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  #1  
Old 12-16-2008, 01:26 PM
flipz
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Default kWh to amps

The back story (jump to what conversion I need if you don't want to read) :

So long story short... I'm in a new construction home that my office is constantly tripping the 15 amp circuit. Wiring company is going to come out to check it but will charge me $95 if I'm overloading it. I KNOW that I'm not because all I have plugged in in this room is a desktop computer (plugged in to a battery backup with voltage regulation, so I know it's pulling a constant power) and a laptop computer that is asleep 99% of the time.

I just need assurance for myself that I'm not overloading it, even though I really know I'm not. So the conversion comes in with me needing to actually figure out how much I'm using. I have tried finding a device that I can plug the computer in to that tells me (kill-a-watt or watts up) but they are all online only, and not cheap.

My UPS will tell me how many kWh a device is using, but will not tell me watts. I know that volts x amps = watts (what I ultimately need to figure out is amps, to ensure I'm not going over 15) yet there seems to be know way to figure out how many watts I'm currently using based on kWh?

Conversion I need :


kWh converted to amount of watts or amps a device is using. Is it possible?
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  #2  
Old 12-16-2008, 01:31 PM
JohnS JohnS is offline
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Default Re: kWh to amps

Quote:
Originally Posted by flipz
The back story (jump to what conversion I need if you don't want to read) :

So long story short... I'm in a new construction home that my office is constantly tripping the 15 amp circuit. Wiring company is going to come out to check it but will charge me $95 if I'm overloading it. I KNOW that I'm not because all I have plugged in in this room is a desktop computer (plugged in to a battery backup with voltage regulation, so I know it's pulling a constant power) and a laptop computer that is asleep 99% of the time.

I just need assurance for myself that I'm not overloading it, even though I really know I'm not. So the conversion comes in with me needing to actually figure out how much I'm using. I have tried finding a device that I can plug the computer in to that tells me (kill-a-watt or watts up) but they are all online only, and not cheap.

My UPS will tell me how many kWh a device is using, but will not tell me watts. I know that volts x amps = watts (what I ultimately need to figure out is amps, to ensure I'm not going over 15) yet there seems to be know way to figure out how many watts I'm currently using based on kWh?

Conversion I need :


kWh converted to amount of watts or amps a device is using. Is it possible?
Well, volts x amps x hours = watt·hours, and
volts x amps x hours/1000 = kilowatt·hours

It really doesn't make sense that the UPS tells you how many kWh a device is using, as that increases as you run it longer.

Anyway, 15A x 120 V = 1800 W = 1.8 kW
Two computers don't pull that.
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  #3  
Old 12-17-2008, 04:31 AM
flipz
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Default Re: kWh to amps

Quote:
Originally Posted by JohnS
It really doesn't make sense that the UPS tells you how many kWh a device is using
So I had my gf check on my UPS for me when I realized it might display the output because I wasn't at home. She said it displayed kWh but I have no clue where she looked because it displays kW.

That makes my conversion of volts x amps = watts a snap.

Thanks for the math though John.
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  #4  
Old 12-17-2008, 12:41 PM
flipz
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Default Re: kWh to amps

Just in case anyone cared. lol

Final tally:

Fish tank = 273W peak and idle. Pretty much had no peak, always pulled the same regardless.

Computer + printer + monitor + powered speakers = 194W peak (during bootup) and 142-152W idle.

Shredder (when in use!) = 84W. Idle was < 1W.

Laptop = 52W peak (bootup). Idle (asleep) was < 1W. That computer is almost always asleep.

House was 123v.

Therefore 123v * x amps = 603W (peak)
x = 4.90 amps during PEAK usage.

During normal daily usage when it keeps tripping
123v * x amps = 425W (idle)
x = 3.46 amps

No way am I overloading the 15 amp breaker!
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  #5  
Old 12-17-2008, 03:34 PM
Carroll
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Default Re: kWh to amps

I don't know if this a proper response to your post as I have never posted before. If this an improper response ,then I stand corrected. To reply to your problem,I would like to make a sugestion.Things are not always as they should be.I would turn off the culpret breaker and see if anything else fails to come on in other parts of the house.You may have feeds to other circuits that are causing the breaker to trip. Also,though it is new construction,the breaker itself may be at fault.Weak breaker.Another cause may be a loose wire connection at the breaker or in the circuit. If you have the problem solved by this time ,I would like to the outcome. Thanks,Carroll
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  #6  
Old 03-09-2009, 09:46 AM
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Thumbs up Re: kWh to amps

I realize this thread is a couple of months old, but I ran across this thread in an semi-related Google search. Check to see if your UPS is plugged into an arc-fault-interrupt breaker, as most newer built homes use for bedroom circuits. The breaker can incorrectly detect the self-test cycle of the UPS as an arc condition and will trip, even though the current load is well beneath the capacity of the breaker. I had this problem as did a friend of mine in his new home.

The solution for both of us was to have a separate non-arc-fault circuit run to the computer location. Based on the question you asked I'd say you're better off hiring a licensed electrician do the work for you, but in our case we ran the new circuit ourselves. It isn't difficult if you know what you're doing and know what portions of the NEC you have to meet.

Hope this helps you find the solution!

Jeremy
[..guest link removed..]
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  #7  
Old 04-16-2012, 12:29 PM
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Smile Re: kWh to amps

Need to convert estimated kWh at a football ground into required amps for an upgrade to the power supply.

Estimated power consumption is 90 kWh across a 3 Phase supply. Biggest pull is 32Kw of floodlights which peak at 250 amps on start-up, but settle back to 160 amps once running. Done survey of overall needs at ground and 90 kWh seems correct. Also planning reddevelopment, so need some spare capacity.

Does a 3 Phase supply with 500 amps per phase sound right?

PS: Im not an electrician, so please respond in layman terms!

Many Thanks
Ian
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  #8  
Old 07-30-2012, 10:32 PM
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Default Re: kWh to amps

I know this post is 2 months old and I don't know where you are(I'm in Cyprus) but from your figures I'd guess your in the states(120V supply)
If that's correct then you will need 250amp per phase for that 90kw, that's neat with nothing to spare, so 300amps per phase would give you a spare 18kw over 3 phases
How to do this is;
kw x 1000 = watts = 10kw x 1000 = 10000w
watts divided by voltage = amps = 10000w / 120v = 83.3 amps
amps x volts = watts = 83.333 amps x 120v = 9,999 watts / 1000 = 10kw almost.....
So if you take the total kw's you need, divide it by 3(3 phases) multiply that by 1000(turn it into watts) and divide that by the voltage(120?) that will give you your required amps per phase.
The whole load should be evenly distributed over the 3 phases as uneven loads can cause higher bills.
Geoff.
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