# I have a simple question about watts...

So if I had a laptop that charged with a 60 watt power supply, could I:

-Charge it with 10 amps at 6 volts? (that is the same as 60 watts)

-Charge it with 6 amps at 10 volts? (that is ALSO the same as 60 watts)

-Charge it with 5 amps at 12 volts? (that is ALSO the same as 60 watts)

-ect...

Watts is just how much 'energy' passes a single point every second (or whatever), so it doesn't matter how you get the watts, watts is still watts?

I'm still trying to grasp the whole concept of watts, so yours answers are infinitely appreciated!!!

active| newest | oldestYes.(two-part answer follows)

2a)

No.Most devices, such as a laptop charger, have an operating voltage.

If you change that voltage, you will damage the device.Because devices have a predicable

load(think resistance, though it is somewhat different)at that operating voltage, theydrawa specific amount of current (amps). And therefore a specific wattage.In the case of a laptop, the load will vary because the battery will change it's state of charge. So the load can increase, but the charging circuit will compensate to prevent damage. The wattage will increase when the battery needs charging.

2b)

Yes.In theory you are correct--for a theoretical device that wouldn't be damaged by different voltages.

A simple high-wattage resistor, for instance. For a change of voltage, there will be a change of current drawn, so the wattage will also change.

3)

Yes.Watts is watts--a measurement of energy consumption.Whyare watts used as a unit of power?Because they allow a single figure "universal" comparison for devices of different voltages and current draw.

Otherwise

boththe amperage and the voltage must be used in the comparison...This light bulb is a 120 volt lightbulb. It will not light up very bright at 12 volts.

In this same way,... your chargers will not work ANYWHERE just because they use the same WATTAGE!!! The charger must put out the correct voltage and amperage for the item being charged.

But no, just because you can get to 60 W by 1V x 60A or 60V x 1A, they are not equivalent, except for measuring the amount of power used (or required)

devices not only require power, but they require electromotive force (EMF, or more commonly, Voltage) and flux or amperage.

imagine this

you try to push N amps thru a diode, which has a forward voltage drop of .6 V. Well, let me tell you, if you have an EMF of 0.1 V to drive that current, i don't give a hoot if you have a million amps available, it ain't gonna pass that diode, since it can't get high enough to jump over the .6V hurdle...

Get the correct charger for the laptop. Or find out what the battery should be charged with, then ask how to build.

L

Steve

"Watts is watts" only in the sense that you can convert from 60W at one voltage to almost 60W at another voltage by using a transformer (for AC) or a DC-to-DC converter (for DC) -- "almost" because you will lose a bit of power in the process -- and that you can get the same amount of work out of 60W however it's supplied IF the circuit which uses that power is designed for that voltage.