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Trying to determine if I really need to upgrade my power supply unit...


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#1 peterk312

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Posted 14 January 2014 - 03:33 PM

(Based on my prior questions about adding a video card to my system this new topic deserves its own thread...)

 

The first question I have is when you go to a website such as http://extreme.outervision.com/psucalculatorlite.jsp and use their power supply estimator, isn't the total that you get, based on the devices that you include in the assessment, assuming that all the devices are running at the same time? It's an important question because, for example, an IDE hard drive is estimated to draw 18 watts, but if you have a second hard drive on your computer that you only run occasionally for back up purposes then why would you include it to have total watts recommended for power supply increase by 18 watts?

Secondly, at least at the above website, the recommended watts for your power supply unit is 50 watts more than the total watts estimated. Why? I understand that you don't want to select a power supply unit that runs at it's max constantly, but again, even if you have a power supply unit that equals the total power supply you need, unless you run all devices at the same time you won't be stressing your power supply. Plus, what's the significance of the 50 watts? Why can't it be having say 20 watts in reserve? I'm just curious why it's 50 watts because in many cases someone will be led to believe their system will fry if not having the "recommended" watts for a power supply unit.



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#2 Kilroy

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Posted 14 January 2014 - 03:55 PM

1.  There is one time when everything is running at the same time, boot.  Kind of like when you start your car, you need a lot more power to start it than to keep it running.

 

2.  Because there are a lot of things that affect a power supply, temperatures being the big one.  The hotter they get the less effective they are.  While 50 watts extra might be over kill in the 200 watt range when you get up to 500 watts it is only 10% of the total.  I couldn't even give you a guess of how many people have issues with their machines because they either bought a cheap power supply or not enough.



#3 peterk312

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Posted 14 January 2014 - 04:04 PM

So then my first question regarding booting the system: If the power supply estimate comes out to 200 watts, and your existing power supply unit is 220 watts, in the amount of time it takes to boot all the devices your power supply unit will fry because you didn't have an extra 50 watts?

 

That's the circumstance I'm kind of faced with.


Edited by peterk312, 14 January 2014 - 04:05 PM.


#4 Kilroy

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Posted 14 January 2014 - 04:12 PM

While your system may not fry it may not behave properly either.  The main word is "estimate".  Personally I'd rather have too much power than not enough.  My estimate was 660w and the recommended power supply was 750w.  So, it looks like they recommend between five and ten percent additional power as a safety margin.



#5 peterk312

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Posted 14 January 2014 - 10:54 PM

Maybe I should be asking the question this way: Does each device connected to the power supply unit require 100% of its recommended wattage just to power up when the computer boots?

Given that in my case all I'm trying to do is install an AGP 4X graphics card, what about the fact that I'm going to be disabling the Intel 82845G integrated graphics controller? Doesn't that get me some free wattage?



#6 waldojim42

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Posted 15 January 2014 - 01:02 PM

1.Electric motors require 3 times their running power to power on. This is why a lot of servers stagger the start up sequence on drives.

2. Power supplies degrade over time. The time it takes depends on how well made the unit is, and how much headroom it was given.

3. Power supply output depends on temperature. A cheaper power supply will not be able to deliver the rated power once the system is up to operating temperatures. Example: A ThermalTake TR2 450watt PSU can deliver approximately 350watts at 40C. Most cheaper units are rated at 25C. That is unrealistic for any pc. Normal operating temperatures are about 35~40C

 

Give yourself a little headroom, and get a quality unit. In the end, remember that a power supply is one of the few components that can take OTHER parts with it when it dies.


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#7 peterk312

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Posted 15 January 2014 - 02:38 PM

1.Electric motors require 3 times their running power to power on. This is why a lot of servers stagger the start up sequence on drives...

Let's consider just this one parameter: The hard drives need 3 times their running power to start up.

 

So, here's my system currently running fine. It's a Compaq EVO D310 http://h18002.www1.hp.com/products/quickspecs/productbulletin.html#spectype=worldwide&type=html&docid=11348 that came with a 220 watt power supply unit (psu). If you're interested, the label for the psu can be seen here: http://www.atlantisgadgets.com/index.php?main_page=product_info&cPath=5_10&products_id=100

 

The power supply estimates below were taken from results here: http://extreme.outervision.com/psucalculatorlite.jsp

 

Here's only the basic devices from my system powered by the original 220 watt power supply unit:

 

2.4 GHz Pentium 4 CPU (Socket 478, Northwood, estimated watts below used CPU at 90% TDP)
1 IDE hard drive 7200RPM
1 DVD/CD-R combo optical drive
2 sticks DDR RAM
3-80mm fans
(My modem is externally powered, so I'm not including it.)

If we use the tool to calculate the power supply at this point, we get:
152 watts required / 202 watts recommended. Note that the recommended estimate is adding 50 watts on top of the required amount, which is some degree of headroom.

But consider that the above quote says the hard drive needs three times its estimated running power when it starts up. If we remove the hard drive from the above estimate and then use the tool to recalculate, the total required watts changes to 134 watts total. That means the hard drive needs about 18 watts. At startup it should need 3 x 18 which is 54 watts, and that's 36 more watts. So now, the required power for the above to run at startup is 188 watts (152 + 36). The recommended headroom applied to this then puts the original 220 watt power unit that came with the system at an underrated amount because the estimator would recommend 238 watts.

But the above devices listed are not all that are running on my system. For example, I've got another IDE 7200 RPM hard drive. So now, we should be adding another 54 watts to the total required watts if it needs 3x the required power for startup. That puts the total required watts at 242 watts. My system should fry at startup because I should need 242 watts and I'm only running a 220 watt power supply unit.

But additionally, I have a PCI soundcard installed. The estimator tool uses 13 watts as the average wattage needed for a PCI card. Tack on the watts for my soundcard and I should require 255 watts. The estimator tool would add 50 watts headroom to this. So now, the recommended power supply unit should be 305 watts. Yet, miraculously, I'm running these devices using the 220 watt power supply unit that came with the computer. I didn't even include the power needed for the Intel 82845G integrated graphics controller, which I intend to disable and upgrade with a low watt AGP video card.

So, I have a 220 watt power supply unit that has for years been running all devices fine, BUT (given the hard drives require 3X the estimated required watts for startup) the recommended power supply unit should be 305 watts. How is it possible? Clearly, the estimated power supply requirements must be inflated or my system would fry when powering on.


Edited by peterk312, 15 January 2014 - 08:44 PM.


#8 peterk312

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Posted 15 January 2014 - 05:38 PM

Come to think of it, why can't I just configure a staggered startup of my components so that it won't be an issue? Is it difficult to do (even if you're not running your PC as a server)?



#9 peterk312

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Posted 16 January 2014 - 01:41 PM

Here's a website http://forums.atomicmpc.com.au/index.php?showtopic=264 where someone compiled the actual watts required for many different video cards instead of the more often quoted recommended minimum power supply unit for a particular video card. He also provides an interesting explanation why some video cards require much more power than others (which includes what you use it for, e.g., 3D graphics and gaming tasks will need more power).

His graph includes the Nvidia GeForce FX 5700 (likely to have similar power consumption as the FX 5500 that I want to install) running at PEAK to be 25 watts. The number is not continual power consumption, which means it won't need to run this high unless you are trying to do certain tasks.

Here's what I think is a less inflated estimate of the power consumption for my system:

2.4 GHz Pentium 4 CPU (Socket 478, Northwood, CPU at 90% TDP)
1 IDE hard drive 7200RPM
1 DVD/CD-R combo optical drive
2 sticks DDR RAM
3-80mm fans
(no USB devices)
(externally powered modem only using the computer's ethernet network adapter)

152 watts total required (same as above, according to the estimator tool)

add 2nd hd drive (+ 18 watts):

170 watts total required

add a PCI soundcard (+ 13 watts, average)

183 watts total required

If all the above devices were running at maximum power requirements for a sustained period they would need 183 watts. My power supply unit can handle a maximum of 220 watts, so the demand would not be greater than what's available. I left out the existing Intel 82845G graphics controller, but it's not important because it's going to be disabled. If you now add a Nvidia FX 5500 video card (+ 25 watts at peak performance) you get:

208 watts total / estimator would recommended 50 more watts for headroom (258 watts).

If this is accurate, I still have 12 watts available from my 220 watt psu for a very modest headroom, but again, the estimate assumes all these devices are running at the same time and maximum power is required from the system. It is highly unlikely that this will ever occur. As far as powering on the computer at startup is concerned, it's a little more unclear just exactly how much power my system actually requires.
 


Edited by peterk312, 16 January 2014 - 05:55 PM.


#10 waldojim42

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Posted 16 January 2014 - 08:30 PM

 

1.Electric motors require 3 times their running power to power on. This is why a lot of servers stagger the start up sequence on drives...

Let's consider just this one parameter: The hard drives need 3 times their running power to start up.

 

So, here's my system currently running fine. It's a Compaq EVO D310 http://h18002.www1.hp.com/products/quickspecs/productbulletin.html#spectype=worldwide&type=html&docid=11348 that came with a 220 watt power supply unit (psu). If you're interested, the label for the psu can be seen here: http://www.atlantisgadgets.com/index.php?main_page=product_info&cPath=5_10&products_id=100

 

The power supply estimates below were taken from results here: http://extreme.outervision.com/psucalculatorlite.jsp

 

Here's only the basic devices from my system powered by the original 220 watt power supply unit:

 

2.4 GHz Pentium 4 CPU (Socket 478, Northwood, estimated watts below used CPU at 90% TDP)
1 IDE hard drive 7200RPM
1 DVD/CD-R combo optical drive
2 sticks DDR RAM
3-80mm fans
(My modem is externally powered, so I'm not including it.)

If we use the tool to calculate the power supply at this point, we get:
152 watts required / 202 watts recommended. Note that the recommended estimate is adding 50 watts on top of the required amount, which is some degree of headroom.

But consider that the above quote says the hard drive needs three times its estimated running power when it starts up. If we remove the hard drive from the above estimate and then use the tool to recalculate, the total required watts changes to 134 watts total. That means the hard drive needs about 18 watts. At startup it should need 3 x 18 which is 54 watts, and that's 36 more watts. So now, the required power for the above to run at startup is 188 watts (152 + 36). The recommended headroom applied to this then puts the original 220 watt power unit that came with the system at an underrated amount because the estimator would recommend 238 watts.

But the above devices listed are not all that are running on my system. For example, I've got another IDE 7200 RPM hard drive. So now, we should be adding another 54 watts to the total required watts if it needs 3x the required power for startup. That puts the total required watts at 242 watts. My system should fry at startup because I should need 242 watts and I'm only running a 220 watt power supply unit.

But additionally, I have a PCI soundcard installed. The estimator tool uses 13 watts as the average wattage needed for a PCI card. Tack on the watts for my soundcard and I should require 255 watts. The estimator tool would add 50 watts headroom to this. So now, the recommended power supply unit should be 305 watts. Yet, miraculously, I'm running these devices using the 220 watt power supply unit that came with the computer. I didn't even include the power needed for the Intel 82845G integrated graphics controller, which I intend to disable and upgrade with a low watt AGP video card.

So, I have a 220 watt power supply unit that has for years been running all devices fine, BUT (given the hard drives require 3X the estimated required watts for startup) the recommended power supply unit should be 305 watts. How is it possible? Clearly, the estimated power supply requirements must be inflated or my system would fry when powering on.

 

 

First off. A short time pull of extra power will not magically fry the power supply. However, continuous loads like that are not good for it.

Next, Heat plays a major role in the total output power. If the power supply was rated correctly for 40C or even 50C, then at room temp - during start up - it would actually be more than capable of delivering more power.

Also, consider the point I made above regarding over-provisioning. For example, my PC Power and Cooling was sold as a 750W power supply, yet is known to remain perfectly stable up to an 850W load. This was done to compensate for long term degradation and allow for startup surge power draws.

Lastly, there is no one-size-fits-all answer. Generally speaking, leave plenty of headroom. I would never leave a 12W headroom in my own PC's. You are begging for instability. a 50W headroom is enough to ensure that even during peak power draw scenarios, you have enough to make a stable system. Though a 100W headroom is what I shoot for. Also, remember that this estimator cannot fully take everything into account, such as how efficient your VRM's are. Some boards are far more efficient than others, and that plays a decent role in the total power consumed. Higher performance hard drives also consume more power than lower performance drives. That 5500 will have very different power demands based on the clock speed (not all boards are the same!) and the power delivery.

 

The estimator is just that. The best way to tell what your system draws, is to stick a meter at the source. Get a Kill-A-Watt device, and see how much power you are drawing from the wall at full load.


Edited by waldojim42, 16 January 2014 - 08:31 PM.

Laptop: Alienware 14 : Intel i7 4700mq : 8GB ram : Nvidia GTX 765 : 256GB Plextor M3 : 1080P IPS display

Test rig: AMD Phenom X4 955 @ 4.0Ghz : MSI 970A-G46 : 8GB Ram : 128GB Plextor M5s : 2x AMD 5770's (Flashed to 6770) : PC Power and Cooling Silencer 750 : Pioneer BR

Hackintosh : Gigabyte GA-H61m : Intel Celeron @ 3Ghz : 8GB ram : EVGA GTX 550Ti : Patriot Torx 2 64GB : Silverstone Strider ES-50 : OSX Mavericks

 


#11 peterk312

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Posted 16 January 2014 - 11:01 PM

I would never leave a 12W headroom in my own PC's. You are begging for instability...a 50W headroom is enough to ensure that even during peak power draw scenarios, you have enough to make a stable system. Though a 100W headroom is what I shoot for.

 

No, I should already have instability based on the estimator tool evaluation, but I don't. If you configure the power supply for startup (with 3X normal running power for each hard drive for startup) I should need 255 watts (see above post #7). According to the estimate that I think is not as inflated (post #9), 183 watts is required, plus 50 watts headroom would require a power supply unit that is 233 watts. Yet, I've been good with 220 watts for years. You would be going with one that's 283 watts (additional 100 watts), but that's not necessarily needed. Nobody can ever argue with it being better when more power is available. My original question was do I really NEED (need does not mean recommended) more power if I'm disabling the integrated graphics and installing a low watt video card.

 

And you also say "That 5500 will have very different power demands based on the clock speed (not all boards are the same!) and the power delivery." The GeForce FX 5500 is a low watt card that draws only 25 watts at peak performance (highest clock speed is only 250 MHz) so it probably requires a little more power than the Intel 82845G integrated graphics that is going to be disabled. It's nothing like the power supply needed for the video cards most gamers are using today.  

 

I thought one of those Kill-A-Watt meters was much more expensive than about $25 on Amazon. Still, $25 might almost be the price of a new 300 watt power supply. As someone already noted, getting a power supply unit to replace what's in the Compaq EVO D310 will a.) not likely be a unit with a form factor that will fit in the case, and b.) probably not have the right connector for the motherboard because Compaq was using a special adapter not widely used.

 

I think I'm going to give it a go with the existing 220 watt power supply unit after I install the video card (won't be until next week). I might disable my second hard drive temporarily when I first set it up just to be on the safe side, and then if everything runs smooth with the video card I'll enable the second hard drive again and see if the power supply stalls and the system keeps rebooting or if it continues to run okay.


Edited by peterk312, 16 January 2014 - 11:19 PM.


#12 waldojim42

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Posted 17 January 2014 - 08:23 AM

Some people get very lucky and can run a system on the bare minimums for years. Generally though, power supplies are not stable enough for a 100% draw for 5 years. The symptoms are not as cut and dry as "power supply stalls and system keeps rebooting". They can range from under-performance to unexplained instability to smoke coming from the PSU. It is up to you to decide how much your hardware is worth. Trying to justify an undersized power supply is never a good idea. Now that I understand you are arguing for the sake of an argument, I will gladly allow you to do so with others.


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#13 Kilroy

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Posted 17 January 2014 - 11:35 AM

I'll second waldojim42.  Sure you can use an exact match or close to maximum power wattage.  It may work fine for you or your machine may be flaky.  Myself personally I'm unwilling to take the chance as my equipment is too important to me.



#14 peterk312

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Posted 17 January 2014 - 05:25 PM

Since when is someone "arguing for the sake of an argument" when he's being told one thing but then the empirical evidence is suggesting something to the contrary? I have no bad attitude here. I'm presenting the numbers as they've been estimated, and I'm presenting the actual devices and my power supply rating, and I'm asking someone to explain for me 1) how my system could be running with not one glitch for years despite it supposedly being undersized for its power supply unit, and 2) why a low watt video card like the GeForce FX 5500 can't be run on the same system when a.) it doesn't pull more than 25 watts at PEAK and b.) the Intel 82845G graphics controller is going to be disabled. All i have as a reason is that I should have 50 to 100 watts more than the required watts for all devices running at the same time but hard drives need to be estimated at 3X the watts needed for normal running power.


Edited by peterk312, 17 January 2014 - 06:25 PM.


#15 hamluis

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Posted 17 January 2014 - 07:59 PM

The first question I have is when you go to a website such as http://extreme.outervision.com/psucalculatorlite.jsp and use their power supply estimator, isn't the total that you get, based on the devices that you include in the assessment, assuming that all the devices are running at the same time?

\

Secondly, at least at the above website, the recommended watts for your power supply unit is 50 watts more than the total watts estimated. Why?

 

After eliminatinfg nonessential wording...the above is what you asked.

 

Seems to me that's a request for opinions about why/how a given website...makes calculations/statements on its website.

 

IMO, the logical place to look for such would be...that website, if you want a definitive answer for what takes place on a 3d-party website.

 

Posing the two questions as you have here....just calls for opinions from members who have no clue how or why a gvien website will do things.

 

Why not mkes your queries at the respective website...if you truly want specific answers to those questions?

 

Louis






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