using laptop charger

James Cameron quozl at
Wed Dec 11 15:09:53 EST 2013

G'day Andrew,

There is a voltage above which the XO-1 will not charge, which had
been often encountered by people using solar panels.  Along would come
a cold sunny day, with a greater than normal voltage, and the charging
would stop.

I don't recall the actual voltage (Richard may remember), but I think
it was somewhere near 18V, and it varied slightly between laptops.

So it might work, or might not.

Instead of using a resistor, you might use two or three large diodes
in series, each of which will provide a "forward voltage" 0.6V drop.
Pick the diodes based on the maximum current 1.85A (usually double
that), and the power that will be released as heat; P = V x I, where V
is 0.6, and I is not to exceed 1.85A, so 1.11W minimum "power
dissipation".  Place them in a way that does not hold the heat in.

p.s. if you find one diode does what you need, then add another in
case of variation in the supply or laptop.  You might even add a
full-wave bridge rectifier instead of two diodes, that way the input
polarity won't matter.

On Wed, Dec 11, 2013 at 01:52:54PM +0000, NoiseEHC wrote:
> Hi!
> I am thinking about using my laptop's charger instead of the OLPC
> charger in the future as I move a lot and it's getting really
> tiresome to bring both chargers with me. The plan is to create a
> converter plug and use only the laptop's but it has different
> voltage levels.
> laptop: TOSHIBA
> part: PA3715U-1ACA
> model: PA-1750-24
> output: 19V - 3.95A
> XO-1.75: DARFON
> model: BBOJ-C
> output: 13.5V - 1.85A
> So can I plug my XO to the TOSHIBA adapter? The page says that
> 11-18V needed, while the laptop's is 19V. Shall I use a resistor to
> drop the voltage or is it unnecessary? Power usage is not an issue
> to me. (BTW I will use the plug from the XO-1's charger, I guess
> that it did not change in the meantime.)
> Thanks,
> Andrew
> _______________________________________________
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> Devel at

James Cameron

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