Laptops and processors - Is this ~ how it works?

[AwesomeFX]

How does a laptop CPU get enough power? Just looking for some confirmation

Some physics:

Laptop processor usage: ca 60-70W?

Battery: Ca 18V@2,78A transformed (18V:15=1,2V, 15x2,78=41,6A) to 1,2V@(ca)41,6A (50W TDP:1,2V = 41,6A) in the VRM's (?)


Now, when transforming voltage down, you end up with an linear increase in amperage. But just how much amperage can a laptop battery give out?

If the battery is of decent quality, and of the type Li-ion or Li-Po, it has a C rating. It is possible to calculate the battery maximum continious amp draw using the formula: ACM = AxC (AmpContiniousMax = Battery Amp multiplied with C rating).

Around 15A (?)x1C = 15A max continious draw





Now to a conclusion. The CPU is the most power hungry component of any laptop. The example above shows a laptop battery capable of giving out 15A continiously (in theory I'm not sure if my C rating guess is correct), but only needs 2,78A to supply the VRMs. Since the Voltage is transformed down 15 times lower for the processor, the amperage is automaticly getting 15 times higher. (2,78Ax15 = 41,6A (Ca) = CPU Amp requirement).

Now lets say we have

A screen
Speakers
Kyboard
Graphics calculator
Touch pad
DVD ROM
A PCI utility


And some other stuff drawing a total of 8A, 2,78 from the battery directly to the CPU

The battery is rated 15A (15A = 15Ah, Amp hour)

Which makes me conclude that this laptop would run a little less than two hours (?)





Thoughts? 1st year student here, not quite the level we're at in class, but I like being ahead

Cheers from Norway!

 

[Supahos]

You have to remember thats why most laptops scale things back when running off battery, most severly nerf everything when running off battery power to keep things lasting longer. Also 60~70watts for the process (in most laptops today) is a bit of a high estimate. But 2 hours of gaming will kill nearly any laptop I've seen running on battery so the time frame you suggested isn't far off base I just think some of your estimates may be a bit off.

 

[AwesomeFX]

You have to remember thats why most laptops scale things back when running off battery, most severly nerf everything when running off battery power to keep things lasting longer. Also 60~70watts for the process (in most laptops today) is a bit of a high estimate. But 2 hours of gaming will kill nearly any laptop I've seen running on battery so the time frame you suggested isn't far off base I just think some of your estimates may be a bit off.

Ok, thanks

But are my estimates off because of the high CPU Wattage, or does that include other factors to (not caused by the CPU W)?

Aiming towards engineer, my math must be flawless

 

[leeb2013]

rather than go through all that, just leave the laptop running, doing some basic tasks and you'll have your answer on how long the battery lasts in around 2 hours.

 

[Supahos]

The math appears to be right (was nearly a mechanical engineer before I changed majors) Just some of the estimates are off a bit. Also have to remember thatn the load distributed is never consistent with computers, especially modern laptops with all the powersaving features they have, they turn parts on and off all the time to try and extend battery life.

 

[AwesomeFX]

rather than go through all that, just leave the laptop running, doing some basic tasks and you'll have your answer on how long the battery lasts in around 2 hours.

The point was to refresh some of Ohms laws and basic electrical principles.

Also, laptops sucks, I'm on a Haswell i7, GTX 780 Ti rig^^

 

[AwesomeFX]

The math appears to be right (was nearly a mechanical engineer before I changed majors) Just some of the estimates are off a bit. Also have to remember thatn the load distributed is never consistent with computers, especially modern laptops with all the powersaving features they have, they turn parts on and off all the time to try and extend battery life.

Awesome, thanks!

I'll keep the last part in mind