[ale] OT need 600-1000W power protection for 3 minutes - cheap

Wed Jul 10 20:39:54 EDT 2013

The information on Volt-Amps was mostly esoteric and aimed at describing 
why things are rated in VA instead of Watts for AC devices (in other 
words there's a real, engineering reason to do it.)

What is fundamentally important in sizing your UPS are the following things:

1.  Total power consumption of your devices.  You can do a multitude of 
things to determine this.  The Kill-A-Watt is one way but you can also 
use the nameplate method (read the sticker on the power supply, assume 
that's the load and go with it.)  The nameplate method usually results 
in overestimation of your power but that's ok, it just extends your run 
time unless you're trying to save every last penny on the UPS.

The nameplate will either have Watts (and should properly also specify 
the power factor if it lists Watts) or it should list Volt-Amps.  I took 
a look at some things around my desk (power bricks, an ATX power supply, 
etc.) and they all are rated in Volt-Amps (one only lists Volts and Amps 
separately so just multiply.)

If the power supply is a switching type and is rated in Watts rather 
than Volt-Amps (improper but possible) then divide by 0.6 to get an 
approximate Volt-Amp value.  That's an average power factor of a 
switching supply, most aren't quite that bad, but you'll get some margin 
out of the underestimation.

Do all your calculations in Volt-Amps, don't worry about Watts.

2.  Decide what kind of runtime you want for your system.  Do you want 
to ride out a blackout for 10 minutes (long enough to shut down cleanly) 
or do you want to stay up and running for over an hour?  Your choice 
here is reflected one of two ways, either you end up with a low power 
UPS that has a massive battery bank or you end up with a UPS that can 
handle a very large load and you'll only use it to a fraction of its 
capacity (which is the equivalent of a really big battery bank.)  So a 
1kW UPS with 1000 Amp-hour battery pack would be similar to a 10kW UPS 
with the matching 1000 Amp-hour battery pack.  The inverter rating gives 
you how much load you can hang off the UPS, the battery pack Amp-hours 
gives you the run time.  But battery packs scale with the inverter 
rating so really big inverters must have really big batteries.  Small 
ones don't need big battery packs but can use them (cooling is important 
here.)

3.  Select a UPS with the appropriate rating.  Your minimum is going to 
be the lowest tier UPS that is larger than your combined load.  Your 
final selection will depend on your choice of run time (small inverter 
with cooling and a giant battery pack or a big inverter with a built-in 
big battery pack.)  Usually the easiest solution that doesn't require 
modifications is the big UPS.  If you don't mind the tinkering, just get 
a small one (with fans) and put a huge battery on it.

On 7/10/2013 09:23, Scott Plante wrote:
> Wow, the third paragraph on mostly went right over my head. I realize
> you were responding to a post, but is that esoteric background or do
> I need to wrap my head around it to decide what size UPS I need.
> Coincidentally, we also need a new UPS and we're trying to figure out
> exactly what we need. I don't have a Kill-A-Watt, but I see I can
> pick one up for ~$20 if it'll help. The blurb on it claims:
>
> * Large LCD display shows kW, volts, amps, watts, Hz and volt amps
>
>
>
> So how would I use that device, or another method, to size the
> correct UPS? And do I need to perform a calculation involving PI?
>
>
> Scott ----- Original Message -----
>
> From: "Alex Carver" <agcarver+ale at acarver.net> To: ale at ale.org Sent:
> Tuesday, July 9, 2013 12:45:45 PM Subject: Re: [ale] OT need
> 600-1000W power protection for 3 minutes - cheap
>
> I have three APC SmartUPS and have no problem whatsoever with
> apcupsd finding them. I get emails when the system goes on battery
> and the auto shutdown works fine across multiple machines with
> apcupsd sending data to other machines hanging off the same UPS
> running apcupsd in ethernet mode (no direct data connection to the
> UPS.)
>
> Here's your BR/BX explanation: http://forums.apc.com/message/23515
> The difference between the SMT and the BR/BX is the Smart Slot where
> you can add Smart Slot accessories like various management cards
> (ethernet) with temperature sensors, etc. Both the SMT and BR/BX have
> the normal USB/serial data port for connecting to a single computer.
> The Smart Slot just allows for direct ethernet connection and
> management by SNMP and APC's PowerChute software.
>
> Measuring in VA instead of W isn't marketing rubbish (entirely),
> it's proper engineering specification for AC circuits. Unless your
> voltage and current are exactly in phase at all times with no
> distortions at all, Watts are meaningless unless you also specify VAr
> or the power factor. Volt-Amps eliminates the need for the power
> factor because it represents the scalar length of the power phasor
> (vector) regardless of where it's pointing in W/VAr space (the 2pi
> radian range of phase angle.)
>
> Using volt-amps for the specification means that a power supply (the
> UPS in this case) can supply varying types of loads with different
> power factors and the total available apparent power (real and
> reactive/imaginary) is constant. A 100 VA motor and a 100 VA light
> bulb require the same amount of apparent power. The light bulb needs
> mostly real power and the motor needs mostly reactive power.
>
> Where the marketing comes in is the fact that the engineers are
> forced (by marketing drones) to pick an average power factor so they
> can label the object. Typical switching supplies (prior to a
> concerted push against manufacturers by power companies to make them
> electrically cleaner) have a power factor of 0.6-0.8 and some really
> crappy Chinese knock-offs have power factors down near 0.4 with
> hideous harmonics. APC assumes a power factor of somewhere around
> 0.65 for connected devices which is why your Watt rating is lower
> because some of the available VA must be used for the VAr portion of
> the load demand.
>
> On 7/9/2013 08:45, Ron Frazier (ALE) wrote:
>
>
>> Hi all,
>>
>> To be honest, I need to save some money for this project, since,
>> when spending $ 200 at a time, and multiple times, it adds up. But,
>> I hope to implement it soon. I might be able to buy one new unit,
>> and reduce the load on one pc to use my old ups with that. Not sure
>> yet.
>>
>> The more I think about my loads, the more I think I need a 1500 VA
>> / ~ 900W unit. A 1200VA/~700W unit might do it, but most product
>> lines seem to jump to 1500 VA after 1000 VA.
>>
>> The last time I bought a UPS, it was from Frys. I have no
>> complaints, but you do pay sales tax and probably an intrinsically
>> higher price. The advantage is easier returns if needed. I can't
>> believe it, but I am actually considering mail ordering a UPS. I
>> understand from Amazon reviews on some, that you have to pay to
>> ship it back to the factory if there is a problem, which can be
>> expensive.
>>
>> Based on prior discussions and my experience, I know APC is a good
>> brand. I also understand that, for the "smart" units, it can be
>> hard to get linux to talk to it, if you want to use the auto
>> shutdown software like apcupsd. I think you guys told me before
>> that Tripplite is good, so I may look at those. Based on some
>> amazon reviews and prior comments here, it sounds like I should
>> stay away from Cyberpower.
>>
>> I think it's total marketing rubbish that they rate these things by
>> VA primarily. My computer is currently pulling 539 VA and 532 W,
>> according to the Kill-A-Watt EZ, with a power factor of .98. The
>> UPS I have is an SMT-750 so you would think it could handle the
>> load. But NO, that's 750 VA. The watts are limited to 500, so the
>> thing yells like crazy if I run this load on it. (So I don't.) So,
>> it should be labeled SMT-500! That unit was capable of handling the
>> load before I upped the load. Yes, I do know what VA means. It's
>> just difficult to remember to cut whatever number I see on the box
>> almost in half to get a realistic load.
>>
>> Charles, thanks for the links. I'll keep the buy batteries local
>> idea in mind. Might not be necessary with Amazon's free shipping.
>>
>> It's nice to see that the major makers are starting to come out
>> with some bigger units, with some smarts, with more reasonable
>> price tags.
>>
>> That Fry's link you posted is actually quite interesting. I found
>> it's bigger brother on Amazon.
>>
>> http://www.amazon.com/APC-BR1500G-BACK-UPS-10-Outlet-1500VA/dp/B003Y24DEU/ref=sr_1_1?s=electronics&ie=UTF8&qid=1373381258&sr=1-1&keywords=br1500g
>>
>>
>>
>>
APC's different model numbers are confusing. For example, I don't know
>> the difference between a BR and a BX unit.
>>
>> This unit is a 1500 VA / 865 W unit, with lcd (or led or
>> something) status display, and AVR (automatic voltage regulation
>> [very cool]); for $ 179 with free shipping and no sales tax. This
>> unit has a BR part number.
>>
>> This is at a price point / capacity point that's really starting to
>> get my attention.
>>
>> Here's a similar unit at Frys.
>>
>> http://www.frys.com/product/5955004?site=sr:SEARCH:MAIN_RSLT_PG
>>
>> It has a BX part number. Go figure. The capacity is the same, but
>> it's $ 210, or $ 225 after sales tax.
>>
>> In any case, much better than the $ 500 Frys wants for the
>> SMT-1500. So, I guess the big question is, what do I give up by
>> going with the BR/BG 1500 and saving $ 300 versus the SMT-1500?
>> I'll have to do some research on that.
>>
>> Alex, good point about the cooling. If I'm using a stock battery
>> and a name brand, it will probably be ok. If I'm using a non
>> standard battery, that may be something I have to look at.
>>
>
>
>
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