Deliberately using incorrect laptop power supply?

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
21 answers Last reply
More about deliberately incorrect laptop power supply
  1. 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 :-)
  2. 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
  3. 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
    >
  4. 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.
  5. 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
  6. 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.
  7. 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
  8. 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.
  9. 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 :-)
  10. 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=&c=uk&cs=ukdhs1&l=en&oc=N1212&qbc=N1212&s=dhs&sbc=ukdhsrsinspn_1150_3


    --
    Please quote "easytiger" for your PlusNet referral :-)
  11. 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.
  12. 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
  13. 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
    >>
    >
    >
  14. 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
  15. 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
  16. 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:
    ....
  17. 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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    >Organization: Road Runner High Speed Online http://www.rr.com
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  18. 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?
    >Date: 8 Dec 2004 20:26:52 GMT
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  19. 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.
  20. 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)
  21. 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:
    >
    > ...
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