some questions. what charger? what are these holes?

[nerys]

You see. NO. kwh is the rate kw is the volume. again incorrect. kw is the DISTANCE kwh is the MPH

a 40w bulb is not 40watts. that would mean the bulb can only work for 1 hour. your average "cheap" incandescent 40w bulb is actually a 60,000w bulb (40watts times estimated lifespan of 1500 hours)

the RATE it consumes power is 40 watts per hour.

the total VOLUME of power it will consume in its estimated lifespan is 60,000watts (1500 hours at 40 watts per hour)

the car does not have a 24 kwh battery. it has a 24kw battery.

IF you draw it down over 24 hours then your draw rate is 1kwh or you draw it down in 1 hour your rate is 24kwh (roughly speaking)

my point is (and thankfully on a regular computer now so much easier to type)

we ALMOST NEVER actually mean "KW" what we mean almost 100% of the time is KWH

but we simply say KW.

do NOT depend on KW or KWH depend on CONTEXT to determine which is being used.

99% of the time you can assume KWH is what is "meant" when KW is typed or spoken.

it is just how we use the terms publicly again 40w bulb 1500w inverter 3000w genny. ALL wrong. its a 40wh bulb a 1500wh inverter and a 3000wh genny.

so when someone says 3.3kw power supply they MEAN kwh. not a total of 3.3 kw. but because this is simply how we do things we say KW.

 

[TimLee]

^^^You have it reversed nerys. Several have explained it, you just don't appear to be comprehending.
kWh is an energy measurement.
kW is the rate at which energy is flowing.
Some people do unfortunately interchange the terms particularly when talking about their power bill.
But important to understand the difference and use the right units.

 

[Slow1]

You see. NO. kwh is the rate kw is the volume. again incorrect. kw is the DISTANCE kwh is the MPH

Ahh - so there is confusion here. From Wikipedia (convenient) to help show that I'm not making this up...:

The kilowatt hour, or kilowatt-hour, (symbol kWh, kW·h, or kW h) is a unit of energy equal to 1,000 watt-hours, or 3.6 megajoules.[1][2] If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt-hours is the product of the power in kilowatts and the time in hours.

You appear to be making the common mistake of thinking kWh is "Kilowatts PER hour" which would imply a rate like "Miles PER hour, Mph". This is an incorrect understanding of the term.

a 40w bulb is not 40watts. that would mean the bulb can only work for 1 hour. your average "cheap" incandescent 40w bulb is actually a 60,000w bulb (40watts times estimated lifespan of 1500 hours)

I'm not sure what the lifespan of a device (lightbulb) has to do with the discussion.

the RATE it consumes power is 40 watts per hour.

Ok - there I agree with you. However "watts per hour" is not Wh, it is "40w" IF burned for one hour, that bulb would burn a total of 40Wh of energy.

the total VOLUME of power it will consume in its estimated lifespan is 60,000watts (1500 hours at 40 watts per hour)

Incorrect - the proper reference would be to say the expected total energy consumed would be 60,000wh or, more commonly referenced as 60Kwh

the car does not have a 24 kwh battery. it has a 24kw battery.

Sorry, incorrect - take a look at the specifications from Nissan if you don't believe me: from http://www.nissanusa.com/electric-cars/leaf/charging-range/battery/" onclick="window.open(this.href);return false;
--------
CELL POWER
The 24kWh lithium-ion battery stores its energy to power ...
-------

my point is (and thankfully on a regular computer now so much easier to type)

we ALMOST NEVER actually mean "KW" what we mean almost 100% of the time is KWH

but we simply say KW.

Well, some folks are more careful than others.. I prefer to say what I mean so that I will mean what I say and as such am very careful about the terms. If I say Kw, I mean Kw (rate of consumption/use) if I say Kwh I mean volume used/consumed/stored.

do NOT depend on KW or KWH depend on CONTEXT to determine which is being used.

Sorry, as an engineer I have to be more precise in my language.

so when someone says 3.3kw power supply they MEAN kwh. not a total of 3.3 kw. but because this is simply how we do things we say KW.

A 3.3Kw power supply can provide up to 3.3Kw of energy. It doesn't tell you anything about how long it will do so or the lifetime amount of power it will provide. IF you run that 3.3Kw power supply and draw it's full rated capacity of 3.3Kw for two hours, you will have drawn 6.6Kwh of power. Your utility bill / meter will increase by 6.6Kwh for that period of time. If you were to run that same 3.3Kw power supply at full capacity for 30 minutes, your utility bill/meter would go up by 1.65Kwh.

 

[TomT]

A simple analogy using water and a tank:

A KW is how fast the tank can be filled. A KWH is how much the tank holds.

 

[finman100]

so a degrading battery has a small "leak" in the tank? The tank shrinks, can't hold as much energy?

 

[nerys]

maybe we have a terminology mismatch or something?

this definition on wikipedia agrees with me

The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour.

kwh is like mph. it is a measure of distance over time (mph) while kwh is a measure of energy over time

where am I wrong? the measurement does not have much meaning without a time reference.

a device can not simply "consume" 40w. you need a time reference for that to make any sense or provide any useful information. 40watts OVER WHAT TIME. well 40wh. 40 watts per hour.

in fact it is not possible to determine power usage without a time value.

 

[Slow1]

so a degrading battery has a small "leak" in the tank? The tank shrinks, can't hold as much energy?

I think of it more like the tank is gathering sludge that over time adds up and thus, while the pond is the same size it has less useful capacity.

The "leak" analogy can be used to help understand why a stored battery will no longer be fully charged after some period of time, but can be "topped off" after that time period - thus the need for a 'trickle charger' that slowly replaces the lost volume as it leaks out.

 

[EVDRIVER]

It is very simple and we have far too many threads confusing new people:

A 1000 watt light bulb consumes 1000 watts at a constant rate as soon as it is on, if it is on for one hour it consumes 1KWH because a KWH is 1000 watts of constant load for one hour.

500 watts for one hour is .5 KWH and 500 watts for two hours is 1 KWH.


It is very simple and there is no need for confusing analogies it is simple math. Watts X Time / 1000 = KWH. 40 watts X 30 hours is 1200 / 1000 = 1.2KWH.

 

[nerys]

no. a kilowatt is not 100 watts at least not like you use it.

it is a watt hour (which is 1 watt for 1 hour no time reference no point)

k is simple 1000. same as kilometer. 1000 meter

1000 watts. all measures are in watts. k just lets you use smaller number values for larger values. it is a UNIT converter. nothing else. nothing special unto itself. no difference than centimeter millimeter decimeter kilometer. its simply an order of magnitude change nothing else. saying 1000 watt hours is PRECISELY the same thing as saying 1 kilowatt hour. its a convenience thing not a unite definition thing.

no a 1000 watt bulb does not simple consume 1000 watts.

turn it on for 30 minutes. that is 500 watts not 1000 watts.

the rating on the bulb is watt hours. usage over TIME. it only consumes 40 watts if left on for 1 hour.

but we are lazy so we just say 40 watts. or 40w.

the leaf does not use a 3.3kw charger. it uses a 3.3 kwh charger. if you use it for one HOUR then it uses 3.3kw (plus overhead etc..) but again. standardized nomenclature means we just "say" 3.3kw.

I really don't understand the problem. I have a feeling we are all saying the same thing just confused on terminology and nomenclature.

 

[EVDRIVER]

no. a kilowatt is not 100 watts at least not like you use it.

it is a watt hour (which is 1 watt for 1 hour no time reference no point)

k is simple 1000. same as kilometer. 1000 meter

1000 watts. all measures are in watts. k just lets you use smaller number values for larger values. it is a UNIT converter. nothing else. nothing special unto itself. no difference than centimeter millimeter decimeter kilometer. its simply an order of magnitude change nothing else. saying 1000 watt hours is PRECISELY the same thing as saying 1 kilowatt hour. its a convenience thing not a unite definition thing.

no a 1000 watt bulb does not simple consume 1000 watts.

turn it on for 30 minutes. that is 500 watts not 1000 watts.

the rating on the bulb is watt hours. usage over TIME. it only consumes 40 watts if left on for 1 hour.

but we are lazy so we just say 40 watts. or 40w.

the leaf does not use a 3.3kw charger. it uses a 3.3 kwh charger. if you use it for one HOUR then it uses 3.3kw (plus overhead etc..) but again. standardized nomenclature means we just "say" 3.3kw.

I really don't understand the problem. I have a feeling we are all saying the same thing just confused on terminology and nomenclature.

You need to proof your posts because they have typos or errors. Regardless, a 1000 watt bulb (not 100) does consume 1000 watts of load, turning it on for 30 minutes is NOT 500 watts it is .5kwh. The load of the bulb does not change based on time, that makes no sense at all. A LEAF does not have a 3.3kwh charger, it has a 3.3kw charger, that is the OUTPUT rating of the charger and no charger is rated in kwh as that would also make no sense. We are not all saying the same thing your terminology is backward in most cases or incorrect.

As you say:

"no a 1000 watt bulb does not simple consume 1000 watts.

turn it on for 30 minutes. that is 500 watts not 1000 watts."

Watts is not a measure of total consumption so how did it consume 500 watts or change its watt rating? I guess I should just buy 30 watt bulbs and run them longer and I will get more light out of them :lol:

 

[billg]

I'm sorry for starting all this, but I really do understand the difference, and I promise to do better in the future. :roll:

 

[2k1Toaster]

Easy to prove for yourself.

Go outside and read your power meter, value of X "KWh" that you get billed.
Go plug in your 1500W hairdryer and 1500W toaster and walk back outside to look at the meter. You will not see X + 3KWh. You will only see X + 3KWh if you leave them plugged in for an hour.

I also agree that the excuse of people misusing the terms is not a valid reason to give up being accurate about it. Just like the accuracy vs. precision common misconception. Engineers need to be precise and mean what they say.

 

[Nubo]

I think nerys is referring to if you look at a light bulb it says right on it 40w. Now we all here know that is referring to the lamp consuming 40 watts per hour, it doesn't say 40whr on it, it just says 40w. He is saying the same thing with a genset, for example if they are listed at say 3000 watts continuous again we know this means 3kWh.

No, we don't "know this means 3kWh". It means what it says -- the device will produce a maximum of 3000 watts of power. No presumption is made about the demand that will be placed on it or for how long. If you're only running a 500W device for TWO hours, then it's put out 1 kWh.

Watt is a unit of power. Watt-Hour is a unit of energy. VERY DIFFERENT. Mixing the terms on a whim only leads to confusion.

 

[Nubo]

Again a 40w bulb is not 40w a 1500w inverter is not 1500w a 3000w genny is not 3000w

Your explanation of these incorrect labels?

It's very difficult to parse your question. A 40 watt bulb is a 40 watt bulb is a 40 watt bulb. At nominal voltage it will consume 40 watts of power for however long it is used.

Now if you're talking about an LED "bulb" it gets a bit more confusing because the manufacturers tend to label these in "Watt equivalence". I.e, an LED bulb that consumes 4 Watts of power may be labeled as "40 Watt equivalent" to inform the consumer that it produces light "comparable to a 40 Watt incandescent bulb". Which in itself is another silly refusal to deal with proper units. Light output is measured in Lumens, not Watts.

 

[Slow1]

I'll just respond one last time (sorry folks, I know I kicked this off, but I think it is valuable info as so many have it confused).

this definition on wikipedia agrees with me

The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour.

kwh is like mph. it is a measure of distance over time (mph) while kwh is a measure of energy over time

where am I wrong? the measurement does not have much meaning without a time reference.

A watt is defined as the energy consumption rate of one joule per second so there is in fact an implicit time reference in this "rate" measurement.

Your confusion might be in your assumption that if the term ends with "h" it means "per h". So, look at it like this:

You travel 60Mph (miles per hour, unit of rate) and go 30 miles (miles, unit of distance) in half an hour.
Your bulb consumes 60w (watts, unit of rate) and will consume 30 Wh (watthours, unit of volume) in half an hour.

Break your mind off the idea that the "h" which does denote "hours" also denotes " per ". You could be correct to express Mph as "Mi/h" as in "Miles per hour", but it is incorrect to express kWh as "kW/h" as in "Kilowatts per hour". Yes, it 'seems' correct but is not in fact the meaning of the term kWh.

 

[nerys]

Yes a watt is an amount of power. This is not hard stuff here.

A 1000watt bulb only consumes 1000watts if you run it for 1 hour.

This is not really rocket science. Lets say you want to solar offset you car. 20kw a day. 10 hours sunlight.

You dont need 3.3kwh. You need 2kwh. 2kw per hour times 10 hours nets you 20kw total produce power.

I dont understand why this is coming across as complicated.

A 1000wh bulb will consume 500 watts of power if run for 30 minutes. Half what it would have consumed if rum for 1 hour.

You are confusing demand power for total power consumed.

For the car example your mixing and ignoring terms

Distance time and fuel (total consumption)

Your rate is 60mph (this is demand power your kwh rating) you time is 30 minutes.

60mph will consume 1 gallon of gasoline (my car 60mpg)

Mpg would actually be a better comparison to kwh where hours is equivalent to gallons.

Thst is part of the confusion we are using hours as both a volume value and a time value.

So at a demand rate of 60mph (40kwh bulb) run for 30 minutes will consume 1/2 gallon or 20 watts of power.

 

[garymelora]

You see. NO. kwh is the rate kw is the volume. again incorrect. kw is the DISTANCE kwh is the MPH

a 40w bulb is not 40watts. that would mean the bulb can only work for 1 hour. your average "cheap" incandescent 40w bulb is actually a 60,000w bulb (40watts times estimated lifespan of 1500 hours)

the RATE it consumes power is 40 watts per hour.

the total VOLUME of power it will consume in its estimated lifespan is 60,000watts (1500 hours at 40 watts per hour)


KW.

Other way around

kw is the rate of power consumption, kwh is the amount
A 40 watt bulb consumes 40 watthours per hour

If you run your Leaf motor at 24 kw (by going about 65 mph) a fully charged battery will last 1 hour before being depleted.

 

[nerys]

Do you not realize what your saying? 40 watt hours is precisely the same thing as .004 kilowatt hours

Kwh is watt hours times 1000. Nothing more.

 

[EVDRIVER]

Yes a watt is an amount of power. This is not hard stuff here.

A 1000watt bulb only consumes 1000watts if you run it for 1 hour.

This is not really rocket science. Lets say you want to solar offset you car. 20kw a day. 10 hours sunlight.

You dont need 3.3kwh. You need 2kwh. 2kw per hour times 10 hours nets you 20kw total produce power.

I dont understand why this is coming across as complicated.

A 1000wh bulb will consume 500 watts of power if run for 30 minutes. Half what it would have consumed if rum for 1 hour.

You are confusing demand power for total power consumed.

For the car example your mixing and ignoring terms

Distance time and fuel (total consumption)

Your rate is 60mph (this is demand power your kwh rating) you time is 30 minutes.

60mph will consume 1 gallon of gasoline (my car 60mpg)

Mpg would actually be a better comparison to kwh where hours is equivalent to gallons.

Thst is part of the confusion we are using hours as both a volume value and a time value.

So at a demand rate of 60mph (40kwh bulb) run for 30 minutes will consume 1/2 gallon or 20 watts of power.

"You dont need 3.3kwh. You need 2kwh. 2kw per hour times 10 hours nets you 20kw total produce power."


Watts and kw are a unit of power and kwh are a unit of energy. Yes 10 hours at 2kw gives you 20kwh of energy or 20,000 wh.

In terms of EV use it is less confusing to use the basic calculation I listed before, there were never issues doing this on this forum before only the basic confusion between kwh and kw. I'm not clear why you are trying to rate chargers with kwh and making power and energy confusing. Most newbies here simply need to know how many kwh they use or have in their pack or produce on solar. That is a simple calculation that is being made more confusing by lack of clarity in units of power and energy. I think most people get the basic calculations that have been corrected here for years so there is no need to confuse them by attaching non-applicable kwh measurements to a charger rating. Chargers are measured by POWER output in watts or kw not units of total energy energy in time.

 

[nerys]

Define power

Define energy

Please