AC Adapter question

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LastYJ

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Nov 13, 2003, 11:08:53 AM11/13/03
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Hi. I don't have much of a clue about electronics, but I have a question
about AC Adapters for a Toshiba notebook.

I have a Toshiba Tecra S1 (PT831C-0ZQ3V). The AC adapter that comes with the
unit has output of 15V and 5A. Another user had a old Tecra 8100 and its
power supply's output is 15V and 4A. Will I damage my Tecra S1 if I use the
AC adapter that has a smaller current?

Thanks!
-lyj


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Barry Watzman

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Nov 13, 2003, 11:24:03 AM11/13/03
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No, you won't damage the computer. You might damage the lower current
AC adapter, but it's VERY unlikely. The low current adapter is not
rated to supply as much current as the computer is specified as
requiring. But note:

1. The low current adapter MAY supply more than 4 amps, in fact it may
supply more than 5 amps.

2. The 5 amp requirement of the computer is worst case, a fully
discharged battery, all drives, PC cards, internal Wi-Fi active at once,
worst-case program CPU instruction mix, maximum memory .... like I said,
worst case. GUARANTEED that this computer does not TYPICALLY draw more
than 4 amps, which is within the rating of the adapter, and if it ever
draws 5 amps, it's probably a fairly exceptional situation.

I do want to point out that there is some risk here, the greatest risk
being that the power adapter could overheat or shutdown, but the risk is
quite minimal. I routinely use a 4 amp Toshiba adapter (PA-2444U) with
a 1415-S173, which is also rated at 5 amps (and which comes with a 5 amp
adapter).

mike

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Nov 13, 2003, 5:04:26 PM11/13/03
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Unless you know what you're doing AND have the equipment to carefully
measure performance,
DO NOT USE ANY AC ADAPTER OTHER THAN THE ONE THAT CAME WITH OR IS
RECOMMENDED BY THE MANUFACTURER.

Some laptops use the AC adapter to regulate battery charge current.
A different AC adapter can damage your expensive battery. If you
take the battery out, you can prevent that, but now you're open to the
adapter going into current limit on peaks, like your disk drive seeking.
That's not good for your drive or the data on it.

So, while it may be likely that you can swap adapters, statistics are
of little comfort when it's YOUR computer that's DEAD.

mike


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Barry Watzman

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Nov 13, 2003, 11:54:40 PM11/13/03
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Your advice is excessively conservative. If the interface betweent the
power adapter and the laptop is a simple 2-wire barrel connector, then
it is safe to use any adapter of the proper voltage and polarity, with a
reasonable current capacity relative to the laptop in question.

If the interface has more than two conductors, then you virtually must
use only the exact manufacturer's power supply, if for no other reason
that in most cases any other power supply probably won't have a matching
connector.

mike

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Nov 14, 2003, 1:37:56 AM11/14/03
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Barry Watzman wrote:
> Your advice is excessively conservative.

Guilty as charged. I object to these "it'll be ok" recommendations
on general principle. Six months from now, some newbie will google
his way across this thread and assume everything will be ok. Eventually,
it won't and there will be one dead computer that didn't need to be.
Or one kid with serious injury when the battery exploded.

>If the interface betweent the
> power adapter and the laptop is a simple 2-wire barrel connector, then
> it is safe to use any adapter of the proper voltage and polarity, with a
> reasonable current capacity relative to the laptop in question.

This is absolutely NOT true. You also need the correct current limit
profile. How many examples do you want?

If the original poster had the
capability to evaluate advice given here, he wouldn't have needed to ask
the question in the first place.

Now, there ARE many examples where your advice might be OK. If you
ACTUALLY OWN the EXACT laptop in question and BOTH adapters and HAVE
PERSONALLY swapped adapters and thoroughly evaluated the result, I defer
to your experience.
If you don't have DIRECT EXACT EXPERIENCE with this case, your advice
is irresponsible. Although it may be LIKELY that the swap is OK,
that's small consolation to the owner when the smoke starts coming out.

The OP is welcome to take your advice. It's no smoke off my computer.
The relevant quote is, "Are you feeling lucky, punk?" ;-)
mike

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Color LCD overhead projector

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Barry Watzman

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Nov 14, 2003, 11:42:34 AM11/14/03
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I still feel that you are being excessively conservative, if it's just a
2-wire connection of the proper voltage and polarity. If the supply
current limits, the voltage will drop and the computer will shut down;
I've never seen a laptop permanently damaged by a too-low voltage. The
DC input voltage to a laptop is not what actually directly powers any
part of the laptop, it's just the input to a multi-output switching
power supply, and those have quite intelligent voltage regulation and
protection circuits as part of their overall makeup.

In the case of Toshiba computers (which I believe was the subject of the
original question), I service these and I use various Toshiba 15-volt
supplies with various Toshiba laptops, have been doing so for 5+ years,
and have never had a problem. I believe that the worst case that you
could encounter with recent generation 15-volt Toshiba products would be
a "rated" 5 amp (worst case maximum) load on a 3-amp rated (rated
output) power supply. It's not an order of magnitude mismatch, but in
the "real world" unless you are both running every drive at once
(including a "burner") and charging a fully discharged battery, with two
PC-Cards plugged in and USB devices drawing 500ma from every USB port,
plus using an external PS/2 mouse and keyboard, all of this at once
(because the "rating" is based on "worst case"), all of this while
running SETI or some other floating point intensive application, the
actual current consumption (as opposed to the "rated" consumption) may
very well not even be exceeding the rating of the power supply in the
first place.

The primary risk here, which is real, is to the power supply not the
computer, since the supply could overheat and in an extreme case be
destroyed if too much current is drawn and it doesn't current limit or
shut down. The one possible case where you could damage the laptop (I
didn't say that the risk was ZERO) would be that the supply fails and in
the process delivers an over-voltage to the computer. But generally the
supplies are current limited and/or fused, as well as highly protected
not to deliver an over-voltage even in a failure mode. However, that
scenario is possible, and while the risk may be small, I am not saying
that it's zero.

As to my qualifications, I'm a degreed EE, industry certified (A+ and
Network+ among others), I service PCs and laptops and I've worked for PC
manufacturers (including laptop mfgrs) in both Engineering and Product
management for much of the last 30 years.

mike

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Nov 14, 2003, 3:55:55 PM11/14/03
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Barry Watzman wrote:
> I still feel that you are being excessively conservative,

I admitted that already.

>if it's just a
> 2-wire connection of the proper voltage and polarity. If the supply
> current limits, the voltage will drop and the computer will shut down;
> I've never seen a laptop permanently damaged by a too-low voltage.

Take yourself a Compaq Aero 4/33C. Short one cell of the battery and
reboot it a few times. Eventually, you'll trash the BIOS chip and
render it dead until you pull the chip and reprogram it externally.
Bad design, but stuff happens. Search the Aero newsgroups to see many
instances of this symptom.

I'm unwilling to risk a disk on the experiment, but try setting your
current limit so it fires when
your hard drive seeks. Depending on how cleanly your supply limits, you
can crash the disk heads.

The
> DC input voltage to a laptop is not what actually directly powers any
> part of the laptop, it's just the input to a multi-output switching
> power supply, and those have quite intelligent voltage regulation and
> protection circuits as part of their overall makeup.

You'd think, but there are BAD designs in the wild. It's possible that
in the mad rush to market, the power supply was thoroughly evaluated,
but I'll bet money that it was never evaluated with any WRONG AC adapter,
much less the particular WRONG ac adapter in question.

>
> In the case of Toshiba computers (which I believe was the subject of the
> original question), I service these and I use various Toshiba 15-volt
> supplies with various Toshiba laptops, have been doing so for 5+ years,
> and have never had a problem.

OK,
Take a Toshiba T4900CT. Stuff 18V into the external jack. The battery
wil take as much current as you let it have.
Take a Compaq LTE Lite 4/25C. Stuff 18V into the external jack. The
battery will take as much current as you let it have.
Take a Compaq Aero 4/33C. Stuff 17.5V into the external jack. The
battery will take as much current as you let it have.

That was just the first three computers I grabbed off the pile. But I'm
beginning to see a pattern.

I believe that the worst case that you
> could encounter with recent generation

I've got no experience with recent generation.

Here's my problem.
A newbie asks a malformed question.
Some knowitall reaches a conclusion that could NOT possibly have
been reached given the (lack of) facts in evidence.

Some other knowitall expands on the first answer with even more
manufactured "data".

It's like a game of telephone. Pretty soon, there are sweeping
generalizations. It's pretty obvious that most of
the contributors haven't even read the thread.

If the newbie had the experience to determine which, if any, of the
contributions were sound, he wouldn't have had to answer the question
in the first place.
All he's got is a bunch of vague, general and conflicting
recommendations with no supporting data and implication that they apply
to his situation.

Six months later, some other newbie googles across part of the thread
and decides that one of those unsupported recommendations is what he
needs...poof!!

The web is full of nice, well-meaning people who are happy to
generalize from (possibly) related experience and give
unsupported answers without ever understanding the question.
It's more about communication than computer knowledge.

In particular, you have described your reasoning. It all sounds nice.
A newbie would be impressed and maybe follow it. If you run SETI, you
must be mucho smart... And many of them would not have a problem.

I'm just warning people, "Don't believe everything you read."
Generalization is a dangerous game.

Then you should know better...

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