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Old 10-11-2015, 14:34   #61
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Re: How many kilowatts per day do you use?

[QUOTE=StuM;1959200]
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Originally Posted by sailorchic34 View Post


AAAAAAAhhhhhhhh!

That's it. I'm done with SC!
You can lead a horse to water.....
Power is energy per unit of time. Power is watts. Energy is watt-hours
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Old 10-11-2015, 19:38   #62
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Re: How many kilowatts per day do you use?

What a confused lot you all are.

kWH is the unit for the rate of power consumption, and is the unit used by the power company to measure your instantaneous power usage for billing. The correct question, and the one I answered, is "How many watts (or kilowatts) does your yacht consume in toto per day, on average."

Joules are irrelevant here, they are a measure of mechanical energy. When discussing electrickery we talk in watts. I'm amazed nobody tried to use calories, it would have made about as much sense.
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Old 10-11-2015, 20:00   #63
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Re: How many kilowatts per day do you use?

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Originally Posted by haiqu View Post
What a confused lot you all are.

kWH is the unit for the rate of power consumption,

No it isn't. kWh is the unit for ACTUAL power consumption. kW is the unit for rate.

and is the unit used by the power company to measure your instantaneous power usage for billing.
No it isn't. It is the unit used by the power company to measure your total power usage over the billing period.

The correct question, and the one I answered, is "How many watts (or kilowatts) does your yacht consume in toto per day, on average."

That is not the correct question. A yacht consumes a number of Watt hours or Amp hours in tot per day. It does not consume either Watts or kiloWatts


Joules are irrelevant here, they are a measure of mechanical energy. When discussing electrickery we talk in watts. I'm amazed nobody tried to use calories, it would have made about as much sense.

Joules make perfect sense, since it is a measure of ANY SORT or energy, including electrical. A Watt is 1 Joule per second ( also 1 Coulomb Volt per second). "One joule can also be defined as: The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one '"coulomb volt""
Guess it's not us lot that are confused

Maybe you should take a look at:
Amps v Amp hours v Amps/Hr
https://en.wikipedia.org/wiki/Watt#C...watts_per_hour
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Old 10-11-2015, 20:45   #64
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Re: How many kilowatts per day do you use?

That was fun to read. I have some brain cells left if anyone needs to borrow a few.
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Old 10-11-2015, 21:09   #65
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Re: How many kilowatts per day do you use?

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Originally Posted by newhaul View Post
That was fun to read. I have some brain cells left if anyone needs to borrow a few.
I could use some. I definitely blew a few cells on that discourse.

I also found this link (kW and kWh Explained - Understand & Convert Between Power and Energy) from which this quote helped me understand the difference between the two:

If you have 30-minute interval data with readings in kWh, but you treat those readings as if they are in kW (average kW, strictly speaking), everything that you calculate further on will be out by a factor of 2:

1 kWh over a 30 minute period = 1 kWh
1 kW over a 30 minute period = 1 * 0.5 = 0.5 kWh (using kWh = kW * h, and 30 mins = 0.5 hours)

Or this equation: kW = kWh/h [i.e., power = energy/time]

At least I hope I understand. I'm going to be calculating my energy budget soon so this is of interest to figure out.
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Old 10-11-2015, 21:14   #66
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Re: How many kilowatts per day do you use?

Ok, Stu made a stab at this with his knots and nautical miles analogy. Let me just try the same thing, but a bit differently:

Knot is used to describe a rate of 1 nautical mile per hour. (knot analogous to Watt, a rate of something per unit time). But let's pretend the term "nautical mile" did not exist, and we defined a knot as 1.69 feet per second.

What is the distance covered if one is going 5 knots for 24 hours? Well, we could say 730,080 feet, but easier would be 5 knot x 24 hours = 120 knot-hours. (knot-hours of course analogous to Watt-hours, a quantity of something).

What is the energy used if using 5 Watt for 24 hours? Well we could say 432,000 Joules, but easier would be 120 Watt-hours.

Luckily we do have the units of nautical miles, so we actually would say for the distance example 120 nautical miles instead of the odd knot-hours. We don't however have the same kind of option with electrical units, so when describing electrical quantities (energy) we normally use Watt-hours.

So, the analogies between speed/distance and power/energy are:
feet analogous to Joules (quantities).
knots analogous to Watts (rates, or quantities per unit time).
miles analogous to Watt-hours (quantities)
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Old 10-11-2015, 21:21   #67
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Re: How many kilowatts per day do you use?

Pretty hilarious discussion.

To the OP's question, 55' trawler, boiler, 5 fan driven heat/air exchangers, microwave, 120 vac lights in the evening, refer and freezer, computer, halfhearted attempts to conserve. 6kw - 7kw per 24 hours period at anchor.

I believe that works out to twelve pecks, three furlongs and four troy ounces of energy. I think.
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Old 10-11-2015, 21:34   #68
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Re: How many kilowatts per day do you use?

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Originally Posted by gamayun View Post
...
1 kWh over a 30 minute period = 1 kWh
1 kW over a 30 minute period = 1 * 0.5 = 0.5 kWh (using kWh = kW * h, and 30 mins = 0.5 hours)....
Right:
1 kWh used over any period remains 1 kWh. It is a quantity (energy).
1 kW for 0.5 hr is 0.5 kWh (rate x time gives quantity).

But also:
If used 1 kWh in a 30 minute period, the average rate of energy usage (power) during that period of time would be 2 kW. (check: 2 kW x 0.5h = 1 kWh).
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Old 10-11-2015, 21:49   #69
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Re: How many kilowatts per day do you use?

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Originally Posted by Delfin View Post
...6kw - 7kw per 24 hours period at anchor.

I believe that works out to twelve pecks, three furlongs and four troy ounces of energy. I think.
I think of course you meant to say 6 to 7 kWh per 24 hour period at anchor.

A quantity of energy used during a 24 hour period.

Pecks, furlongs, and troy ounces are also all quantities (volume, length, weight), so could be used in 24 hours, but need to find something other than energy to measure with those units.
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Old 10-11-2015, 21:53   #70
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Re: How many kilowatts per day do you use?

Quote:
Originally Posted by Delfin View Post
Pretty hilarious discussion.

To the OP's question, 55' trawler, boiler, 5 fan driven heat/air exchangers, microwave, 120 vac lights in the evening, refer and freezer, computer, halfhearted attempts to conserve. 6kw - 7kw per 24 hours period at anchor.

I believe that works out to twelve pecks, three furlongs and four troy ounces of energy. I think.
You obviously haven't understood any of the discussion since you have just made the same fundamental error!
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Old 10-11-2015, 22:05   #71
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Re: How many kilowatts per day do you use?

Quote:
Originally Posted by gamayun View Post
I could use some. I definitely blew a few cells on that discourse.

I also found this link (kW and kWh Explained - Understand & Convert Between Power and Energy) from which this quote helped me understand the difference between the two:

If you have 30-minute interval data with readings in kWh, but you treat those readings as if they are in kW (average kW, strictly speaking), everything that you calculate further on will be out by a factor of 2:

1 kWh over a 30 minute period = 1 kWh
1 kW over a 30 minute period = 1 * 0.5 = 0.5 kWh (using kWh = kW * h, and 30 mins = 0.5 hours)

Or this equation: kW = kWh/h [i.e., power = energy/time]

At least I hope I understand. I'm going to be calculating my energy budget soon so this is of interest to figure out.
Yes! That is exactly it.


That is a great link. What's the chance of SC reading it?

The other point is that if your 30 minute interval data is reading both a ammeter for current (Amps or kW) and an amp hour meter for energy used( Amp hours or KWh) your readings will be:

Time-----------Ammeter------ Amp Hour Meter
At 30 minutes:------1kW---------------0.5 kWh
At 60 minutes:------1kW---------------1.0 kWh
At 90 minutes:------1kW---------------1.5 kWh
...
At 1440 minutes:----1kW---------------24 kWh
(One day)
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Old 11-11-2015, 00:50   #72
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Re: How many kilowatts per day do you use?

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Originally Posted by a64pilot View Post
1,000 Watts, is a 1,000 Watts total.
Stating a time defines rate, not total.

I don't know why this confuses, if I said I burned 10 gl of Diesel today everyone would understand. It should be the same if I state I burned 1000 Watts today. I don't need to state I burn 1 gallon per hour and ran for ten hours do I? I do not need to say I consumed 100 Watts per hour for ten hours?
Because watts is analogous to gal/hr

100watts per hour would imply you started at X watts and over 10 hours your draw steadily increased to (X+1000) watts. Your consumption over an 10 hours would therefore be (10X+5000) watt-hrs. Without knowing the initial draw (X) we don't know how much the total consumption is.

I don't know of any electrical device that has that kind of consumption pattern.
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Old 11-11-2015, 00:55   #73
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Re: How many kilowatts per day do you use?

Where some people get confused is when a question is asked interms of daily consumption, they make assumptions that are often false.

Another analogy would be watts ~ gal/min

If you buy a 5gal/min pump, how many gallons do you pump in a day?

The answer is you don't know until you tell us how long the pump will run each day.

Someone may come back and say that it was assumed the pump was running all day, so we can calculate how many gallons but that's not a typical application.

Take a fridge that draws 168w when the compressor is running. How much the compressor runs in a day can very wildly. If it's 100F and the windows are all closed, it might run 90% of the day desperately trying to keep the fridge cool. If it's winter and the outside temp is 40F, it might only run 10% of the day or less.

So you have to be careful when people ask for daily consumption not to assume that device is on and drawing X watts for 24hrs unless that is stated.

I also see people confuse instantaneous watts and average watts. If you have a pump that draws 100watts when on. The instantaneous is 100watts. The average can vary between 0 and 100 watts depending on what percentage of the time the device is running. Since most devices list the instantaneous watts, that is what is normally assumed when someone tells you a device uses X watts.
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Old 11-11-2015, 03:00   #74
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Re: How many kilowatts per day do you use?

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Originally Posted by valhalla360 View Post
I also see people confuse instantaneous watts and average watts. If you have a pump that draws 100watts when on. The instantaneous is 100watts. The average can vary between 0 and 100 watts depending on what percentage of the time the device is running. Since most devices list the instantaneous watts, that is what is normally assumed when someone tells you a device uses X watts.
Yep, and if the question is how much power do you use in a day( 24 hours), then the formula is average Watts x 24 hours = Watt hours.

So if your 100W pump is run on average for 6 minutes per hour, its instantaneous watts is 100 Watts, its average Watts is 10 Watts and its daily consumption ( i.e. for 24 hours) is 10 x 24 = 240 Watt hours.

It really is that simple, I just don't understand how so many seemingly intelligent people can't grasp this basic idea.
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Old 11-11-2015, 06:31   #75
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Re: How many kilowatts per day do you use?

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Originally Posted by StuM View Post

AAAAAAAhhhhhhhh!

That's it. I'm done with SC!
You can lead a horse to water.....
Ah, if only. [aside: Bites like a crocodile, doesn't he?]

I've got a perfectly good speedo for sale. It measures in furlongs per fortnight, I'm sure you'd love it.
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