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Will a larger PSU give me a larger bill at a co location center?

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July 3, 2012 3:04:04 AM

If I can make due with a 500 watt PSU and put in a 2000 watt PSU into a server. Will that make the computer use more amps and thus might necessitiate me paying extra at a colocation center or will the computer draw the same amps either way?

Here is something to make things clearer

http://serverfault.com/questions/62339/how-can-i-calcul...

The guy in the first answer says

"The only way to be sure about your system's utilization is to measure your server's utilization under your expected load. A PSU that can draw 500 watts, if you've got 220v power, can draw up to 2 amps, but it may draw only .5 amps under typical loads for your workloads."
July 3, 2012 3:44:13 AM

mishav1 said:
If I can make due with a 500 watt PSU and put in a 2000 watt PSU into a server. Will that make the computer use more amps and thus might necessitiate me paying extra at a colocation center or will the computer draw the same amps either way?

Here is something to make things clearer

http://serverfault.com/questions/62339/how-can-i-calcul...

The guy in the first answer says

"The only way to be sure about your system's utilization is to measure your server's utilization under your expected load. A PSU that can draw 500 watts, if you've got 220v power, can draw up to 2 amps, but it may draw only .5 amps under typical loads for your workloads."


The correct answer is... Yes, the computer will use the same wattage either way. A computer will only draw the amperage that it needs, you could put a 2.5 megawatt PSU in your server, it will still only draw the amperage (use watts) needed. If your energy draw increases through the addition of hardware or above average usage that will directly impact what you pay (using more watts) but how much wattage your PSU is capable of will not.
Did I make any sense there?
July 3, 2012 4:06:01 AM

However using a PSU designed to power a 2000W system on a 200W system will draw more power due to losses IRL. In theory though it doesn't.
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July 3, 2012 12:47:04 PM

Yes you were both clear. Thank you.
July 3, 2012 1:58:01 PM

I don't know anything about the server PSU market, but generally speaking, the efficiency of a power supply changes across it's load levels.

Buying a high efficiency, high wattage PSU, but running it at mid-range or low wattage levels may end up reducing it's overall efficiency depending entirely on it's design.

An example (all these numbers are BS):
A 500W PSU, supplying 350W to the internal components, may draw something on the order of 400W of Real AC Power from the wall, converting it to DC power at an efficiency of 87.5%.
A 2000W PSU, supplying 1400W to different internal components, may draw 1600W of Real AC Power from the wall, converting at an efficiencty of 87.5%.
However, that same 2000W PSU on the original 350W components, may draw 500W from the wall, significantly less efficient than it's 500W counterpart at that load level, but not to a ridiculous degree.

The reason is essentially that the PSU is designed for efficiency at the load levels it's most likely to run at, usually they have some efficiency designed in for low power levels, and at levels near their specced output level.

In general, if you are running one or two servers with overkill PSUs, I would expect you probably won't see a gigantic difference (probably not enough to make it worth buying a smaller PSU now and needing to buy a larger one later on), however if you are building a whole farm of servers, you should probably use PSUs efficient at your expected load level.
July 4, 2012 1:44:25 PM

It s just that I contacted a colocation center and they told me that for every amp over the limit they allow. Which I think is 1 amp, I need to pay $50 a month extra.
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