21 July 2006

Solar power on the go

On 3rd of August we'll be going to Romania for two weeks, and I want to test a 'theory' of mine regarding powering my mobile devices only by using solar power.
Since April I am using a system of solar panels in the windows, connected to a 7A 7.2V Lithium Ion battery, which is connected to a 5V voltage regulator so I charge my cellphone that way.
However, taking this system with me is impractical for quite a few reasons:
1. The solar panels are big.
2. The battery pack looks pretty much like a bomb, with scotch tape, voltage regulator with aluminium heatsink and wires sticking in an and out of it. I highly doubt they'd let me on the plane with that thing :D And for good reasons, because you can actually use those batteries as a bomb. Have you seen that video of the Dell laptop exploding in Japan?
3. That system is a little inefficient, and it's not designed for portable use.

Now, I will have two portable devices with me:
AAA powered MP3 player.
My cellphone/PDA.

My estimate is that the cellphone will require at least 1 Amp/hour per day, possibly more if I plan to use it for games as well.
So two 225 mAh 6V solar panels should be enough. The problem is that I want to actually store that energy during the day, and recharge it at night. This turned out to be quite problematic. One option would be to use 4AA NiMh batteries, but I tried this already and it doesn't work very well. Apparently 6V - 0.2v for the diode is not enough to charge them fully. Making a DC-DC converter to increase the voltage is out of the question, because I am not really that great when it comes to electronics, and it would look ugly anyway.
So what I did was to buy an USB charger, that has an input of 5V, and an output of 5V, using a lithium ion battery. It should have it's own DC DC converter, it's small, and relatively cheap. Something similar to this one: http://cgi.ebay.com/5000mAh-external-portable-battery-for-PSP-NDSm-GBA-SP_W0QQitemZ230009146028QQihZ013QQcategoryZ122516QQrdZ1QQcmdZViewItem but it has an USB male and an USB female connector, and it's only 2.5A.
Should be here just in time, it ships from HK.

Once I put everything together, I will post some pictures.


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