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-   -   Would this UPS (Uninterrupted Power Supply) protect and power my gear? (http://duc.avid.com/showthread.php?t=304793)

D_Japan 07-23-2011 01:01 PM

Would this UPS (Uninterrupted Power Supply) protect and power my gear?
 
I have a MacPro with Dual 2.66 Xeons. Apparently it has a 1,000 Watt powersupply.

I also have powered speakers, my 003, and a couple audio processors that total 500 Watts

I don't really get the VA ratings of these UPS systems. Can anyone tell me if this one will do the job?

http://www.amazon.com/APC-SMT750-Sma...1449486&sr=1-1

And how do you know?

Park Seward 07-24-2011 08:53 AM

Re: Would this UPS (Uninterrupted Power Supply) protect and power my gear?
 
A UPS wil last longer the more capacity it has. If you just need a few minutes of charge, a small unit will be fine, If you want it to run for an hour, you need a much bigger unit. Most units will have a chart showing the runtime vs. load.

At 500 watts, this unit will run for only five minutes and it can't take more than 500 watts. I'd get a bigger unit. At minimum, I'd get the SMT1000.

How do I know? I did a Google search.

http://www.apc.com/products/resource...e&list=SMT750;


Converting VA to Amps (voltage fixed)

The conversion of VA to Amps is governed by the equation Amps = VA·PF/Volts)

For example 12 VA·0.6/(12 volts) = 0.6 amp

Converting KVA to KW (Kilovolt-amps to Kilowatts)

The conversion of KVA to KW is governed by the equation KVA = KW/PF)

For example, if the power factor is 0.6
120 KVA·0.6 = 72 Kilowatts

Converting Watts to KVA (watts to kilovolt-amps)

The conversion of W to KVA is governed by the equation KVA=W/(1000*PF)


For example 1500W/(1000*0.83) = 1.8 kVA (assuming a power factor of 0.83)
F
Converting Amps to VA (voltage fixed)

The conversion of Amps to VA is governed by the equation VA = Amps · Volts/PF

For example 1 amp * 110 volts/0.6 = 183 VA

http://www.powerstream.com/VA-Watts.htm

KMcK 07-24-2011 09:19 AM

Re: Would this UPS (Uninterrupted Power Supply) protect and power my gear?
 
Or you could use the handy UPS product selector on APC's website. http://www.apc.com/tools/ups_selector/

D_Japan 07-24-2011 11:17 AM

Re: Would this UPS (Uninterrupted Power Supply) protect and power my gear?
 
KMcK, indeed I did use the handy APS product selector and this is the machine that it recommended for "best performance." However, I am a bit nervous looking at stats that don't aren't listed in a scientific unit that is readily understandable to me.

Also, Park, how about one equation that begins with "W=" that would answer my question?
_*_*_*_*_*_*_*_*_*_*_*_*_*_*__*_*_*__*_*_*_*___*_* _*_*_*_*_*_*_*

So after further research, apparently the manufactures use VA because it's technically more accurate than Watts given this power factor thing.

In short, you can use W and VA interchangeably.

The caveats


(1) a Mac Pro is overbuilt; capable of generating 1000 Watts, but typically drawing far less, say 500W.

(2) The power supply is inefficient, so there is a "power factor" PF that says: if a supply is only 80% efficient you will need 625W going in to get your 500W. However, most modern power supplies are around 95% efficient, due to http://bit.ly/oQVyb1 PF correction designs.


So, the caveats are small.
As for me, to be safe, I'm going to assume that it will be drawing 1000 Watts when the power goes out, and get the 1500 VA rated unit.

Park Seward 07-24-2011 04:23 PM

Re: Would this UPS (Uninterrupted Power Supply) protect and power my gear?
 
Quote:

Originally Posted by D_Japan (Post 1818335)

Also, Park, how about one equation that begins with "W=" that would answer my question?
_*_*_*_*_*_*_*_*_*_*_*_*_*_*__*_*_*__*_*_*_*___*_* _*_*_*_*_*_*_*

In short, you can use W and VA interchangeably.

Here is a calculator to convert VA to watts. It's a 1:1 ratio. I thought most people knew that.

http://www.thecalculatorsite.com/conversions/power.php

The conversion for Watts to Volt Amperes assumes a purely resistive load and does not take into account any reactive power (VAr); therefore effectively unity power factor.


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