Vispera lite v1.0
After creating the solar charging station, which is working well at the moment. I decided to create a portable version so that I could charge my phone anywhere. Existing portable solar chargers that I have come across here in South Africa and from looking on ebay, fall into one of two categories they are either ridiculously expensive; in excess of R700 or they are the cheap and rubbish ones which are too small and take long to charge up.
My design would address these issues, I came up with requirements for the charger:
- Be able to charge high end smart phones
- Small size
Now that I have my design set out, I started experimenting with different solar panel sizes, circuit configurations and the possibility of using batteries to store the energy when the charger is in the sun.
My first design worked as follows; the solar panel charges a pack of nimh batteries when there is sunshine, then when you want to charge your phone, energy from the battery pack would then be used. This approach is inefficient because you are losing energy during the conversion from solar to nimh battery pack then to cell phone battery. My prototype dropped the nimh battery, so its direct from solar panel to cell phone.
After various configurations I eventually came up with a viable prototype which performed well, now I have the task of cutting down on the cost.
This should be a relatively simple undertaking since I have been in contact with various Chinese manufacturing companies who are able to supply components at around a quarter of what they cost here in South Africa.
The next prototype would include better dc-dc conversion for increased efficiency and have a soft neoprene back to protect the back of the solar panel.
When folded up the size is about half that of an a4 page, which is perfectly suitable to fit in a school bag.
Velcro strips on the back so that it can be stuck onto your bag when in use.
Recently I acquired a Raspberry pi computer board to be used as a gateway for my sensor mote in our backyard that is monitoring the water temperature and water level of the fish pond. I also wanted the whole system to run off solar power, so I went and bought a 35 Watt solar panel and went about designing a power supply for the system.
The specifications of the power supply were that I wanted to be able to charge 3 smart phones and run my Raspberry pi all at the same time. To accomplish this, the power supply would need to be able to output 5V and supply about 2.5A of current. I decided to build a switching power supply instead of simply using a linear regulator because of its inefficiency (calculations suggest that about as much as 15Watts of power will be dissipated as heat).
The solar panel
Testing the circuit…
Here I was busy charging my phone while the raspberry pi was playing HD video on the TV, from the multimeter I could see the power supply was outputting 0.8A of current. So far its working fine, I just need to do more load testing and then put the components onto a board.
Then I would have my own solar power station which cost me like R400 to build and will last a long time 😀
This is me on the 3rd of June 2013