Curious electrical question at 4am

[rvr6000]

So when you think of appliances and light bulbs - they're power usage is usually given in Watts......I bought a 100W light bulb, my washing machine uses 500 Watts, etc. But when you buy a power tool they are generally rated in Amps.

I understand how to convert watts to amps and voltage and all that stuff......but is it somewhat correct to say the amp rating of something can be thought of as how much power it has?

In other words.....my 15 amp circular saw can cut through a 2x8 easier than my 10 amp circular saw with everything else being equal.

 

[wrench409]

Just think what a 5,000 watt laser could do to that board.

 

[Drew_flux]

Watts is the term of power. is it correct to use amps as a term of power? Not realy bt it still happens.

 

[Doug Arthurs]

It could be your 12 amp saw has poorer bearings etc and just draws more amps to do the same job as your more efficient 10 amp model.

 

[Speedy Petey]

So when you think of appliances and light bulbs - they're power usage is usually given in Watts......I bought a 100W light bulb, my washing machine uses 500 Watts, etc. But when you buy a power tool they are generally rated in Amps.

I understand how to convert watts to amps and voltage and all that stuff......but is it somewhat correct to say the amp rating of something can be thought of as how much power it has?

In other words.....my 15 amp circular saw can cut through a 2x8 easier than my 10 amp circular saw with everything else being equal.

I have never seen a washing machine rated in watts. Only amps.

Watts is power used by the load.
Amperage is the load on the circuit.
Directly related things, but not nearly the same.
Funny thing is, both change with changes in voltage.

 

[Gunnert]

To me:

Volts: fuel
Wattage: Miles per gallon
Amps: Hp/Tq
Resistance: Weight

 

[rlitman]

Watts are a unit of power. Amps are not always directly related to power on an AC system when you are talking in terms of motors.

The problem is that for a resistive item (such as a lightbulb or a heater), it is easy to determine the watts that the item draws. But for something like a motor, it is not, as the watts will depend a lot on how much work the motor is doing. In that case, a tool was often rated in terms of horsepower (which IS directly proportional to watts), but because of test methods that can be used to give ludicrously inflated HP ratings, tools are back to amp ratings.

Amp ratings do not lie, but they also do not give the complete picture of how much power a tool has. Is a 15A saw more powerful than a 12A saw. Maybe. Is it more powerful than a 6A saw. Yeah, I'd believe that one at least.

 

[Larwyn]

volts x amps = volt amps and that only equals watts when the current is in phase with the voltage (power factor of 1).

 

[duude]

To me:

Volts: fuel
Wattage: Miles per gallon
Amps: Hp/Tq
Resistance: Weight

Haha. I like this. It's a good analogy.

 

[kbs2244]

To answer your question,
Yes.
As said amps equal power.

 

[rvr6000]

To me:

Volts: fuel
Wattage: Miles per gallon
Amps: Hp/Tq
Resistance: Weight

Thanks Gunnert....this is kinda what I was getting at......can you roughly compare the amps of an electric motor to horsepower of a gas powered engine.

Like I said.....it was 4am and a really quiet night at work. Who knows what I'll be thinking tomorrow at 4am.

 

[williaty]

To me:

Volts: fuel
Wattage: Miles per gallon
Amps: Hp/Tq
Resistance: Weight

This is a very bad analogy, really. Well, resistance=weight is pretty good.

Watts are the one similar to horsepower. Both Watts and horsepower are measuring power.

I would suggest you think of volts like engine speed (RPM) and amps like torque. Volts and amps together gives you power, just like engine speed and torque together give you power.

There's a good reason most tools and appliances are labeled in amps: it's the one you care about for circuit loading. After all, we already know what voltage the tool is getting connected to by looking at the shape of the plug. What we need to know from the label is if we can run, say, the circ saw and the sander on the same 15 amp circuit. We need to know what size extension cord we have to have to use the drill 300' from the house. All of that comes from amps. Sure, the label could give us the power and the power factor and we could calculate amps from that but they're nice and just tell us the amps straight up.

The odd one out is actually the light bulb. I'm really not sure why they tell us the Watts and not the amps. Things like microwaves get sold by Watts because it allows the advertising people to use bigger numbers. However, turn the microwave around and you'll see a label with amps on the back of it.

 

[larry_g]

.....but is it somewhat correct to say the amp rating of something can be thought of as how much power it has?

.

Some what true, but there is an efficiency factor that comes into play. Some motors are are just better at converting electricity to mechanical motion. Also an amp rating without voltage cannot give you the power. A 6A saw on 120vac will have ~half the power as a 6A saw on 240vac.

Also think of the amp rating of a devise as what it consumes and not what it delivers.

lg
no neat sig line

 

[ForceFed70]

On a system with a fixed voltage - watts and amps basically tell you the same think (which is how much energy it uses).

The reason power tools usually come rated in amps is due to 2 reasons:
- Historically that's what was used. They are stuck with it now. People compare tools by the amp ratings. If a manufacturer was to suddenly start rating in watts the average Joe wouldn't know how to compare them.
- Power tools use an electric motor. Motors are not a fixed load like a lightbulb. Your 15A saw will only draw 15A when it's very bogged down to the point of burning out the motor. Typical cutting will only see a 10A current draw. Free spinning the blade will only pull approx 1A once the saw is up to speed. Rating them is a bit tricky, so manufactures typically state the max continous current draw instead of trying to apply a wattage number to it.