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Old 06-18-2008, 08:17 AM   #16
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Amp / Watt analysis


I was referring to the second question of the original post about the 1875 watt Hair dryer.

1875 / 110 would be about 17 amps but here is the trick:

1875 / 125 would give 15 amps.

I'm sure that if you look closely at the Hair dryer you will see it is rated at 1875 watts at 125 volts. So its a B.S. marketing trick to have "more power"
example:

It features 1875 watts of maximum drying power, high/low heat settings and a cool shot button that locks style into place. A detachable styling nozzle is included. Hairdryer is full size with a UC standard ALCI safety plug. Power AC 125V/60HZ. Length of dryer is 8".


Last edited by evmsmd09; 06-18-2008 at 08:23 AM.
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Old 06-18-2008, 05:48 PM   #17
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Amp / Watt analysis


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Originally Posted by InPhase277 View Post
OK.

With a generator, as long as it keeps turning, the difference of potential is kept up, so current will flow as long as a path is present between it's poles.


InPhase277
Actually, if you only spin a generator with the prime mover it won't generate a voltage unless the machine is excited. That, and the current flow is from the armature (stator) and not the poles (rotor).

- pete

ps..You made a very good point, I'm just BSing...lol
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Old 09-19-2011, 02:38 AM   #18
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Amp / Watt analysis


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Originally Posted by InPhase277 View Post
These are great questions that even some electricians don't understand. Keep it up.

The amount of current that flows (amps) in a circuit is dependent on two things: the voltage across the circuit, and the resistance of the circuit. The relation is known as Ohm's Law, and is as follows:

Amps = Volts / Resistance (ohms)

Now, you can rearrange that algebraically to get anything you want.

If the resistance stays constant in a circuit, then a change in voltage changes the amount of current linearly. A hair dryer that uses 1875 watts at 110 volts would have an internal resistance of about 6.5 ohms.

So, do the math with me:

Amps = 110 / 6.5 = ~17 A

Now do 220 V:

Amps = 220 / 6.5 = ~34 A

You see?

InPhase277


Ok here is my question.

Amps = Watts divided by Volts


now here in SA we use 220 volts. So if im using 1875 watts of power, its less amps than if it was 110, because unlike Ohms law, in this equation, higher volts drops the amps.

1875 watt / 220 volts = 8.52 amps
1875 watt / 110 volts = 17 amps


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Old 09-19-2011, 02:45 AM   #19
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Amp / Watt analysis


Quote:
Originally Posted by InPhase277 View Post
These are great questions that even some electricians don't understand. Keep it up.

The amount of current that flows (amps) in a circuit is dependent on two things: the voltage across the circuit, and the resistance of the circuit. The relation is known as Ohm's Law, and is as follows:

Amps = Volts / Resistance (ohms)

Now, you can rearrange that algebraically to get anything you want.

If the resistance stays constant in a circuit, then a change in voltage changes the amount of current linearly. A hair dryer that uses 1875 watts at 110 volts would have an internal resistance of about 6.5 ohms.

So, do the math with me:

Amps = 110 / 6.5 = ~17 A

Now do 220 V:

Amps = 220 / 6.5 = ~34 A

You see?

InPhase277


Ok so here is my question. HairDryer = 1875 watt

Amps = Watts divided by volts

We use 220volt here, so

Amps = 1875 / 220
= 8.2

Or


Amps = 1875 / 110
= 17



So unlike Ohms law, in this equation, more volts = less amps.

I Still can't see how a hello kitty hair dryer is gonna such 15 amps. Then a stove on grill would take like 80 amps, more than a average house hold breaker.
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Old 09-19-2011, 05:53 AM   #20
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Amp / Watt analysis


You still have much to learn !

A hair dryer can easily pull 1800w.
Due mainly to the heating element.
Most heating elements use a rather large amount of power.

And a stove grilling element would easily pull a like wise amount of power.
But 80a is not not just for the grill.
That would be everything at once.
oven , grill , and hot plates all together.

In Australia 240v mains,
stove circuits are usually 30 to 40a.
Cause your half that voltage 120v,
You would be double that amperage.
So 60 to 80a would be about right.

Keep reading and digesting !

Last edited by dmxtothemax; 09-19-2011 at 06:10 AM.
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Old 09-19-2011, 06:10 AM   #21
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Amp / Watt analysis


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Originally Posted by dmxtothemax View Post
You still have much to learn !

A hair dryer can easily pull 1800w.
Due mainly to the heating element.
Most heating elements use a rather large amount of power.

And a stove grilling element would easily pull a like wise amount of power.
But 80a is not not just for the grill.
That would be everything at once.
oven , grill , and hot plates all together.

In Australia 240v mains,
stove circuits are usually 60 to 80a.

Keep reading and digesting !
So one device on full and the whole house would be maxed? Let alone the geyser, lights, other heaters, TV, PC, etc etc. Our plug circuit is a 10 amp, so this does not make sense to me.

Dont forget that even the greatest minds of electricity, pretty much all say that at best, we know nothing about current and electricity.
To em there are alot of contradictions, some stuff seems to work most of the time, but in certain cases, it does not work out.

Also if you couldn answer my question on why Ohms law increases Amps, where as amps = watts over volts decreases it.


Now for pudding
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Old 09-19-2011, 06:56 AM   #22
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Amp / Watt analysis


Ohm’s Law: P=IE E=IR

Change them anyway using standard mathematics.

P=IE is the same as I=P/E…plug in some numbers….E=240, P=1800, do the math and I=7.5

Now if E=120, P=1800, I=15.

In the case of a 1800 watt hair dryer, the value of P (watts) is fixed. So if ‘P’ is fixed and ‘E’ is changed, that means ‘I’ will have to change in order for ‘P’ to still equal 1800.

In the case of P=IE, I & E are inversely proportional. If one goes up, the other must go down in order for ‘P’ to be the same.
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Old 09-19-2011, 07:00 AM   #23
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Amp / Watt analysis


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Originally Posted by SD515 View Post
Ohm’s Law: P=IE E=IR

Change them anyway using standard mathematics.

P=IE is the same as I=P/E…plug in some numbers….E=240, P=1800, do the math and I=7.5

Now if E=120, P=1800, I=15.

In the case of a 1800 watt hair dryer, the value of P (watts) is fixed. So if ‘P’ is fixed and ‘E’ is changed, that means ‘I’ will have to change in order for ‘P’ to still equal 1800.

In the case of P=IE, I & E are inversely proportional. If one goes up, the other must go down in order for ‘P’ to be the same.

Then why is there a equation Apms = Watts / volts


Im using 2000 Watts @ 220 volts


Amps = 9
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Old 09-19-2011, 07:13 AM   #24
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Amp / Watt analysis


When changing from 110v to 220 v the ampergae will go down, actually in half.
This is why some motors are rated to be wired either way. It is be economical to run at higher voltage and lower amps.
Ex. swimming pool motors.
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Old 09-19-2011, 07:35 AM   #25
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Amp / Watt analysis


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Originally Posted by LivingLight View Post
Then why is there a equation Apms = Watts / volts
Because P=IE, P=Watts, E=Voltage, I=Current (Amps). Divide both sides of the equation by E, and the equation becomes I=P/E. Divide both sides of P=IE, by I and it becomes E=P/I.

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Originally Posted by LivingLight View Post
Im using 2000 Watts @ 220 volts

Amps = 9
You divide 2000 watts by 240 volts, not 220V, as the system nominal voltage is 240V. Your answer is I=8.333~
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Old 09-19-2011, 09:01 AM   #26
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Amp / Watt analysis


For everyday electrical purposes just use watts equals volts times amperes.

At all times, for heating elements, amperes equals volts divided by resistance (Ohm's Law). Ohm's law is also true for motors, inductive loads,and electronics where it is stated as amperes equals volts divided by impedance and the actual mathematics is somewhat more complicated (for you math whizzes, complex, no pun intended).

For load calculations in the U.S., assume (and use in your calculations) 120 volts or 240 volts.

The actual amperes drawn and watts consumed by heating appliances given a slightly different voltage (like 110 or 208) is not predictable because the temperature of the heating elements varies with the voltage and the resistance varies with the temperature.

You do not compute amperes required by measuring the resistance of the heating element when it is cold and the power is off (power off is mandatory for resistance or continuity measurements)
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Last edited by AllanJ; 09-19-2011 at 10:15 AM.
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Old 09-19-2011, 09:53 AM   #27
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Amp / Watt analysis


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Originally Posted by AllanJ View Post
For everyday electrical purposes just use watts equals volts times amperes.

At all times, for heating elements, amperes equals volts divided by resistance (Ohm's Law). Ohm's law is also true for motors, inductive loads,and electronics where it is stated as amperes equals volts divided by impedance and the actual mathematics is somewhat more complicated (for you math whizzes, complex, no pun intended).

For load calculations, assume (and use in your calculations) 120 volts or 240 volts.

The actual amperes drawn and watts consumed by heating appliances given a slightly different voltage (like 110 or 208) is not predictable because the temperature of the heating elements varies with the voltage and the resistance varies with the temperature.

You do not compute amperes required by measuring the resistance of the heating element when it is cold and the power is off (power off is mandatory for resistance or continuity measurements)
Nitty gritty details....but accurate......

And....where was that "Hello Kitty" hair dryer made? China? I would be willing to bet that it is not pulling the full 1800W.....good chance the 'rating' is based on perfect conditions with maybe the supply voltage 'tweaked' a little to get the wattage up.

By the time you add up the voltage drop due to your wiring and the cheap cord (which most likely has 16 gauge or smaller wire) they put on there....I doubt your doing more than about 1500w...
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Old 09-20-2011, 06:40 PM   #28
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Amp / Watt analysis


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Originally Posted by NJMarine View Post
When changing from 110v to 220 v the ampergae will go down, actually in half.
This is why some motors are rated to be wired either way. It is be economical to run at higher voltage and lower amps.
Ex. swimming pool motors.
No matter what voltage you run a motor on,
The amount of power used is still the same.
Voltage might change but power doesnt !
Cause as one changes the other also changes.
SEE - SAW !
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Old 09-21-2011, 01:43 AM   #29
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Amp / Watt analysis


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Originally Posted by dmxtothemax View Post
No matter what voltage you run a motor on,
The amount of power used is still the same.
Voltage might change but power doesnt !
Cause as one changes the other also changes.
SEE - SAW !
I strenuously disagree...


Amps = Watts DIVIDED by VOLTS



How can volts going up not change amps in a three way formula?



Last edited by LivingLight; 09-21-2011 at 01:46 AM. Reason: missing a "e"
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Old 09-21-2011, 06:31 AM   #30
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Amp / Watt analysis


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Originally Posted by LivingLight View Post
I strenuously disagree...


Amps = Watts DIVIDED by VOLTS



How can volts going up not change amps in a three way formula?


It does, but watts is watts.

100w/120v=.833amps
100w/240v=.416amps

Watts is the measure of power.

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