# Watts

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•  Subject
• Author
• Posted on
•  Watts
• 07-23-2005

All of this time I thought Watts was a drummer in the greatest rock &
roll show in the world.

I need a twelve-volt adapter to run my 15" Powerbook.  THe last one I
had was 45 watts.  It worked OK until I started burning CD's.  Then
it started smoking and smelled of electrical mishap.

PowerBooks, instead of the 70watt, which should also be adequate on the
15"?

What uses more juice?

Would the 120watt charge faster than the 70?

Would the 120watt put a greater demand on my 12-volt source?

As an aside, Is China in partnership with IBM on that Thinkpad thing?

## Re: Watts

Power (in Watts) is equal to current (Amperes) times the Voltage (Electric
Force) or P = I X E.  (I = Amperes) (E = Volts) (P = Watts)

All the rating in Watts says about a power source or supply is that is the
maximum power it is able to deliver, reliably.  That power is used by the
battery charging system to charge the battery.  The battery is only able to
absorb power at a specific rate, otherwise it can burn or short out.  The
battery charging circuit handles that aspect of things and all it needs is
the maximum power the battery can accept and stay whole.  Putting a larger
power source (Watts, not volts) will do nothing to increase the charge time.
The normally delivered power supply  will handle any surge required by the
load (notebook) for normal operation.  It is likely that if the notebook
manufacturer has delivered a 70 Watt power supply, that is all that is
needed.  Using a more expensive 120 Watt unit will not likely aid the
notebook in any way, nor charge the battery faster.  The only gain is in the
life of the supply as you will be under using it, thus keep the heat
generated by the components down.

## Re: Watts

The only gain is in the

Which is not a bad thing at all.

Dave

## Re: Watts

Sun, 24 Jul 2005 (07:21 +0100 UTC) dave stanton wrote:

The heat generated to produce a given wattage is dependent on the capacity
of the device producing the wattage?  Does that mean that a heater capable
of 2500 W. set at 900 W. produces less heat than does a 1500 W. heater set
for 900 W.?

I think the heat generated would be the same, but the higher-rated device
would be designed to withstand greater heat than would the lower-rated
device.

--
oK+++
Computers are potentially the most addictive drug yet devised.
-R. U. Sirius

## Re: Watts

In general, I'd go along with that. I'd substitute the word "dissipate"
for the word "withstand." Electronic devices generally produce heat as
an unwanted byproduct, and use large (often finned to increase surface
area) chunks of metal (heat sinks) to dissipate the heat to the outside
world, as well as fans and ventilation slots.

The "efficiency" of the device in question determines the percentage of
power that's wasted in heat generation. So if you're comparing two
things with the same efficiency, I'd totally agree with you. The higher
rated power supply would feel cooler to the touch not because it's
producing less heat, but because it's dissipating it better.

## Re: Watts

Efficiency in a switching power supply such as used in this case varies
with the load. Generally it is highest near the rated output and is less
efficient at lower loads. The result is that the larger rated supply
used at a lower power will quite often be less efficient and dissapate
greater heat and run hotter!

Get the supply reccomended by the manufacturer.

Ross

## Re: Watts

rossbernheim@speakeasy.net (Ross Bernheim) wrote:

Hmm, I didn't know that about switching power supplies. I wonder whether
that's theoretical or real-world, or both? In other words, if the
efficiency of a larger supply drops because it's not running near
capacity, would the increased heat dissipating capability built into it
fall short of compensating for the extra heat that's being generated? If
the efficiency drops from 70% to 65% when you go from 90% load to 50%
load, let's say, then I wouldn't think the larger supply would really
run hotter to the touch than a smaller supply running closer to max. Or
does efficiency drop much more radically than that? (I realize we're
talking about something with a whole lot of variables, here.)

However, the OP is talking about a "wal-wart" type adapter for a
powerbook. Those aren't really switchers, are they? I thought they were
unregulated, barely filtered linears. But, I'm often wrong about
things...

Since the OP's previous adapter went up in smoke, I don't blame him for

## Re: Watts

Many of the wall wart supplies for computers and even external drives
are small switchers these days. The majority of the electronics have
been shrunk to a single inexpensive chip and the requisite inductor and
switching transistor are relatively small and inexpensive.

The old transformer based linear supplies are rapidly disappearing due
to the high cost of the transfomers and the shipping weight. Also the
switchers can relatively easily be made 110/220 auto sensing.

Ross

I've been a pedestrian ever since I could walk. (Graffiti: Gene Mora)

## Re: Watts

rossbernheim@speakeasy.net (Ross Bernheim) wrote:

It will typically be less efficient and dissapate more heat but it may
run cooler since it's designed to handle a higher overall power
dissipation.

--
Clark Martin
Redwood City, CA, USA               Macintosh / Internet Consulting

"I'm a designated driver on the Information Super Highway"

## Re: Watts

I mean anything which contains electronic components should be run at the
lowest temp you can to prevent premature failure.

Dave

## Re: Watts

And if I remember correctly, integrated circuit failure increases with
the _fourth_ power of absolute temperature.

--Fred

## Re: Watts

Obfus Kataa wrote:

The thermal energy dissipated would be the same, but the 2500 watt heater,
if it is a typical design, would be running at a lower temperature than the
1500 watt when both were set for 900 watts.

It is not heat, per se, that is bad for electronics, it is temperature
sustained over time.  A 200 watt power supply that is being used to power a
device drawing 20 watts will typically operate at a much lower temperature
than a 20 watt supply being used to power the same device, and so may be
expected to last longer.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

## Re: Watts

China is partners with everyone on everything.  Learn Chinese

## Re: Watts

On 23 Jul 2005 16:14:00 -0700, "-oo0-GoldTrader-0oo-"

Will run slightly cooler, should u not mind the added bulk.

Yes, if your cpu is going full throtle and HD/CD being accessed
constantly.

No if notebook is in idle, sleep, standby etc.

Yes.

---------------
engineers/administrators and home users who are stuck

Thank you.

## Re: Watts

No, IBM sold their PC business to a company called Lenovo.  So ThinkPads
now come from Lenovo, not IBM.

MK.

## Re: Watts

Using a higher power adapter is always fine as long as it has the
correct voltage, connector and polarity.

The adapter does not determine the amount of power used, the laptop
does.  The adapter should be an "all you can eat buffet" for the laptop
..... "here is 15 volts, take as much as you want, UP TO {maximum amount}.

With regard to {maximum amount}, watts = volts * amps

So, a 60 watt 15-volt adapter is capable of supplying any amount of
current UP TO 4 amps.  What it does, however, is offer the laptop 15
volts, and the laptops decides how much it will take, again, UP TO the
limit of the adapter (4 amps for a 60 watt, 15-volt adapter).  If the
laptop only takes 3 amps, then the adapter, fully capable of operating
at 60 watts, is only actually operating at 45 watts.