Power Supply Volts and Amps and Consequences

I have been given a old laptop that is DC rating 19V 3.42A

Power supply that has been used is 18.5V 4.9A 80W

How important is the power supply volts and amps? It runs it but what the consequences?

 

Guessing from what I have heard, voltage being higher could be damaging but I guess you are lucky that voltage is lower and it still works. For amperage, the laptop won't pull more than it needs so that being higher in the power adapter should be okay.

Note: I can only hope that what I'm writing isn't 100% wrong.

 

You are correct, and 19V vs 18.5V is not of real significance but wouldn't vary much lower than that. It's only about 3% difference. And that is a 65W PSU vs. 90W PSU.

 

Yup. Amps on the supply need to at least match the maximum input the laptop needs. Voltage should be identical but a 0.5V difference probably won't hurt anything.

That being said (for those reading this later) don't go any lower or you might risk not being able to charge the battery OR risk other damage to components.

 

HTWingNut: 65W v's 90 W ? the psu says 80W and would this make any difference to the battery?

Greg: Isn't a maximum input a maximum?

 

Are you sure it says 80W? Coz that's wrong. If the PSU is rated at 18.5V and 4.9A and power = I*V, then its power rating should be 18.5*4.9 = 90.65 watts. And like others said, no it wouldn't make any difference to the battery. Current supplied depends on how much current is needed by the chip. Current is not the discretion of the PSU.

Yes it is a maximum. Like I said, current supplied is the amount of current supplied by the PSU based on how much the internal circuitry DEMANDS. So if there was a laptop that required 6A of current, at 18.5W, that PSU wouldn't work because it would not be able to source 6A. On the other hand, a PSU rated at 18.5W and anything greater than your laptops ampere rating would be fine. Higher current rating does not damage components. Higher voltage rating does. If you supplied 50V to something that requires 19, the current would flow in rivers through the chips and burn them.

 

I got microfying glass out and is 90W. You are right, the print is small and bad.

Simply then, this is what I have learnt the Voltage is close enough to be inconsequential and the higher PSU Amps are fine because the laptop only draws the current it needs. Maximum is the maximum it consumes and PSU needs to be able to supply that or more. It has no affect on battery.

I will not pay money out for a genuine PSU for this old laptop. I just use the one I have.

Thanks all for your responses.

 

Glad to be of help. Definitely no reason to spend money when you don't have to.

 

Just as an FYI, ANYTHING that draws current, not just a laptop or something that uses chips but anything at all, even a table fan will always draw the current it needs. Of course, this is assuming your voltage is at the rated value. You go higher in voltage, and, well that is why you fry your electronics as the current is forced through it more than what it can handle. If you ever overvolt your GPU, well, don't.

 

Just do Voltage * Amps and that will give you your watt power. Plus most laptop power supplies are 40W/65W/90W/120W

 

Bricks are rated to supply the amps at rated voltage. In actuality under low amp draw the voltage may be higher than the rating. Laptops will run fine under low fluctuations so 18.5v is fine as since your rated amps are higher there should be, and I state should be, no problem. There is no guarenty though so watch the system.

Now if it were 18.5v at 3.25a for 60w it would be a real gamble as under high load the system may not be able to supply the needed voltage...............