Amp / Watt Analysis - Electrical - Page 3 - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical


Thread Tools Display Modes
Old 09-21-2011, 06:59 AM   #31
Join Date: Sep 2011
Posts: 6
Rewards Points: 10

Originally Posted by jbfan View Post
It does, but watts is watts.


Watts is the measure of power.
Thanks you, that was my point


LivingLight is offline   Reply With Quote
Old 09-21-2011, 08:37 AM   #32
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 7,963
Rewards Points: 1,532

Originally Posted by dmxtothemax View Post
No matter what voltage you run a motor on,
The amount of power used is still the same. !
Some of the economy from choosing the higher(est) voltage the motor is rated for is due to less power loss in the wires feeding the motor.

The number of volts (not the percentage of volts) dropped in a given piece of wire depends on the amperes flowing. Losing 10 out of 240 volts is less significant compared with losing 10 out of 120 volts.

For the typical multi-voltage motor the amperes drawn (and the voltage drop in the lines) with the motor set for 240 volts is about half that compared with 120 volts. So we are now talking losing 5 out of 240 volts compared with losing 10 out of 120 volts in the wires. (example only)

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?
Increasing the voltage and leaving everything else the same (not reconfiguring the motor for the higher voltage) generally does increase the amperes drawn.

The load (motor, etc.) has a given resistance. Since amperes equals volts divided by resistance at all times, doubling the volts will also double the amps if the resistance stays the same. In practice the resistance usually increases in this situation because the load heats up and the resistance increases so it is not a proportional increase in amperes for an increase in volts.

When the motor is reconfigured for the higher voltage, its resistance is greater so the motor delivers about the same output in terms of work performed, the watts consumed is about the same as before under the lower voltage, and the amperes drawn is less.

Undervoltage can also burn out motors. The physical load imposed causes the resistance to go down (due to such factors as lowered RPM), the amperes drawn goes up, and the motor can oveheat.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

Last edited by AllanJ; 09-21-2011 at 09:09 AM.
AllanJ is offline   Reply With Quote
Old 09-21-2011, 09:50 AM   #33
a7ecorsair's Avatar
Join Date: May 2010
Location: Minnesota
Posts: 2,052
Rewards Points: 1,000

Originally Posted by LivingLight View Post
Ok so here is my question. HairDryer = 1875 watt

Amps = Watts divided by volts

We use 220volt here, so

Amps = 1875 / 220
= 8.2


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.
I see your problem
BTW 1875/220=8.5 amps - needed to make numbers work
Ohms Law is a three part equation. Voltage, Current, and resistance (or impedance)
The flaw in your above example is that power is constant regardless of the applied voltage to the hair dryer. The only thing constant is the resistance of the hair dryer so the resistance of your hair dryer is 220/8.5=25.9 ohms

If you were to plug this hair dryer into a 110 power source:
I=E/R so I=110/25.9=4.25 amps as compared to 220/25.9=8.5 amps.
If the hair dryer would even operate at 110 volts the power used would be 110*4.25=468 watts

Power is also this: P=IR and therefore R=P/I
P=IR or 4.25*25.9=468 watts

In regards to the 80 amps for the stove, are you adding the value of two 40 amp breakers?


Last edited by a7ecorsair; 09-21-2011 at 10:02 AM.
a7ecorsair is offline   Reply With Quote
The Following User Says Thank You to a7ecorsair For This Useful Post:
LivingLight (09-22-2011)

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Switching from incandescent to CFL Mooe Electrical 8 12-25-2007 11:27 AM
help me solve this mystery please lindaberrien Roofing/Siding 17 06-12-2007 01:06 AM
100 Watt Max Big Bill Electrical 2 03-29-2007 05:34 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1