equations are hard....

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Nick Drage

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Sep 27, 2014, 9:15:25 AM9/27/14
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So....

If my energy monitor says I'm drawing 230 or so Watts, and my house runs
on 240 volts, does that mean the entire house - with n computers and a
dishwasher running right now - as A = W/V - the entire house is only
drawing an Amp?

Considering a modern smartphone draws 2 Amps I have clearly got my sums
wrong somewhere... I presume the Watts listed aren't actual Watts?

I can't help feeling it's time for my annual visit to Northackton so
someone can have another go at explaining the magic that is electricity
to me again...

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Adrian Godwin

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Sep 27, 2014, 9:25:49 AM9/27/14
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A smartphone draws 2A at 5V. that's 10W. Allowing for some inefficency, it's only about 50mA at 240V.

Having said that, 230W is pretty low for the whole house. Unless the only things running are chargers and things in standby, it seems unlikely to be correct. A laptop might be taking half of that.

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Divya Pujara

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Sep 28, 2014, 5:20:20 AM9/28/14
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That does seem very low especially if you have a dishwasher running which might typically consume 1600W (see here:http://www.rapidtables.com/calc/electric/energy-consumption-calculator.htm)
However it's not necessarily going to consume that continuously, it might peak for example when it has its water heater on. Similarly for the n computers in the house which will peak in power consumption when they are being worked hard showing videos for example.

It really does depend greatly on what exactly your energy monitor is reporting. You might be better served asking your energy monitor how many KWH of electricity were consumed over the preceding hour during which time your dishwasher ran through a full cycle. From that you can work back to an average current consumption rather than a peak or quiescent current draw which is what your assumption seems to be. (That incidentally might be exactly what your 230 watts is indicating i.e. average power)

Regards
Divya ooo-xxx

Stephen Bridges

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Sep 28, 2014, 11:30:21 AM9/28/14
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If the dishwasher had finished heating and was just sloshing the water round the motor might come across as an inductive load which cheap watt meters don't measure well as the power consumed is out of phase with the current. I've never really tried to measure my usage enough to see how widespread this problem is though. It might be moot.

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Nick Drage

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Sep 28, 2014, 6:08:17 PM9/28/14
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On Sun, Sep 28, 2014 at 02:20:20am -0700, Divya Pujara wrote:

> It really does depend greatly on what exactly your energy monitor is
> reporting. You might be better served asking your energy monitor how
> many KWH of electricity were consumed over the preceding hour during
> which time your dishwasher ran through a full cycle. From that you can
> work back to an average current consumption rather than a peak or
> quiescent current draw which is what your assumption seems to be.
> (That incidentally might be exactly what your 230 watts is indicating
> i.e. average power)

I've had a new fuse box fitted, which is much safer than the old one,
but it means if the load around the house hits a certain limit it'll
trip... and while I have my fair share of UPSs it'll still be less than
ideal... so I'm trying to figure out how many amps I'm drawing now so I
know how many I've got to go.

The unit I have is a Southern Electric branded version of this:

http://www.currentcost.com/product-theclassic.html

Any experience on how good a reading they give? It appears to update
about every ten seconds or so.
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