[sf-lug] AC adapter compatibility

Michael Paoli Michael.Paoli at cal.berkeley.edu
Tue Feb 24 21:39:37 PST 2015

And, back to the list, as I'm presuming that's where this was intended to
go to.  And yes, you make good point about the acual barrel plug or whatever
the connector is.  I was hoping that was covered by my statement of
"plug type" - but that may have been too ambiguous.  Plug family
certainly would've been insufficient to guarantee suitable physical
plug hardware match, perhaps I should've said "properly matched
plug" or something like that - and yes, inside and outside diameters
do vary, as also does the clear insertion length portion of the
plug.  They also do have maximum current ratings, but that can vary by
plug/receptacle, but if one is obtaining that as part of an assembled
power supply or device (e.g. laptop), one needn't worry about that,
as the connector used will handle at least the current used by the
device / provided by the power supply.

Also, there's somewhat of an exception on laptops and voltages.
Typically they're designed to accept DC voltages from about 12VDC up to
around whatever their power supply or input is rated for, notably so they
can use simple vehicle, and similar adapters, that are just direct
electrical connections, with nothing more than typically a cheap fuse
for some overcurrent protection.  So, a power supply of slighlty lower
DC voltage is likely to be fine - it may just charge your battery a
bit more slowly.  Another factor to watch if the DC voltage is somewhat
lower, is total power.  That would be Watts = Volts X Amps.
If the voltage is a bit lower, but the total power output of the power
supply is >= max power consumption of the laptop, you're likely also
still okay.  But that's probably even not an issue, as even if the
input voltage goes down, the current draw may go up, (or not, or even
down), but in any case the laptop current draw probably still never
has a sustained draw greater than its rated maximum input current.
This situation would be quite different if we were talking A.C. - and
especially AC motors and some other types of AC loads.  Also, if we
were talking something other than laptop DC input voltage, the
requirements might be much more stringent.  Also, this "wiggle room"
on DC input voltage on laptops generally does NOT apply to laptop battery
types/chemistry, voltage, capacity, etc.

So ... 18.5 VDC 3.5A power supply (with suitable connector and polarity)
would likely work quite fine for a laptop spec.ed for 19VDC 3.42A.  So
maybe it'd take your laptop battery up to 10% longer to fully (re)charge,
but that's likely the only difference, if any, that might be noted.
(time on the battery charge may not be linear - it may be closer to
proportional to the power supply voltage less the battery voltage,
battery voltage likely to be someting a bit under 12VDC -
the battery on my laptop - again peekin' at my log file:
Rating 11.1V 5200mAh, 58 Wh
... and certainly more convenient than pulling the battery out,
as I'm typing this from that laptop).
So ... if we guestimate a battery voltage of 11.1V,
and presume replacing a 19VDC power supply with 18.5VDC power
supply, we might guestimate increased charge time of ...
$ echo '((19-11.1)/(18.5-11.1)-1)*100' | bc -l
About 6.75% ... but may vary fair bit from that estimate, based upon
the particular electronics and charging circutry.

> From: "Ken Shaffer" <kenshaffer80 at gmail.com>
> Subject: Re: [sf-lug] AC adapter compatibility
> Date: Tue, 24 Feb 2015 20:23:36 -0800

> The other item of incompatibility is potentially the actual barrel plug --
> they come in different lengths and diameters (both inside and out).
> I can offer you for free an old HP Compaq V3000 adapter 18.5v  3.5a with a
> plug of 10mm long, 5mm outside diameter, and 1.5mm or 2mm inside (positive
> inside).  I'd think the 18.5v and 19v differences may be just marketing
> roundoff. ;^)
> The HP part no is 380467-004 with replacement 381090-001
> Ken
> On Tue, Feb 24, 2015 at 6:38 PM, Michael Paoli <
> Michael.Paoli at cal.berkeley.edu> wrote:
>> If the power specifications match, including voltage, type (AC & frequency
>> or DC), current (it's mostly the maximums that matter on current), plug
>> type and polarity, with the current of the supply equal or greater than
>> that of the device to be powered by the supply, in general you're okay.
>> In the specific example you cited, the laptop apparently has a higher
>> current rating (3.42 A), than the proposed replacement supply (3.16 A),
>> so that most notably runs risk of damaging the proposed replacement
>> supply, so I wouldn't recommend trying that - unless you don't mind
>> damaging that supply.  If it's a reasonably safe supply (UL listed?),
>> it shouldn't overheat or burst into flames or anything like that.
>> The difference is "small enough" that it might manage to work, or mostly
>> work.  The current ratings are generally max/peak sustained draw, so,
>> also, ... it might appear to work, ... then fry your supply when the
>> laptop some later hour/day/month/year, actually draws peak current for
>> some reason (e.g. battery very low, CPU maxed out, memory & GPU and drive
>> being pounded upon, hot with fan going on high).
>> Best to check the actual machine (laptop) specifications (e.g. check with
>> Zareason, or other suitable authoritative information source).  Also, if
>> you
>> have the data on the original supply, you could compare against that.
>> E.g. I have in my log (but this is my model, and may not at all match
>> yours):
>> 2011-12-15
>> ...
>> Strata 6880
>> ...
>> Rating: 19V 6.3A
>> ...
>> Power supply:
>> label:
>> INPUT: 100-240 V ~ 2.0A 50-60 Hz
>> OUTPUT: 19V 6.32A
>> (+ in center, - on outside of connector)
>> C.C.: GZ  REV.: 00
>> S/N: B0VW13M00XF
>> ...
>> Also handy if one ends up in situation where folks are trying to figure
>> out who's supply is who's, or if someone in fact has your lost/stolen
>> power supply - also have the serial number (though not all power supplies
>> necessarily have serial numbers; can also be handy to have serial number
>> of your USB devices - as they may look identical to others).
>> You'll also note on mine, the voltage on device and power supply match,
>> and the current rating on the supply is >= that of the device to be powered
>> by it.  That's what one would expect and should have.
>> Having stuff logged like that is handy (easy to search and find in the text
>> ... my system log is currently 19,524 lines long.  But can also do the
>> "quick and dirty" - take a digital photo, and save that (the later also
>> good, perhaps even better, for property protection, insurance, etc.).
>>  From: "Christian Einfeldt" <einfeldt at gmail.com>
>>> Subject: [sf-lug] AC adapter compatibility
>>> Date: Tue, 24 Feb 2015 18:03:16 -0800
>>  Hi,
>>> I have recently misplaced my AC adapter for my Zareason, and have found
>>> another adapter, and would like to ask this list if you think that it is
>>> okay to use the other adapter.  My computer is a Zareason UltraLap-440,
>>> which seems to be a re-branding of a Compal VAW70.  The sticker on the
>>> bottom of the machine says that it is 19 V (volts) and 3.42 A (amps).  The
>>> adapter says that it is 19 V and 3.16 A.  Can I safely use that adapter
>>> without frying my machine?
>>> Here is the link to the Zareason machine
>>> http://zareason.com/shop/UltraLap-440.html
>>> Here is the link to the Compal VAW70:
>>> http://www.asipartner.com/Solutions/Mobile/ASINotebookSolutions/
>>> CompalVAW70/tabid/1071/Default.aspx
>>> Here is a link to the adapter:
>>> http://www.pchub.com/uph/laptop/46-16927-1714/Acbel-
>>> Polytech-API-7629-AC-Adapter-Laptop.html
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