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# How to accurately calculate power draw and choose a fitting power supply - Page 4

Quote:
 Originally Posted by meticadpa I know what my point was, you really don't need to tell me that. TDP isn't power usage. At all. In any universe. ANYWHERE. The HD5870's TDP was 188W if I remember correctly, but its power consumption was closer to 150W from the tests that shinji2k performed here on OCN, so no, it's not an accurate way of measuring power consumption. TDP and power consumption are completely different things. I may have been out of the game for a while, but you're not able to tell me anything about PSUs.
Okay, that's fine. 150w/12v = 12.5a - 188w/12v = 15.7a (roughly)

Comparing to amperage on power supply labels; which one would you use when trying to determine overall power usage of a machine? Actual usage, or theoretical maximum? Better safe than sorry I say. What I wrote up is still useful, even if not 100% accurate.

Quote:
 Originally Posted by grishkathefool His point is valid and not addressed in your OP, though. TDP is NOT the same as the power requirements for a chip, whether it be the CPU, the GPU, or the RAM. Put simply, according to thermodynamics, a CPU, for instance, is going to draw more power than you can measure by it's heat output. In order to measure a 95W TDP, the CPU MUST be using more than that, as not 100% of the energy is going to be converted to heat.
Correct me if I'm wrong, but he said that the TDP was 188w and the card only has uses 150w of power, then you post the above. Which is right?

Quote:
 Originally Posted by meticadpa Thank you.
I'm confused now. You thanked him for posting something that contradicted your statement.

I jest, but there are two conflicting stories.
 The 5 Year Plan (16 items)
 The 5 Year Plan (16 items)
I also would like to say that the OP is not without merit. You should make note that the TDP is only a starting point. When considering that the efficiency rating of the PSU is going to modify the requirements, perhaps add another 10 to 15%.

In addition to that, you must also consider the size and number of drives and fans; not to mention any other peripherals such as CCFLs, et al, that may be attached to the PSU.

I have found that the extreme power supply calculator is a good place to start.

For instance, I just used it to calculate the requirements of my system. It recommends a 482w supply. If I multiply that by an 80% efficiency rating, I get 578w. I add an additional 15% to that and get 650w. This why I bought a 750w PSU, for overhead and expansion. (482w x 1.35=650w)

Edit: You are correct, I don't understand how the input power that meticapada showed as 150w can be less than the TDP. I wasn't referring to that part of his statements when I said
Quote:
.
I also edited my math.
Edited by grishkathefool - 6/11/11 at 12:05pm
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Quote:
 Originally Posted by grishkathefool I also would like to say that the OP is not without merit. You should make note that the TDP is only a starting point. When considering that the efficiency rating of the PSU is going to modify the requirements, perhaps add another 10 to 15%. In addition to that, you must also consider the size and number of drives and fans; not to mention any other peripherals such as CCFLs, et al, that may be attached to the PSU. I have found that the extreme power supply calculator is a good place to start. For instance, I just used it to calculate the requirements of my system. It recommends a 482w supply. If I multiply that by an 80% efficiency rating, I get 578w. I add an additional 15% to that and get 650w. This why I bought a 750w PSU, for overhead and expansion. (482w x 1.35=650w) Edit: You are correct, I don't understand how the input power that meticapada showed as 150w can be less than the TDP. I wasn't referring to that part of his statements when I said . I also edited my math.
Again, correct me if I'm wrong, but doesn't efficiency only judge how much the system will draw from the wall, not how much the components will take? Components should just draw what they need, I don't believe they care about the efficiency of what they're drawing it from.

Using that calculator to work out power draw for my system, it gives me 313W. I highly doubt my system, with an integrated GPU, will ever draw that much. I left CPU TDP at 90% and system loading at 90%, didn't touch capacitor aging. My overclocked CPU wattage comes to 146w, so all the other components (single hdd, single ssd, 2 led fans and one regular) somehow draw 150w? I'm sorry, but that doesn't seem right to me. Again, if i am wrong, say so.

EDIT: Okay, we have reached an agreement. Now what do we argue about?
 The 5 Year Plan (16 items)
 The 5 Year Plan (16 items)
Have you ever looked at a car that is all dressed up with emblems and cosmetic effects and all these visual adds just seem to add something and make the car look faster just standing still? (I hope you have) well this is kind of my idea with a P/S that has a wild wattage rating. It is all for show intended to attract a buyer.

On the other hand if I look at the money I have overspent on P/S's (probably 175.00 over a course of about 7000.00 in hardware) it really does not matter.

If your goal is to demonstrate that you can be very accurate in your determination of power consumption and selection of a P/S that delivers what it claims, well then you have your game to play along with me having my game to play.
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lol,

Rule of Thumb: Better safe than sorry?
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Quote:
 Originally Posted by PCCstudent Have you ever looked at a car that is all dressed up with emblems and cosmetic effects and all these visual adds just seem to add something and make the car look faster just standing still? (I hope you have) well this is kind of my idea with a P/S that has a wild wattage rating. It is all for show intended to attract a buyer. On the other hand if I look at the money I have overspent on P/S's (probably 175.00 over a course of about 7000.00 in hardware) it really does not matter. If your goal is to demonstrate that you can be very accurate in your determination of power consumption and selection of a P/S that delivers what it claims, well then you have your game to play along with me having my game to play.
Erm, I think that the OP has an important message. I have noticed many posts from users asking what size PSU to buy. There should be a Thread here that gives a general understanding of how to figure that need. I was just pointing out that it's a bit more than just totaling the TDP of the CPU, GPU, and primary HDD.

To add to my Rule of Thumb, buy the most PSU you can afford!
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Quote:
 Originally Posted by PCCstudent Have you ever looked at a car that is all dressed up with emblems and cosmetic effects and all these visual adds just seem to add something and make the car look faster just standing still? (I hope you have) well this is kind of my idea with a P/S that has a wild wattage rating. It is all for show intended to attract a buyer. On the other hand if I look at the money I have overspent on P/S's (probably 175.00 over a course of about 7000.00 in hardware) it really does not matter. If your goal is to demonstrate that you can be very accurate in your determination of power consumption and selection of a P/S that delivers what it claims, well then you have your game to play along with me having my game to play.
You've lost me. There's more to a PSU than function? Of course. I like that my current PSU is black, fully modular, has a thermally controlled fan and is 80plus bronze rated, as well as having an x year warranty (trying to find it but Silverstone's website is broken). At the end of the day it's a box that supplies power, and I really couldn't care if it was bright yellow and had alternating flashing LED's and a bright orange cables that are so long the excess fills up my case.

Quote:
 Originally Posted by grishkathefool lol, Rule of Thumb: Better safe than sorry?
I suppose so? Just not *too* safe that it becomes woefully inefficient

Quote:
 Originally Posted by grishkathefool Erm, I think that the OP has an important message. I have noticed many posts from users asking what size PSU to buy. There should be a Thread here that gives a general understanding of how to figure that need. I was just pointing out that it's a bit more than just totaling the TDP of the CPU, GPU, and primary HDD. To add to my Rule of Thumb, buy the most PSU you can afford!
 The 5 Year Plan (16 items)
 The 5 Year Plan (16 items)
I changed my little personal message under my name due to your thread, bro. Thanks for the inspiration!
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Quote:
 Originally Posted by grishkathefool I changed my little personal message under my name due to your thread, bro. Thanks for the inspiration!
Haha, nice one.

Oh by the way, Intel and AMD have different definitions of TDP:

http://www.silentpcreview.com/article169-page3.html

The plot thickens.
 The 5 Year Plan (16 items)
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Damn man, had to try the OCCT PSU Tester... =
It took quite a beat-in.
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