# using laptop charger

James Cameron quozl at laptop.org
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.

https://learn.sparkfun.com/tutorials/diodes

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
> _______________________________________________
> Devel mailing list
> Devel at lists.laptop.org
> http://lists.laptop.org/listinfo/devel

--
James Cameron
http://quozl.linux.org.au/

```