# Power usage of a kettle

#### BundyRoy

##### Dedicated elf
I bought one of those plug into the wall power usage/current draw meter things the other day and I have been having a bit of a play.

I set it up with the power cost of \$0.31/kWh and then plugged it into the kettle. Got a bit of a shock. The kettle draws just over 9A and the meter said it was 2400W and it used about \$4 worth of power to boil the water. I know these meters are probably not going to be highly accurate but was wondering if these numbers are normal.

I then checked the kettle and it says it is 2200W. So that's within 10%. I thought the house circuits are only rated at 10A so when I saw 9A I was a bit concerned.

I think our last power bill said we were using about \$7/day so \$4 to boil the kettle seems high.

I guess 2200W/240V= 9A so maybe it's close. Do those formulas work for AC.

Anyway if anybody is qualified to give me their opinion on these numbers I would appreciate it.

Thanks

#### BundyRoy

##### Dedicated elf

2200W=2.2kW
2.2kW x \$0.31/kWh=\$0.68/h

Say kettle took 2 minutes to boil

2min=2/60hours

\$0.68/h x 2/60 = \$0.02

If this is right I guess I have the cost put in the meter wrong.

Would still appreciate any info about the current draw though.

#### nzlongfellow

##### Dennis from NZ
The approximate cost of boiling a kettle, based on a rate of 31c per kwh and a 1.5 litre kettle, the cost is 114c.
[/size]I only put in the water I need at the time. Some fill it to the top and it can get VERY expensive per cup.

#### BundyRoy

##### Dedicated elf
Thanks NZLF. Could you please show us how you came up with those numbers so I can understand it better.

#### AAH

##### I love blinky lights :)
Community project designer
Most of the figures are right.
The kettle will be drawing about 2.2kw or 9A at 240V. \$0.02 works out about right. I have no idea why the meter would say \$4 to boil the kettle unless it was calculating the instantaneous power it was measuring over the kettle boiling as being the load that it would be using for 24hrs.
Individual power outlets are rated at 10 Amps but circuits which could contain 10 or more power points are either 16A for the few prehistoric houses that are still running on fuses or 20A if you are running off circuit breakers

#### BundyRoy

##### Dedicated elf
AAH said:
I have no idea why the meter would say \$4 to boil the kettle.
I do. My guess is the mere male who refused to read instructions put the price in wrong.

Thanks for the feedback on the amp rating of the circuits. I knew there were multiple powerpoints on a circuit. That was why I was worried that if the circuit was 10A and one powerpoint was using 9A. Our house has been rewired so I guess we are on 20A circuit breakers. I know we are definitely on circuit breakers just don't know the ratings.

It made the kids nervous when I plugged it in to the ipod recharger and told them they had to pay me back for the power they use. That was until they worked out that it was using stuff all.

#### scamper

##### Dedicated elf
At a guess I would say that because the power usage is in kwh (kilowatt hours) then your reading is what it would cost at that rate for an hour, as a measuring device is reading actual current at that time. I assume it is not counting up as you are taking the reading.
So if your kettle took 1 hour to boil then it would cost \$4

#### BundyRoy

##### Dedicated elf
Found the problem. Apparently it costs a fair bit to boil the kettle when the price is \$31/kWh instead of \$0.31/kWh. A bad error. Now my wife tells me it is cheaper to get her coffee from the coffee shop.

#### davrus

##### Silent elf
When I first saw this thread title, I thought it was going to be something like comparing running your light show, with the power you need to boil water ! (As in "running your show has the same power usage as a kettle")

Can one of you scientific calculating geniuses make that comparison ?

#### AAH

##### I love blinky lights :)
Community project designer
There's kettles and kettles just like shows and shows. It's going to be a very big kettle at Shell_NZ's place this year and it's just as well that she's boiling a lot of water as there will be plenty of crowds there after a drink.
If you felt like working out your power usage at 100% full white which isn't going to happen too much during a show you can use 0.3W per 5V pixel and 0.72W per 12V pixel. Add 30,000 pixel channels (10,000 pixels) to your display and that's 3kW worth of 5V pixels or 7.2kW of 12V pixels (that works out to about 15A at 240V (30A @110V) for the 5V ones or 32A at 240V (67A @110V) for 12V ones). Just make sure you're not boiling the kettle whilst all those lights are on or things might go dark all of a sudden.