Calculating energy usage for appliances

[CobyRupert]

I got 30 amps from the breaker rating, for a rough estimate. Tonight I checked the manual and it's drawing 12 1/2 watts at 240 volts, the electrical rating is 3000 watts.
Thanks for the answers. Calculating loads is one of those niggling things which I should know how to do but didn't. I don't intend to do any wiring, yet it's good to know things like this.



^^^^
This is what I thought, but wasn't completely certain.

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

 

[ponytug]

...Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

Yes, units are messed up, but it doesn't seem likely to change anytime soon. Quick, how big is a barn-mega parsec" https://en.wikipedia.org/wiki/List_of_humorous_units_of_measurement

Well, I don't think it is just the US that answers distance with time, and personally I think "about two hours" is way more useful than "oh, it is 32 miles", that omits there are 372 hairpins on the thirty two miles...Of course, you always have to factor in local wisdom, about the road and knowing that you have to dog leg through aunt Susie's sister's yard to actually stay on the road.

The one that always strikes fear into my heart in a new area is "oh, you can't miss it!"

All the best,

Peter

 

[LD1]

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

I see the point.

IF anything its backwards actually.

HAving a heater rated for 3000w and using it for 2 hours and sayting you used 6kwh of electric...

Should it not be that the heater is rated at 3000w/hrs and that if you run it you simply just use 6kw of electric?

 

[Jstpssng]

I see the point.

IF anything its backwards actually.

HAving a heater rated for 3000w and using it for 2 hours and sayting you used 6kwh of electric...

Should it not be that the heater is rated at 3000w/hrs and that if you run it you simply just use 6kw of electric?

You just hit on the source of confusion which caused me to start this thread.

 

[Drewintoledo]

Get yourself a kill-a-watt meter or knock off. Not only will it measure amperage and wattage used, but you can track kWh too for under 30 bucks. If it’s 220v you can install a Sense unit or something similar but it’s more expensive.
for the curious, would you mind posting a photo of your sterilizer?
here’s how the sense unit works

 

[CobyRupert]

You just hit on the source of confusion which caused me to start this thread.

“Should it be 3000W/hrs?”
I don’t think so.
Power (Watts), like speed (mph), is a RATE. The rate of something else. Power is the rate of Energy used and Speed is the rate of distance traveled, based on Time.

The term “Watt” already has the “per second” or (“per time”) built into it. (It’s a Joule/sec) It’s already a RATE, so making it into another rate like Watt/hr (the rate of a rate) doesn’t really make sense (for anything related to this discussion).

It’s also nicely designed that if we know the Power (rate of energy), we can easily calculate the rate of electrons (current /Amps) the circuit requires to achieve that power.

(Example: Say it takes 1 kW-hrs (3600kJoules) of energy to boil a pot of water. That doesn’t tell us if it takes 2 hours or 2 days. Only knowing the power can we calculate the time (and current). Same with distance. Destination is 100 miles away, only knowing the speed rate can we calculate time.)

Another way to think of the same thing is to say we can calculate the total Energy applied and the total Distance traveled by knowing the rate applied, and for how long (time). [Energy= Power x time, Distance = speed x time)

You can only label a heater with its Power (it’s Rate of Energy usage) because you don’t know how long it will be turned on for, so there’s no way to know it’s total ENERGY usage.

Watt/hr is like saying MPH/hr.
…but a Watt-hour is like saying MPH-hour. In both cases you’re canceling out the Time component, no longer talking about a rate, but are expressing a cumulative total of Energy and Miles.

Clear as mud?

 

[sea2summit]

Get yourself a kill-a-watt meter or knock off. Not only will it measure amperage and wattage used, but you can track kWh too for under 30 bucks. If it’s 220v you can install a Sense unit or something similar but it’s more expensive.
for the curious, would you mind posting a photo of your sterilizer?
here’s how the sense unit works

Beat me by that much.

 

[DarkBlack]

I think you mean it draws 12.5 amps. At 240V, 12.5 amps would be expected for a 3000W rated heater. (240v x 12.5A = 3000W)
Running this heater for 2.5 hours consumes 7500watt-hrs (7.5kW-hrs)

Watt-hours is a rather weird unit to use for Energy. The System International (SI) (metric) unit for Energy is the Joule (similar to a BTU).
Remembering that Power is the rate of energy (Power = Energy/time); 1 Watt = 1 Joule/second.
So it’s weird to express Energy as a Watt-hr (1 Watt x 1 hour) because that’s the same as saying it’s:
1 Joule/sec x 3600 seconds, this gives you 3600 Joules/sec-seconds; or what we would just call 3600 Joules.

Using the term “watt-hours” is sort of like saying a distance of 100 miles is a distance of “100mph-hours”. It’s kind of silly. (It doesn’t matter if it’s 50mph for 2 hours, or 200mph for a .5 hours, etc..JUST SAY 100 MILES! ..or Joules!)

…of course in the U.S. we say “How far is it? Oh, about 2 hours.”

Like you said- watt is a rate of energy- the same as MPH.
You’re making it confusing by confusing that with time duration. Watt/hours or kwh is rate * time duration to give you work done. Just like saying something was 50 mph, is the rate, but “50 mph for 10 minutes “ tells the rate and time duration which tells the work done

 

[CobyRupert]

Like you said- watt is a rate of energy- the same as MPH.
You’re making it confusing by confusing that with time duration. Watt/hours or kwh is rate * time duration to give you work done. Just like saying something was 50 mph, is the rate, but “50 mph for 10 minutes “ tells the rate and time duration which tells the work done

Watt/hours is very different than watt x hours (watt-hours). Watt-hours are just Joules (energy).
While mph x hours = miles traveled (distance), mph/hr would be a measure of acceleration ( often measured in ft/sec^2, or meters/sec^2) .
Not sure where Watt/hr would ever be used as a measurement or rating. I guess it would be if you were describing how the wattage varies over time.
Example: if something’s power input (or output) changed from 6000 Watts to 8000 Watts over 2 hours, you could say this thing has a Watt/hour rating of 1000 W/hr; but that does nothing to tell you what power it operates at or how much energy it used. This wouldn’t be used to describe the output of a heater with a fixed resistance and constant wattage, as its Watts/hr rating will always be zero. Just like a car at a fixed mph speed is experiencing an acceleration of zero.

 

[DarkBlack]

Watt/hours is very different than watt x hours (watt-hours). Watt-hours are just Joules (energy).
While mph x hours = miles traveled (distance), mph/hr would be a measure of acceleration ( often measured in ft/sec^2, or meters/sec^2) .
Not sure where Watt/hr would ever be used as a measurement or rating. I guess it would be if you were describing how the wattage varies over time.
Example: if something’s power input (or output) changed from 6000 Watts to 8000 Watts over 2 hours, you could say this thing has a Watt/hour rating of 1000 W/hr; but that does nothing to tell you what power it operates at or how much energy it used. This wouldn’t be used to describe the output of a heater with a fixed resistance and constant wattage, as its Watts/hr rating will always be zero. Just like a car at a fixed mph speed is experiencing an acceleration of zero.

I meant watt-hours. Pretty sure you know that