Actual experiences mod'ing laptop bricks?

Discussion in 'Electronic Design' started by Don Y, Jan 8, 2014.

  1. Don Y

    dp Guest

    On Thursday, January 9, 2014 5:14:05 PM UTC+2, Don Y wrote:
    > ...
    > I can also imagine a power supply telling the laptop how much power
    > it is *actually* using (adding those monitoring components *outside*
    > the physical constraints of the laptop itself) so the laptop can
    > better calibrate its battery monitoring algorithms (instead of
    > just watching Vbat without any real idea as to how quickly it
    > *should* be falling -- when operating on battery).

    Hi Don,
    of course we can imagine lots of things but moving the charger
    control part outside of the laptop would likely be impractical.
    For the time being, that is :D . Wait until they get as thin as
    a sheet of paper....

    It does not take much, here is most of the charger circuitry
    of a one-off thingie I did for a university lab not so long ago: . Not that much one can save
    in terms of space - and I have been conservative (e.g. put a 3.3V
    zener and don't think how ADC inputs on the MCU react to clamping
    currents into on a neighbour input). (here is the whole
    thing: , , ).

    OTOH I know what a pain it can be to connect to a power adapter you
    have not tested. I went to lengths I still can't believe myself :D
    on the netmca to protect against various power input events (it has
    no battery to buffer things somewhat, the input feeds the convertors
    directly). Things were even more complicated given that the processor
    (an MPC5200B) needed certain rise times on its 1.5V power so its
    PLL feedback amp would not go into saturation before the oscillator
    would get to work OK.... In hindsight if I had made the power adaptor
    identifiable and somehow simply not starting the whole thing unless
    the ID has been seen things might have been easier (not so sure but it
    could have been an alternative path).
    Having a battery makes things easier to control but with li-ion things
    also can get hazardous so it might be not such a bad idea to have the
    charger identify itself, at least from a legal point of view.


    Dimiter Popoff, TGI
    dp, Jan 10, 2014
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  2. Don Y

    Chris Jones Guest

    On 08/01/2014 12:01, Don Y wrote:
    > Hi,
    > I've got a ~200W laptop brick on which I'd like to tweek the
    > output voltage (~5% -- 19.5V down to 18.5V). Anyone know what
    > sort of margins they design into these? I'm not keen on risking
    > the laptop for the sake of a $10 power supply... (i.e., "it
    > *should* work" is not an acceptable reply :> )
    > Thx,
    > --don

    Why not get a couple of power Schottky diodes and put them in series
    with the DC output, to drop the voltage a bit. You can get the diodes
    out of an old ATX power supply from a dumpster. The diodes could be
    bolted to a 1 inch wide piece of aluminium strip as heatsink and spliced
    inline with the DC cable and covered with heatshrink. It would be
    somewhat wasteful and would get a bit warm if the laptop ever really
    draws 200W, but it would avoid cracking open the plastic case of the
    charger and reverse engineering it. Also there is very little risk of
    the diodes not behaving as one would expect them to, at least within
    their ratings.

    Chris Jones, Jan 10, 2014
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