Solar Laptop



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):


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.


Price (Each) $


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  

Additional Links

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Page Last Edited (though probably not for content): 14 September 2010