Using a lower-current adaptor with my laptop

hi,

I'm after a smaller/lighter adaptor for my thinkpad. The
laptop is rated at 16V, 3.36A. There's one that I'm
looking at that is rated at 16V, 2.2A. It also looks
a fair bit smaller. What I'm wondering is, can I safely
use it with my laptop?

I get about three hours use on a 3.1AH battery, so the
actual current consumption is nowhere near 3.36A I'm
assuming. It also takes quite a long time to recharge,
so the charging current can't be too high either.
Apart from the coax power plug which may be different, is
there anything i'm missing out?

it's a thinkpad 240x, the adaptor's for another thinkpad.


thanks!

--

 

The average power requirement is, with certainty, less than the peak
power requirement. For example, if you are doing something as simple as
defragmenting the HD, the power required during the defrag can be
several multiples of the average power. Burning CDs is another heavy
power consuming process. Only you can determine what the peak power
requirement might be. Operating with an AC adapter that is rated too
close to the average power requirment leaves little surplus for
supplying the peak power. If the AC adapter is operated in excess of
its capacity, the voltage drops and all manner of potential problems can
be proposed: HD write failure, memory read/write failures, CPU
auto-shutdown, overheating from reduced fan speed, adapter overheat/auto
shutdown, etc. OTOH, depending on your computing habits, none of the
above might apply.

Q

 

In a word, nope. NEVER use an adapter whose 1) output voltage(s) isn't
the same as the one your component requires, AND 2) whose output current
capability is LESS than the MAX. current rating of your component.

It's okay if your adapter is capable of MORE current, though.

"Ampere-Hours" has little to do with how much current ("Amperes," or
"Amps") your laptop uses at any given time. AH and A are two different
units.

Even though the battery is rated @ 3.1AH, it's no doubt quite capable of
providing the 3.36A *continuous* that your laptop MAY demand of it...
only, if you do the math, the battery will last under an hour at such a
high, constant load:
(3.1AH / 3.36A = ~ 55 min.).

 

What I was hoping is, during those peak power periods, is that
the battery would kick in. I assume if i can pull the plug
out while the laptop is running without affecting anything, that
the battery is connected car-style - always inline, with the
charger behaving like an alternator.

Being a small laptop, it doesn't have a burner or even a
cdrom drive.


--

 

The original adaptor is actually rated at 4.5A but my friend
who has the same laptop got a 3.36A adaptor with his. The rating
on the laptop is the same. Dunno why they gave me a bigger one.

Yes, but since I get about three hours before getting a low
battery warning, the average current draw would be quite a bit
less. It also puts out only 11.1V, so the draw at 16V should be
lower.

I'm not sure at what discharge rate the 3.1Ah is for, but
if the laptop actually took 3.36A, the batt life should be much
less than 55min.

There would no doubt be peaks like when the hdd spins up after
sleeping or something. I'm hoping that the battery would kick
in during those peaks.

Does anyone know if that is the case?


thanks!


--

 

Are you aware that on some laptops, the CPU speed is slowed down when the
system is running on batteries, and the LCD screen is dimmed, in order to
conserve power, and that the speed doesn't increase when the adapter is
plugged in (screen does get brighter), unless you reboot.

Stick with the plate ratings, even though what the other posters said is
correct. Try finding a smaller physical adapter with the same or great
power rating.

 

Re: "If the AC adapter is operated in excess of its capacity, the
voltage drops and all manner of potential problems can be proposed"

More likely, however, are two different scenarios:

1. The adapter supplies the increased power, but it overheats, perhaps
to the point of failure or damage [and, in rare cases that should not
happen, even if the adapter is overloaded, fire].

2. The adapter senses that too much power is being drawn and "crowbars
itself" -- shuts down, totally, completely, instantly. Note, this is
non-destructive, and if you then shut down, the adapter will be fine and
will work again, but, of course, if overloaded again, it will shut down
again.

To the original poster's question, if he never tries to run the computer
AND charge a significantly discharged battery at the same time, he would
likely [but not definitely] be ok.

 

You are putting your laptop at risk if you use a power adapter that was not
specified by the laptop manufacturer.

 

Well, on my laptop (an Apple Powerbook G4), a prior-generation
lower-power AC adapter works OK, it just charges slower.

But you need replies from some other thinkpad users who have tried
this with theirs. Try and find a thinkpad users' forum.