Pushing the 12v rail

AVcableguy · Jan 13, 2005

If I were to use a PSU to power a single 12v device and wanted to pull maximum power from the PSU on the 12v rail, how would I go about doing this? I read that the +5v lead and the +12v lead can be tied together to pull around 16v. Does this also increase your overall available amps? The PSU I am thinking about doing this with is the Fortron 530. Also, I'm a little unclear on the 12v rail amp stat. It says 16/28.....????? Thanks.

Oklahoma Wolf · Jan 13, 2005

I posted a response to your 16/28 question in two threads already, such as this is one:

http://www.ocforums.com/showthread.php?t=258903

If you're looking to run a single 12v device, the best option is a dedicated 12v PSU. Not sure I'd recommend this with the FSP 530w, but it's up to you.

AVcableguy · Jan 14, 2005

Thanks for getting to that 16/28 question. I must say, Brilliant! :attn:

Why would you not recommend the 530 for a dedicated PSU? Okeeeee. I cancelled the order. Tell me kimosabi, what PSU should I get to run a 226 watt pelt @ 24 amps and a 80 watt pelt @ 8 amps?

Oklahoma Wolf · Jan 14, 2005

The 530w has minimum load specs that need to be met.

226w @ 12v is 18.8A
80w @ 12v is 6.6A

Try and find something like the Meanwell S-350-12 - good for 29A all on the single 12v rail. If that's too close for comfort, there should be something over at www.meanwell.com that'll do the job. Not sure where to get these in the US - I'll leave that up to someone else who isn't fighting off the cold of the century

AVcableguy · Jan 14, 2005

It's a great excuse to take Robitussum....Sorry bout the ill health. From what I can tell about meanwell is that they look pretty weak compared to other PSUs. At the moment, a meanwell is probably the last thing I would buy. But then again I may not know about their secret weapon.

Oklahoma Wolf · Jan 14, 2005

Hehehe - no Robitussin around here unfortunately - I get to fight it without medical aid

One other option you might consider is replacing your main PSU with something that can take the pelts and the system combined, such as the Zippy/Emacs units at Newegg above 600w. I haven't seen the PSU that can top a Zippy - every model is rated at 40 degrees.

larva · Jan 14, 2005

Oklahoma Wolf said:
... I haven't seen the PSU that can top a Zippy - every model is rated at 40 degrees.

Just bear in mind that the fan that keeps a Zippy there is going to be (clearly) audible. 80mm fans are no longer any more adequate for power supply applications than they are for case fans. I like Zippy and the Fortron 550s a lot, but the fans are just plain rinky-dink.

AVcableguy · Jan 14, 2005

IMHO, what you are paying for in an expensive power supply is stability and clean power. You need this to run a system. But to power a couple of pelts you simply need raw power. And as you have mentioned both the meanwell and Zippy as good choices, their price tags and stats indicate stability rather than power. Taking a PS like a Rosewill 550 watt delivers 35 amps on the 12 for a cheap price tag, but not so cheap that you begin to think that it might spotaneously blow up on you. I think it might just be a high powered beast perfect for the application of running TECs.

AVcableguy · Jan 14, 2005

larva said:
Just bear in mind that the fan that keeps a Zippy there is going to be (clearly) audible. 80mm fans are no longer any more adequate for power supply applications than they are for case fans. I like Zippy and the Fortron 550s a lot, but the fans are just plain rinky-dink.

You're right. It may even become a big issue when you are pushing a zippy or a fortron to their limits.

larva · Jan 14, 2005

Actually, that was exactly the point I (thought I) already made.

AVcableguy · Jan 14, 2005

larva said:
Actually, that was exactly the point I (thought I) already made.

You made the point that the fans are audible and that they are rinky-dink. My point is that just because a fan is "audible" and "rinky-dink" does not mean it is inadequate to perform cooling. Furthermore with a high wattage powersupply like the Fortron 530, the possibility of running into heat related issues increases when extra cooling is not considered. That is why many of the new Fortron model releases are being released with either dual 80mm fans or a single 120mm fan or a combination thereof. And yes, there are some PSUs with dual "rinky-dink" 80mm fans that are both adequate and inadequate in cooling.

AVcableguy · Jan 14, 2005

Back to the original question, is it the -5v lead that you wire in with the +12v lead to get upwards of 12v and upwards of the 12v amp rating?

Oklahoma Wolf · Jan 14, 2005

Nope - doing that would increase the power to 17v. The 530w will be able to meet the 28A as long as the 5v isn't too heavily drawn. The 2A minimum on the 5v should be enough load to get it to work properly.

larva · Jan 14, 2005

AVcableguy said:
You made the point that the fans are audible and that they are rinky-dink. My point is that just because a fan is "audible" and "rinky-dink" does not mean it is inadequate to perform cooling. Furthermore with a high wattage powersupply like the Fortron 530, the possibility of running into heat related issues increases when extra cooling is not considered. That is why many of the new Fortron model releases are being released with either dual 80mm fans or a single 120mm fan or a combination thereof. And yes, there are some PSUs with dual "rinky-dink" 80mm fans that are both adequate and inadequate in cooling.

Believe it or not I know what point I made, having composed and typed it. Yes they are innadequate, if you have stringent noise standards. And were it not powerful supplies like the 530 we were discussing, I would not have made the comment, as it would have been untrue. In fact it was the even-more powerful (and thus thermally demanding) Zippy and 550 Fortron I was directly referring to. You needn't guess what I meant and tell me what you are guessing when I so clearly stated my meaning in the first place.

AVcableguy · Jan 14, 2005

larva said:
Believe it or not I know what point I made, having composed and typed it. Yes they are innadequate, if you have stringent noise standards. And were it not powerful supplies like the 530 we were discussing, I would not have made the comment, as it would have been untrue. In fact it was the even-more powerful (and thus thermally demanding) Zippy and 550 Fortron I was directly referring to. You needn't guess what I meant and tell me what you are guessing when I so clearly stated my meaning in the first place.

Just because you are running a 550 watt power supply doesn't mean you are using 550w. Some people buy 550w power supplies for their high grade parts and dependable/stable power rails. In other words, a person could own a 550w PSU and only pull 300w. In this case a crappy 80mm would be perfect, especially if the fan speed is variable. Please step away from the brick wall :bang head

and expand your mind to think from more than one POV at a time. Root beer can help... :beer:

Please remember the emphatical nature of my original statement:

avcableguy said:
You're right. It may even become a big issue when you are pushing a zippy or a fortron to their limits.

In otherwords a crappy fan will ONLY become an issue when pushing the PSU to the limit. I didn't want to be overly direct to begin with, but now I see I must, and thus I emphasize "may" with "ONLY".

AVcableguy · Jan 14, 2005

Oklahoma Wolf said:
Nope - doing that would increase the power to 17v. The 530w will be able to meet the 28A as long as the 5v isn't too heavily drawn. The 2A minimum on the 5v should be enough load to get it to work properly.

What about when using a different power supply?

larva · Jan 15, 2005

AVcableguy said:
Please remember the emphatical nature of my original statement: In otherwords a crappy fan will ONLY become an issue when pushing the PSU to the limit. I didn't want to be overly direct to begin with, but now I see I must, and thus I emphasize "may" with "ONLY".

What forum is this? People are not buying things like Fortron 550s because they are looking to drive loads that could be driven by lesser units. Don't put words in my mouth, I know what I said, and I said what I meant. 80mm fans are rinky dink in the context of a power supply of modern porportions.

If a power supply relies on you not excercising its full output to prevent the limitations of its cooling to be readily apparant, that is a rinky-dink cooling solution.

I'm not sure why you started this thead, asking questions, when in fact your opinion is the only one of value to you. It sounds like you need to answer your own questions.

Oklahoma Wolf · Jan 15, 2005

AVcableguy said:
What about when using a different power supply?

Not sure... combining -5 from one and +12 from another could result in anything from failure of one or both to them just shutting down for protection. It would be far safer to use a standalone PSU with the output voltage desired... the 530w cannot manage output that high anyway without shutting itself down.

Celemine1Gig · Jan 15, 2005

The problem IMHO, when combining the -5V and the 12V rail to get 17V is the following.

The 12V rail on most of today PSUs is rated above 15A, so that should not be the problem. But the -5V rail is very often rated under 1A and only rarely above 1A.

Now let's assume that the your 12V rail is rated at the stated 15A and your -5V rail is rated at 0.5A. Then you wire up some fans to the combined 12V and -5V rails, resulting in 17V. If these fans draw more than 1A, you could have a serious problem. AFAIK, the power is drawn half-half. That means if the fans need 1.5A, then 0.75A are sucked from the 12V rail and the other 0.75A would be sucked from the -5v rail. That would exactly be the problem, as this would exceed the rating of the -5V rail.

If I'm wrong, please correct me. I'm just at the beginning of my EE-studies.

Pushing the 12v rail

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