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Join Date: Mar 2017
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How Do I Determine My Maximum Power Consumption?

03/01/2017 9:04 AM

Hi. I'm asking this because I'm not very well versed in Electrical Abbreviations, symbols and such. I want to buy a new Generator but I want to first figure out how much KVA Generator that I need. I have a Power and Energy Logger Machine (PEL 105) which I used to record the Power Consumption of my house for a week. (screenshot found in images below). But which of these figures do I look at to determine my peak energy consumption and NOT the total amount of energy consumed throughout the whole week.

Recording Duration : 148hr 30min

Energy Totals:

Ep (Wh) -32.899 kWh

Eq (varh) -16.859 kvarh

Es(VAh) 316.5 kVAh

Thank you,

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#1

Re: How do I determine my maximum power Consumption

03/01/2017 9:16 AM

fuzzy.. 6KW?

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#2
In reply to #1

Re: How do I determine my maximum power Consumption

03/01/2017 9:21 AM

on which screenshot?

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#3
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Re: How do I determine my maximum power Consumption

03/01/2017 9:29 AM

Red bars on bottom bar-chart.

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#5
In reply to #3

Re: How do I determine my maximum power Consumption

03/01/2017 12:18 PM

Quite. GA

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#13
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Re: How do I determine my maximum power Consumption

03/02/2017 9:43 AM

and add some capacity for reactive demand, looks like 3 kVAR peakat the time of kW peak, so 6.7 kVA, 89% PF seems reasonable on average. Then you need to find your largest motor on the system, and add some capacity, as tcmtech says, to get that motor started. You need some kw and lots of kvar to get the motor started, especially if a compressor for ac, for instance. This is needed for seconds, so your meter won't show that peak, or you didn't show it to us.

Take a look at this link below, to cover generator surge capacity, already done for us, and check out your ac system, probably the one most likely to influence your sizing. It looks like it is well done.

http://www.generators.smps.us/start.html

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#4

Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 11:49 AM

3rd one, you get the peak reading and add some 25%or 40%. Say for example 8 kW x (1.25)=10kW if you want to have the specs of the genset you want to purchase.

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#6

Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 12:20 PM

A generator?

What does A Transformer need with a generator? Or shouldn't we ask?

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#7

Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 2:47 PM

Unfortunately your given info does not appear to give any references to any real peak point load values like which happen when large loads like central air conditioning compressor motors start.

On first look you might see your central air system has a 22 amp @ 230 VAC single phase rating on its name plate or such which would imply it uses ~ 5000 watts and would thusly run off a 6000 watt genset without problems.

Unfortunately the reality is that the large electric motor in the compressor may take 5 - 6 times that listed amp value for 1 - 2 seconds which would equate to a massive 25 - 30,000 watt peak surge value way beyond what even a conservatively rated 15 KW genset would be able to start up without producing a substantial system voltage and frequency drop if it could do it at all.

Same with looking at what any short term high wattage loads may appear to be on a hour by hour power consumption readout.

I have a electric water heater that has two 4500 watt elements that if needed can both come on at the same time resulting in a 9000 watt load yet in normal use it only runs for a 5 - 10 minute at a time a few times a day at most thus making it appear on a hour by hour measurement of only taking around 1000 - 1500 watts not 4500 - 9000!

So until you can define those types of loads peak limits and run times it's impossible for anyone us to recomend a sufficiently sized genset for you.

Personally if my power consumption rates were graphed as your are I would appear to have a base load of may 300 - 500 watt with a peak of maybe 5000 in a typical day but in reality if I wm working in my shop plus have everything else running as well I would need a 30 KW commercial genest with a high overload service factor on top of it to keep thing running properly.

However if I shut off all the 240 volt circuit high load stuff I can easily keep my place up and running off my old 1950's Fairbanks Morse 3 KW genset with room to spare.

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#8
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Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 3:02 PM

5-6X?! that's rather serious.. I looked at this calculator and found some numbers just over 4x for industrial motors, but most were well below.

Watt do you think of the calculator?

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#9
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Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 3:21 PM

I go by standard commercial application DOL estimates that factor standard multi HP single phase motor start up currents to be at least 500 - 600 % of normal peak running currents.

Motor starting and running currents (NEMA standards)

I also factor that most light duty gensets the typical residential home owner will by rarely even put out their nameplate wattage capacity let alone have any measurable reserve power above that.

Ever look at any small portable gensets and see a rating like 5000 watts (5250 surge) Vs a commercial grade unit aht may be rated like 30/50 KW which means it will hold its specd voltage and frequency output at 30 KW continuous and take up to 50 KVA surge while staying within nominal working spec limits?

That's what I go by when sizing loads to gensets.

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#10

Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 7:06 PM

You need to estimate your peak load by going around and counting all your electrical requirements...determine your starting current needs for compressors and motors....You can just turn on everything in the house and take an amp reading at the main, then just add starting currents....Most people will have a separate panel that the generator feeds for emergency use that only includes essentials....of course everybody has their own definition of what's essential....In any case the salesman for the generator will probably be glad to assist you...or possibly a local electrician....

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#11
In reply to #10

Re: How Do I Determine My Maximum Power Consumption?

03/01/2017 7:17 PM

Yep. Essentials.

I remember back in 1999 dealing with a few coworkers who were ready to bug out and go full stand alone off grid when Y2K wiped out the world.

#1 request was setting them up with dedicated gensets that would allow then to run normal lives 24/7 which meant that even at 1999 costs that would have put most of them at $50 - $200+ per day operating costs assuming fuel somehow stayed at 1999 prices ans was still available after the world shut down.

Houses with 100% electric heat and everything else take a buttload of generator fuel to keep going here in January.

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#15
In reply to #11

Re: How Do I Determine My Maximum Power Consumption?

03/02/2017 12:43 PM

Down here the hot setup is to have natural gas and run the generator on that, then you don't have to stockpile fuel or, even worse, have to find it during a crisis, but the natural gas piped underground is the most reliable infrastructure....I would make a list of the electrical appliances and watt load and starting requirements for everything and what could be run at one time, then label the breakers....that way you can have more variety with a reasonably sized generator...restrict A/C to a backup room unit for sleeping....only one burner on the electric stove at a time, of course if you have gas you should have a gas stove, gas dryer and gas water heater, this makes it much easier....but if you don't, then you have to decide what is the minimum electrical requirement you can survive comfortably on....

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#12

Re: How Do I Determine My Maximum Power Consumption?

03/02/2017 2:28 AM

The attached recording sheets are illegible.

What we know-almost for sure-is one horizontal division represents 12 hours and one vertical division is 1[kW,kVAr,kVA,kWh,kVArh,kVAh???] [maximum is 2 digits then it could be 10)

It is weird the active power is so small-and negative-and the reactive power is so elevated. It seems to me the generator it is already in operation and is delivering [or consuming] reactive energy.

Integrating the red recordings it seems to be the reactive energy indeed if each vertical

division is 2 kVAr.

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#14

Re: How Do I Determine My Maximum Power Consumption?

03/02/2017 11:03 AM

The following is a model from another industry, but should work well on electrical demand. Estimate your peak consumption hour by looking at total consumption for a week and taking 21% for the peak day load. Multiply the result by 18% to get the peak hour load.

Since your measurement period is 19.5 hours short of a week, you will have to extrapolate. 19.5 hours is 11.6% of a week. However, that assumes average power consumption in the unmeasured period. Consumption could be higher if the unmeasured period is on a weekend; if that were the case I would add increase 11.6% by about 25%. The important part is to get close and then buy more than your calculation to account for random demand spikes or changes in consumption patterns and demand.

Information on converting power consumption measurements can be found at: http://www.powerstream.com/VA-Watts.htm

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