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Deliberately using incorrect laptop power supply?

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Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 1:58:51 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

[xposted]

I have a Dell Inspiron 1150 that has a PSU with output 19.5v 4.62A

To save lugging PSUs around, I have access plenty of spare older Dell
Latitude PSUs rated ouput 20v 3.5A. Can I use these safely? I'm guessing
they are underpowered and this may affect some things (eg speed of
background charging). I'm also guessing the extra .5v above 19.5v is not to
much to worry about ( just over 2.5% extra?)

Would this work without causing damage?

They have different connectors obviously, but that shouldn't be a problem
with a quick visit to Maplins.

Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 2:24:14 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Lordy wrote:
> [xposted]
>
> I have a Dell Inspiron 1150 that has a PSU with output 19.5v 4.62A
>
> To save lugging PSUs around, I have access plenty of spare older Dell
> Latitude PSUs rated ouput 20v 3.5A. Can I use these safely? I'm
> guessing they are underpowered and this may affect some things (eg
> speed of background charging). I'm also guessing the extra .5v above
> 19.5v is not to much to worry about ( just over 2.5% extra?)
>
> Would this work without causing damage?
>
> They have different connectors obviously, but that shouldn't be a
> problem with a quick visit to Maplins.
>
> Lordy

I regularly swapped a Dell Inspiron 20V power supply and an HP Omnibook 19V
power supply with no ill effect on either device. They even had the same
connector :-) I'm not sure what the amp ratings were but I suspect you'd be
fine.

--
Please quote "easytiger" for your PlusNet referral :-)
December 8, 2004 3:32:48 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Tiny Tim wrote:
> Lordy wrote:
>
>>[xposted]
>>
>>I have a Dell Inspiron 1150 that has a PSU with output 19.5v 4.62A
>>
>>To save lugging PSUs around, I have access plenty of spare older Dell
>>Latitude PSUs rated ouput 20v 3.5A. Can I use these safely? I'm
>>guessing they are underpowered and this may affect some things (eg
>>speed of background charging). I'm also guessing the extra .5v above
>>19.5v is not to much to worry about ( just over 2.5% extra?)
>>
>>Would this work without causing damage?
>>
>>They have different connectors obviously, but that shouldn't be a
>>problem with a quick visit to Maplins.
>>
>>Lordy
>
> I regularly swapped a Dell Inspiron 20V power supply and an HP Omnibook 19V
> power supply with no ill effect on either device. They even had the same
> connector :-) I'm not sure what the amp ratings were but I suspect you'd be
> fine.

Some Dell laptops can sense that the power supply you have plugged in
does not supply enough power. My laptop has a 3.5A power supply. When
I plugged it into my boss's laptop (also a Dell) a messagebox appeared
warning that the powered supply was not meaty enough.

However, I can't remember if it still worked anyway.

--
Paul
Related resources
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 3:43:19 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Lordy <spam_box@gmx.net> wrote:

>I have a Dell Inspiron 1150 that has a PSU with output 19.5v 4.62A
>To save lugging PSUs around, I have access plenty of spare older
>Dell Latitude PSUs rated ouput 20v 3.5A. Can I use these safely?
>I'm guessing they are underpowered and this may affect some things
>(eg speed of background charging). I'm also guessing the extra .5v
>above 19.5v is not to much to worry about ( just over 2.5% extra?)
>Would this work without causing damage?

Generally speaking.
.... output voltage must match
.... output current must be equal to or greater than

I wouldn't assume that the only problem will be speed of background
charging, I think the system is more complex than that.

Technically speaking, for what it's worth. The system expects a
certain voltage. The required system current is at that voltage. Your
source current is a maximum. As long as the source voltage is
correct, the system will use only the required current and no more.
That is why the source current rating can be greater than needed by
the system. But again, the voltage must match.






>They have different connectors obviously, but that shouldn't be a
>problem with a quick visit to Maplins.
>
>Lordy
>
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 3:51:34 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

"Tiny Tim" <_tim_dodd@hotmail.com> wrote:

....

>I regularly swapped a Dell Inspiron 20V power supply and an HP
>Omnibook 19V power supply with no ill effect on either device. They
>even had the same connector :-) I'm not sure what the amp ratings
>were

Then IMO you didn't know what you were doing.

>but I suspect you'd be fine.

But you aren't going to pay if it isn't fine.
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 3:54:00 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

John Doe <jdoe@usenet.is.the.real.thing> wrote in
news:Xns95B944620F3A7wisdomfolly@151.164.30.48:

> Technically speaking, for what it's worth. The system expects a
> certain voltage. The required system current is at that voltage. Your
> source current is a maximum. As long as the source voltage is
> correct, the system will use only the required current and no more.
> That is why the source current rating can be greater than needed by
> the system. But again, the voltage must match.
>

Cheers. So my 20v3.5A PSU will be under constant strain if the laptop
expects 19.5V @ 4.6A.

By "voltage must match" is half a volt at 19.5V (2.5% error) really
significant considering manufacturing tolerances etc?

Cheers to all thus far!!

Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 4:00:36 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Lordy <spam_box@gmx.net> wrote:

(for context, please see the prior post)

>By "voltage must match" is half a volt at 19.5V (2.5% error) really
>significant considering manufacturing tolerances etc?

I don't know. As far as the voltage goes, I guess that would depend on
the design specifications. I would seek advice from the maker. One
thing you do know is how much your laptop cost. Good luck.
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 4:07:01 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

John Doe <jdoe@usenet.is.the.real.thing> wrote in
news:Xns95B947508B04Dwisdomfolly@151.164.30.48:

> I don't know. As far as the voltage goes, I guess that would depend on
> the design specifications. I would seek advice from the maker. One
> thing you do know is how much your laptop cost. Good luck.

Cheers. Think I'll get another official PSU :) 

Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 4:23:57 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

John Doe wrote:
> "Tiny Tim" <_tim_dodd@hotmail.com> wrote:
>> I regularly swapped a Dell Inspiron 20V power supply and an HP
>> Omnibook 19V power supply with no ill effect on either device. They
>> even had the same connector :-) I'm not sure what the amp ratings
>> were
>
> Then IMO you didn't know what you were doing.
>
I knew full well what I was doing, thank you. Voltage range was within
acceptable tollerance (deemed by me) and the available current was adequate
from both. Just because I don't remember the figures today - this was three
years ago - does not mean I didn't know what I was doing back then. Let's
say it was a judgement call on the risk and I decided it was low enough.

To quote from - http://www.claudelyons.co.uk/energy_saving.htm - "The
Electricity Safety, Quality and Continuity Regulations 2002, which came into
force on the 31st January 2003, replacing The Electricity Supply Regulations
1998, formally confirm the UK standardised supply voltage tolerances at
230V -6% to +10%.". I don't know just how good the regulation is in these
power adapters but it's fair to assume they are faced with varying input
voltage of several % possibly within minutes or seconds.

Portable consumer electronic devices seem quite happy working on 1.5V
alkalines and 1.2V NiMH batteries. That range is far bigger than a trivial
5% between the two power supplies in question. That's +25% from one
viewpoint and -20% from the other.

>> but I suspect you'd be fine.
>
> But you aren't going to pay if it isn't fine.

Correct. I never told anyone to do it. I just said I thought it would be
fine. To be honest I'd be more concerned about getting the polarity right
than worrying about a 5% voltage swing. As for the current, I note that Dell
offers its laptops with a choice of power supply - e.g. 65W standard or 90W
option. Well at 20V it's 3.25 Amps to deliver 65W and it's 4.5 Amps to
deliver 90W. But what's the point in offering both options for the same
laptop? Surely the laptop needs what the laptop needs.

I'd say if the lower rated power supply feels like it's overheating then
quit while you're ahead, and before you start a fire. But an extra 1V is not
(IMHO) going to screw up a laptop rated for 19V.
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 4:36:11 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Tiny Tim wrote:
<snip>
> As for the
> current, I note that Dell offers its laptops with a choice of power
> supply - e.g. 65W standard or 90W option. Well at 20V it's 3.25 Amps
> to deliver 65W and it's 4.5 Amps to deliver 90W. But what's the point
> in offering both options for the same laptop? Surely the laptop needs
> what the laptop needs.
> I'd say if the lower rated power supply feels like it's overheating
> then quit while you're ahead, and before you start a fire. But an
> extra 1V is not (IMHO) going to screw up a laptop rated for 19V.

Just noticed the OP was talking about a 0.5V difference, so not even the 1V
that I was using.

I've also checked the Dell website and the standard power supply for the
I1150 is rated at 65W. i.e. under 3.5A. There is also a 90W option.
19.5*4.62 = 90W so the OP has the uprated power supply for his I1150. But
the old Latitude power supply should still handle the current demand at 65W.

So I stand by my opinion that the OP will probably be fine.

--
Please quote "easytiger" for your PlusNet referral :-)
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 4:39:28 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Tiny Tim wrote:
> Tiny Tim wrote:
> <snip>
>> As for the
>> current, I note that Dell offers its laptops with a choice of power
>> supply - e.g. 65W standard or 90W option. Well at 20V it's 3.25 Amps
>> to deliver 65W and it's 4.5 Amps to deliver 90W. But what's the point
>> in offering both options for the same laptop? Surely the laptop needs
>> what the laptop needs.
>> I'd say if the lower rated power supply feels like it's overheating
>> then quit while you're ahead, and before you start a fire. But an
>> extra 1V is not (IMHO) going to screw up a laptop rated for 19V.
>
> Just noticed the OP was talking about a 0.5V difference, so not even
> the 1V that I was using.
>
> I've also checked the Dell website and the standard power supply for
> the I1150 is rated at 65W. i.e. under 3.5A. There is also a 90W
> option. 19.5*4.62 = 90W so the OP has the uprated power supply for his
> I1150.
> But the old Latitude power supply should still handle the current
> demand at 65W.
> So I stand by my opinion that the OP will probably be fine.

p.s. here's the link to the Dell in question - just page down to the power
supply section....
watch for line wrap.

http://configure.euro.dell.com/dellstore/config.aspx?b=...



--
Please quote "easytiger" for your PlusNet referral :-)
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 5:42:29 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

"Tiny Tim" <_tim_dodd@hotmail.com> wrote in
news:41b7006e$0$9359$ed2619ec@ptn-nntp-reader02.plus.net:

>
> Portable consumer electronic devices seem quite happy working on 1.5V
> alkalines and 1.2V NiMH batteries. That range is far bigger than a
> trivial 5% between the two power supplies in question. That's +25%
> from one viewpoint and -20% from the other.

That's what I suspected. 20V is within tolerance of 19.5V. (You've
accedentally dropped a couple of decimal points BTW! Here ya go "..")
>
>>> but I suspect you'd be fine.
>>
>> But you aren't going to pay if it isn't fine.
>
> Correct. I never told anyone to do it. I just said I thought it would
> be fine. To be honest I'd be more concerned about getting the polarity
> right than worrying about a 5% voltage swing.

As for the current, I
> note that Dell offers its laptops with a choice of power supply -
> e.g. 65W standard or 90W option. Well at 20V it's 3.25 Amps to deliver
> 65W and it's 4.5 Amps to deliver 90W. But what's the point in offering
> both options for the same laptop?

From the link you kindly researched, its the difference bet Pentium 4 and
Celery models.

>
> I'd say if the lower rated power supply feels like it's overheating
> then quit while you're ahead, and before you start a fire. But an
> extra 1V is not (IMHO) going to screw up a laptop rated for 19V.
>
Yes. Amps is the killer. I suspect (as a complete layman) its the old
power supply that's most at risk. but if it starts to fail then my laptop,
and ultimately my life, is at risk from being hooked up to a PSU that is in
meltdown mode! Although a .5V difference at 19.5V is not significant I
suspect 1A is??

Thanks again.
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 6:08:53 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

John Doe <jdoe@usenet.is.the.real.thing> wrote in
news:Xns95B944620F3A7wisdomfolly@151.164.30.48:

> That is why the source current rating can be greater than needed by
> the system.

Just had an idea .. . two old identical power supplies in parallel :) 

Bwa ha ha ha ...

Just googled for it, and it looks possbile, but its also equally possible
that they both die!

Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 11:02:08 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

As a general guideline, your comments are correct. However, for
day-to-day use, they probably overly conservative.

First, the voltage tolerance is at least 5% and may be 10%. At 19.4
volts, that 1 to 2 full volts (approximately), so using a 20 volt supply
with a laptop designed for 19.4 volts is unlikely to cause a problem.

Second, the current requirement of the laptop is equal to or less than
the current output of the "correct" supply. But that current is a
MAXIMUM -- presume, for example, charging a fully discharged battery
while using 2 PC Cards and drawing 500ma from each USB port, while
burning a CD with an auxilliary keyboard and mouse plugged in and
running a highly CPU intensive application that draws maximum power.

It's unlikely that a user would actuall do all of that, so a power
supply with a capacity lower than that of the "correct" power supply
will likely run the machine in "normal" operation just fine. I run lots
of laptops from generic supplies with half the capacity of the OEM supply.

Finally, while it may not work, it's unlikely to do hardware damage, and
if it does, it's more likely to be to the power supply than to the computer.

But, there is indeed some risk -- however small -- and you have to be
willing to take that.

Also, all of this applies only to power supplies with simple "2-wire"
interconnects to the computer. If the power supply has a multi-pin
connector, then it's more than just a power supply (often part of the
charging circuit is in the "Power Supply"), and then you definitely
should use a correct OEM supply.


John Doe wrote:
> Lordy <spam_box@gmx.net> wrote:
>
>
>>I have a Dell Inspiron 1150 that has a PSU with output 19.5v 4.62A
>>To save lugging PSUs around, I have access plenty of spare older
>>Dell Latitude PSUs rated ouput 20v 3.5A. Can I use these safely?
>>I'm guessing they are underpowered and this may affect some things
>>(eg speed of background charging). I'm also guessing the extra .5v
>>above 19.5v is not to much to worry about ( just over 2.5% extra?)
>>Would this work without causing damage?
>
>
> Generally speaking.
> ... output voltage must match
> ... output current must be equal to or greater than
>
> I wouldn't assume that the only problem will be speed of background
> charging, I think the system is more complex than that.
>
> Technically speaking, for what it's worth. The system expects a
> certain voltage. The required system current is at that voltage. Your
> source current is a maximum. As long as the source voltage is
> correct, the system will use only the required current and no more.
> That is why the source current rating can be greater than needed by
> the system. But again, the voltage must match.
>
>
>
>
>
>
>
>>They have different connectors obviously, but that shouldn't be a
>>problem with a quick visit to Maplins.
>>
>>Lordy
>>
>
>
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 11:07:44 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

No, you won't be under constant stress, and half a volt is within the
tolerance (of course, the 20 volt PS has it's own tolerance and might be
putting out 21 or even 22 volts).

The 4.6A is the maximum that the correct supply can provide. The laptop
can be presumed to need that OR LESS in a WORST-CASE scenario. 3.5 amps
is likely to be more than the laptop actually uses in typical operation.
Also, most supplies can supply more than their rated capacity.

If it was me, I'd do it. In fact, I run lots of Toshiba models with 4A
factory supplies from supplies with only 2 amp or 3 amp ratings. There
is some risk, but it's small, and the risk to the supply is greater than
the risk to the computer. Also, however, don't forget the risk of
losing your work if the computer crashes or locks up, even if no
permanent hardware damage is done to anything. Finally, if you do it
and things seem to be working, feel the supply to see if it seems
excessively warm. If it does, that's an indication that you really are
overstressing it, and should get a beefier supply.

Also, if the interface is not a simple "2-wire" interface, then don't
even try it.


Lordy wrote:

> John Doe <jdoe@usenet.is.the.real.thing> wrote in
> news:Xns95B944620F3A7wisdomfolly@151.164.30.48:
>
>
>>Technically speaking, for what it's worth. The system expects a
>>certain voltage. The required system current is at that voltage. Your
>>source current is a maximum. As long as the source voltage is
>>correct, the system will use only the required current and no more.
>>That is why the source current rating can be greater than needed by
>>the system. But again, the voltage must match.
>>
>
>
> Cheers. So my 20v3.5A PSU will be under constant strain if the laptop
> expects 19.5V @ 4.6A.
>
> By "voltage must match" is half a volt at 19.5V (2.5% error) really
> significant considering manufacturing tolerances etc?
>
> Cheers to all thus far!!
>
> Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 8, 2004 11:26:52 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote in news:kaJtd.56936
$MG3.28526@fe2.columbus.rr.com:

> The 4.6A is the maximum that the correct supply can provide. The laptop
> can be presumed to need that OR LESS in a WORST-CASE scenario. 3.5 amps
> is likely to be more than the laptop actually uses in typical operation.
> Also, most supplies can supply more than their rated capacity.
>

All sounds good except from Tiny Tim's link it says ...

http://shorl.com/hyfronegebryhy

The 4.6A is continuous (clumn 3) and I'm fairly sure the 3.5A max for 4sec,
is a typo,
and is more likely 8.5 or similar? Doesn't help doesit!!

Note if you try to select the Pentium 4 model and the lower spec PSU
(column 2) (ie similar to my existing older PSUs) the website rejects it.

More worryingly the specs for the old PSU (see Latitude Tab - 4th column),
do not mention continuous.

Still in the spirit of hackerdom I'm sorely tempted ....

--
Lordy
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 8:20:38 AM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

You have some nice speculation/theories there.

Your power supply tolerance figure of 5% to 10% sounds slack to me.
Have you ever seen the input power specifications for the laptop
computer in question? Have you ever even seen any input power
specifications for a laptop computer?

When I experiment with something, I consider the replacement cost. A
laptop computer cost a lot of money. I suspect the input circuit
would reject an inadequate supply, but I've never seen that
information from the engineers who know.

There is nothing ambiguous about a correct power supply. In a
competitive market, a manufacturer cuts costs. Since higher current
output power supplies cost more money, a manufacturer is not going to
include a significantly greater power supply than what is necessary
for the device it is intended to run. There might be exceptions.

If I were you, I would demand more information. Have you ever
measured current while using the correct power supply? If not, and if
you have never seen the specifications, I would say your practices
are a little bit reckless.


Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote:

>As a general guideline, your comments are correct. However, for
>day-to-day use, they probably overly conservative.
>
>First, the voltage tolerance is at least 5% and may be 10%. At 19.4
>volts, that 1 to 2 full volts (approximately), so using a 20 volt
supply
>with a laptop designed for 19.4 volts is unlikely to cause a
problem.
>
>Second, the current requirement of the laptop is equal to or less
than
>the current output of the "correct" supply. But that current is a
>MAXIMUM -- presume, for example, charging a fully discharged battery
>while using 2 PC Cards and drawing 500ma from each USB port, while
>burning a CD with an auxilliary keyboard and mouse plugged in and
>running a highly CPU intensive application that draws maximum power.
>
>It's unlikely that a user would actuall do all of that, so a power
>supply with a capacity lower than that of the "correct" power supply
>will likely run the machine in "normal" operation just fine. I run
lots
>of laptops from generic supplies with half the capacity of the OEM
supply.
>
>Finally, while it may not work, it's unlikely to do hardware damage,
and
>if it does, it's more likely to be to the power supply than to the
computer.
>
>But, there is indeed some risk -- however small -- and you have to
be
>willing to take that.
>
>Also, all of this applies only to power supplies with simple "2-
wire"
>interconnects to the computer. If the power supply has a multi-pin
>connector, then it's more than just a power supply (often part of
the
>charging circuit is in the "Power Supply"), and then you definitely
>should use a correct OEM supply.
>
>
>John Doe wrote:
>> Lordy <spam_box@gmx.net> wrote:
....
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 8:34:26 AM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote:

>The 4.6A is the maximum that the correct supply can provide. The
>laptop can be presumed to need that OR LESS in a WORST-CASE
>scenario. 3.5 amps is likely to be more than the laptop actually
>uses in typical operation.

The correct power supply is rated 4.62A. If that is grossly higher
than necessary, why is it measured in tenths of an amp?

How do you know 3.5 amps is more than enough?

Have you ever seen the specification?

Have you ever even measured the current?

How much guesswork?






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>Subject: Re: Deliberately using incorrect laptop power supply?
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Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 8:46:25 AM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

Lordy <spam_box@gmx.co.uk> wrote:

(see the prior posts for context)

>Still in the spirit of hackerdom I'm sorely tempted ....

It's your property.

After you change the connector, go for it at your own risk.

But do this first.

.... splice one of the power supply wires of both supplies
.... measure current through the correct supply given various
well-established circumstances
.... repeat that for the weak power supply
.... if the results are identical, then maybe it's OK
.... if the results are significantly different, then you have
received some bad advice

After you do that, please be sure to post about it.








>Path: newssvr12.news.prodigy.com!newsdbm03.news.prodigy.com!newsdst02.news.prodigy.com!newsmst01a.news.prodigy.com!prodigy.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
>From: Lordy <spam_box@gmx.co.uk>
>Newsgroups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt
>Subject: Re: Deliberately using incorrect laptop power supply?
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Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 8:51:05 AM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

I wrote:

>... splice one of the power supply wires of both supplies

By the way, my advice assumes the experimenter knows basic
electricity/electronics.
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 10:40:53 AM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

John Doe wrote:

> Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote:
>
>>The 4.6A is the maximum that the correct supply can provide. The
>>laptop can be presumed to need that OR LESS in a WORST-CASE
>>scenario. 3.5 amps is likely to be more than the laptop actually
>>uses in typical operation.
>
> The correct power supply is rated 4.62A. If that is grossly higher
> than necessary, why is it measured in tenths of an amp?

Probably because that's was the rating on the one the lowest bidder offered.

> How do you know 3.5 amps is more than enough?
>
> Have you ever seen the specification?
>
> Have you ever even measured the current?
>
> How much guesswork?
>
>
>
>
>
>
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
Anonymous
a b B Homebuilt system
a b D Laptop
a b ) Power supply
December 9, 2004 6:40:59 PM

Archived from groups: comp.sys.laptops,alt.comp.hardware.pc-homebuilt (More info?)

The DC input to a laptop is simply the input to a switching power supply
within the laptop. It's not used "raw", except by the switching power
supply as it's input (and sometimes by the charging circuit for the
battery).

Switching power supplies have a very wide tolerance on their inputs.
Obviously, this is a generalization, but I'm a degreed engineer who has
worked for laptop manufacturers, and -- as a generalization -- there's
quite a bit of slack in the input voltage tolerance, and little risk of
hardware damage if you are out of the range unless you are pretty
significantly high.

[all of this applies only to laptops which have a simple 2-wire input
from their power supplies. When there is a multi-conductor connection,
part of the logic and charging circuits may be in the power adapter, and
all bets are off]



John Doe wrote:

> You have some nice speculation/theories there.
>
> Your power supply tolerance figure of 5% to 10% sounds slack to me.
> Have you ever seen the input power specifications for the laptop
> computer in question? Have you ever even seen any input power
> specifications for a laptop computer?
>
> When I experiment with something, I consider the replacement cost. A
> laptop computer cost a lot of money. I suspect the input circuit
> would reject an inadequate supply, but I've never seen that
> information from the engineers who know.
>
> There is nothing ambiguous about a correct power supply. In a
> competitive market, a manufacturer cuts costs. Since higher current
> output power supplies cost more money, a manufacturer is not going to
> include a significantly greater power supply than what is necessary
> for the device it is intended to run. There might be exceptions.
>
> If I were you, I would demand more information. Have you ever
> measured current while using the correct power supply? If not, and if
> you have never seen the specifications, I would say your practices
> are a little bit reckless.
>
>
> Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote:
>
>
>>As a general guideline, your comments are correct. However, for
>>day-to-day use, they probably overly conservative.
>>
>>First, the voltage tolerance is at least 5% and may be 10%. At 19.4
>>volts, that 1 to 2 full volts (approximately), so using a 20 volt
>
> supply
>
>>with a laptop designed for 19.4 volts is unlikely to cause a
>
> problem.
>
>>Second, the current requirement of the laptop is equal to or less
>
> than
>
>>the current output of the "correct" supply. But that current is a
>>MAXIMUM -- presume, for example, charging a fully discharged battery
>>while using 2 PC Cards and drawing 500ma from each USB port, while
>>burning a CD with an auxilliary keyboard and mouse plugged in and
>>running a highly CPU intensive application that draws maximum power.
>>
>>It's unlikely that a user would actuall do all of that, so a power
>>supply with a capacity lower than that of the "correct" power supply
>>will likely run the machine in "normal" operation just fine. I run
>
> lots
>
>>of laptops from generic supplies with half the capacity of the OEM
>
> supply.
>
>>Finally, while it may not work, it's unlikely to do hardware damage,
>
> and
>
>>if it does, it's more likely to be to the power supply than to the
>
> computer.
>
>>But, there is indeed some risk -- however small -- and you have to
>
> be
>
>>willing to take that.
>>
>>Also, all of this applies only to power supplies with simple "2-
>
> wire"
>
>>interconnects to the computer. If the power supply has a multi-pin
>>connector, then it's more than just a power supply (often part of
>
> the
>
>>charging circuit is in the "Power Supply"), and then you definitely
>>should use a correct OEM supply.
>>
>>
>>John Doe wrote:
>>
>>>Lordy <spam_box@gmx.net> wrote:
>
> ...
!