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Old 09-11-2015, 21:30   #31
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Re: How many kilowatts per day do you use?

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Originally Posted by StuM View Post
"power per day" ? is that sort of like "knots per day" ?
More like Joules per day, but in a easier to understand wrapper. So 1 kw = 3,600,000 joules
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Old 09-11-2015, 21:31   #32
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Re: How many kilowatts per day do you use?

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Originally Posted by sailorchic34 View Post
Kw being a unit of power, So 1kW per day, which is quite proper usage BTW. Not to be confused with kWh which is a unit of energy... two different thingys.
Sorry, that's not right. We've had this discussion elsewhere, but I have to respectfully say that "1 kW per day" is not an appropriate measurement. Since you apparently do *not* mean that 1 kWd = 24 kWh, I'm not even sure what it might mean in this context. "kWh per day" is the thing to use here.
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Old 09-11-2015, 21:40   #33
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Re: How many kilowatts per day do you use?

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Originally Posted by AFKASAP View Post
Hi,

What size is your boat?
What significant appliances do you have running?
Is it winter or summer where you are?

How much electricity do you use per day while living aboard (Longterm, not weekenders).

I am talking about comfortable living...
In my first reply I included KWH figures while on shorepower.

I'm back on the boat and looked up our 12VDC AH consumption when away from the dock with 2 refrigeration units and 1 freezer running, microwave, heat, lights, and all the other amenities previously mentioned.

We average about 160 12VDC AH/24 hours in winter, which converts to just under 2 KWH/day for 12VDC usage. [160AH*12VDC/1000]

I don't have figures for when the generator is running [6-12 hours/week in winter] as the amp meter is analog and split between the two hot legs of the circuit with a selector switch [i.e., AC amps are not recorded...]

I hope this 12VDC supplement is also useful.

Cheers!

Bill
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Old 09-11-2015, 22:06   #34
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Re: How many kilowatts per day do you use?

While underway it really varies because of autopilot, radar, plotter use, etc. While at anchor, between 4-6 kWh/day no refrigeration, solar hot water, diesel heater, no a/c. lots of power tools, air compressor, notebook computer, a couple always-on boat systems monitoring... While at the dock, 5-9 kWh/day. Big difference is we have the SFF computer w/400W power supply and 23" monitor on more while in a slip.
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Old 09-11-2015, 22:10   #35
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Re: How many kilowatts per day do you use?

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Originally Posted by sailorchic34 View Post
More like Joules per day, but in a easier to understand wrapper. So 1 kw = 86,400,000 joules per day.
No, it's NOT more like Joules per day.

True: 1kW is the same as 86,400,000 joules per day. But I don't think you understand the implication of that.
And "1kW" is different to "1kW per day"

So when you say "1kW per day", which do you mean:

(a). A constant draw of 1kW all day and night - in which case you are consuming 24 kWh per day and your figure of 86,400,000 joules above is correct
or
(b). A total consumption of 1kWh per day or 3,600,000 Joules per day.

Either of these are equally plausible, but vastly different interpretations of your fuzzy statement.

Based on your 75-ish Ah, your situation is (b).

So your calculation of 86,400,000 Joules is in fact 24 times more energy that you do use.

Good job you didn't get an electrical engineer to spec your power storage based on the 86,400,000 Joule requirement. You wold have ended up with 24 times as many batteries.
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Old 09-11-2015, 22:23   #36
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Re: How many kilowatts per day do you use?

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Originally Posted by Paul Elliott View Post
Sorry, that's not right. We've had this discussion elsewhere, but I have to respectfully say that "1 kW per day" is not an appropriate measurement. Since you apparently do *not* mean that 1 kWd = 24 kWh, I'm not even sure what it might mean in this context. "kWh per day" is the thing to use here.
Ah sorry, my bad. So when I say I use 1 kw of power per day, which equals 1000 watts or 3,600,000 joules or 1Kwh per day, it's really all the same to my poor mind. 1 joule = 1 watt per second. Pretty simple.

So many units to chose from. I could have said I used 3412 Btu/hr in a day which again is a measurement of power. 3412 btuh = 1kwh =1000 watts per hour. Most are units of power, though kWh is a unit of energy used per hour.

Myself I'd rather not use kWh as first I don't use 1000 watts in an hour and second saying one kWh per day is not very elegant.
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Old 09-11-2015, 22:28   #37
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Re: How many kilowatts per day do you use?

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Originally Posted by sailorchic34 View Post
More like Joules per day, but in a easier to understand wrapper. So 1 kw = 3,600,000 joules
Ah, I see you have edited your earlier post. And still got it wrong!

Watts are power, Joules are energy. You can't equate them.
You can't say the x kW = x Joules without a time factor.

1 Watt = 1 Joule per second so:

1kW = 1000 Joules per second or
1kW = 60,000 Joules per minute or
1kW = 3,600,000 joules per hour or
1kW = 84,600,000 joules per day

So out of the four numbers above, how many Joules do you actually consume per day with "1kwd (kiloWatt days?) or 1kw per day"
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Old 09-11-2015, 22:32   #38
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Re: How many kilowatts per day do you use?

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Originally Posted by StuM View Post
So when you say "1kW per day", which do you mean:

(a). A constant draw of 1kW all day and night - in which case you are consuming 24 kWh per day and your figure of 86,400,000 joules above is correct
or
(b). A total consumption of 1kWh per day or 3,600,000 Joules per day.

Either of these are equally plausible, but vastly different interpretations of your fuzzy statement.
The answer is B of course or is that (b). Sorry it's late at night where I am and miss fumble fingers mis-keyed her hp50 rpn calculator. My batteries could however supply ~18,720,000 joules, depending on load and temperature and assuming 100% SOC. I would love a 86,400,000 joule battery bank, but would need a few more batteries.

Nite all. I'll be signing off from this thread as I don't want StuM to have a coronary.
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Old 09-11-2015, 22:39   #39
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Re: How many kilowatts per day do you use?

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Originally Posted by StuM View Post
Ah, I see you have edited your earlier post. And still got it wrong!

Watts are power, Joules are energy. You can't equate them.
You can't say the x kW = x Joules without a time factor.

1 Watt = 1 Joule per second so:

1kW = 1000 Joules per second or
1kW = 60,000 Joules per minute or
1kW = 3,600,000 joules per hour or
1kW = 84,600,000 joules per day

So out of the four numbers above, how many Joules do you actually consume per day with "1kwd (kiloWatt days?) or 1kw per day"
Nope 3600000 joules is the same amount used for one kwh or for my 1000 watts consumption per day. Both equal 3,600,000 joules.

Nite
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Old 09-11-2015, 22:46   #40
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Re: How many kilowatts per day do you use?

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Originally Posted by sailorchic34 View Post
Ah sorry, my bad. So when I say I use 1 kw of power per day, which equals 1000 watts or 3,600,000 joules or 1Kwh per day, it's really all the same to my poor mind.

But not to everyone else. How are we supposed to know which interpretation is correct when you constantly mix units like this?


Quote:
Originally Posted by sailorchic34 View Post
1 joule = 1 watt per second. Pretty simple.

So many units to chose from. I could have said I used 3412 Btu/hr in a day which again is a measurement of power. 3412 btuh = 1kwh =1000 watts per hour.
Wiggling yet again?

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Originally Posted by sailorchic34 View Post
Most are units of power, though kWh is a unit of energy used per hour.
ALL are units of power. Why differentiate kWh from the others. They are all the same thing: Power = Energy divided by Time.

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Originally Posted by sailorchic34 View Post
Myself I'd rather not use kWh as first I don't use 1000 watts in an hour

Of course you don't, you don't USE any "watts in an hour". Once again Watts are power, not energy. That's like saying "covering six knots in an hour".


Quote:
Originally Posted by sailorchic34 View Post
and second saying one kWh per day is not very elegant.
It might not be very elegant in your eyes, but not saying it is downright ugly in my eyes. It is the only correct usage
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Old 10-11-2015, 00:16   #41
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Re: How many kilowatts per day do you use?

Once again, sailor chick proves she doesn't understand engineering calculations.

For those new to this discussion and wondering what the back and forth is about, there was a recent thread, where she insisted amps equal amp-hr among other nonsense. She was repeatedly corrected by at least half a dozen people but still insists she understands the difference.

Kilowatt-hours (KWH) is the correct measure for a discussion of the total electricity consumption used at dock. It's what the power company uses and they might know what they are talking about.

For battery usage at anchor, it's typical to use amp-hr (at 12v) but KWH is acceptable. If you run at some other voltage than the standard 12v system, you either need to state that if using amp-hr or switch to KWH.

Stating you used X KW each day has no real meaning in terms of total consumption without stating how long the KW draw occurred. (you could say you average X KW and that would infer you used 24*X KWH each day but it's rather cumbersom if the goal is to determine what the electrical bill will be.)
Stating you used X KW/day, implies a change in consumption but without knowing how many KW you were drawing at the start and for how long, you have no idea how much was consumed.

I shall now resist further discussion of sailor chic's misunderstanding of engineering calculations.
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Old 10-11-2015, 10:17   #42
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Re: How many kilowatts per day do you use?

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Of course you don't, you don't USE any "watts in an hour". Once again Watts are power, not energy.[/COLOR]
Watt is defined as one joule per second and can be used to express the rate of energy conversion or transfer with respect to time.

If I had said, I used 1000 watts, I would agree that it does not define a time unit. But I said I used 1kw per day which is 1000 watts in a day. That is exactly the same as saying I used 1kWh in a day. kWh is a lovely unit. But I don't use it much as I have not had in electric bill in well over 10 years.
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Old 10-11-2015, 11:02   #43
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Re: How many kilowatts per day do you use?

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Originally Posted by valhalla360 View Post
For battery usage at anchor, it's typical to use amp-hr (at 12v) but KWH is acceptable. If you run at some other voltage than the standard 12v system, you either need to state that if using amp-hr or switch to KWH.

Stating you used X KW each day has no real meaning in terms of total consumption without stating how long the KW draw occurred. (you could say you average X KW and that would infer you used 24*X KWH each day but it's rather cumbersom if the goal is to determine what the electrical bill will be.)
Stating you used X KW/day, implies a change in consumption but without knowing how many KW you were drawing at the start and for how long, you have no idea how much was consumed.

I shall now resist further discussion of sailor chic's misunderstanding of engineering calculations.

Good morning Valhalla360. I hope your having a lovely day.

So I can use ah or kWh, but I can't use watts. Wow so limiting.

Does not my saying I used "1 kw per day" define an energy use over time. Really?. I believe day defines a unit of time, just as hour defines a unit of time. watt or kilowatt is a unit of energy.

So lets break it down.

My fridge uses roughly 36 watts in an hour or 0.036kWh. Though when It's running it's consuming 168 watts. So the fridge uses the lions share of the power at 864 watts per day or 0.864 kWh. The other 136 watts are used by the laptop at ~12 watts per hour for ~6 hours, cabin lights a 9 watts for 5 hours, anchor light at ~8 watts used per night and phone that is roughly 5 watts used every 3-4 days.

All that adds up to about 1000 watts consumed in a day or as I said 1 kw per day or 1kWh. I'm so happy there is more then kWh to define energy use over time.

At the same time saying I used, oh, 1 kwh does not define how fast that energy was consumed. I could have used 60kw for a single minute in one hour, or 6kw for ten minutes in an hour. Both result in 1 kWh. or 1000 watts consumed
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Old 10-11-2015, 11:19   #44
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Re: How many kilowatts per day do you use?

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?
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Old 10-11-2015, 11:40   #45
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Re: How many kilowatts per day do you use?

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Originally Posted by sailorchic34 View Post
Does not my saying I used "1 kw per day" define an energy use over time. Really?. I believe day defines a unit of time, just as hour defines a unit of time. watt or kilowatt is a unit of energy.
Watt (or kiloWatt) is a unit of power, not energy. Power is the rate of work done, or rate of energy use.

A Watt is defined as 1 Joule per second, and is a rate of energy transfer per unit time.

So when you say "1 kW per day" you are saying "1000 Joules per second per day". Does not make any sense.

A kWh (kilo Watt hour) is an energy value. For 1 kWh = 1000 Joules/sec X 60sec/minute x 60 minutes/hour x 1 hour = 3,600,000 Joules. Both Wh (as well as kWh) and Joule are units of energy, but Wh is the one commonly used in engineering.
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