Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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How do you charge a laptop battery with a solar panel ? - RF Cafe
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: How do you charge a laptop battery with
a solar panel ? Posted: Thu Jul 16, 2009 1:33 am
Joined: Tue Dec 30, 2008 1:53 pm
I'm thinking of
trying to charge my Lenovo Thinkpad x60s battery with an R-14 Powerfilm
flexible solar panel.
I hope this question is not too elementary
for this august forum.
Anyway, the idea is to charge the battery
with it in the laptop, but with the laptop turned off. I think having
it turned On will most likely not work (as follows.)
told me that since the wattage of the solar panel is much less than
the draw of the Thinkpad, it won't work. I'm not an electrical engineer,
although I did quite well in physics. The only problem is, it's been
quite a few years (of disuse.)
Here are the numbers :
The Powerfilm is rated at 15.4V and .9A ( ~14 watts)
Lenovo Thinkpad X60s Laptop
The battery is 14.4v / ~5200 mAh
I measured the current draw of the Thinkpad - when OFF (battery charging
only) - at .25A and 115v (= 29watts ).
When On, it's something over
I measured this straight out of the wall, before the inline
transformer that converts the 110v to ~20v (?). (I'm not sure what the
charging voltage is, but the charger says 20v / 3.5A = 70watts - probably
what's need to actually power a running computer)
I had thought
that the battery charging would charge at a much lower current, like
a trickle current, .1C or so, but this is not necessarily the case with
Lithion batteries it seems. See Lithium Ion Battery Charging Basics
It's more like .2 to .7C actually.
One idea, if this is not going
to work, is to pull the battery off and charge it outside the laptop,
but this looks complicated as there are about 8 or 9 contacts on the
battery, and I have no idea what is what. It sounds a little risky anyway.
If anyone could be of help that'd be great.
Post subject: Re: How do
you charge a laptop battery with a solar panel ?Posted: Thu Jul 16,
2009 3:41 pm
Joined: Sun Aug 03, 2003
Location: Erie, PA
If you don't mind spending a few bucks, you might get away with
buying one of the chargers made to plug into a car cigarette lighter
and interfacing it with your solar panel. The voltage specs seem to
agree well. Should be a simple 2-wire connection between the two devices.
This one is made for the ThinkPad
- Kirt Blattenberger
RF Cafe Progenitor &
Post subject: Re: How do
you charge a laptop battery with a solar panel ?Posted: Fri Jul 17,
2009 1:29 am
Joined: Tue Dec 30, 2008 1:53
Yes, I have one of those bookmarked actually.
In fact a few months ago I bought an inverter to plug into the cigarette
lighter, and now I'm thinking I should have just used one of those.
But this time I'm powering off the solar panel.
And it still
seems to me that the laptop will try to draw more than the panel will
That's what I'm trying to figure out actually, if someone
can fill me in.
But thanks, nevertheless.