Solar Laptop
(Archived from 2002)
I've been experimenting with a setup to use a solar panel to
charge batteries to power a laptop while bicycle touring. I was inspired
by Ken Kifer's account named Bicycle
Touring with a Solar Laptop and used that article as a starting point.
I tested the setup on a four day winter tour in Southern Arizona.
Solar Panel
I used the same solar panel as Ken, but per Ken's suggestion, I
added a homemade wooden frame around it to provide some support. I also
put some water resistant foam padding (the kind that can be used as a cheap pad
for camping) between the panel and the frame to provide some cushioning against
road shock. That seemed to work well.
Here's a picture of the solar panel mounted on the bike (click
on the picture for a larger image):
Batteries
The input from the power cord on my laptop is 15V (DC), while
the laptop battery is 10.8V. Ken used a 15V battery made up of
D-cells. However, I used a 12V battery, since I already had a couple of
12V water bottle batteries for my bike lighting systems at home. (The
battery in the picture was a homemade battery made up of 10 C-cells crammed into
a water bottle.) The laptop worked fine with the 12V battery plugged
directly into it.
The batteries were fully charged after about two days of riding
(and maybe less). The maximum charging rate for the panel is 600 mA, and
the batteries had a capacity of 3000 mAh, so under ideal conditions it would
have taken approximately 5 hours to charge the batteries. Of course, short
winter days with the sun low in the sky aren't ideal conditions for charging, so
I think the panel performed quite well under the actual conditions.
Now that the test worked out OK, I'll make a 12V battery out of
10 D-cells to provide more run time. Overcharging the batteries shouldn't
be a concern, but I'm a little concerned about excessive discharge during use,
since I won't be able to use the laptop's power management system. For
this tour I took a multimeter along to make sure I didn't drain the batteries
too low, but perhaps I may look into these "gas
gauges" as a more elegant solution.
A few web links from Ken's page brought me to a Toshiba Libretto
page that shows how to
build an external battery for the Libretto. The Libretto is a little
different in that it won't "see" the 12V battery, since it's expecting
15V. So it has to be "tricked" into seeing the battery by
sending at least 15V to it first. I had built the following gizmo (shown
on that web page) for doing this, but it turns out I didn't need it. When
you press the switch, the capacitor provides some additional voltage for about
half a second, long enough for the Libretto to "see" the battery.
Parts list for gizmo
These are all Radio Shack part numbers to make life easier. This is
everything except the Molex connectors and wire.
Part No.
|
Description
|
Quantity
|
Price (Each) $
|
Remarks
|
| 273-1720 |
Adaptaplug "Q" |
1 |
1.99 |
6.3 mm OD x 3.0 mm ID |
| 273-1743 |
Replacement Adaptaplug Socket |
1 |
1.99 |
|
| 276-149A |
Generic circuit board |
1 |
1.49 |
|
| 276-1101 |
Diode 1N4001 |
2 |
0.99 |
Later I was able to find a 10 ohm, 3W
resistor |
| 272-1016 |
100 uF capacitor |
1 |
0.99 |
|
| 275-1549A |
SPDT mini momentary switch |
1 |
2.99 |
|
| 276-271A |
LED w/resistor |
1 |
1.99 |
|
| 271-1313 |
Resistor 220 ohm, 0.25W, 5% tol |
5 |
0.49 |
Comes in package of 5 in the store |
| 271-1321 |
Resistor 1000 ohm, 0.25W, 5% tol |
5 |
0.49 |
used 1000 and 4700 ohm in parallel instead of
820 |
| 271-1330 |
Resistor 4700 ohm, 0.25W, 5% tol |
5 |
0.49 |
used 1000 and 4700 ohm in parallel instead of
820 |
| Total |
|
|
13.90 |
|
