Laptop Power Adapter (Voltage/Amps)

[bitwise]

How important is it that the voltage and the amps on a given power adapter match the power requirements listed for the laptop? In the three questions below assume that the laptop in question requires an 18.5V / 2.5amp power adapter.

#1. Would it be ok to use a 18.5V / 3.5amp power adapter?

#2. Would it be ok to use a 19.5V / 2.5amp power adapter?

#3. Would it be ok to use a 25V / 4.5amp power adapter?

If your question to #3 is "no" because the adapter is putting out too much voltage, then what if the amps where such that the wattage was the same?

18.5V * 2.5amps = 46.25 Watts (This is what the given laptop requires.)
25V * 1.85amps = 46.25 Watts

So, would a 25V / 1.85amp power adapter be ok for a 18.5V / 2.5amp laptop seeing that the wattage is the same?

Thanks a lot for any help.

 

[edfair]

#1 Yes , the extra won't be used.

#2 Probably , there is some variation allowed. +/- 10% usually OK

#3 No, because the voltage is much higher than the +10% that would probably be OK.
The 2.5 amps is the current draw, what ever supply you use would need to provide that much. The voltage is what the input circuits are looking for

#4 The higher voltage and lower amps for equal wattage is not the answer. It dowsn't run on watts, it runs on amps pushed through by voltage.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[G0AOZ]

I agree with Ed's answers.

Components in the power input circuitry are selected to match the overall voltage requirements, in this case 18.5v plus or minus a small variation. If you exceed the design parameters, then those components are more likely to fail, or at best have a much shorter life because of fatigue, overheating, etc.

A 3 volt flashlight bulb is designed to give a reasonable life expectancy when attached to a 3 volt battery. Stuff a higher voltage into it and will glow brighter but its life will be shortened, often dramatically...

ROGER - G0AOZ.

 

[paparazi]

bitwise
1* yes! the laptop will only draw what it needs so "as long as the adapter is 2.5amp or over.... tis OK

2* Probably as edfair says but personally I wouldn't

3* Agreed! NO! Laptop power supplies are of a regulated type so just because the overall wattage may appear the same doesn't make it compatible,the voltage is just too high.
I can see where you are coming from with this analogy and for non voltage sensitive electrical items (electric motors for instance) this makes absolute sense but computers are fairly voltage sensitive and so only operate withing tight parameters.
Martin

We like members to GIVE and not just TAKE.
Participate and help others.