power consumption

I want to calculate power consumption for followings.
Could you please let me know how to calculate .

I have a laptop which is 18V. 3A written on specification sheet.


It is connected to 10V 4000mah battaery.

How much current it drains from the battary.
In practically I cannot use the laptop more than 40Mts with fully charged battary.

Does it drain more than double the current from the battary if it pluged low volatag battery.

Much appreciate your answer.

mpj111 said:

I want to calculate power consumption for followings.
Could you please let me know how to calculate .

I have a laptop which is 18V. 3A written on specification sheet.


It is connected to 10V 4000mah battaery.

How much current it drains from the battary.
In practically I cannot use the laptop more than 40Mts with fully charged battary.

Does it drain more than double the current from the battary if it pluged low volatag battery.

Much appreciate your answer.

Click to expand...

Hi,

Roughly around twice the current, or about 6 amps.
That's if the boost circuit is decent, and it probably is because 4/6 of an hour is 40 minutes.

The actual calculation is as follows...

Pout=3*18=54 watts

With the efficiency equal to 80 percent we have:
eff=0.80
Pin=Pout/eff=54/0.8=67.5 watts
Iin=Pin/Vin=67.5/10=6.75 amps

With the efficiency equal to 85 percent we have:
eff=0.85
Pin=Pout/eff=54/0.85=63.5 watts
Iin=Pin/Vin=63.5/10=6.35 amps

And finally with the efficiency equal to 90 percent we have:
eff=0.90
Pin=Pout/eff=54/0.90=60 watts
Iin=Pin/Vin=60/10=6 amps

HAHA you really show use a multimeter to know that. The laptop will consume the current that its internal circuit needs. Not all the current the battery can give to it. 6 amps? My god!! with that your battery would explode!, haha.

That's the typical operation of a voltage boost circuit. If the output voltage
is double then the input current is also double. It's rather simple really.
The battery apparently did not explode, but some batteries will in fact heat up
when enough current is drawn from them.

The max power used by the computer is 54W. It doesn't draw max power all the time, only when it is number crunching and doing hundreds of things at the same time.

The battery might be rated at the 10 hour (400mA) or 20 (200mA) hour rate to reach 4Ah and at 1C or 0.5C its life per charge might be much less than you think.