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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