What is a watt is a watt?

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ffiill

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I pose this question as I am again without power-just isolate my supply and plug in the 800watt generator and I am back in business.
However the 1500 watt hoover will not work(oh what joy to me but annoyance to my wife) because of course its 1500 watts-but then again my big freezer should not work as it needs about 1000 watts to start up.
My big freezer does work all be it with a total power drop when it starts so what about the 1500 watt hoover-well I know its slow start and possibly brushless and yes it works!
I am sure we all are attracted to both power tools and domestic appliances which tend to be priced according to wattage.
So whats going on-my Hoover does note that its also 200 air watts which sounds like its true wattage so what is the 1500 watts?
 
A watt is the rate that energy is used. Got it wrong: Its the rate of work done at constant velocity against an opposing force.



I shall wait to be flamed now. I'd rather not.
 
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ffiill said:
I pose this question as I am again without power-just isolate my supply and plug in the 800watt generator and I am back in business.
However the 1500 watt hoover will not work(oh what joy to me but annoyance to my wife) because of course its 1500 watts-but then again my big freezer should not work as it needs about 1000 watts to start up.
My big freezer does work all be it with a total power drop when it starts so what about the 1500 watt hoover-well I know its slow start and possibly brushless and yes it works!
I am sure we all are attracted to both power tools and domestic appliances which tend to be priced according to wattage.
So whats going on-my Hoover does note that its also 200 air watts which sounds like its true wattage so what is the 1500 watts?
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The only way would be to measure it, ideally look at the voltage drop across a resistor as you start it up and run it, but a ring clamp current meter will give you the basics of what's going on.

Any electric motor requires more current to start up than it does to run. It's because of the electrical impedance of the motor, basically. Similarly, any capacitors in the circuit will take more current to charge them up than to run. The manufacturer should quote the maximum power required, because that affects whether you can run it or not but will probably quote the running power as well, somewhere. And that's without the marketing department deciding which figure is going to sell more hoovers ....
 
dgadee said:
Related question: how many electrons flow in an amp hour?
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1 amp is one coulomb per second, and one electron has a charge of 1.6x10^-19 C, so the answer to your question is 2.25x10^22 electrons

But why do you want to know? and why is it a related question?
 
AliM said:
But why do you want to know? and why is it a related question?
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I have a mental model based upon trying to keep electrons in my battery and just wondered what the flow in physical terms actually is. Question is about 'quantity' of electric power.

Thanks for the answer.
 
Your vacuum requires a continuous 1500 watts to run the motor and considerably more to get started, more than the generator is capable of. Your freezer just needs a large (1Kw) kick to start it and get the motor turning then drops down to an acceptable (for the generator) level. So the freezer motor starts to turn and reduces the consumption before the generator complains.
 
dgadee said:
I have a mental model based upon trying to keep electrons in my battery and just wondered what the flow in physical terms actually is. Question is about 'quantity' of electric power.

Thanks for the answer.
Click to expand...

For every electron that flows out of the negative terminal of your battery another one flows in through the positive terminal.
 
If the load is not purely resistive, then watts in not an accurate measure. VA (volt amperes) is a better measure.

The current leads the voltage if the load is inductive as is the case with motors although power factor correction capacitors are usually fitted to restore the PF to 1.

(Electricity suppliers used to get upset if you didn't correct the power factor because you can use more KVA than watts and its watts the old watt-hour electric meters measure and are used to calculate your bill)

Ian
 
"Air Watts" seems to be something that vacuum cleaner makers quote so that you can compare the amount of suction (or effective work) that their machines produce. In essence if the cleaner has an electric consumption of 1500 watts, and produces 200 "air watts" output then IMHO it is being claimed to be 13.3% efficient, which sounds about right for a vacuum cleaner.
 
Cariadco said:
So, go on then, who's going to pipe up about Hole and Electron Flow, Co-valent bonding and Crystal Lattice structures????....Arghhhhhhhhhhhh
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Or how about electron tunnelling or behaviour in a quantum well, we could go on to solve Schroedingers equation for a quantum well. :) (although I've forgotten how to do it) :o

But simply put, the vacuum needs more oomph to get the motor spinning than the freezer. The wattage quoted on the appliance is for steady state operation - you could fit your hoover with a soft start mechanism.

http://en.wikipedia.org/wiki/Motor_soft_starter

But it would probably be cheaper to buy a bigger generator.
 
CreakyDecks said:
For every electron that flows out of the negative terminal of your battery another one flows in through the positive terminal.
Click to expand...

And if you angle your battery so the positive terminal is higher than the negative one the electrons fall down and fill up the negative side again giving you free electricity.:D

I also turn off all my plugs to stop those blighters escaping and putting up my electricity bill.
 
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