puzzled about cooling behaviour of IBM laptop.

[John S]

I'm curious about the cooling behaviour of my IBM R51 laptop.
I often use it in the lounge to read newsgroups, with the mains power
adaptor plugged in, to keep the battery in a charged state.

I've noticed the internal fan runs frequently and sends out a substantial
stream of hot air. At a rough guess I'd say it puts out the heat you would
get from, say a 40 watt light bulb.

However, if I pull out the power adaptor plug from the back of the laptop
and run on battery power, the internal fan either stops or goes very quiet,
and there is no noticeable flow of hot air from the laptop - it just seems
to run cool. There is a slight drop in screen brightness, but it's hardly
noticeable, and I can run the laptop for about 4 hours before the battery
warning appears.

What I can't understand is why there should be such a big difference in the
amount of heat dissipated - to my thinking it shouldn't matter whether the
power is coming from the battery or the adaptor - you would think the
amount of power needed by the laptop would be about the same?

Incidentally, the IBM power adaptor has a rated output of 16 vdc, 4.5A.

Any ideas why the computer behaves in this way?

Cheers,

John S

 

[Mike Walsh]

There are several reasons a laptop PC could use less power when running on the battery. The default setting for screen brightness could be lower. The processor could run at a lower voltage and clock speed. The fan could run less to conserve power, although this will result in higher internal temperature.

 

[kony]

I'm curious about the cooling behaviour of my IBM R51 laptop.
I often use it in the lounge to read newsgroups, with the mains power
adaptor plugged in, to keep the battery in a charged state.

I've noticed the internal fan runs frequently and sends out a substantial
stream of hot air. At a rough guess I'd say it puts out the heat you would
get from, say a 40 watt light bulb.

However, if I pull out the power adaptor plug from the back of the laptop
and run on battery power, the internal fan either stops or goes very quiet,
and there is no noticeable flow of hot air from the laptop - it just seems
to run cool. There is a slight drop in screen brightness, but it's hardly
noticeable, and I can run the laptop for about 4 hours before the battery
warning appears.

The cooling fan is often set up to cool the CPU, per it's
temp, and when running on battery power many laptops are set
(through bios or software utility) to run the CPU at lower
speed and voltage so by default the CPU is already using
less power, creating less heat).

What I can't understand is why there should be such a big difference in the
amount of heat dissipated - to my thinking it shouldn't matter whether the
power is coming from the battery or the adaptor - you would think the
amount of power needed by the laptop would be about the same?

No, the whole point in these changes like CPU speed
reduction and display dimming is to use less power.
Granted, sometimes the reduction is not as much as we'd
hope for, but for the processor it is a pretty big power
savings just dropping to a lower voltage. I don't have
power consumption figures so I'll make a random guess that
it might produce under 40% as much heat.

 

[John S]

snip

The cooling fan is often set up to cool the CPU, per it's
temp, and when running on battery power many laptops are set
(through bios or software utility) to run the CPU at lower
speed and voltage so by default the CPU is already using
less power, creating less heat).


No, the whole point in these changes like CPU speed
reduction and display dimming is to use less power.
Granted, sometimes the reduction is not as much as we'd
hope for, but for the processor it is a pretty big power
savings just dropping to a lower voltage. I don't have
power consumption figures so I'll make a random guess that
it might produce under 40% as much heat.

Thanks for the comments Kony and Mike Walsh.
Makes sense. I haven't noticed any obvious speed hit, but just browsing
newsgroup messages probably wouldn't show up cpu speed reduction I guess.

Thanks again,

John S

 

[Noozer]

Thanks for the comments Kony and Mike Walsh.
Makes sense. I haven't noticed any obvious speed hit, but just browsing
newsgroup messages probably wouldn't show up cpu speed reduction I guess.

Right click MY COMPUTER and look at the properties. What speed does it say
the CPU is on battery and on AC?

 

[John S]

Right click MY COMPUTER and look at the properties. What speed does it say
the CPU is on battery and on AC?

Thanks Noozer,

Well, that's a revelation.
Says 1.6 Ghz; then when I remove the power adaptor it says 591 Mhz.

If I wanted to, is there a way to run at lower speed whilst on mains power?

Not that I would normally want to do this, but speed isn't all that
important when reading newsgroups, reading and writing emails etc (and I
guess it would be better for the computer to run not quite so hot).

Cheers,

John S

 

[kony]

Thanks Noozer,

Well, that's a revelation.
Says 1.6 Ghz; then when I remove the power adaptor it says 591 Mhz.

If I wanted to, is there a way to run at lower speed whilst on mains power?

Not that I would normally want to do this, but speed isn't all that
important when reading newsgroups, reading and writing emails etc (and I
guess it would be better for the computer to run not quite so hot).

Cheers,

John S

Look in the bios, and/or on your windows start menu, in the
system tray area for an icon, or on the notebook
manufacturer's website for a power management application
that allows setting and changing these within windows per
power state.

 

[John S]

Look in the bios, and/or on your windows start menu, in the
system tray area for an icon, or on the notebook
manufacturer's website for a power management application
that allows setting and changing these within windows per
power state.

Thanks,

I found a setting in the BIOS and have set the AC setting the same as the
battery setting. Now the My Computer properties reports 599Mhz on AC.

Will try this for a while just to see how the laptop behaves.

Cheers,

John S