65W Vs. 90W AC Adapter, how to choose?
Date:2010-5-19
Laptop A watt is a unit of measurement. This particular unit measures power£¬ or capacity to do work. Watt¡¯s law states that one watt (1W) is how much power is in an electrical circuit where one ampere (1A)£¬ or amp£¬ of current flows across a difference of one volt (1V). AC adapters convert electricity in alternating current form from one voltage to another. If you are looking at two AC adapters that both convert£¬ say£¬ 120V AC to 12V AC£¬ it can be confusing to see different wattage ratings (such as 65W vs. 90W) for the two adapters.
An AC adapter with a rating of 90 watts with an output of 12 volts AC will have a maximum electrical current output of 7.5 amps (12V x 7.5A = 90W). Therefore£¬ an AC adapter with a higher power rating (measured in watts) will be able to supply more current to a device it¡¯s connected to.
While an AC adapter with a higher power rating will allow for faster battery charging times and increased electrical loads£¬ an AC adapter with a lower power rating may suffice£¬ especially where there is a concern about excess heat or higher cost.
Similarly£¬ since the power rating is considered to be a "maximum allowable power" indication£¬ an AC adapter may be used to power devices that are rated at or below their power rating. If a device requires 12V and 3A (36W)£¬ either the 65W or 90W power supply may be used to power it.
Cost may also be a factor. Usually£¬ since AC adapters with a higher power rating must be capable of delivering more electrical current for the same amount of voltage£¬ the components required to assemble an AC adapter must be more robust than that of a lower-power-rated AC adapter.
AC adapters with higher power ratings also give off more heat than adapters with lower power ratings. If excess heat is a consideration£¬ an adapter with a higher power rating may not be suitable for the application.