulting.
The term "ignorant" shouldn't be insulting. It merely means one does not know.
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Old 04-01-2008
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This is why i always say to my fellow local IT forumers whose looking for help/recommendation regarding their future PSU, you should get either a single 12v rail unit -or dual REAL 12v rails unit ala CWT PUC platform- or multi 12v rails with more than just 2 virtual 12v rails on it, especially when the dual 12v rails unit follows ATX 12v standard closely (no more than 240 VA on each 12v rail).

For example, Silverstone Element 500w, such a good PSU, as jonny ATE can attest to that claim. But in some instances, in relation to system load balancing, its JUST dual 12v rails could very well also be its achilles heel, since the amount of its accumulative (additive) 12v rails amperage matches the combined amperage of its 12v rail output.

http://c1.neweggimages.com/NeweggIma...256-008-04.jpg
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This is why i always say to my fellow local IT forumers whose looking for help/recommendation regarding their future PSU, you should get either a single 12v rail unit -or dual REAL 12v rails unit ala CWT PUC platform- or multi 12v rails with more than just 2 virtual 12v rails on it, especially when the dual 12v rails unit follows ATX 12v standard closely (no more than 240 VA on each 12v rail).
That's like suggesting one extreme or the other.

PSU's that tend to "adhere closely" to the ATX12V with only two +12V rails, only 240VA per and only the CPU on a rail with everything else on another tend to be units that are < 600W. On the other hand, PSU's with "true" multiple +12V, like the CWT PUC, are 1000W+.

What about everything in between 550W and 1000W that have four +12V rails?

Again, it needs to be treated on a case by case basis. People are making arguments for arguing sake if I use a 800W with four +12V rails with a total combined wattage listed on the label as an example and then someone else whips out a 500W with two +12V rails with no total combined wattage listed on the label.
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Originally Posted by Killy View Post
So it's not actually 'trapped' power - it's just that if you don't spec and group rails properly, you could potentially starve them of current. That would be the same thing as putting a floppy connector on a single 18A rail and the rest of the mobo connectors on another rail - you've trapped power on the floppy rail if the other m/b connectors end up drawing more than 18A on the other rail.

But yes, I do see your point. (Finally).
Right. The OCZ 700W is a prime example of a PSU that does have too many rails, not enough connectors, and "trapped power": They put ONE PCIe connector on a rail capable of 18A. The put another connector on another 18A rail. CPU on another 18A rail and then everything else on a fourth rail.

So you can use this PSU for SLI or one card with two PCIe connectors like the 8800 Ultra, but that's about it. For one, it's proof positive that most people don't need a PSU anywhere near 700W because you're not even using 1/3 of the power capability of three of the four +12V power connectors. If the OCZ 700W works for you... so would a good 500W power supply!

And if you use Molex to PCIe adapters to power a pair of Ultra cards, you overload the rail supplying power to all of the Molexes! Dumb dumb dumb.

If I were OCZ I'd send all of those units back to FSP and tell them to solder down a second PCIe connector to each of those two PCIe rails and make that PSU have a total of four PCIe connectors. Otherwise, it's no better of a unit than any good 500W SLI power supply.

(I say this with all due respect to OCZ. I am NOT an OCZ hater. They just happen to have a good example of a PSU gone horribly wrong.)

BFG's 800W was the same way. It's an 800W with only two PCIe connectors. WHAT?!?!! First thing I did when I started working at BFG was to take the 4000 units sitting in the warehouse and solder down a couple more PCIe connectors.

So there ARE examples of "trapped power" out there. It's just not very common. And that also goes back to looking at units on a case by case basis too.
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