AC Power Adapter for HP

Archived from groups: comp.sys.laptops (More info?)

Hello,

I've got an HP n620c and I need to get another AC adapter for it.

On it's specifications says that must be supplied by 18.5 V and 3.5A,
I supose that is a 65W adapter.

We have got another 90W AC adapter that gives 18.5V and 4.9A.

Could be dangerous for my computer to plug this laptop with a 90W
adapter?

Thank's in advance,

...Gerard

Archived from groups: comp.sys.laptops (More info?)

Gerard, go with Williams answer and it will work fine. Wattage (power) is a
function of voltage and the current draw. The ratings on the adapter are
the maximums that it will work properly at. The formula is P (wattage)= I
(current) Times E (voltage). So you other adapter could provide 100 A at
18.5 V or 1850 watts and it would still work just fine.

"Gerard Forns" <gforns@gmail.com> wrote in message
news:9ee7f578.0505180136.280b487c@posting.google.com...
Hello,

I've got an HP n620c and I need to get another AC adapter for it.

On it's specifications says that must be supplied by 18.5 V and 3.5A,
I supose that is a 65W adapter.

We have got another 90W AC adapter that gives 18.5V and 4.9A.

Could be dangerous for my computer to plug this laptop with a 90W
adapter?

Thank's in advance,

...Gerard

Archived from groups: comp.sys.laptops (More info?)

Gerard Forns wrote:
> Hello,
>
> I've got an HP n620c and I need to get another AC adapter for it.
>
> On it's specifications says that must be supplied by 18.5 V and 3.5A,
> I supose that is a 65W adapter.
>
> We have got another 90W AC adapter that gives 18.5V and 4.9A.
>
> Could be dangerous for my computer to plug this laptop with a 90W
> adapter?
>
> Thank's in advance,
>
> ..Gerard

First thing I'd do is fully discaharge the battery and measure the
current from the ac adapter while charging with the laptop off.
if it's less than 3.5Amps, you're probably good to go. If it's 3.5A or
more, you can expect that the battery charge current is limited by the
adapter. In that case, you'd risk overcharging your battery with the
bigger adapter. YMMV.

There's maybe an easier way to do the measurement. Measure the open
circuit voltage from the disconnected ac adapter. Then measure it again
while charging the battery. If it's much lower while charging, then the
adapter is limiting the charge current. Still need to make up some
kind of test adapter to get at the measurement points.
mike

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Archived from groups: comp.sys.laptops (More info?)

Barry Watzman wrote:
> There is no risk of overcharging the battery by using an AC adapter with
> a higher current capacity than the original adapter. The charging
> current is controlled by the charging circuit in the laptop. The only
> role that the adapter plays is to be capable of supplying the requested
> current. The charging circuit still determines the current actually used.
>

You obviously lack experience with charging systems that do NOT meet
the above criteria. Just because a well designed system should NOT
depend on the AC adapter, doesn't make it so. Just because your system
doesn't have the problem doesn't guarantee that mine won't.
Measure it and be SURE!!

I'll agree that it's OFTEN OK, but
telling someone it's OK when you haven't actually measured the result
on the exact same model is irresponsible. There's a reason that the
manual tells you to use ONLY the recommended AC adapter.
mike

>
> mike wrote:
>
>> Gerard Forns wrote:
>>
>>> Hello,
>>>
>>> I've got an HP n620c and I need to get another AC adapter for it.
>>> On it's specifications says that must be supplied by 18.5 V and 3.5A,
>>> I supose that is a 65W adapter.
>>>
>>> We have got another 90W AC adapter that gives 18.5V and 4.9A.
>>> Could be dangerous for my computer to plug this laptop with a 90W
>>> adapter?
>>>
>>> Thank's in advance,
>>>
>>> ..Gerard
>>
>>
>>
>> First thing I'd do is fully discaharge the battery and measure the
>> current from the ac adapter while charging with the laptop off.
>> if it's less than 3.5Amps, you're probably good to go. If it's 3.5A
>> or more, you can expect that the battery charge current is limited by the
>> adapter. In that case, you'd risk overcharging your battery with the
>> bigger adapter. YMMV.
>>
>> There's maybe an easier way to do the measurement. Measure the open
>> circuit voltage from the disconnected ac adapter. Then measure it again
>> while charging the battery. If it's much lower while charging, then the
>> adapter is limiting the charge current. Still need to make up some
>> kind of test adapter to get at the measurement points.
>> mike
>>



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Archived from groups: comp.sys.laptops (More info?)

Gee, I got my ham radio license in 1963, my 1st class commercial FCC
lisense to run 50,000 watt broadcast transmitters in 1965 (at age 15), I
have a BSEE, I'm A+ and Network Plus certified, I repair laptops (and
other computers), I've been both an engineering manager and and a
maketing manager for my entire 30+ year career in the PC business
(including two major laptop vendors and one switching power supply vendor).

Obviously, I lack experience.

But you don't know what you are talking about.

The AC adapter for a laptop is simply a DC power supply. The laptop
decides what it will take. Your suggestion to the contrary is about
like suggesting that if I remove a 100 watt light bulb from a lamp and
plug in a 60 watt bulb, the 100 watts that the wall socket can clearly
supply will blow out the 60 watt bulb. Which some people are ignorant
enough to accept if told (because it does sound superficially
plausible). But everyone's common experience tells us that while a wall
socket is fused at 15 or 20 amps (roughly 1500 or 2000 watts), you can
use a 4-watt night light, a 60 watt bulb, a 100 watt bulb or a 1,500
watt hair dryer in the exact same wall outlet without changing anything
at the fuse box or the wiring or the utility company's generators.

And that is EXACTLY the analogy that applies here. The laptop is like
the light bulb, and whether you use an adapter CAPABLE of supplying 60
watts or 100 watts or 10,000 watts (at the correct polarity and
voltage), the only thing that matters is that both are more than what
the laptop needs (say 50 watts). The use of an adapter capable of
supply more current than the laptop needs is of no more consequence than
plugging a lamp with a 60-watt bulb in it into a wall socket that is
also capable of operating a 1,500 watt hair dryer.



mike wrote:

> Barry Watzman wrote:
>
>> There is no risk of overcharging the battery by using an AC adapter
>> with a higher current capacity than the original adapter. The
>> charging current is controlled by the charging circuit in the laptop.
>> The only role that the adapter plays is to be capable of supplying the
>> requested current. The charging circuit still determines the current
>> actually used.
>>
>
> You obviously lack experience with charging systems that do NOT meet
> the above criteria. Just because a well designed system should NOT
> depend on the AC adapter, doesn't make it so. Just because your system
> doesn't have the problem doesn't guarantee that mine won't.
> Measure it and be SURE!!
>
> I'll agree that it's OFTEN OK, but
> telling someone it's OK when you haven't actually measured the result
> on the exact same model is irresponsible. There's a reason that the
> manual tells you to use ONLY the recommended AC adapter.
> mike
>
>>
>> mike wrote:
>>
>>> Gerard Forns wrote:
>>>
>>>> Hello,
>>>>
>>>> I've got an HP n620c and I need to get another AC adapter for it.
>>>> On it's specifications says that must be supplied by 18.5 V and 3.5A,
>>>> I supose that is a 65W adapter.
>>>>
>>>> We have got another 90W AC adapter that gives 18.5V and 4.9A.
>>>> Could be dangerous for my computer to plug this laptop with a 90W
>>>> adapter?
>>>>
>>>> Thank's in advance,
>>>>
>>>> ..Gerard
>>>
>>>
>>>
>>>
>>> First thing I'd do is fully discaharge the battery and measure the
>>> current from the ac adapter while charging with the laptop off.
>>> if it's less than 3.5Amps, you're probably good to go. If it's 3.5A
>>> or more, you can expect that the battery charge current is limited by
>>> the
>>> adapter. In that case, you'd risk overcharging your battery with the
>>> bigger adapter. YMMV.
>>>
>>> There's maybe an easier way to do the measurement. Measure the open
>>> circuit voltage from the disconnected ac adapter. Then measure it again
>>> while charging the battery. If it's much lower while charging, then the
>>> adapter is limiting the charge current. Still need to make up some
>>> kind of test adapter to get at the measurement points.
>>> mike
>>>
>
>
>

Archived from groups: comp.sys.laptops (More info?)

Barry Watzman <WatzmanNOSPAM@neo.rr.com> wrote:
>The AC adapter for a laptop is simply a DC power supply.

And, as always, here's a counter example. Recent Dell power supplies
communicate with their connected laptops, which can tell which of (3?)
different supplies is connected. They'll either refuse to charge or
charge at one of two different rates depending on the capacity of the
supply.

[However, the HP supply that the OP writes about very probably isn't
this complex]

Archived from groups: comp.sys.laptops (More info?)

Barry Watzman wrote:
> Gee, I got my ham radio license in 1963, my 1st class commercial FCC
> lisense to run 50,000 watt broadcast transmitters in 1965 (at age 15), I
> have a BSEE, I'm A+ and Network Plus certified, I repair laptops (and
> other computers), I've been both an engineering manager and and a
> maketing manager for my entire 30+ year career in the PC business
> (including two major laptop vendors and one switching power supply vendor).
>
> Obviously, I lack experience.

Credentials imply credibility. And I'm sure we're all impressed with
yours.

Credentials notwithstanding...

You are generalizing from something that you believe to be true to
something that looks close but is NOT the same. It's a common mistake
among people who have a lot of related experience, but not with the
exact issue. So don't get down on yourself for being wrong. Get down
on yourself for stating that a light bulb bears any relationship
to a laptop battery charging system.

I sold off most of my laptops at the last swap meet, so in order to be
ABOSLUTELY SURE I'M BEING ACCURATE and giving you statements that CAN BE
VERIFIED and that I HAVE VERIFIED, I'll give you an example from an
older Compaq Aero 4/33c laptop. Look at the schematic pages 19 and 20.
You'll see that the positive ac adapter terminal goes thru a diode then
directly to the + battery terminal. There's a BIG honkin FET from the
negative battery terminal back to the negative ac adapter terminal.
This FET turns on and stays on until the thermistor inside the battery
pack tells the laptop to turn it off. And yes, I have sat there monitoring
voltage, current and temperature for hours at a time while the battery
charged and discharged.
The charge current is whatever the ac adapter can supply.
READ THAT AGAIN. THE CHARGE CURRENT IS WHATEVER THE AC ADAPTER CAN
SUPPLY!!!!
I learned this the hard way with a car battery. I still have the board
with the big black hole where the FET used to be.

Not every laptop has this problem, but I've owned about a dozen that do.
All you gotta do is hook up your metered power supply to the AC adapter
hole and watch the meters when the battery goes into charge mode.
With different laptops you'll find a bewildering array of behaviors.
Many of them will take enough current to do damage.

So, there enough laptops around having this problem that a blanket
statement to "not worry about it" will eventually cost some innocent
newbie his/her laptop...or at least negatively impact the battery lifetime.

SOAPBOX ALERT!!!
As experienced engineers, we have the obligation to provide newbies with
accurate information. I'm no doctor, but I do believe in, "first, do no
harm."
Remember that these postings stay around forever. Some time in the
future, some newbie is gonna take a posting out of context and believe
it's true. Then he's gonna apply additional extrapolation based on
his own related, but inaccurate, experience.
If the newbie could distinguish between accurate information and the
musings of a "credentialed expert", he wouldn't have asked the question
in the first place.

So, you've given examples of light bulbs and extrapolated that to laptop
charging sytems.
I've described the (verifiable) circuit of a specific laptop. And
described specific personal expeirence with it.
Who would you believe?

I have no experience with a HP n620c, but I do have enough experience
to advise caution and I described how to test for the problem condition.
When in doubt, check it out.
-.-- --- ..- .-. -- --- ...- .
mike


>
> But you don't know what you are talking about.
>
> The AC adapter for a laptop is simply a DC power supply. The laptop
> decides what it will take.

YES THAT'S EXACTLY MY POINT. THE BATTERY CHARGING CIRCUIT DECIDES HOW
MUCH TO TAKE. AND FOR AT LEAST SOME LAPTOPS, HOW MUCH == ALL!!!! THAT
CAN BE SUPPLIED.

Your suggestion to the contrary is about
> like suggesting that if I remove a 100 watt light bulb from a lamp and
> plug in a 60 watt bulb, the 100 watts that the wall socket can clearly
> supply will blow out the 60 watt bulb. Which some people are ignorant
> enough to accept if told (because it does sound superficially
> plausible). But everyone's common experience tells us that while a wall
> socket is fused at 15 or 20 amps (roughly 1500 or 2000 watts), you can
> use a 4-watt night light, a 60 watt bulb, a 100 watt bulb or a 1,500
> watt hair dryer in the exact same wall outlet without changing anything
> at the fuse box or the wiring or the utility company's generators.
>
> And that is EXACTLY the analogy that applies here.

THAT'S YOUR ERROR. YOU BELIEVE THAT IT IS AN ANALOGY.

The laptop is like
> the light bulb, and whether you use an adapter CAPABLE of supplying 60
> watts or 100 watts or 10,000 watts (at the correct polarity and
> voltage), the only thing that matters is that both are more than what
> the laptop needs (say 50 watts). The use of an adapter capable of
> supply more current than the laptop needs is of no more consequence than
> plugging a lamp with a 60-watt bulb in it into a wall socket that is
> also capable of operating a 1,500 watt hair dryer.
>
>
>
> mike wrote:
>
>> Barry Watzman wrote:
>>
>>> There is no risk of overcharging the battery by using an AC adapter
>>> with a higher current capacity than the original adapter. The
>>> charging current is controlled by the charging circuit in the
>>> laptop. The only role that the adapter plays is to be capable of
>>> supplying the requested current. The charging circuit still
>>> determines the current actually used.
>>>
>>
>> You obviously lack experience with charging systems that do NOT meet
>> the above criteria. Just because a well designed system should NOT
>> depend on the AC adapter, doesn't make it so. Just because your
>> system doesn't have the problem doesn't guarantee that mine won't.
>> Measure it and be SURE!!
>>
>> I'll agree that it's OFTEN OK, but
>> telling someone it's OK when you haven't actually measured the result
>> on the exact same model is irresponsible. There's a reason that the
>> manual tells you to use ONLY the recommended AC adapter.
>> mike
>>
>>>
>>> mike wrote:
>>>
>>>> Gerard Forns wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I've got an HP n620c and I need to get another AC adapter for it.
>>>>> On it's specifications says that must be supplied by 18.5 V and 3.5A,
>>>>> I supose that is a 65W adapter.
>>>>>
>>>>> We have got another 90W AC adapter that gives 18.5V and 4.9A.
>>>>> Could be dangerous for my computer to plug this laptop with a 90W
>>>>> adapter?
>>>>>
>>>>> Thank's in advance,
>>>>>
>>>>> ..Gerard
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> First thing I'd do is fully discaharge the battery and measure the
>>>> current from the ac adapter while charging with the laptop off.
>>>> if it's less than 3.5Amps, you're probably good to go. If it's 3.5A
>>>> or more, you can expect that the battery charge current is limited
>>>> by the
>>>> adapter. In that case, you'd risk overcharging your battery with
>>>> the bigger adapter. YMMV.
>>>>
>>>> There's maybe an easier way to do the measurement. Measure the open
>>>> circuit voltage from the disconnected ac adapter. Then measure it
>>>> again
>>>> while charging the battery. If it's much lower while charging, then
>>>> the
>>>> adapter is limiting the charge current. Still need to make up some
>>>> kind of test adapter to get at the measurement points.
>>>> mike
>>>>
>>
>>
>>



--
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Archived from groups: comp.sys.laptops (More info?)

Graeme wrote:
> A little education is in order here and, in fact what Barry says is (as
> usual) quite true. Start with Ohms law E=I*R.
>
> The fact that some AC adaptors may have current limiting is very
> commendable. However if you know your electrical theory you will know
> that the light bulb example is EXACTLY what happens when any device is
> powered from whatever source it is powered from.
>
> Current is DRAWN by the device. The power source is rated for the
> maximum current that it can SUPPLY. The (laptop in this case)draws a
> certain current. If the device (AC adaptor) cannot supply that current
> it heats up (W=E*I) overloads and eventually fails (meltdown...smoke
> gets out...see the smoke theory of electronics).
> If you have a fault in the internal invertor/charger in your laptop
> excessive current may be drawn resulting in even further damage to the
> laptop.
> In this instance it would be nice to have some current limiting in the
> AC adaptor but thats not the cause of the problem so quite irrelavant.
>
> Current limiting would just help to protect the AC Adaptor not the
> faulty circuit it may be supplying (and it adds to the cost of
> manufacture).

I give up.
If people want to ignore an actual circuit description and risk their
laptops on your ill-considered application of the light bulb analysis to
their laptop charging circuit, I guess they will.
I've published how to test for the condition.
I'm done.
Good luck to all.
mike

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Archived from groups: comp.sys.laptops (More info?)

Toshiba alone has produced over 500 laptop models, so I will acknowledge
the old addage that any absolute statement is going to be wrong. But
even if the current capacity of the AC adapter was the determining
factor for the charging current (which we all agree would be a horrible
design), the battery would still have to have a thermal cutoff, it
simply would not get UL approval without it.

Think about the implications of a system in which the power supply
current capacity was the only determinant of battery charge rate: A
laptop could be idle or running "Seti@home"; it could be accessing a CD
or not. It could have an external keyboard and mouse or not. It could
have the screen at high or low brightness. It could have PC cards or
not. It could have maximum memory or not. And the battery itself could
be in anything from brand new condition to cells with dead shorts. Yet
the same AC adapter with the same current rating would have to run the
laptop and battery equally well under all of these diverse (indeed
wildly diverse) configurations. And even then, it is still not the AC
power pack that is the final sole determinant of charge current, because
the charge current will still vary with the internal resistance of the
battery and the battery's open-circuit voltage.

The situation painted is so far "out there" (and would be so
irresponsible on the part of the manufacturer), that IF it exists, in my
view it's still not a valid basis for a general discussion of the
subject. Such a design would be unsafe and irresponsible to the point
of creating a liability and product recall issue for the manufacturer
(and, in fact, there have been quite a few product recalls associated
with laptop batteries and power supplies, although not, as far as I
know, for this particular reason).

And you are right, batteries do develop dead shorted cells, and I've
watched an IBM Thinkpad with a bad battery begin smoking profusely, in
spite of the fact that I know that this laptop model does have an
"intelligent" battery charger with current limiting. Problem is, if a
battery is dead shorted, the design current levels, while still being
within the design limits, can cause catastrophic consequences.


BillW50 wrote:

> "Barry Watzman" <WatzmanNOSPAM@neo.rr.com> wrote in message
> news:428BADDA.4010105@neo.rr.com...
> Date: Wed, 18 May 2005 21:04:24 GMT
>
> There is no risk of overcharging the battery by using an AC adapter with
> a higher current capacity than the original adapter. The charging
> current is controlled by the charging circuit in the laptop. The only
> role that the adapter plays is to be capable of supplying the requested
> current. The charging circuit still determines the current actually
> used.
>
> Whoa! Wait a minute here Barry. My credentials are also quite impressive
> btw. As I started out for example repairing and adding my improvements
> to computers that guided missiles for the military (which sort of makes
> me like a rocket scientists, doesn't it?). And I got to tell you, not
> all EE engineering by others are good designs at all (although some are
> just genius as well). And I know because I have seen many bad designs
> myself. And Mike hints that he has seen some that are really poorly
> designed. Although I plan to question Mike too, and I believe he too has
> some flaws in his logic.
>
> Normally I would agree with you and all of the others in this thread. As
> normally having a supply with more amps doesn't make any difference. As
> it should work just normally anyway since the load will only take as
> much as it needs anyway.
>
> But what Mike is saying is that he sees a design that uses the supply as
> a current regulator. That would be indeed odd, rare and perhaps even
> dangerous. But if there is any truth to what Mike is saying, then a
> supply with more amps than the original very well could be a very bad
> thing to do. And quite frankly, I would never design such thing to work
> this way. And it sounds like nobody here would do so either. But
> according to Mike, some have.
>
> NOW A NOTE TO MIKE:
>
> Mike, I really like to know what type of battery this was for this
> design that you are referring to? You know, the one with a diode and the
> FET. I haven't seen the schematic, but I did follow what you had said.
> And while I don't care for such a design (especially if it was a Li-Ion
> type which would be truly dangerous). I also admit when things are
> working fine, 18.5V supply can only pump so much into a correctly
> functioning battery at a time. Even if a million amps is available by
> the supply, the battery has its own internal resistance and is only
> going to take so much for a given voltage. Yes, very much like the light
> bulb example given by others.
>
> You also mentioned that you had a FET vaporize after connecting it up to
> a car battery. Well if the original supply was say between 12v to 14v, I
> can't really see this happening! I'm not saying that it can't, I'm just
> saying it is very unlikely (or a very poor design). Although what I am
> saying is I believe there was a fault that caused this to happen from
> the 500 to 1000 amp car battery that vaporized this FET. As one of the
> faults of a failed battery of some types, is they can short. And if this
> is the case, your vaporized FET totally makes sense under the design
> that you had found.
>
> I sure like to hear more details of course. <grin>
>
>
> Cheers!
>
>
> ______________________________________________
> Bill (using a HP Pavilion 8655 & Windows 2000)
> -- written and edited within Word 2000
>