[SOLVED] Laptop charging question

[Jem777]

Hi All
I cannot find the answer to this question anywhere, hopefully someone here can answer it.

if i charge my laptop while its turned off, does it use the same amount of power as if it was turned on or would it uses less power?

an example

my Gigabyte P55. The power supply is a 19.5v 9.23 amp, will it use all of this to charge the laptop while its turned off?
Thanks

 

[Eximo]

No simple answer. Let me see if I can provide additional information that will get you thinking along the right lines.

Short answer, probably no, depending on the power limits of the charging circuit, and the batteries. Cooling becomes an issue at high charge rates, and the fans and heatsink aren't connected to the battery.

Long answer:

19.5V x 9.23A = 180 Watts
The power supply has that as its output to the laptop's charging/power circuits.

The consumption of the laptop will vary on the load. So the computer might take anywhere from 20-250W to run. (Some laptops will discharge the battery even when plugged in if the load is high enough, why you see really high end laptops with multiple power bricks)

The battery itself will have a charging circuit, temperature limits, etc. So, if I have the right model, a 63 Wh battery. So at 63W discharge it will last one hour. If the battery has a maximum charge rate of 1C, then it should take 1 hour to charge at 63W, This is not likely as that would make a fairly slow charge. So if we assume a .5C charge, then that would just about equal 30W. Which should allow the laptop to use about 150W and still charge the battery.

However, we know it is a 6-cell battery. Lithium cells, of these type (18650), max out at 4.2 volts, so it is likely we are looking at a set of 3 in series in parallel, which should double the charge rate. So back to the 1C 63W charge rate. Hard to say without the exact cells and charging circuit.

Now batteries don't often charge linearly, even Lithium cells, which have quite close to linear charging, but they do taper off at the top end, and a full charge will almost always take longer than max charge rate. Also some loss in heat as always with electronics.

To actually find out, you can measure it at the wall. You can locate the battery specifications in a white paper from the manufacturer of the battery (hard to do, usually, they often don't want to be compared to the competition)

 

[Jem777]

Thanks for the response but i think im more confused now.
My gut feeling is that 9+ amps is too much for a laptop battery, i charge my car battery with 8 amps!

i think the adapter would step down to a lower rating but im not sure.
Thanks for your response.

 

[Eximo]

Yes, and what I showed was that it is very unlikely that the charging circuit will allow greater than 60W or so to charge the battery, roughly 3 amps. That is on the high side as well and I don't expect that to be the case. Just going on what I know about your average 18650 lithium cell and common arrangements inside of a battery pack. For temperature and lower risk of fire hazard, it could be significantly less. Without special equipment you could measure this by discharging the battery and seeing how long it takes to charge fully with the laptop off, that would get you a rough time to charge and you can back calculate power draw.

12V @ 8A for a car battery is .2C for a 40Ah battery. Lithium cells actually charge much faster then your typical lead acid. Also have to keep in mind that your car battery is quite large and can absorb a lot more excess heat.